Of the Earth The effect of solar radiation variations on the climate
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The effect of solar radiation variations on the climate
of the Earth
By M. I. BUDYKO, Main Geophysical Observatory, Leningrad, M . Spasskaja 7
(Manuscript received September 25, 1968, revised version December 18, 1968)
ABSTRACT
It follows from the analysis of observation data that the secular variation of the mean
temperature of the Earth can be explained by the variation of short-wave radiation,
arriving at the surface of the Earth. In connection with this, the influence of long-term
changes of radiation, caused by variations of atmospheric transparency on the ther-
mal regime is being studied. Taking into account the influence of changes of planetary
albedo of the Earth under the development of glaciations on the thermal regime, it is
found that comparatively small variations of atmospheric transparency could be suffi-
cient for the development of quaternary glaciations.
As paleogeographical research including ma- Taking into account this consideration, we
terials on paleotemperature analyses has shown shall examine in the present paper the possibi-
(Bowen, 1966, et al),the Earth's climate has lity of using quantitative methods of physical
long differed from the present one. During the climatology to study the problem in question.
last two hundred million years the temperature Firstly we shall dwell upon the problem of
difference between the poles and equator has climate change regularities during the last
been comparatively small and there were no century. Fig. 1 represents the secular variation
zones of cold climate on the Earth. By the end of annual temperature in the northern hemi-
of the Tertiary period the temperature at tem- sphere that was calculated from the maps of
perate and high latitudes had decreased ap- temperature anomalies for each month for the
preciably, and in the Quaternary time subse- period of 1881 to 1960 which were compiled at
quent increase in the thermal contrast between the Main Geophysical Observatory. Line 1 in
the poles and equator took place, that waa fol- this figure characterizes the values of anomalies
lowed by the development of ice cover on the that are not smoothed, line 2 the anomalies
land and o c e m a t temperate and high latitudes. averaged by ten-year periods.
The size of Quaternary glaciations changed As is seen from this figure, a rise in tempera-
several times, the present epoch correspbnding ture that began a t the end of last century
to the moment of a decrease in the area of gla- stopped in about 1940, and a fall in tempera-
ciations that still occupy a considerable part of ture started. The temperature in the northern
the Earth's surface. hemisphere that increased in the warming
To answer the question of in what way the period by 0.6"C then decreased by the middle of
climate will change in future, it is necessary to the fifties by 0.2"C. A comparatively short-
establish the causes of Quaternary glaciations period rise in temperature with smaller ampli-
initiation and to determine the direction of tude was also observed in the last years of the
their development. Numerous studies on this XIXth century.
problem contain various and often contradic- The curve of secular temperature variation
tory hypotheses on the causes of glaciations. can be compared with the curve of secular
The absence of the generally accepted view- variation of direct solar radiation with cloudless
point as regards this seems to be explained by sky that was drawn by the data from a group of
the fact that the existing hypotheses were based stations in Europe and America with thelongest-
mainly on qualitative consideratiow allowing period series of observations. This curve pre-
different interpretation. senting the values of solar radiation smoothed
Tellus XXI (1969),6
39 - 692891612 M. I. BUDYKO
"C
0.60
0,so
IMl
0.30
0.20
0.4n
0
-an
- 0.20
- 0.30
- 0.40
- as
- a,@
f04 %
902
do0
98
96 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 85 40 95 1900 05 40 15 20 25 30 95. 40 45 50 55 i960
Fig. 1. Secular variation of temperature and direct radiation.
for ten-year periods corresponds to line 3 in 0.33"C higher than that in the former, and the
Fig. 1. As is seen from the above figure, the direct radiation by 2.0 % higher.
direct radiation had two maxima-a short- To estimate the corresponding change in total
period one a t the end of the XIXth century radiation, it should be taken into account that
and a longer-period one with the maximum the atmospheric transparency changes after vol-
values of radiation in the thirties. canic eruptions as a result of propagation of
The problem of the causes of secular variation dust with particles of the order of 1 EL in the
of direct radiation was already discussed by lower stratosphere. This dust considerably in-
Humphreys (1929, and others) who considered creases the short-wave radiation diffusion, as a
that it was determined by the change in the