Long and short term variability of climate

Lecture Notes in Earth Sciences Edited by Somdev Bhattacharji, Gerald M. Friedman, Horst J. Neugebauer and Adolf Seilach...

Author: Heinz Wanner | Ulrich Siegenthaler

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Lecture Notes in Earth Sciences Edited by Somdev Bhattacharji, Gerald M. Friedman, Horst J. Neugebauer and Adolf Seilacher

16 H. Wanner U. Siegenthaler (Eds.)

Long and Short Term Variability of Climate

Springer-Verlag Berlin Heidelberg NewYork London Paris Tokyo

Editors PD Dr. Heinz W a n n e r Universit&t Bern, G e o g r a p h i s c h e s Institut Hallerstrasse 12, C H - 3 0 1 2 Bern, Switzerland PD Dr. Ulrich Siegenthaler Universit&t Bern, Physikalisches Institut Sidlerstrasse 5, C H - 3 0 1 2 Bern, Switzerland

ISBN 3 - 5 4 0 - 1 8 8 4 3 - 6 Springer-Verlag Berlin Heidelberg N e w York ISBN 0 - 3 8 7 - 1 8 8 4 3 - 6 Springer-Verlag N e w York Berlin Heidelberg

Library of Congress Cataloging-in-Publication Data. Long and short term variability of climate / H. Wanner, U. Siegenthater, eds. p. cm.-(Lecture notes in earth sciences; 16) Papers presented at a symposium held in Bern, Oct. 10-11, 1986, organized by the Swiss Commission for Climate and Atmospheric Research. Includes index. ISBN 0-38?-18843-6 (U.S.) 1. Climatic changesCongresses. I. Wanner, Heinz. I1.Siegenthaler, U. (Ulrich), 1941-. II1.Schweizerische Naturforschende Gesellschaft. Schweizerische Kommission fur Klima- und Atmosph~.renforschung. IV. Title: Variability of climate. V. Series. QC981.8.C5L65 1988 551.6-dc lg 88-6542 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. Duplication of this publication or parts thereof is only permitted under the provisions of the German Copyright Law of September 9, 1965, in its version of June 24, 1985, and a copyright fee must always be paid. Violations fall under the prosecution act of the German Copyright Law. © Springer-Verlag Berlin Heidelberg 1988 Printed in Germany Printing and binding: Druckhaus Beltz, Hemsbach/Bergstr. 2132/3140-543210

Lake

of

walking

Constance, on t h e

winter

frozen

lake.

1830:

The

people

of

Rorschaeh

enjoy

PREFACE

This

volume

held

at

includes

Bern

organized

on

by

organized held

by

this in

Birkh~user

to

a

series.

The

their

The

symposium

them

together

form,

was

of

Atmospheric

planned

the

R. were

possible

one

had been

C.

this to

seine

FrShlich; lectures

appeared

submit like

met

natural

Lecture

our

by H.

Commission

for

C.

of

the of

thanks

Academy by

FrShlich,

A.-C.

involved

preparation

Swiss

symposium

ed.

mainly

Rickli,

administration

The

ready

and

Klima,

a n d we w o u l d

Research),

SchGpbach

express

were

Climate

(Das

it

in

was

second

symposium and

which

Notes

their

papers

to t h a n k

them

collaboration.

president

the

The

reception,

authors

for

Pfister.

1985).

for

first

1983

good

in c a m e r a - r e a d y

the

a symposium

1986,

the

StSrungen,

Verlag,

publish

in

at

11,

was

commission;

und

very

and

Commission It

Bern

Ver~nderungen

presented

10

Swiss

Research.

also

with

October

the

Atmospheric

papers

in

to all

of

providing

G.

the

book.

(then

Climate Furrer

Vogel-Clottu

conference. this

Oeschger

and and

and

organization U. We

Neu

assisted

should

like

December

1987

E. and in to

of them.

Sciences the

made

the

necessary

symposium financial

support.

Bern,

C.

H.

Wanner

U.

Siegenthaler

CONTENTS

Introduction

OBSERVATIONAL

Variability C. F R ~ H L I C H

STUDIES

of the

Solar

"Constant"

Hemispheric and Global Temperature P.D. J O N E S a n d P.M. K E L L Y

Climatic Information in W i d t h a n d D e n s i t y F.H. S C H W E I N G R U B E R

Data 18

of the Past H u n d r e d Y e a r s of C o n i f e r G r o w t h R i n g s 35

V a r i a t i o n s in the S p r i n g - S u m m e r C l i m a t e of C e n tral E u r o p e f r o m the H i g h M i d d l e A g e s to 1850 C. P F I S T E R

57

N o r w e g i a n S e a D e e p W a t e r V a r i a t i o n s over the L a s t C l i m a t i c Cycle: P a l e o - o o e a n o g r a p h i c a l Implications J.C. D U P L E S S Y , L. L A B E Y R I E a n d P.L. B L A N C

83

MODELLING

STUDIES

Numerical Models H. G R A S S L

of C l i m a t e

S e n s i t i v i t y of P r e s e n t - D a y Astronomical Forcing C. T R I C O T a n d A. B E R G E R

117

Climate

to

C a u s e s a n d E f f e c t s of CO 2 V a r i a t i o n s the G l a c i a l - I n t e r g l a c i a l C y c l e s U. S I E G E N T H A L E R

Subject

Adresses

Index

132

During 153

172

175

INTRODUCTION

The

awareness

only

the

growing

that

mankind

local but

also

interest

in

which

experimental

techniques,

climatic

patterns has made

answered, related causes

new

The of

also

of

in

the

problems

natural

climate.

have

thereby

the

of

research and

novel

time,

questions

recognized.

on

climate have been

One

is a b o u t the

not

information

same

some

change

against

are

have

all

question

the n a t u r e

background

from

up

deal

reviews

more

of

the

the

knowledge

character

studies

to

with

of

the

obseryational

variations

going

been

volume

papers

The

year-to-year

At

improved

wealth

While

climatic

this

others

contribution.

past.

modify

to a s t r o n g l y

Strengthened

of a

and

led

and

which

be v i e w e d .

to

Some

topic,

influence

use

yielded

variations,

contributions

current

made

much progress.

changes must

to

climate has

research.

have

to a n t h r o p o g e n i o

man-made

able

climate

activities,

modelling

is

the g l o b a l

variabilitY

of

cover

an

the

range

glacial-interglacial

instrumental

data

to

to

results

a

original from

contrast, from

proxy

records.

The

question

has

long

available

whether

been when

atmosphere.

data

of

are

obtained

unequivocal the

year.

by

with it

be

the

with or

since

been

of

it

shows

to

of

short

radiometers

t r e n d of a

outside the

time

became

"constant"

as

detect the

decrease

and The

satellite

well

as

the

solar of

the

operating

By u s i n g

radiometers

possible

with

only

with

solar

absolute

a long-term

1980

deals

spacecraft.

high-precision

varies data

undertaken

FrShlich of

output

reliable

could

C.

rockets

has

evidence

period

energy

but

c a r r i e d out

balloons,

measurements

For

paper

variability

measurements on b o a r d

sun's

measurements

The

longer-term

the

considered,

spot first

constant.

-0.019

%

per

P.D.

Jones

and

temperatures temperature activity, El

probable well

as

the

of

of t h e

ENSO

0.1

at s o m e

time

eruption

or

for

A

effect

within

between

30

critical

and

exert

regional paid

a

the

pares -

the

The

is

plained gruber

by

reduction cates in

that

years

the

Pfister

data

records

the

end

of

the

a

next

of

1270 of the

warm

the

the

the v o l c a n i c responsible in

the

and

of

one

Switzerland 1945

are

than being

The a u t h o r

for

more

than

temperature maps

and

he com-

of t e m p e r a t u r e width

factor

anomabe

He

growth

also

governed

by of

ex-

Schwein-

of c l e a r

1954.

(July

Europe.

cannot alone.

a phase and

for

density

irregularities for

is

trees.

patterns

strongly

field

site

formation

attention

maximum

climatic

strong

large

ring

tree-ring

in

The

den-

of c o l o u r e d

anomaly

between

of that

shows

like

anDmalies

and

patterns

indi-

deficits the

last

dendroelimatological

re-

years.

investigates

between

harvest til

open

as

it o c c u r s

problems

persisting

a set

width

observed

the

and are

He

great

signals

temperature

that

and

individual

changes

using of

ring

growth

well

within

period

By

influence be

and

climatic

precipitation.

may

search

C.

the can

summer

growth

between

demonstrates

the

duration

variability

on growth

reason,

density

but

of

The

after

Schweingruber.

sites

pattern

obvious,

possibilities

F.

that

of

maximum

coincidence

lies

For

abrupt

spatial

on

effects,

factors

interannual

influence

anomalies.

September),

two

the most

eruptions

6 months

immediately The

the

the by

incorporate

precipitation

similar of

the

temperature

temperature.

order

years

of

stronger

that

years

have

and

are

volcanic

the solar

records.

into

selection

emphasizes

the

event.

%

given

conditions.

to

three

cold 50

insight is

both

the t w o

or

mean

in

activity

phenomenon

global

for

variations

explosive

hemispheric

is of

temperature

droclimatology factors

0.2 °C, on

warm

hemispheric

in

hemispheric

causes

volcanic

(ENS0)

Large

phenomenon

to

maximum

scale.

that

dioxide,

variations

time

annual

possible

find

Oscillation

of

year

mean

discuss

They

carbon

Southern

causes

100

calculated

and

variations.

/

I to

Kelly 1861

increasing

Ni~o

order

P.M.

since

and this

the warm

"Little period

weather

1425

of

patterns

and

compares

period

with

Ice the

Age". High

of

the

vegetation

tree-ring

corresponding

Although Middle

and

data

continuous Ages

are

grape un-

proxy

not

yet

available, than

once

became the

he

every

very

High Middle and

was

when

of

long-term

average

the

in the

few

The

past

Blanc

is

which

much

the

180/160

changes

ratio

lysis

had

there, today

during

the

of

a

is

Europe!

two de-

began

compared of

the

at the

with the

has

impact

of

1420

the

strong

question

Europe

human

One

certainly

view

Central

for

of the

about

Europe

In

they

m a r k e d b y the

was

centuries,

by

1400

climate

only

month

more

measured

form

ari-

witnessed

or

just

mean

re-

135,000 years

They

now

Norwegian

not

have a

as

is

for

sea to

with

water

careful

isotope

ana-

the

the

the of

of

disen-

fact

freezing

significantly

function

be u s e f u l

conti-

temperature

using

near

low

ratios

able by

with

the

between

Sea,

been

table a

by

been

and temperature

present

that will

have

temperature

water

to

isotope

were modified

The

d u r i n g the

water

ocean

oxygen

about

studies.

lower of

fractionation

the

therefore

was

a n d P.L.

cycles,

sediment

f r o m the

authors

from

ocean

Labeyrie

amounts

the

of ice v o l u m e

time.

last

in

however,

deep-water

ratio

L.

water

large

transferred

isotope

cores

ocean

in o c e a n

because

French

can

tope

Duplessy,


recorded

the

The

and

glacial

is

variability.

Central

by

J.C.

the

which,

effects

that

of

been

sediment

point

by

180/160

sediments,

the

and

induced

learned

is

affecting

of

took

millenium

excursions

present,

This

carbonate.

After

the w a r m

enormous

last

earlier

were

been

at

ice.

deep-sea

tangle

years

history

ratio

nental

an

1339.

occurred

fluctuations.

has

than

for

the p a p e r

isotope

ice age

and

of

by

the

Western

weather

natural

subject

oxygen

for

from

Ice Age"

advanced

reported here

and

watershed"

shift

in W e s t e r n

was

anomalies

occurrence

"climatic The

within

and

1269

single

"Little

harvest

ses w h e t h e r

present

A

to the

August

anomalies

a

characterized

the w i n e

end

not

century.

years

positive

between

and

century.

Age

warmest

that

decade

fourteenth

cades

show

rare,

seventeenth

early

the

can

lower

oxygen time

for

isothe

stratigraphic

studies.

The

part

three

problems mate. points

of

papers.

He

and

the H.

book Grassl

some

distincts

to the

dealing

with

discusses

important

results

meteorological

three principal

climate

basic of and

sources

modelling

includes

applications,

numerical climate

of e r r o r s ,

models

the

main

of

cli-

applications which

and

are n u m e -

rical

and

parameterization

incomplete

equations.

climate

model

climate

system,

not

available,

ceeds

the

to

because

agree global

that

much

more

The

difficult

to are

the

is

now

C.

sorbed mate.

and

U.

A.

the

still

have

While

will

lead

4.5

K,

modify

re-

modelto it

processes

particles

ex-

efforts

and

a

the

a is

(e.g.

the

cli-

for

air

the

that ice

explain

why

glaciations to

climate

alone.

The

chan~es

in

ocean

events.

glacial

ice

the

ages,

the

ac-

earth's

variation

been

radiation

relevant

absorbed years

of

the

considered

the

more

the

of


instead is

for

and

so ab-

cli-

radiation discuss

as o n e

is of

of

which, to

cores.

C02

CO 2

may

for the

the

C02

however, appears

consider

interactive

the

about

model

in

both

climate

and

contri-

result

that a

re-

this would

hemispheres,

Milankovitch

have

shown

percent

largely

importance;

necessary

complex

30

Climate model

been

variations may

measure-

have

significantly The

synchronous from

was

have

special

of

They

Holocene.

level

temperatures.

were

it

implication

ice

d u r i n g the

understand

Thus,

the

of

Hemisphere

cause

cycles

simultaneously

the

has

200,000

polar

lower

age

Southern

hard

in

than

the

CO 2 v a r i a t i o n s

the

the

which

concentration

the

is

of

geometry

Generally,

discusses

of

that

of

past

occluded

cold

the

the

computed

the

ice age

indicate the

theory

contribution.

sult

the

1.5

chemical

consider

have

in

climatic

that of

system will

content

by

is s t i l l

a model

climate

atmosphere

surface,

cooling

fact

how

cause

Berger

Berger

atmospheric

to

of

Sie~enthaler on

during

studies

and

latitudes

made the

buted

model

atmosphere.

CO 2

in

accepted.

top

earth's

in t h e i r

Finally,

lower

the

aerosol

variations

widely

the

different

that

aware

Strong

between

Milankovitch,

the

the

Tricot

Tricot

ments

and

of s u c h

the

the

estimate

fundamental

at

at

results

or

which

insolation far.

of

increase

reactions)

astronomical,

cycles,

question how

to

well

caused

compartments

resources.

of

errors

are

relevant

complexity

doubling

as

ocean-atmosphere

composition

a

well

its c o m p o n e n t s .

cording orbit

the

temperature

photochemical and

coupled

the

changing

lers

all

computing

to a n s w e r

the

mean

mate

testad

as

modellers

include

available

been made act

Although

should a

errors

must

been for the

a

t h e o r y of have

been

i n i t i a t e d by unterstanding carbon

cycle

climate-CO 2 system.

Obviously,

the

survey.

think,

We

articles strate

dealing

very

faced with. some

papers

with

well We h o p e

important

in

this

however,

the

a

book

that

do

not

represent

constitute

number

of t o p i c a l

issues

climate

research

that

this volume

contributions

of

term variability

Bern,

1987

U.

may provide

current

a

complete

a collection

problems

long and short

December

they

and

an

research

is

thus

illu-

presently

insight in

Europe

of c l i m a t e .

Siegenthaler

of

H. W a n n e r

into on

VARIABILITY OF THE SOLAR "CONSTANT"

C.Frohlich Physikalisch-Meteorologisches O b s e r v a t o r i u m World Radiation Center CH-7260 D a v o s Doff, Switzerland

1.

Introduction

Since the first clear evidence of c h a n g e s in the solar "constant" S0 from the records of the Active Cavity R a d i o m e t e r for Irradiance Monitoring (ACRIM, Willson, 1979) on the Solar M a x i m u m Mission (SHM) a n d of the Hickey-Frieden r a d i o m e t e r (Hickey et al, 1980) on NIMBUS 7 proving t h a t the s u n is indeed a "variable" star, the interest on solar i r r a d i a n c e v a r i a b i l i t y on all t i m e s c a l e s h a s v e r y m u c h i n c r e a s e d (Willson, 1984: Frohlich, 1987). A t m o s p h e r i c physicists and climatologists are concerned, b e c a u s e of p o s s i b l e e f f e c t s on t h e e a r t h ' s e n e r g y balance. Solar physicists, on the other hand, became interested, b e c a u s e global c h a n g e s of the solar o u t p u t h a v e been d o u b t e d for a long time and their reality obviously leads to some revision of the u n d e r s t a n d i n g of the b e h a v i o u r of the s u n .

2. Solar Irradiance

Measurements

The solar "constant" is the solar irradiance at I a s t r o n o m i c a l unit (I A.U.= m e a n s u n - e a r t h distance) i n t e g r a t e d over the whole spectrum. I n s t r u m e n t s for the a c c u r a t e m e a s u r e m e n t of this q u a n t i t y are the so-called a b s o l u t e r a d i o m e t e r s (e.g. Kendall et al., 1970: Geist, 1972: Willson, 1979; B r u s a et al., 1986) which are also used as reference i n s t r u m e n t s for the calibration of operational r a d i o m e t e r s in meteorological networks. They are all b a s e d on the m e a s u r e m e n t of a heat flux t h r o u g h an electrically calibrated heat flux t r a n s d u c e r . The radiation is a b s o r b e d in a cavity which e n s u r e s a high a b s o r p t i v i t y (typically >99.95~.) over the spectral r a n g e of interest for solar r a d i o m e t r y (200 n m - 10 ~m). The heat flux t r a n s d u c e r consists of a t h e r m a l i m p e d a n c e a n d of t h e r m o m e t e r s (e.g. thermopile, resistors) to sense the t e m p e r a t u r e difference a c r o s s it. Heat developed in the cavity is c o n d u c t e d to the heat sink of the i n s t r u m e n t a n d the resulting t e m p e r a t u r e dif-

ference across the thermal impedance is sensed. The sensitivity of the heat flux t r a n s d u c e r is calibrated by shading the cavity and measuring the t e m p e r a t u r e difference while dissipating a known a m o u n t of electrical power in a heater element which is mounted inside the cavity. In the so-called active mode of operation an electronic circuit maintains the t e m p e r a t u r e signal constant by accordingly controlling the power fed to the cavity heater - independent of the mode, that is whether the cavity is shaded or irradiated. The substituted radiative power is then equal to the difference in electrical power as m e a s u r e d d u r i n g the s h a d e d a n d i r r a d i a t e d periods respectively. In the ideal case of a perfect substitution of radiative by electrical power, the irradiance S would simply be: S = (P,-P~)/A w h e r e P. a n d P, is the electrical p o w e r d i s s i p a t e d with the cavity shaded and irradiated respectively, and A is the area of the detector. However, there are many deviations from this ideal behaviour and the 1/A term will have to be replaced by a more elaborate expression accounting for these effects. The process of experimentally determining the size of t h e s e effects is called e x p e r i m e n t a l c h a r a c t e r i z a t i o n (Brusa et al., 1986). The uncertainty of the characterization determines the absolute accuracy of the radiometer which is of the order of -+0.2~ for present state-of-the-art solar radiometry.

,

03

E" C

O

o~

O

E 0

q~ o .%.-'--"

o

-

C O

0

CO

cw~l z

d! ~

z:

67 68 69 70~71

72 73 74 75 76 77 78 79 80 81 82 83 84

F i g u r e 1: Measured values of total solar irradiance 1967 to 1983 (for the labels see text). The full curve labeled with crosses represent the result of the satellite m e a s u r e m e n t s (one data point every month) for 1978 to 1980 from NIMBUS-7 (Hickey et al, 1982) and for 1980 to 1985 from SHH/ACRIH (Willson et al, 1986). For the discussion of the trends see section 4.

The solar r a d i a t i o n is depleted in the earth's a t m o s p h e r e by absorption and scattering, which depends strongly on the wavelength. Thus accurate determinations of So can only be made from high altitude balloons (above 35 km), rockets or spacecrafts. Determinations of $o from mountain tops were performed by the Smithsonian Institution under the leadership of Abbot (e.g. Abbot, 1942) continuing the pioneering work of Langley. Although sophisticated methods were applied to correct for the atmospheric extinction the results only marginally revealed the small solar " c o n s t a n t " v a r i a t i o n s (e.g. F o u k a l et al., 1977, Hoyt, 1979). Direct m e a s u r e m e n t s f r o m balloons, r o c k e t s a n d s p a c e c r a f t s s t a r t e d in the late sixties and have been continued to present with a g a p b e t w e e n 1971 a n d 76. The r e s u l t s are s h o w n in Fig.l: t h e Soviet balloon flights KN~, KN2 and KN3 (Kondratyev & Nikolsky, 1970, 1979), the X-15 rocket airplane flight DRW ( D r u m m o n d et al, 1968), radiometry on the Mariner Vl and VII spacecraft PLA ( P l a m o n d o n , 1969), the balloon flights of the Denver University group MUI to MU4 (Murcray et al, 1969: Kosters & Murcray, 1981), the balloon flight WIL of Willson (1973), the NASA calibration rocket flights ABI, AB2, and AB3 (e.g. Willson, 1981), the PHOD/WRC balloon flights WRI, WR2, and WR3 (Brusa, 1983) and the spacecraft m e a s u r e m e n t s on NIMBUS 7 (Hickey et al, 1982) and on SMM (Willson, 1984). These data are supplemented by the results from two rocket flights with PMO and ACR instruments: WR4 & 5 and AB4 & 5, and u p d a t e d data from SMM (Willson et al, 1986). This s u m m a r y d e m o n s t r a t e s the i m p r o v e m e n t s achieved in absolute radiometry especially since 1980. The s c a t t e r b e t w e e n the individual r e s u l t s in the late sixties is mostly instrumental, whereas the variability after 1980 is mostly of solar origin.

N

z

'`

s

Eo •--

s

a~

~z

i'` la

ts

2~

22

z',

UT-hours, Day 269 1984

c~

=-

r'l "'I 'T'I 2

~

6

8

1B

UT-hours,

12 Day

~4 189

i[ ~G

18

=-

2@

22

24

1980

Figure 2: SHM/ACRIM individual solar irradiance m e a s u r e m e n t s (every 131 s) d u r i n g one d a y in 1980 (lower panel) a n d 1984 (upper panel). The periodically missing data are due to the modulation by the spacecraft orbit around the earth with a period of 94 to 96 minutes.

3. Variability

of the Solar

"Constant"

The solar irradiance variability on time scales from a few minutes to several months is illustrated by the time series shown in Fig.2 to 4 for two different periods d u r i n g the solar activity cycle: 1980 (lower panels) around the maximum and ~984 (upper panels) close to the minimum of the solar cycle 21. Fig.2 shows the variability during one

c~

260

c~

262

26~

266

268

Eo

27~

272

274

276

278

280

Day 1984

A

~

N

N

i

180

a82

184

le6

188

i90

192

19~

19s

198

200

Day 1980

Figure

3:

days

SMM/ACRIM

in

J.980

solar

(lower

irradiance

panel)

and

data

1984

(orbital

(upper

means)

during

20

during

180

panel).

¢~

148

160

180

200

E

220

240

260

280

300

320

188

208

Z28

248

Day 1984

G8

8~

188

128

148

~68

Day 1980

Figure 4: days

SMM/ACRIM solar irradiance data (orbital means) in 1980 (lower panel) and 1984 (upper panel).

10

day. These short-term variances have a mean peak-to-peak (p-p) amplitude of about 200 ppm (parts per million) and are very similar during b o t h periods. For the 20 d a y s period s h o w n in Fig.3, however, the b e h a v i o u r in 1980 is quite d i f f e r e n t from the one in 1984 with p-p variations of 0.06~. and 0.03~. respectively. Also the main periods of the variability are quite different. This is even more pronounced for the period of 180 d a y s shown in Fig.4: the 1984 variance remains at the same level whereas the 1980 variance reaches several tenths of a percent. The short-term variations of Fig.2 are mainly due to solar press u r e oscillations (e.g. W o o d a r d , 1984, Frdhlich et al., 1984) a n d p a r t l y due to g r a n u l a t i o n . S o m e of the variability of Fig.3 m a y be caused by internal gravity oscillations with periods from several hours to d a y s (e.g. Fr~Jhlich et al., 1984: Frdhlich, 1986). The following discussion will mainly concentrate on the variations shown as time series in Fig.4 and on the trends indicated in Fig.1. The variability of the solar irradiance on time scales of days has been discussed by several a u t h o r s (e.g. Willson et al, 1981: Hickey et al, 1982) and several models have been established for the explanation of the variance mainly by sunspot blocking and facular e n h a n c e m e n t (e.g. H u d s o n et al, 1982: Schatten et al, 1982: Hoyt & Eddy, 1983~ Foukal & Lean, 1986: Pap, 1986). Host of these models are tested against the records of ACRIH/SHH and of H-F/NIMBUS-7. One issue in this context is the question whether the energy blocked by the s u n s p o t s is immediately balanced by the emissions in faculae (e.g. C h a p m a n , 1984) or whether the blocked energy has to be stored below the active regions and emerges only slowly over periods of months or years (e.g. F oukal et al., 1983). Even if the energy were exactly balanced, the irradiance at 1 A.U. would still vary because of the different spatial distribution on the solar surface and the different angular emission pattern of the two features. Recent results indicate that the facular contribution to So is at least comparable to that of spots, when integrated over m o n t h s (Foukal & Lean, 1986). This issue is very important for our u n d e r s t a n d ing of the behaviour of active regions and for adequately modelling the solar i r r a d i a n c e m o d u l a t i o n which in t u r n is needed to u n d e r s t a n d climate changes forced by solar variability. Fig. 5 shows the power spectra of ACRIM/SMM data in the frequency range up to 10 ~Hz (11.6 ~Hz corresponds to a period of I day) for 1980 and 1984. These m e a s u r e m e n t periods are before failure and after repair of the accurate pointing system of the SHH spacecraft and cover 9 and 8 m o n t h s respectively. The difference in the spectra is mainly due to the difference of the activity level of the sun during these periods. The two major peaks at low frequencies with periods of 51.4 and 23.5 d a y s are reduced by more than a factor of ten to a broad peak centered around a 17-days period in 1984 (half power points at periods of 46.3 and 10.6 days respectively). The period of 51.4 days is also found in the o c c u r r e n c e of high e n e r g y flares (Rieger et al, 1984), in the Zi/rich sunspot n u m b e r and in solar diameter data (Delache et al, 1985). Although the power spectrum o£ the projected sunspot area in 1980 shows a significant peak at 27 days, the peak in irradiance is shifted to

11

23.5 days. Cross-spectral analysis of the two spectra also reveals a very weak coherence between irradiance and sunspot area at 27 days (FrShlich, 1984, Foukal & Lean, 1986). Furthermore, the phase between the signals from sunspots and irradiance at 27 days indicates that it is more likely an enhancement which could be due to faculae than a depletion by spots. Obviously, the differences in spatial distribution of spot and faculae on the solar surface and their different evolution in time make that the individual contributions to the total irradiance signal can no longer be distinguished. The depletion of the irradiance due to sunspot blocking seems also to depend on the age o£ the spot and not only on its projected area: young and active spots have a stronger influence than old and passive spots and indeed a frequency analysis of the evolution of young and active spots in 1980 shows the same period of days as the ACRIM/SHH irradiance (Pap, 1986). Other significant peaks in the spectra are found at 7.0, 4.8, 3.4 and 1.3 days. The 4.8 and 1.3 days periods are found in the spectra of both years. In the 1984 spectrum also m a n y significant peaks between 5 and 9 ~Hz similar to the 1.3 days peak are found, the origin of which is still unknown.

23.5

4

~

8

7.0d

SMM/ACRIM 1980

i t~

Day 49-325

N ~ 3.4d

SMM/ACRIM 1984

Day123-366

7.0d

i

[2°

4.8d

,.io i

.

2

4 6 FREQUENCT ~HICROHERTZJ

8

.

.

.

~B FREQUENCT f~CROHERTZ)

Figure 5: Comparison of power spectra of ACRIH irradiance data during 1980 (277 days, left panel) and 1984 (244 days, right panel). The label R3 refers to Delache et al., 1985, and is a period found in the occurence of flares (Rieger et al., 1984). Note the lack o£ a 27-days peak present in power spectrum of the 1980 sunspot data.

Table 1 summarizes the distribution of the variance in the power spectra of 1980 and 1984. Host of the variance is concentrated in the range below about 2 ~Hz (more than 97% in 1980 and 92% in 1984) and it is also here where the biggest change in variance by nearly a factor of 7 (2.6 in amplitude) from 1980 to 1984 occurs. In the range from 2 to 5.8 ~Hz the amount is less than I% of the total variance and also the c h a n g e is m u c h smaller (factor of 2.8 in v a r i a n c e a n d 1,7 in amplitude). Above 5.8 wHz the variance is for both years very small relative

12

to the total and of the s a m e m a g n i t u d e for both years. In s u m m a r y the solar activity influences the variance of the total irradiance significantly, especially at low frequencies.

Table I: Variance of Solar Irradiance to 80 ~Hz in 1980 and 1984. Range Frequency MHz

Period days

for the frequency

Variance ppm 2 1980

1984

-

110

177000

27200

5.6

-

110

2.0

-

5.6

10

1.2

-

2.0

-

40

0.29

-

1.2

-

80

0.14

-

0.3

172000 1480 276 791 535

24900 518 236 770 635

0.1

-

80

0.14

0.1

-

2.1

2.1

-

5.8

5.8

-

10 40

range

from

0.1

Standard Deviation ppm 1980 1984 421

164

416

158

38.5

22.8

16.6

15.4

28.1

27.7

23.1

25.2

4. Long-term Trends

Trends purportedly found in the early m e a s u r e m e n t s of S0 by the Smithsonian Institution were generally doubted on the basis of the l a r g e a t m o s p h e r i c c o r r e c t i o n s involved. D e t e r m i n a t i o n s , m a d e occasionally from aircraft, balloons, X-15 rocket aircraft, and mariner satellites in the late 1960's seemed also too uncertain in both calibration and intrinsic error to allow comment on real variations in So during that period. The modern satellite data together with spot measur e m e n t s from sounding rockets and balloons, however, allow for the first time to assess confidently possible trends in So. Critical reviews of m e a s u r e m e n t s of So made after 1967 have been given e l s e w h e r e (FrShlich, 1977: Fr~hlich & E d d y , 1984" Fr~hlich, 1987). Host of the earlier v a l u e s h a v e been a d j u s t e d from original published values to conform to a common standard, the World Radiometric R e f e r e n c e (WRR). This w a s done in the m a n n e r d e s c r i b e d earlier by Fr6hlich (1977). In addition, to i n s u r e u n i f o r m i t y the a t m o s p h e r i c correction for all balloon m e a s u r e m e n t s was recomputed using the scheme adopted in the reduction of the PHOD/WRC results (Brusa, 1983). The results of the 1980 experiment of the University of Denver (HU4) can be directly compared with the results of the rocket experiments AB2 and AB3 and the balloon fights WR1 and WR2 using the NIMBUS 7 record for interpolation. Thus an absolute value can be attributed to MU4 independent of atmospheric transmission correction. As MU1 in 1969 and HU4 in 1980 were carried out at the s a m e altitude and with the same instrument, the calibration for MU4 can be transferred to HUl making use of the difference of 0.38 per cent between the two determinations reported

13

by K o s t e r s and H u r c r a y (1981). The result is labeled HUT in Fig.1. The close a g r e e m e n t between HUI, HU2 and HUT d e m o n s t r a t e s the stability of the D e n v e r i n s t r u m e n t a t i o n and s u p p o r t s the u p w a r d trend. The linear regression analysis to the spot m e a s u r e m e n t s before 1981 s h o w n in Fig. 1 s u g g e s t s an increase of the solar c o n s t a n t until 1980 at a rate of 0.029 per cent per year. This t r e n d is significantly different from zero at the 99.9 per cent confidence level. It is of the s a m e sign as the c h a n g e of 0.38 per cent between 1969 a n d 1980 noted by K o s t e r s and H u r c r a y , 1981, a l t h o u g h the slope is only a b o u t threeq u a r t e r s as great, Higher-order analysis gives an i m p r o v e d fit to the composite data, shown as the curved line in Fig. I and indicating a m a x i m u m a r o u n d 1979. One m u s t bear in mind, however, t h a t most of the d a t a t a k e n in the early p a r t of the set were the results of inherently l e s s - r e l i a b l e balloon m e a s u r e m e n t s w h i c h could be i n f l u e n c e d by a c o m m o n s y s t e m a t i c o v e r e s t i m a t i o n of the s t r a t o s p h e r i c t r a n s m i t t a n c e . In this case, one would have to a s s u m e either an a n o m a l o u s (high) concentration of s t r a t o s p h e r i c ozone a b o u t 1.5 times the climatological value - or an increased opacity due to an e n h a n c e d a b u n d a n c e of highaltitude aerosol. The latter might e n s u e from a major volcanic eruption, a l t h o u g h there was none r e p o r t e d in this period. All this s e e m s

1370

980 .....

; .....

198t ; .....

; ......

t982 ; .....

; .....

t983 ; .....

; .....

t984 ;,,:,,;

.....

1985 ;

t368

0 C

"0 m

1366 0 IROCKET/ACR SMM/ACRIM I ROCKET/PMOD 8ALLOON/PHOD

0 • [] •

t364

500 Days

iO00 since

Jan.

1.

1980

Figure 6: Time series of S H H / A C R I H daily m e a n results for the period from 1980 to 1985. The linear least s q u a r e fit s h o w n has a slope of -0,019~ per year. I n d e p e n d e n t total irradiance o b s e r v a t i o n s by s o u n d i n g rocket and balloon e x p e r i m e n t s show good a g r e e m e n t with ACRIH results (from Willson et al., 1986).

14

unlikely (see also Eosters & Murcray, 1981). Furthermore, the results from Mariner and the X-15 should be exempt from atmospheric effects and they support the lower values of the early balloon measurements. Thus it is concluded that the low values of So from the late 1960's are most probably real. For the period since 1980 the ACRIM data have been used to determine the trend as shown in Fig.6. A full discussion of this result is given by Willson et al., 1986. The linear fit for this period is calculated from the daily means of the ACRIM data and yields a trend of 0.019 per cent per year. This trend is confirmed by the NIMBUS 7 d a t a and the spot m e a s u r e m e n t s during this period and is the first clear evidence of a long-term trend of the solar constant. The extant m e a s u r e m e n t s of So from 1967 to 1985 suggest a slow oscillation in absolute value which could be part of a 22-year modulation with a peak-to-peak amplitude of about 0.4 per cent coincident with the magnetic cycle of the sun. Due to the missing data between 1971 and 1976, however, it is not clear whether the trend between 1969 and 1980 was continuous or had a dip during the minimum. Even if the l a t t e r would be the case t h e lower d a t a in 1969 could still be explained by the fact that the activity maximum in 1969 was only about two thirds of the s t r e n g t h of the one in 1980.

5.

Conclusions

The p o w e r of the i r r a d i a n c e variability s p e c t r u m from 100 nHz (110 days) to 80 ~Hz (3.5 hours) can be divided into major domains with the following characteristics:

about three

-From 100 nHz to 2 I/Hz (5.8 to 110 days) the spectrum is dominated by solar activity the power of which changes during the course of the solar cycle by up to one order of magnitude. Moreover, the spectrum is characterized by prominent peaks at periods of 51,4, 23.5, 7.0 a n d 4.8 days, The v a r i a n c e in this r a n g e a m o u n t s to 172000 and 24400 ppm 2 for 1980 and 1984 respectively.

- From 2 to 15 ~ z (18.5 hours to 5.8 days) the spectrum follows a I/~ 2 law, which may be partly due to internal gravity modes. The v a r i a n c e in this r a n g e is 1915 a n d 908 p p m 2 for 1980 a n d 1984 respectively. -From 15 ~Hz to 80 ~Hz (18.5 to 3.5 hours) the spectrum follows a I/~ law, which m a y be partly due to instrumental noise. The variance in this range is 1200 p p m 2 for both years. As to the long-term changes, trends of the order of 0.02 per cent per year do exist. The question whether the up and down trends with a

15

peak around 1980 belong to an o s c i l l a t o r y m o d u l a t i o n of t h e solar o u t p u t with a period of 11 or 22 years can only be a n s w e r e d in the future. The decrease of So from high to low activity could be due to the s a m e m e c h a n i s m in the sun which produced the "little ice age" in the 17th century in Europe, when the solar activity was very low over a period of m a n y solar cycles (e.g. E d d y , 1977). The question of the 11 and/or 22 years modulation of the solar o u t p u t is also very i m p o r t a n t in the c o n t e x t of the r e s u l t s of a n a l y s i s of a n c i e n t v a r v e s (e.g. Williams & Sonett, 1985: Sonett & Trebisky, 1986) which indicate also a modulation of the climate with a major period of 11 years and a minor one of 22 years. M o r e o v e r the r a t i o of the 11/22 y e a r s m o d u l a t i o n amplitude seems to decrease with time. As the a n s w e r is not only important for the interpretation of changes of the earth climate but also for the u n d e r s t a n d i n g of the sun itself, monitoring of the solar "constant" has to be continued.

,4cknowladgemen~% I t h a n k R.C.Willson, Jet Propulsion Laboratory, Pasadena, U.S.A,, for providing unpublished ACRIM d a t a and for m a n y helpful discussions. A c k n o w l e d g e m e n t s are extended to the Swiss National Science Foundation for their continuous s u p p o r t of this work at PHOD/WRC.

REFERENCES

Abbot, C. 1942: Revised Results of Solar C o n s t a n t Observing 1923 to 1939, /Inn. Sm.z'thBon, Ast.rophy~%Obsez'v., 6, 83, Brusa, R.W. 1983: Solar Radiometry, Dissartation ETH No, 7181, Zurich. Brusa, R.W. & FrShlich, C. 1986: Absolute R a d i o m e t e r s (PMO6) and their Experimental Characterization, 2ppl, Opt,, 25, 4173. Chapman, G.A. 1984: On t h e E n e r g y B a l a n c e of Solar A c t i v e R e g i o n s ,

Nature,

308,

252.

Delache P., Laclare, F. & Sadsaoud, H. 1985: Long Period Oscillations in Solar Diameter M e a s u r e m e n t s , Nature, 317, 416. Drummond, A.J., Hickey, J.R., Scholes, W.J. & Laue, E.G. 1968: New Value of the Solar C o n s t a n t of Radiation, Nature, 218, 259. Eddy, J.A. 1977: Climate and the C h a n g i n g Sun, Clim, Change, I, 173. Foukal, P., Mack, P.E. & Vernazza, J.E. 1977: Effect of S u n s p o t s and Faculae on the Solar C o n s t a n t , 2Btroph, J., 215, 952. Foukal, P., Fowler, L.A. & L i v s h i t s , H. 1983: A Thermal Model of As~roph, J,, 267, 863. S u n s p o t Influence on Solar Luminosity, Foukal, P. & Lean, J. 1986: The Influence of F a c u l a e on Total Solar Irradiance and Luminosity, Astroph, J., 302, 826. FrShlich, C. 1977: C o n t e m p o r a r y M e a s u r e m e n t s of the Solar C ° n s t a n t " in "The Solar O u t p u t a n d Its Variation, " ed. O.R.White, C o l o r a d o Associated University Press, Boulder, p.93. FrShlich, C. 1984: Solar V a r i a b i l i t y for P e r i o d s of D a y s to M o n t h s , Adv, Space Res,, 4, No.8, 117, Frohlich, C. & Delache, P. 1984: Solar G r a v i t y M o d e s f r o m A C R I H / S M M Irradiance Data, in "Solar SsismoYogy from Space'; ed. R.K.Ulrich,

16

JPL Publ.84-84, Pasadena, CA., 173. Frohlich, C. & Eddy, J.A. 1984: Observed Relation between Solar Luminosity and Radius, 2dv,~qpace Res., 4, No.8, 121. FrShlich, C. 1986: Solar Gravity Modes from ACRIM/SMM Irradiance Data, 2 d v a n c e s in HeYio a n d 2stroseismoYogy, ZAU S y m p o ~ i u m _/23, Aarhus. FrShlich, C. 1887" Variability of the Solar "Constant" on Time Scales J.Geophys.Re~% 92, D1, 796, of Minutes to Years, Geist, J. 1972: Fundamental Principles of Absolute Radiometry and the N a ~ A B u r , S~and, U.~%% Philosophy of this NBS P r o g r a m (1968-1971), Tech, Note, 5941. Hickey, J.R., Pellegrino, P., Mashhoff, R.H., House, F. & Vonder Hear, T.H. 1980: Initial Solar I r r a d i a n c e D e t e r m i n a t i o n from NIMBUS 7 Cavity Radiometer Measurements, Science, 208, 281. Hickey, J.R., Alton, B.M., Griffin, F.J., Jacobowitz, B., Pellegrino, P. & Smith, E.A, 1982: Observations of the Solar Constant and its V a r i a t i o n s E m p h a s i s on NIMBUS 7 Results, in "Proc, I ~ M A P Red, Comm. ,?rd Scientif-l'c 2ssembly, Ha/~burg l.q~¢l"; NCAR, Boulder. Hoyt, D.V. & Eddy, J.A. 1983: Solar I r r a d i a n c e Modulation by Active Regions from 1969 through 1981, Geoph, Res, L e ~ e r s , 10, 509. Hoyt, D.V. 1979: The Smithonian Astrophysical Observatory Solar Constant Program, Rev, Geophys.Space Phy~%, 17, 427. H u d s o n , H.S., Silva, S., W o o d a r d , M. & Willson, R.C. 1982: The Effect of Sunspots on Solar Irradiance, ~qolar Phys,, 76, 211. Kendall, J.M. & Berdahl, C.M. 1970: Two Blackbody Radiometers of High 2fpl, Opt,, 9, 1082. Accuracy, Kondratyev, K.Y. & Nikolsky, G.A, 1970: Solar Radiation and Solar ActiQuart, J,Roy, Meteor.Soc,, 96, 509. vity, Kondratyev, K.Y. & Nikolsky, G.A. 1979: The Stratospheric Mechanism of Solar and Anthropogenic Influences on Climate, in "qolar Terres t r i a l Influences on W e a t h e r a n d Climate", ed. B . M . M c C o r m a c & T.A.Seliga, Reidel , Dordrecht, Holland, p.317. Kosters, J.J. & Murcray, D.G. 1981: Change in the Solar Constant between 1968 and 1978, in "VarJat1"ons of- the Solar Co/~stan~", ed. S.Sofia, NASA Report CP-2191. Murcray, D.G., Kyle, T.G., Kosters, J,J, & Gast, P.R. 1969: The MeasTelurements of the Solar Constant from High Altitude Balloons, .lus, XXI, 620. Pap, J. 1986: Variation of the Solar Constant during the Solar Cycle,

2 s ~ r o p h y s . S p a c e Sci.,

127,

55.

Plamondon, J.A. 1969: The Mariner Mars 1969 Temperature Control Flux Monitor, JPL Space Science P r o g r a m S u m m a r y 3, 162. Rieger, E., Share, G.H., Forrest, D.J., K a n b a c h , G., Reppin, C. & Chupp, E.L. 1984: A 154-day Periodicity in the Occurrence of Hard Solar Flares?, Nature, 312, 623. S c h a t t e n , K.H., Miller, N., Sofia, S. & Oster, L. 1982: Solar Irradiance Modulation by Active Regions from 1969 through 1980, Geoph. Res. Letters, 9, 49. Sonett, C.P. & Trebisky, T.J. 1986: Secular Change in Solar Activity derived from Ancient Varves and the Sunspot Index, Nature, 322, 615.

17

Williams, G.E. & Sonett, C.P. 1985: Solar S i g n a t u r e in S e d i m e n t a r y Cycles from the late Precambrian Elatina Formation, Australia, Nature, 318, 523. Willson, R.C. 1973: New R a d i o m e t r i c Techniques and Solar C o n s t a n t Measurements, Solar Energy, 14, 203. Willson, R,C. 1979: Active Cavity R a d i o m e t e r Type IV, 2ppY, Opt,, 18, 179. Willson, R.C. 1981: Solar Total Irradiance O b s e r v a t i o n s by Active Cavity Radiometer, Solar Physics, 74, 217. Willson, R.C. 1984: M e a s u r e m e n t s of Solar Total Irradiance and its Variability, Space Science Rev,, 38, 203. Willson, R.C., Gulkis, S., Janssen, M., Hudson, H.S. & Chapman, G.A. 1981: Observations of Solar Irradiance Variability, Science, 211, 700. Willson, R.C., Hudson, H.S., Frohlich, C. & Brusa, R.W. 1986: Observation of a L o n g - t e r m D o w n w a r d Trend in Total Solar Irradiance, ~cience, 234, 1114, Woodard, M. 1984: Short-Period Oscillations in the Total Solar Irradiance, Ph.D. Thesis, Un.,'v. CaY2f.. at San Diego, La Jolla, CA.

CAUSES

OF I N T E R A N N U A L

VARIATIONS

P.D.

Jones

Climatic School

O V E R THE PERIOD SINCE 1861

and

P.M.

Research

Norwich

of E a s t

NR4

United

7TJ

and Global

Understanding ture

of the

variations

developments. and

Sciences

Anglia

Kingdom

Hemispheric

back

Kelly

Unit

of E n v i r o n m e n t a l

University

GLOBAL TEMPERATURE

in the

has

and

station

past

record

improved

the

into data

on

Second,

data

markedly

improving

global

or

it

record data

is

spatial

areas

been been

found

have

tempera-

two

recent

extended

previously

have

when

air by

has

were

based

rejected ocean

surface

significantly

where

which

from

the

of

land-based

areas

and corrected

factory.

Data

been

First,

time

homogeneity

Temperature

to

been

sparse

tested

for

be u n s a t i s -

incorporated,

representativeness

of

the g l o b a l

record.

As an

far

overall

new

the

the

National for that

changes

1986a). the

Some

in

series

applied

are

1985;

the

stations been

Library have

in

been

station

a series

et al.,

1985,

Bracknell,

such

on

and

and

technical

UoK.

The pos-

fluctu-

as

station et

others

details the

exthose

where

(Jones

Complete

analyses

of this

contain

correction

1986b).

All

through

assessed,

so

has b e e n

particularly

factors and

of

used.

records

problems.

homogeneity

there

unearthed

archives,

required

of t h e s e in

concerned,

non-climatic

records

available Jones

Many

from

because used,

et al.,

of

instrumentation,

station

stations

is

has

Meteorological

result

omitted

number

data

homogeneity.

ations

record

of m e t e o r o l o g i c a l

temperature

moves, to b e

in the

temperature

searches

individual sible,

land-based

increase

station

haustive of

as

al., had

of all

corrections

reports

(Bradley

19

Data

from

1951-70

usable

reference

latitude-longitude tion

network.

grid

Figure

for

the

the

last

Northern century.

includes

d a t a for

alone

perature. the

of

historical

million

covers

Marine

the

ease

at

ships

have

the

has

problem of

In

is a

cooling

many

or

located the

in

warmer

than

the e a r l i e r

in

data

base

It is 1940

generally and

intake

(Barnett,

1984).

it

tem-

land.

For

taken

by

compilation

as

COADS

(Com-

et

al.,

1985;

of

the

marine

ob-

approximately

temperature

land

the

the

in the

the

(SST).

bucket

It

that

of

was

The

water

and

to be

common

of

the m a r i n e of o b s e r v known

SST

from

the

use water

the

the of

a

for

latter

0.3 a n d 0.TD observations

observation

measurement

more

SST

very

observa-

well

using between

For m o s t each

of

supplying

Readings

In

fabric

most

to

ho-

land-based

the m e t h o d

pipes

method.

their

in w h i c h

speed

measuring

sea

shown

bucket

by

to

1987).

the

homogeneity

of

known how

measurement

are,

way

about

intake

subject Kelly,

for

recorded.

engines.

is not

and

size,

method

been

data,

than

the

never

have

assumed

in

a bucket

ship's

technique

the h e m i -

is

types

are

problems

information

in in

measurement

the

the

affecting

was

change

all

Goodess

overcome

and

cases,

lost

the

to

the

1984;

to

taken

thermometer

thermometer

like

data,

occurred

known

surface

in i n s t r u m e n t a t i o n ,

are

all

been

are,

(Barnett,

marine

globe

(Slutz

which

sea

of

complete

is

Set)

set c o n t a i n s

of

of

only

hemispheric

observations

most

data

areas of

the

use

The

of

middle curve

1979.

difficult

sea

database.

use

1854 to

Changes

tions

ing

numerous

observations

more

series.

data

problems of

nature,

This

the

Hemisphere

land

of

to

Data

most

since

sta-

estimates

1957.

area

instrumental

observations

the y e a r s

mogeneity

the

the

the

a regular

temperature

picture

necessary

Atmosphere

the

irregular

mean

f r o m the

opportunity'.

marine

1986).

servations, 63.25

of

is

overcome

Southern

true

from

onto

since

a

30% of

it

departures

Hemispheres

the

give

about

Ocean

Woodruff,

that

observations

'ships

prehensive

Southern

not

to

as

interpolated

annual

the A n t a r c t i c

areas,

so-called

were

in o r d e r

Note

may

0nly

marine

expressed

I shows

and

Meteorological spheres

stations,

p e r i o d mean,

w a s made.

prevailed after

before

that

time

20

1850 1,0 I

I

1870 I

I

1890 i

I

1910 I

I

1930 I

.... I

1950 I

I

I

1990 I....

I

I

I

I

I

I

I

I

I

I

I

I

I

1970

I

10

1.0

0.0

I

Fig.

I:

I

1

;

1878

ese

l

1898

I

l

1910

i

i

t930

I

l

1950

I

I

-1.o

19~

1990

Annual temperature estimates from land-based d a t a for the Northern and Southern Hemispheres. Data are exp r e s s e d as a n o m a l i e s ( d e g r e e s C e l s i u s ) f r o m the 19511970 r e f e r e n c e p e r i o d (see J o n e s et al., 1 9 8 6 a , c ) .

1850 1.0

1870

1890

1910

1930

I

I

l

I

I

I ........ I

I

I

I

|

l

i

I

1950

" I'"

l

1970

I

I

1990

I

8.0

Northern Hemisphere (degree~ C) -1.0

!

!

!

r

I..... i

1,0

|

0,0

Southern Hemisphere (degrees C)

I 1850

Fig.

I 1878

I

I 1890

I

I 1910

I

I 1930

I

I 1950

I

I 1970

I

-1.0 1990

2: A n n u a l temperature estimates f r o m SST o b s e r v a t i o n s for the Northern and Southern Hemispheres. Data are expressed as a n o m a l i e s (degrees Celsius) f r o m the 19501979 r e f e r e n o e period (see Jones et al., 1986d). Upd a t e s o f the S S T s e r i e s for the f i n a l six years have been made from adjusted Climate Analysis Center a n a l y s e s ( R e y n o l d s a n d G e m m i l l , 1984).

21

Large-scale on

board

Hemispheric compared

the

have

and

with

Intuitively, be

averages

ships

ces

between

The

consistency

Once

time

the

between

of

Figure

case

2 shows

are

similar

~

0.85).

since

of

all

SST

the

data

between

the

southern

tip

Combining forward.

Figure

series

areas.

land

3

and

shows

the

MAT

or

SST

Northern

equally while

for

1.5 t i m e s

land

ent

of

sistent

by

these

effects

the

land

and

features,

in

and

ocean.

is 1986).

ocean

Agreement even better

the N o r t h e r n MAT

186]-1979

for

N H and

Hemisphere

the

Arctic

representative 45°8.

and

variations

There

is

Ocean, of

the

are p r a c t i -

and Antarctica

data

may

the

is

land and

be

except

relatively

near

ocean

(SAT)

used land

Southern

to

ocean

Hemisphere account

Figures

I,

2

the

and

for

3

warming

model levels

the

the

ocean are

ocean

is

the d i f f e r many

con-

between

trend

the

exhibited

predictions of

for

hemisphe-

portions

show

similarities

The

with

atmospheric

series

represent

and

to

consistent

straight-

The h o m o g e n i s e d

in o r d e r

Hemispheres.

increasing

( W i g l e y et al.,

for

except

and

45°8

particular,

Southern

series of

equator

Hemisphere,

weighted

Northern

be

Northern

only

Hemispheres.

weighted

area

over the

is

combined

and Southern for

For

approach. comparison

of S o u t h A m e r i c a .

the

the N o r t h e r n ric

available

(r 2

oceans

curve

oceans between

series.

estimates

series.

hemispheric

for

northern

cally

no

anomalies The

SaT

southern

MAT

this

should

should

differen-

two

similar

SST

been data.

comparison.

curve

Hemisphere

the

the

a

MAT estimates

have

systematic

justifies

corrected,

1854.

the

COADS

(1986d).

land-based

correct

the

al.

two data sets

between

correct

and

to t h o s e

of

Southern

to

SST

Whilst

representative the

been

on

any

to

hemispheres

has

annual mean

Hemisphere

very

used

(MAT) m e a s u r e d et

reliable

Thus,

of the M A T / l a n d

Southern

SH:

be

based

differences

used

hemispheric

in the

may

Jones

f r o m the

1985).

between

be

by

more

estimates

the

series

may

on the

et al.

series

and

MAT

technique

than

the

temperature

temperatures

based

(Wigley

air

homogenised

regional

those

hemispheric

same

through

of m a r i n e

been

greenhouse

of

the

gases

22

1850 l.O

t

1878 I

I

1990 t'

I

1910 I'

I

I

I

l

I

|

I

J

1930 I '"

I

1950 I

1970 I

....

1990 I

0.0

-1.0

Northern I

HemL~here (degrees C) 1 I i I (

1.0

0.0

Southern Hemisphere (degrees C)

i

l

1850

Fig.

3:

forcing

made

(KSppen,1873), the

scales.

the

two

have

activity

first

1

I

191El

'J

1930

with

the

potential

considered

to

global

mean

Wigley

et

for

commonly

example,

E1

I

t

t

195~

-I.B

I.......

1970

the

1985,

effects

ENSO phenomenon,

for of

global

most on

solar

K8ppen,

!99e

I

of

on h e m i s p h e r i c

to

mechanisms

These

(ENSO)

Here,

factors,

temperature.

forcing volcanic to-

phenomenon

dioxide,

of

year

time-

factors,

carbon

review).

these

or

and

were

to ex-

longer

activity

causes 100

proposed and

Oscillation

probable the

temperature

been

1914).

increasing

a recent two

have

considered in

of

mean

year-to-year

Ni~o/Southern

effects be

on

variations

temperature

al.,

the

most

of

mechanisms

variations

been

(see,

estimates

causal

observed

The

factors

compare

I

factors

since

and

J

I$~'0

1878

Ever

gether

I

Annual temperature estimates from a combination of land-based data and SST observations for the Northern and Southern Hemispheres. Data are expressed as anomalies (degrees Celsius) f r o m the 1950-1979 reference period (see Jones et al., 1986d).

Possible

plain

i

variations

time

scale

we

consider

volcanoes

and

are in (see and the

23

Volcanic

effects

Explosive

volcanoes

mosphere.

Once

to

two y e a r s .

formed

into

aerosol ing

Over

in

the

from that

to cool

the

The

the

case

precipitation, immediate

ash

sun

and

the

of

a

vicinity

I: S e l e c t e d

gas

surface

(Lamb,

Volcanic

aerosols

are t r a n s -

as

secondary

scatter

Earth,

by one

or

T h e net

effect

should

the

aerosols

Volcanoes it is affect

for

amount

incom-

of

to

of the v o l c a n o

gases

known

of

are

which

solar

only

inject

readily washed

out by

the

weather

in

Events

Year

Month

1902

5

~ 14 N

61.2W

4

Ksudach

1907

3

51.8N

157.5E

5

Latitude

Longitude

VEI*

Novarupta

1912

6

58.3N

155.2W

6

Bezymianni

1956

3

57.1N

160.7E

5

Krakatau

1883

8

6.1S

I05.4E

6

Tarawera

1886

6

38.2S

176.5E

5

Azul

1932

4

35.78

70.8W

5

Agung

1963

3

8.3S

115.5E

4

Two

Soufriere) 4.

The

used

in

eruption this

scured by was

the

included

See K e l l y

Index

volcanic occurred

eruptions during

later

that

because eruptions of

(1984)

its for

the

1902.

year

earlier because

in

May

analysis

a n d Sear

the

a f e w days.

Pelee/Soufriere

NOTE:

two

resident

Event

*Volcanic Explosivity

at-

for up

the

where

likely

upper

reduce

volcanic

1970).

the

can remain

sulphur

eruption.

the

into it

process

sulphate

large

only

a

thus

troposphere,

are

and

months, in

and

surface whilst

i n t o the

ash

the s t r a t o s p h e r e

initial

reaches

the

inject

aerosols

stratosphere

material

Table

the

formation.

percent

in

can

reaches

sulphate

energy

radiation

be

ash

in

the

effects

Dust

further

(VEI

are

year. Veil

(Pelee

eruptions

Guatemala

in t h a t

high

Caribbean

Both

=

were 5)

Index

details.

=

w a s not

l i k e l y to The Agung

and VEI

be

ob-

eruption

(Lamb,

1970).

24

In

order

to

is n e c e s s a r y Various of

determine

to a s s e s s

workers

have

historical

Lamb,

1970;

tion tainty

and

of

Nevertheless, tions

most

careful

it

is

synthesis eight

were

likely

tion

drew

(1981) 1

1981).

possible

of

published

heavily

on

used

lists

had

Kelly

and

is the

uncer-

availabe. erup-

basis Sear

effects. of

of

of

which

The

Lamb

the

a

(1984) selec-

Simkin

from

date

of erup-

1881-1980

catalogue

the

(e.g.

with

and

periode

information

volcanoes

basis

on

historical

On

climatic

geological

supplementary

these

the

significant

the

the

material,

the

so

that

climate.

during

on

fraught

it

eruptions.

assessment

is

identify

climate,

and

information

affected

volcanoes

catalogues

evidence,

effect

to

have

on

volcanic

Inevitably,

limited

to

to h a v e

and

eruption

climate

the

likely

identified

Table

et al.

influence

of p a s t

geological

potential

because

volcanic

compiled

accounts,

Simkin

size

the

the m a g n i t u d e

et

al.

(1970).

major

erup-

tion.

To

examine

the

temperature, 1962;

see

carried

out.

months as

a

also

First,

after

each

dual

The

and

analysed

the N o r t h e r n used

in

results. 1861

and

One-tailed cause

the

500 1980

land

assess

were

have

warming. line.

the

of

used

and

Hemisphere.

been The

ocean

determine used

as

A

indivifea-

Hemisphere We

series

for

approach

was

of

the

events

between

significance

levels.

volcanoes

significance

level.

significance

5%

36

eruptions).

Carlo

chosen

the

common

temperature

randomly

60

b y month,

four

the

was

the

for

(Northern

Monte

statistical

four to

4a

Hemisphere A

Pollak,

temperature

emphasises

Figure

(Southern

combined

to

dashed

4b

in

month

the

mean

1987) for

temperature

averaging

in t h i s w a y

shown

Southern

analyses

tests

surface

horizontal

Figure

and

order

are

expressed,

by

and

et al.,

estimates

prevailing

formed

hemispheric

(Conrad

temperature

the

on

a n d Sear

hemispheric

then

Averaging

analysis

1984,

date were

mean

event, was

results

eruptions) have

the

eruptions

epoch ~ear,

hemispheric the

response

responses.

tures.

and

eruption

from

before

composite

of t h e s e

superposed Kelly

departures

months

effect

level

are is

unlikely plotted

as

to a

25

-38 I

e,5

-2e I

-10

0

40 I '

10

20

30

I

I

I

....

.

~X

I

50

60

I

Ii

~) _~

0.0

.... . ~ . ~

n~

I

"i ~ ,~~ +i

•

-e.5

I

I

Ho~thernHemisphere (degreesC>

I

I

I

S..~.~...S~..~...?..+'Y~.

'

I -3e e,5

-30 I

I -20

I -10

-20 I

-10 I

I

""

°

I

I

0.5

.'. . . . . . . . . . . ~ . .

+'+

Southern Hemisphere (de~ree~ C) 'I I I l I -e.5 le 20 30 48 5~ &O

0 8

18 I

20 I

38 I

48 I

50 I

b)

. . . . .

Northern Hemi~phePe (degree~ C) -0.5

1

I

. _

I

I

I

1

1

1

IL.. .I~'&!._L~_ pnn.~

_ _ _

. . . . . . . . .

I -:so

4:

Figure

The

about

of Northern

temperature 0.3°C cooling

effect

of

is d e l a y e d

Hemisphere the

event.

So~thern Hemisphere (degree~ C> l I I 1 I I -e.s le 28 3e 4e 5~ 6e

o

with to

to

have

a

month

Hemisphere

the

Hemisphere

Hemisphere

extremely within

prior

Southern

appear

Southern

is

occurs

slight

tions

I -1o

maximum

few

signifloantly,

of monthly hemispheric SST estimate). (a) N o r (b) S o u t h e r n Hemisphere

eruptions

rapid

-

the

months

zero

on N o r t h e r n

maximum

of

the

eruption.

can

be

considered

on

southern

effects,

about

effect

0.2°C.

eruptions

by

0.15°C,

about

noise.

Northern

cool some

two

of The The

temperatures

on t e m p e r a t u r e s

southern

Hemi-

response

eruptions

a negligible but

0.°

. . . . . . . . . .

Superposed epoch analysis temperature data (land and thern Hemisphere eruptions; eruptions.

effect

sphere

I -2e

6.5

the

erupin the

Northern

years

after

26

Whether tion

of

these

this

tribution,

or

from

each

hemisphere

that

the

to

greater

rapidly The

than

oceans

the

land

of

the

magnitude

Northern

Southern

of

the

Hemisphere

pollutants Southern

were

less

eruptions

substantial known

to

after

the

have

land

is

to

in

the

were

in

the

northern

affected

the

characteristics

(1987)

has

tures

is

curve

The

that

events

of g l o b a l

in t h e

tropical

warming

Southern

characterised

by

The

Oscillation

tremes global

Walker

of the

Oscillation The the

most

of

Southern

are

the

to

the

Southern

in

and

northern seen

and is

Europa

most

of

the

this

may

response.

on be

zone

seen

summer the

1969;

a

the

are

Bradley tempera-

in

and

the

upper

known

to be

The

Oscillation

Carpenter,

one

extreme

1932;

in

relevant

the of

and

major southern

1957). to

events) Taken as

WMO,

indices.

Pacific,

also

together,

the

in

the the

positive may

of

1985),

shifts

complementary (cold

referred

and

with

Bliss,

measure

central

now

Rasmussen

associated

(Berlage,

exbe

of

these

E1Nifio/Southern

phenomenon.

commonly in

Ocean

departures is

collectively

(ENS0)

difference

are

Circulation.

significance

variations

Pacific

Walker

negative

distribution

so-called

the

and

Hemisphere

were

or

can

reduce of

Phenomenon

(Bjerknes, events

Oscillation

Southern

the

Finally,

effect

This

Oscillation

significance

These

pressure

volcanic

latitudes

equatorial

of

more

4a.

E1Niflo/Southern

1982).

the

seasonally-dependent.

in F i g u r e

E1Niflo

the

noted

spring

or

most

of

due

inertia.

delay

Northern

1970).

also

respond

in is

is

transported

sunsets

(Lamb,

to

thermal

Most

the

eruptions have

been

dis-

ocean

explanation

to

southern to

and

However,

higher

have

Remarkable

eruption

able

quantities.

loca-

Hemisphere

tend

in

land

lower

effect.

the

seasonal

likely

their

of m a t e r i a l

occurred.

Krakatau

Northern

were

large

were

transport

most

the

Hemisphere

likely in

of

The

to

volcanic

eruptions

Hemisphere

Hemisphere

The

owing

from

their

percentages

in

area.

areas

result

eruptions,

certain.

response

ocean

response

of

relative

not

rapid

in

sample

the

is

more

the

differences

particular

used monthly

index mean

of

the sea

Southern level

Oscillation

pressure

is

between

27

Tahiti,

Society

Oscillation

Index

Ropelewski back

to

Darwin this

Islands,

and

1866

(SOI)

Jones

based

I

has

Australia.

recently Here,

been we

Chile,

in p l a c e

in F i g u r e

1880 I

190B I

1

I

of

This

extended

use

on d a t a f r o m D j a k a r t a ,

are p l o t t e d

18~

Darwin,

(1987).

and Santiago,

index

and

a

Southern

to

1882

further

Indonesia, Tahiti.

by

extension in p l a c e

Annual

of

values

of

5.

1920 I ' l

1940 I

I 1929

I 1946

I

1760 l

I

1988 I

8.0

-3,8

Figure

E1

is

extremely America. Peruvian (1987)

I

I 1900

defined

cold water Using

I

Quinn

SST and

relationship

temperature and,

the

is

second,

et

I

I

I 19'68

23

al.

warm

1980.

between examined through

occurrence

coast

variation

identified 1880

by

off the

the

coastal

between

relation sis.

best

have

The mean

I ! 88e

I

I 1 ~8~

5: A n n u a l ( J u l y - J u n e , d a t e d b y the J a n u a r y ) e x t e n d e d S o u t h e r n O s c i l l a t i o n Index.

Ni~o

events

I

of

and

The y e a r s the

ENS0

in two the u s e

and Ecuador catalogue

the

events

SOI,

(El are

listed

first,

of

warm

or

in S o u t h E1

Bradley

Ni~os)

indicators ways:

of the

of e x t r e m e l y

Peru

(1978)

values

and

et 20

in T a b l e

Ni~o al. cold 2.

and hemispheric by

of s u p e r p o s e d

direct epoch

cor-

analy-

28

Table

Warm

2: E N S O W a r m

and Cold Events

(El Niflo) y e a r s :

1884

1888

1891

1896

1899

1902

1904

1911

1913

1918

1923

1925

1930

1932

1939

1951

1953

1957

1963

1965

1969

1972

1976

1886

1889

1892

1898

1903

1906

1908

1916

1920

1924

1928

1931

1938

1942

1949

1954

1964

1970

1973

1975

Cold years:

a) D i r e c t

Correlation

Coefficients SOI

and

perature

The

formed

over

stability plained

ture

two

the

some

should

spring

This

by

have any

SOI.

increased

immediate

when

months.

The

each

global

effect

the

25

and

of

m a y be

should of

an SOI

0.15°C, of

the

accounted

six months

with by

ex-

tempera-

30%

is t h e n

departure

eruption

12

the

was

the

temperatures

temperatures of

check

variance

about

event,

to

was per-

period.

series

+ve/-ve

1982/3

to

leads

Between

up

analysis

more

the SOI

of

the tem-

intervals

The

earlier

Global

for

the e x t e n d e d with

1926-1984,

temperature

value.

0.05°C

particular

and

lag relationship

forecasting

lowered/raised this

six

6.

Slightly

is s t r o n g e s t

between

averages

monthly

d u r i n g the

the h e m i s p h e r i c SOI.

by

in F i g u r e

relationships.

about

computed

1867-1925

relationship

by

of

S0I

shown

periods,

the

the

series

mask

were

temperature

the

are

relationship

for b y

of

lagging

results

of

by

variance

of

determination

series

months.

The

of

12-month hemispheric

E1

be

one u n i t of

N

-3,

enough

to

Chichon

in

1982.

b) Sup,erposed epoch method Superposed volcanic events separate

epoch case.

listed

analysis The

in

analyses.

was

Januarys

Table The

2

applied

in the

of

warm

were

results

the used are

as shown

same (El

the in

key

way

Ni~o)

as

months

Figures

in the

and

7a

in

cold two

(warm)

29

and

7b

using

(cold).

the

priate

number

here,

Two-tailed

Monte

Carlo

of

compared

events. to

significance

technique

the

The

by

levels

randomly

significance

volcanic

case,

were

assessed

selecting levels

the

are

because

appro-

much

there

lower

are

more

events.

0.5 I N ° r t h e r n

#

Hemisphere

I

0

1

2

3

0.5

]Southern

°'°

0

O.5

I

R~

I

6

7 8

9 1'0 1"1 1"2

Hemisphere

~ ~ ~, 5

Globe

0.25

~, g

~

~ ~

§ 1'01'i 1'2

~-

-1925

---

"~"

~"

0.0

0 1 2 3 4 5 6 7' 8 9 10 11 12 L a g ( m o n t h ) of the 1 2 - m o n t h l y t e m p e r a t u r e aeries behind the 1 2 - m o n t h l y SOl Figure

Most

6:

warm

of t h e

year

during

the

cold

Lagged coefficients of determination between the Southern Oscillation Index and hemispheric temperature series (land and SST estimate).

(El with

Niflo) the

following

periods.

temperature

uary

the

of

lags of

of

Figure

when

six months

the

effect

year

of

7

or

year.

one

behind the

on t e m p e r a t u r e

tend here

The

the

the

10

to

results

considers

warm

The

that

some

to

that

SOI which,

or

of t h e

cold warm

commence

showing

July.

shows

occurs

selected 6

used

June

Figure

spheric

events

SOI

event and

the

timing

around greatest

is s i m i l a r

maximum 16

months

are

turn,

cold

some

lags six

events

is

the

hemi-

the with

temperature

by

turn

for on

after

compatible

the in

effect

the

response

Janthose

response

the

January

months.

The

similar:

a

30

warming/cooling January low

key

temperatures

Bradley

of

0.1

date.

et al.,

-8.25

to 0 . 2 ° C

Note

the

during

some

apparent

the

10

to

16

precursor

previous

year

months of

(Figure

after

a warm 7a,

the

event:

see

also

1987).

0

-38

-28

-18

10

20

30

40

5~

60

I

l

I

I

i

I

I

,

~

i

i

I

-30

-20

-10

IO

2~

30

40

50

60

-30

-20

-10

10

20

30

40

50

6~

t

I

I

i

Northern Hemisphere (degrees C) I t I I I I

0.25

So~thern Hemisphere (degrees C)

!

I

O

I

-0.

b) O.BO ................

I

,'},

n.,~

I

I

,

~...~.....~-,.,~-

II. . . . . . . . . . . . .

7:

(desPees C) I I

_rl..f

,-,~thern

Figure

misphere I

I

I

I

l

-3O

-28

-I0

Superposed epoch temperature data (El N i ~ o ) events;

Hemisphere (degrees C)

!

!

!

le

28

3~

,

|

I

48

58

69

analysis of monthly hemispheric ( l a n d a n d SST e s t i m a t e ) . (a) W a r m (b) c o l d events.

31

Conclusions

Large

explosive

volcanic

eruptions

and

the

ENSO

phenomenon

have 0

been on

shown

to

have

hemispheric

lived.

The

months

and

similar

temperature.

duration

mediately

of the

it

occurs

after

the

at

The

are

responsible

annual,

high

frequency

of the

are

effect

time

or

for

order

effects

maximum some

volcano

factors

ture

effects,

warm

or

between

variability

50 in

of the

cold and

the

to 0.2C,

relatively

is

within

of 0.1

the

short-

order

of 6

two

years

im-

event.

These

two

50%

of

the

hemispheric

inter-

tempera-

records.

Ackngwledgements

This ergy

work

was

under

acknowledge

supported contract

by

the

number

the c o m m e n t s

United

States

Department

DE-FG02-85ER60316.

of Ms.

C.M.

Goodess

The

of

En-

authors

on an e a r l i e r

draft

of the m a n u s c r i p t .

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in

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P.D.,

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1984.

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Southern

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surface

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surface

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objective analysis.

global Tropical

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1987: Monthly

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surface

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in wind

354-384.

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temperature

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temperature

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Southern press).

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Monthly

monthly

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to

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SCOPE

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Set

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P.M.,

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NOAA

Technical

CLIMATIC INFORMATION FOR THE PAST HUNDRED YEARS IN WIDTH AND DENSITY OF CONIFER GROWTH RINGS

F.H.

Schweingruber

Swiss Federal

Institute of F o r e s t r y Research

CH-8903 Birmensdorf

i. Introduction

Growth rings of trees growing in areas with a seasonal climate c o n t a i n climatological subject, made,

information.

e.g. Fritts

There is an extensive literature on this

(1976). However,

most d e n d r o c l i m a t o l o g i c a l

although many studies have b e e n

investigations

in the n o n - a r i d zones

of the earth h a v e met with little success and r e c o n s t r u c t i o n s on a y e a r - b y - y e a r basis h a v e seldom proved possible. All r e c o n s t r u c t i o n s

so

far a t t e m p t e d h a v e been formulated in terms of one or another moving average over a defined period,

e.g. a decade,

and h a v e almost exclus-

ively been based on measurements of ring width. r e c e n t l y given rise to new approaches,

Those limitations h a v e

which are d i s c u s s e d below.

- Greater a t t e n t i o n is b e i n g paid to the selection of sites and individual trees,

since it has been shown that site factors exert a

stronger influence on growth ring formation than regional c l i m a t i c conditions,

e s p e c i a l l y in areas with a temperate climate.

- To allow due c o n s i d e r a t i o n of the great v a r i a t i o n in growth ring anatomy,

the l o n g - e s t a b l l s h e d p r o c e d u r e of dating through pointer

years has been b r o u g h t into r e l a t i o n s h i p to c l i m a t i c and e c o l o g i c a l factors, with proper a t t e n t i o n to abrupt changes r a d i o d e n s i t o m e t r i c methods h a v e b e e n expanded;

in ring width;

tissue analysis has

36

been refined;

and isotope research related to growth rings and cli-

mate has been undertaken. Figures

la und lb show the morphological

ria in dendroclimatological

features used as crite-

research.

The examples given below illustrate how these new methods can greatly extend the present knowledge on dendroclimatology and that growth rings,

as sources of proxy data, can supply information on

climatic conditions over long periods of time and great geographical distances.

a

bl 1980 t974 o_o ~ t961 ~ 1958 b2

1 2 maximum densities

1,0

3

4mm

0

lJ ring widths 0,8 Q

.~ 0,6 0,4

0,2b

J

Fi~. %a Growth ring sequence from a fir displaying pointer years (growth changes within one or two years) and abrupt growth reductions (persisting for several years). Those changes which can be identified and dated by the naked eye are expressions of severe changes in the physiology of the tree. Such changes are often triggered by extreme effects of the climate (summer drought, cold periods, extremely low temperatures in winter, etc.). Fi 9 . ib Parallel diagrams from a larch sequence with pointer years; bl: tomicrograph, b2: corresponding density profile. Five different ameters of such curves are selected for interpretation. Maximum sity and ring width contain by far the greatest climatological mation.

phopardeninfor-

37

2. Temperature reconstructions

Studies by Parker and Hennoch Hughes et al.

from conifers

(1971),

in Europe

Schweingruber et al.

(1978) and

(1984) have shown that the maximum density of different

species of conifer growing on cold and wet sites in the Alps and in Scotland generally contain information on temperature during the summer months from July to September. density chronologies

Response functions

for maximum

from northern Scandinavia provide data on tem-

perature during July and August,

while those from the mountain ranges

of Central and Southern Europe supply information on conditions during July, August and September.

Ring width, on the other hand,

clearly related to weather conditions,

is less

since it is far more strongly

influenced by local site conditions prevailing d u r i n g the relevant vegetation period and the preceding year. Maximum density integrates climatological

information to a greater degree than ring width, be-

cause it is mainly an expression of the cell wall thickness of the latewood cells.

Since these survive for 2 to 3 months,

upper and northern timberlines, growth factors,

even at the

they are able to reflect limiting

in this case temperature.

Ring width,

an expression of the performance of the cambium,

in contrast,

is

whose main activity

is limited to two to four weeks in early summer. These considerations and observations led to the construction of an ecologically uniform sample net. In order to maximize the reflection of temperature

in the growth-ring patterns,

samples were taken

from normally grown trees on the coldest and the wettest sites in both the upper and the northern timberline zones, ologies

i01 local indexed chron-

(2 cores from each of 12 trees per site) were used to con-

struct 22 regional chronologies.

The growth-ring data (maximum den-

sity) were calibrated by comparing maps of annual anomaly patterns of densities or their index values, with maps of the corresponding perature anomalies

(= departures

tem-

form the the long-term average).

The

reference period for maximum density was the overall temporal range of the chronologies,

that for summer temperature the reference period

1881-1980 considered by Jones et al.

(1982).

Visual comparison of the maps revealed similar to very similar patterns

in 4/5 of the cases

(Fig. 2, Appendix).

Discrepancies can be

explained through gaps in the meteorological data and through differences in growth limiting factors in various regions of Europe, instance,

for

the growth period is limited to July and August in northern

38

Scandinavia but extends from July to October in southern Italy. Furthermore,

the possibility cannot be excluded that in years with ex-

treme conditions,

e.g. 1948, growth was not limited by temperature

alone on some sites. Similar growth maps were constructed on the basis of ring width, but it has not yet proved possible to decode the climatological mation they contain in year-by-year

infor-

terms.

This study shows that density analysis permits very reliable reconstruction of temperature patterns sphere

(boreal zone, upper timberline

for the whole Northern Hemiin mountains).

Reconstruction of

precipitation over fairly large areas is equally possible. dition, however,

The con-

is that the samples be uniformly taken the lower

timberline zone, where precipitation is essentially the only growthlimiting factor (Fig. 3; Fritts 1974, Stockton et al. 1981). Networks comprising trees on differing sites are unlikely to provide uniform climatological

signals.

Consequently,

year-by-year

reconstructions

cannot be made on the basis of data from such networks, structions

and recon-

for longer periods are always accompanied by broad,

incalculable deviations

3. Limitations of dendroclimatolo~ical

The influence of growth-limiting

research

factors varies greatly between spe-

cies and between sites, especially on non-extreme sites. study such relationships,

often

(Shiyatov and Mazepa 1986, Fritts 1974).

Lingg

In order to

(1986) investigated the differences

between spruce and fir over the past 80 years along altitudinal transects in the Valais

(Fig. 4). Ecophysiological behaviour differs quite

considerably from species to species.

In firs both maximum density and

ring width in trees growing on low and high altitude sites correlate with each other.

Only in trees of the subalpine zone does maximum

density fail to reflect differences between site or species. probable that too little attention

is being paid to the difference

ecophysiological behaviour between species dendroclimatological

networks.

It seems

in the construction of

in

39

0 C3

-0,5

°°i/la --I

00 -~ F i 1600

I

~

,

I

i

A i

i

1650

~

I

'

1700

i

L

i

f

~

1750

i

i

;

I

i

1800 Year

~

i

i

~

i m--~T'7

1850

1

i

1900

,

i

,

I

1950

Fi 9 . 3 R e c o n s t r u c t e d fluctuations in temperature and p r e c i p i t a t i o n based on new ring width chronologies from the Great Plains, USA. Relationships b e t w e e n ring widths and recorded m e t e o r o l o g i c a l parameters are calib r a t e d for the period 1900-1970. (Circles: m e t e o r o l o g i c a l measurements, lines: reconstructions, smoothed with a low pass filter). After Fritts (1983).

Climatic differences,

varying from year to year,

are strongly

modified by local site factors and affect ring formation accordingly. In a r a d i o d e n s i t o m e t r i c a l

study Kienast 1985 clearly shows the re-

l a t i o n s h i p b e t w e e n different growth ring parameters and relief. The influence of site factors on growth ring formation in the mountainous

areas of the temperate zone is summarized below

- Where the regional climate is cold and moist, altitude sites is severely limited, altitude sites is o p t i m u m

-

(Fig.

5).

growth on moist, h i g h

while growth on shallow-soil

low

(Type A).

Where regional climate is warm and dry the situation is reversed: growth is o p t i m u m on moist, h i g h altitude sites but minimal on shallow-soil low altitude sites

(Type B).

- Where regional climate is cold and dry, growth is o p t i m u m on b o t h dry, h i g h a l t i t u d e sites and moist,

low sites, but limited on moist,

h i g h altitude sites by the low summer temperatures and on shallow, low altitude sites by low p r e c i p i t a t i o n

(Type C).

40

fir

fir/spruce

spruce

E EEEEE

EEEEEE

E EEEEE

uu

~el~e

840mN 1230mSW

~

1740 m N

O ~

®

(~)@~ID

1850mSSE ® O e ~

a

® ®

ice® eee eee eee e•

®iO

•

D~-

w

•

•Oe

!

e•e

classes of gleichl~ufigkeit O 59,2-63,0 p=0,05 ® 6 3 , 1 - 6 7 , 3 p =0,01 6 7 , 4 - 7 1 , 9 p =0,001 7 2 , 0 - 76,0 76,1 - 79,9 • > 80

ring width 840 m N 1230 m SW 1240 m S 1510 m N 1740 m N 1850 m SSE

Fig.

ee®®

I

'o~ o

4

Relationships (Gleichl~ufigkeit) of maximum density and ring width between firs (Abies alba; le~t), spruces (Picea abies; center), and (right) between firs (vertical) and spruce (horizontal), along an altitudinal profile in the Valais, Switzerland for the period 19001980. Firs and spruces are from common sites; cores were taken from 12 firs and 12 spruces at each site. After Lingg (1986). The difference in behaviour between the two species and the ring parameters is evident. Firs display greater similarity over a fairly wide spectrum than spruces. This may be mainly due to the different types of root systems. While the deep root system of fir allows an efficient water supply throughout the year, the shallower, more superficial one of spruce often leads to growth inhibition through low precipitation, p a r t i c u l a r l y on low altitude sites. Fir:

maximum density: ring width

trees on all sites behave similarly. trees on sites above 840 m behave similarly, the low altitude site (840 m) behaves differently.

Spruce:

maximum density:

the trees on the lowest two sites (840 and 1230 m), the two sites at 1230 m and 1240 m, and the three highest sites display relationships among themselves. the trees of the four lowest (840-1510 m) and two highest sites display relationships among themselves.

ring width

Fir/spruce r e l a t i o n s h i p maximum density: ring width

the two lowest sites differ clearly from all the higher ones. the pattern is similar to that of spruce alone.

41

climatic conditions cold-moist

warm-dry

cold-dry

Type A

Type B

Type C

dry--moist

dry~mdist

E

t

g°

i __

cD

dry--moist

Fi~.

5

Idealized dendro-ecological diagram, showing the relationships b e t w e e n different altitudes (ordinates) and site moisture (abscissae) during years with differing weather patterns. Optimum ring growth is represented by black shading, minimum growth by white. After Kienast (1985).

year dendroecologicaI diagram and type maximum density

1910

1911

1912 maximum density or ring width

A

m very high m C

C

high

[]moderately high moderately low

ring width ]low ] weather temperature

very tow

oC 20 o

I II III IV precipitation quarters and months

I II III IV

Temperatureand precipitation abovethe long-term mean (1901-1971) m

Fi@.

Temperatureand precipitation below the long-term mean

6

Temporal series of dendro-ecological diagrams for maximum density and ring width in trees growing in the Valais (Switzerland) and the nearby meteorological station at Sitten. Arrangement of sites (squares) as in Figure 5 (vertical: altitude, horizontal: dry-moist). Growth at high altitude sites was considerably reduced during the cold years 1910 and 1912, while the dry conditions of 1911 impaired growth on the lower sites. After Kienast (1985).

42

Fig. to year

6, however,

shows that the limiting factors vary from year

in their effect on the specific ring p a r a m e t e r

the weather pattern.

That means that it is p o s s i b l e to extract

mation on d i f f e r e n t climatic components ring sequence,

p r o v i d e d that a number of site c h r o n o l o g i e s

e m p l o y e d in d e n d r o c h r o n o l o g y

infor-

from one and the same growth

ered in r e l a t i o n to each other. Unfortunately,

functions)

according to

are consid-

the p r o c e d u r e n o r m a l l y

for the analysis of time series

does not permit the limiting ecological

(response

factors to be deco-

ded on a y e a r - b y - y e a r basis.

% 1885 93 60'

94 191t

30. o,

t2

21

22

42

44

48

49

50

62

65

68

74

76

m

_n l.l_n..n N-m._l.N.m.mn

1400-1500

203

1300-1400

12

12001300

182

,_.,.Inn.n..l_.,

1100-1200

140

mmm,_ln,,,,m..,N_.mll

1000--t100

79

900-1000

66

800-~ 900

112

700°° 800

48

400-700

48

. ,

.llmmmll

n,n,.nl.,n,nl..nm n,.,,.,n Innn nNNN-

30-

0

144

t500-1600 i186

:":'"'":I;:::]

6c

height&sJ. ~max 1600-1900

I.,n,l.l..i I• l n t . t . ! 70%

. n . ,

nno;,

nm.liimn_llm

,,°Z

A l t i t u d i n a l d i s t r i b u t i o n of pointer years in spruce in the Valais, Switzerland, since 1885. The height of the columns represents the p e r c e n t a g e of spruces at p a r t i c u l a r altitudes with pointer years (Nmax.: m a x i m u m number of spruces investigated). It is n o t i c e a b l e that pointer years are only formed on h i g h a l t i t u d e sites during cold years, e.g., 1912. In n o n - e x t r e m e dry years they are m a i n l y formed on sites at lower altitudes, e.g., 1942, 1944. After Kontic et al. (1986).

43

A l t i t u d i n a l r e l a t i o n s h i p s have been d e s c r i b e d by Kontic et al. (1986),

the i n t e r p r e t a t i o n being mainly b a s e d on pointer years,

that

is, growth rings which,

for the m a j o r i t y of trees on a p h y t o s o c i o l o g i -

cally h o m o g e n e o u s

are m a r k e d l y wider or narrower than the pre-

site,

ceding or subsequent ones

(Fig. 7).

In the upper timberline zone,

tree growth is mainly limited b y

low temperature during the vegetation period, 1965,

for example.

as h a p p e n e d

At lower elevations the limiting factor is p r e c i p i -

tation during summer,

witness

1921,

1942,

1944,

1949,

1976 etc. On

medium altitude sites in the temperate zone the limiting greatly,

in 1912 and

factors vary

indeed to such an extent that it is not yet even possible

to

explain the o c c u r r e n c e of pointer years coinciding over wide areas. These three cases show the overriding n e c e s s i t y of extreme care in selecting sites for d e n d r o e c o l o g i c a l

% 70

studies.

spruce, canton of Solothurn n = 480 lOO E

"3

~ 6o

8o 60 ,~

z _c 40-

so20-

1900

ao g

ii

i

10

20

30

40

50

60

70

1980

Fi 9 . 8 S u m m a t i o n diagram for spruces with growth reduction in the canton of Solothurn, Switzerland. The d i a g r a m shows the p e r c e n t a g e of trees whose growth has b e e n reduced since 1910 in c o m p a r i s o n to the p r e c e d ing period (black: over 71%, hatched: 56-70%, white: 40-55% growth reduction). The fluctuations are evident. The phase of growth reduction b e t w e e n 1945 and 1954 is conspicuous.

44

Abrupt growth changes were long regarded in dendrochronology disturbances, disease,

as

since they often reflect individual changes such as

injury to the photosynthetically

active crown, or alteration

in the vertical position of the tree. Recent studies, however, have shown that abrupt growth changes persisting for more than three years incorporate climatic signals. A supra-regional

study of growth patterns over the present cen-

tury in several thousand conifers of different

species in Switzerland

revealed a certain trend towards a periodicity of 11-16 years, seems to be mainly governed by deficits (Figs.

which

in summer precipitation

8, 9). It is quite obvious that some of these growth changes

are due to local pollution,

disease,

or impairment of the site through

soil compaction or sinking of the ground water level. dendrochronological

It is a task for

research to clarify the origin of these irregu-

larities. a) duration of growth reduction

1910 Valais

spruce

1920 t

1930

1940

I

Solothurn Mittelland Aargau Fricktal

I

1980 n I I ] 327 I

I I

197

,,I I

i

,,,

202

t I

500

t

634

F............ ~'i~ ~................ t 4

Valais Solothurn

480

I I

I

Chur

fir

1970

1960

1950

p...~

!

Aergeu

I Chur.910~10 VaEaie c duration of grovvth-b) summagon diagram ._ ,g 14 I reductions V

,[

[

464

I I

620

II

494

I

Pine

,.V.16

Vll

621

rV__ 12

5539

.u / / / / ~ . .

--~g d) precipitation deficits

o

o_ & 3oo

""

"

" ~ _

l!i year

1910

1920

1930

1940

1950

// ',

if !ll,li I 1960

1970

1980

Fig. 9 Duration of growth reduction phases in different conifers (5539 trees) growing in different regions of Switzerland in relation to precipitation deficits in the months May-August as measured at the meteorological stations Rheinfelden, Olten and Aarau. The fluctuations are closely related to periods with low precipitation. After Schweingruber et al. (1986).

45

:~:;::i::i::!iiii:;::iiii~if

t

~

I

J

I

'

[

J

I

i ,--~'--~

~

~

~

~

o

E o~ LU i~ o

~

~

~

o

T

°

46

,,iF k ii/p ii/p ..

47

.......... i~i~i~i~i~i~i~i~ ~i~i~i~i~i~i~i~i~ili~i~i~i~i~ili ........................

48

~l~~ ~~

49

IW

50

51

#

52

f~

53

54

iiIF

55

References

Fritts, H.C., 1974: Relationships of ring widths in arid-site conifers to variations in monthly temperature and precipitation. Ecological Monographies 44, 411-440. Fritts, H.C., 1976: Tree rings and climate. Francisco. Academic Press, 567 pp.

London,

New York,

San

Fritts, H.C., 1983: Tree-ring dating and reconstructed variations in Central Plains climate. Transactions of the Nebrasca Academy of Sciences, XL: 37-41. Hughes, M.K., Schweingruber F.H., Cartwright, D., Kelly, P.M., 1984: July-August temperature at Edinburgh between 1721 and 1975 from tree-ring density and width data. Nature 308, 341-344. Jones, P.D., Wigley, T.M.L., Kelly, P.M., 1982: Variations in surface air temperature: Part i. Northern hemisphere 1881-1980. Monthly Weather Review ii0, 59-70. Kienast, F., 1985: Dendro~kologische Untersuchungen an H~henprofilen aus verschiedenen Klimabereichen. Ph.D. thesis, Univ. ZUrich, 129 pp. Kontic, R., Niederer, M., Nippel, C.A., Winkler-Seifert, A. 1986: Jahrringanalysen an Nadelb~umen zur Darstellung und Interpretation von Waldsch~den (Wallis, Schweiz). Eidgen~ssische Anstalt fur das forstliche Versuchswesen, Berichte 283, 1-46. Lingg, W., 1986: Dendro~kologische Studie an Fichte (Picea abies) und Weisstanne (Abies alba) im subkontinentalen Klimagebiet (Wallis, Schweiz) Eidgen~ssische Anstalt fur das forstliche Versuchswesen. Berichte. 287, 1-81. Parker, M.L., Henoch, W.S.E., 1971: The use of Engelmann Spruce latewood density for dendrochronological purposes. Canadian J. of Forest Res. l, 90-98. Schweingruber, F.H., Fritts, H.C., Br~ker, O.U., Drew, L.G., Schaer, E., 1978: The X-ray technique as applied to dendroclimatology. Tree-Ring Bull. 38, 61-91. Schweingruber, F.H., Albrecht, H., Beck, M., Hessel, J., Joos, K., Keller, D., Kontic, R., Lange, K., Nippel, C., Spinnler, A., Steiner, B., Winkler, A., 1986: Abrupte Zuwachsschwankungen in Jahrringabfolgen als ~kologische Indikatoren. Dendrochronologia, 4, 125-183. Shiyatov, S.G., Mazepa, V.S., 1986: Natural fluctuations of climate in the eastern regions of the USSR based on tree-ring series. Paper presented at the workshop on Regional Resource management. September 1985, Albena, Bulgaria. Collaborative Paper Internat. Inst. for Applied System Analysis. A-2361 Laxenburg, Austria. Vol. I: 47-73.

56

Stockton, Ch.W., Mitchell, L.M., Meko, D.M., 1981: Tree-ring evidence of a relationship between drought occurrence in the western United States and the Hale Sunspot Cycle. In: LAWSON, M.P., BAKER, M.E., (eds.). The Great Plains. Perspectives and Prospects. University of Nebraska Press, Lincoln and London, 83-110.

VARIATIONS IN THE SPRING-SUMMER CLIMATE OF CENTRAL EUROPE FROM THE HIGH MIDDLE AGES TO 1850

C h r i s t i a n Pfister U n i v e r s i t y of Berne D e p a r t m e n t of History Engehaldenstrasse

4

3012 B e r n e / S w i t z e r l a n d

Does

I.

the climate of the High Middle Ages

include elements for

a

w a r m i n g scenario?

Warm periods in the past may provide elements for a s s e s s i n g the

clima-

tic and human c o n s e q u e n c e s of the global w a r m i n g w h i c h is p r e d i c t e d for the

next century,

if the present trend in c o n c e n t r a t i o n of g r e e n h o u s e

gases in the a t m o s p h e r e continues sea

ice around G r e e n l a n d would

(WMO,

1986).

It is assumed that

the

retreat towards its northern coast

in

the early stage of a w a r m i n g period and then c o m p l e t e l y d i s a p p e a r in

a

later stage. The Arctic Ocean w o u l d become ice free while the c o n t i n e n tal

ice-dome at the Antarctic would persist.

during the Late T e r t i a r y for the last time.

Such a situation existed Flohn

(1984:

7, 265) con-

cludes

from

coasts

of the M e d i t e r r a n e a n together with the Alps

Europe

(up to latitudes 48 - 50 N) might obtain a w a r m - t e m p e r a t e

mate

with

the climatic evidence of this period that

some r e d u c t i o n of summer rains,

season droughts, 2

months

from

the

periods Central

i.e.

the

and

northern

south-central

with

frequent

cliwarm

while the v e g e t a t i o n period w o u l d be increased by I -

(Flohn,

1984:

9).

botanical

evidence

over

past

the

Europe

was

summer

temperatures

present

average.

This

On

the

other

available

700'000

from

years

not

mediterranean

may

have

suggests

been a warm

hand

the warm

that at

2

-

Frenzel

the that

3

interglacial vegetation

time

degrees

and moist

concluded

summer

in

although above

the

climate.

What do we know about the w a r m period in the High Middle Ages?

AD

985

Norse colonists from Iceland settled in Greenland around modern Narsaq, J u i i a n e h a a b and G o d t h a a b d i s t r i c t s

(Mc Govern,

1981:

407).

The colo-

58

nists

were

able to bury their dead deep in soil that has

p e r m a n e n t l y frozen. the

the present normal

(Lamb,

1982:

165 f).

coasts of Iceland only on the average for a 1945). ding

farther

Bohemia,

north,

1986),

settlements country;

(Koch,

1982:

170),

reports on grape h a r v e s t s

vines

(Ale-

were grown on a l t i t u d e s of 600 to 700 m in (Scherer,

1874).

wheat 1984:

was

the

In Norway, also,

36);

grown almost to the latitude of the Polar

farm hill

Circle

in the Alps p a s t u r e s could be grazed up to 2800

1976). A c c o r d i n g to

Lamb

a

from

were s p r e a d i n g up to 200 m h i g h e r than before on the

(R~thlisberger,

m

(1984: 37) m i d s u m m e r s during

"Little Optimum" were p r o b a b l y between 0.7 and 1.0 ° C w a r m e r than twentieth-century

Central Europe

A

few weeks per year

the

m e d i e v a l v i n e y a r d s in England are known up to

p r e a l p i n e v a l l e y of T o g g e n b u r g

this

warmer

T h u r i n g i a and Belgium are included in m e d i e v a l sources

xandre,

the

or more,

Drift ice reached

In Central and W e s t e r n Europe c u l t i v a t i o n of the vine was sprea-

latitude of 53 ° N (Lamb,

(Lamb,

been

In the m i l d e s t period in the early twelfth century

w a t e r in the fjords was at least sometimes 4 ° C,

than

since

(Lamb,

average in England and 1.0 - 1.4 ° C 1982:

warmer

170).

d e t a i l e d a n a l y s i s of the c l i m a t e in the Middle Ages m i g h t

allow

us

anomalies

in

to learn more on the seasonal w e a t h e r p a t t e r n s

therefore

and

that might be c o n n e c t e d with the w a r m i n g trend.

on

This

the know-

ledge may be helpful for a s s e s s i n g the economic and societal impacts of a

w a r m i n g in the future.

spring-summer this

In the f o l l o w i n g the w e a t h e r patterns

p e r i o d between 1270 and 1425 will be

data will be c o m p a r e d with the known v a r i a t i o n s

the end of the s o - c a l l e d

in climate

M a n - m a d e data and their l i m i t a t i o n s

For

the 350 years before the c r e a t i o n of the n a t i o n a l w e a t h e r Switzerland

the m o n t h l y patterns of weather and climate

described

and q u a n t i f i e d based upon a body of data

man-made.

It

surements,

until

c o m p r i s e s e x p l i c i t w e a t h e r data

that

service could

are

and proxy-data,

weekly

i.e. a v a r i e t y of infor-

w h i c h r e f l e c t s the c o m b i n e d effect of several

d u r i n g a period of several months

be

mostly

(early i n s t r u m e n t a l mea-

q u a n t i t a t i v e and q u a l i t a t i v e d e s c r i p t i o n s of daily,

and m o n t h l y w e a t h e r patterns) mation

and

"Little Ice Age".

2.

in

in the

investigated,

weather

factors

(e.g. o b s e r v a t i o n s on the freezing of

59

lakes

and the ripening of grapes and measurements of maximum tree-ring

density on logs from the upper timberline). all

types

1985 a) types

of

has of

evidence in the CLIMHIST weather allowed

data,

same has

to

data

to compare and to mutually check

to refine the interpretation and

indices for temperature and precipitation

Prior

The synchronous display of

(Pfister,

to

bank

(Pfister,

the

different

derive

monthly

1984).

the early sixteenth century man-made sources become

at

the

time less abundant and less rich in meteorological entries. two consequences:

creases,

and

This

the time resolution of the reconstruction

de-

the spatial dimension of the analysis must be increased.

The data are scattered within a large area,

which begs the problem

of

interpolation in space and reduces the reliability of the estimates, particular for precipitation. neous

proxy-data

patterns

that

are required for

estimating

the

temperature

of the vegetative period are more difficult to obtain.

sionally

phenological

Ages

order to determine and compare temperature patterns

in

standing years:

in

Also, continuous quantitative and homoge-

Occa-

observations have also been made in the

a friar of the order of St.

Dominic,

Middle in

out-

who was born in

1221 and lived in Basel and in Colmar, has included phenological observations in his Annales Basilienses et Colmarienses. earliest springs of the present millenium, first

rye

March

19th,

ears appeared around January 8th, the vine got leaves on April Ist,

sold on May 17th, date

In 1283, one of the

he wrote for instance:

the

the rye was in bloom the first new rye

the peas could be harvested from June 8th,

strawberries and cherries were ripe (Annales,

1861).

the same But

observations were not systematically carried on for some years, Thus

on was

these such as

those

made in the eighteenth and nineteenth century.

allow

quantifying roughly the thermic character of climatic anomalies.

they

only

Grape

harvest dates are available from the mid fourteenth century when

several chroniclers and annalists began to keep track of the date the

wine

1971:

50).

harvest

was fixed by public proclamation

However

(Le

Roy

Ladurie,

the records are often incomplete for many

Measurements of the maximum density of tree-rings at the upper line

are

Lauenen a

the only continuous evidence for this time.

(Bernese Oberland)

originates

The

in 1269 (Schweingruber,

when

years. timber-

series

of

1978). In

near future it will be extended back to the year 1000 (communication

by Dr. Schweingruber).

60

3.

Guidelines for the spatial extrapolation of data

Given

the

Middle

insufficient density of man-made and natural

Ages,

data

in

the

it is essential to assess which biases might occur

from

extrapolations within large areas. For this reason the spatial patterns of

temperature variation in Europe must be known for the present

tury. to

change

over time with the changing climate.

analysis

of spatial correlations

ning

instrumental

of

large

measurements.

This type of

the

analysis

will

machine

be upon

readable

1985).

the present context the spatial correlations of temperatures in the

vegetative

period

(April to September)

1901-60 and 1851-1900

If

reason

Institute of Berne based

number of long series readily available in

form (US Dept of Energy,

In

For this

should be extended back to the begin-

attempted for Europe at the Geographical a

cen-

Moreover we need to know to what extent those patterns are bound

Zurich

and in summer are provided

for

(table 1).

is chosen as a reference station the covariance of

temper-

ature patterns in the vegetative period is very high (R 2 of 65%) up

to

the shores of the Atlantic over a distance of almost 800 kilometers and still Alps

remarkable (Vienna).

August) ment

is somewhat weaker in most cases.

with

series

across the Alps to Northern Italy and to the Eastern

The covariation between the summer temperatures

of

These results are in

the significant correlations that have been vine harvest dates over distances of 800

between Geneva and Vienna)

(Flohn,

found

agreebetween

kilometers

The use and misuse of historical sources

The

meteorological

evidence contained in the chronicles and annals

the Middle Ages has been included in large compilations.

seeking to reconstruct past climates.

Historians

have drawn on the results of these reconstructions.

of

At first sight

compendia seem to provide a convenient ready-made data bank

it is therefore not surprising that they have been much used by tists

(e.g.

1985: 96).

4.

these

(June-

in their

and

scienturn

61

cO 0

0

c~

o'~

co

0

~

t~

q

-4

~

o

o ch I

cO o o

co

un

~

E

0 r~

N o c~

•

tlh ~0 ko

co

0 0 0

r0

~ 0

0 .,~

03 u5

r~ ¢J

0 o~

~ cO

I'~ ~D

~D

CO

O0

q

),

-eo. -7~.

I,

:',

I

o

I

I ;.J__4.' I? \ k ~ ' z ,

tl

J.'_;__(

--eO

-QO 1

,

oo~o

,

~

t

I

o

poo

I

I

~

o

i

,

o~

z)o, 7s' oo. 4~' ao,

90 7G ~D 4~ 30

o,

D

-ao -4S

' '

-co,

-Ts

•

-ao,

~oo

,,,o

,7o i)o.

,.o

~o

~o

, MID-MONTH

,~o

,,,o

~o

~o

,6o

4°

V

40

I°

INSOLATION

,k . . . .

~o

V

'

-O0

'

--90

,~o

7

o

JANUARY

~O 7S; 80 4~ 30

eoaoIsO-30

-

-,Is

-

-eo

-

-?i; -oo

0 --IG

If(All1 I ' ' ' I

LU

eo

I::)

4~ :)o

'

I

°°

I

, °

I

, , .~r-~ I 0

O0

I

~,, ...... '

--00

I° ° ° ° ° i

I

I

I gO 7~; O0 4~ 30 IG

o

0

'" ":° -7g

--30

-

I °

oo ,

I

.

i

e o

~ o

I

,

~ i D

o

o I

--7~; --r~O

o ,

I

I

I

I

60

7~ 60 4~ 30 o.

0

I I / "~ / -~s

t I,.)o'~ ,,.,j i

,"

~"

~._..,,o d

"'

"

•

b I oo

eo

eo

70

YEARS

SO

SO

BEFORE

40

30

aO

I0

-

--00

-

-90

0

PRESENT

Figures 2.a-b. Long-term variations of the deviations (from their present value~) of mid-month daily insolations for January. These values are given here in Wm ~ and for periods extending from i00 to 200 kyr BP (part a) and from present to 100 kyr BP (part b). For each time period, the top panel is for the insolation at the top of the atmosphere, the middle one for the incident insolation at the surface and the bottom one for the absorbed insolation at the surface. The solid lines are for the positive deviations (insolation higher than today) and the dashed lines characteristize the insolation below their present values.

144

"7°

'~, '.°

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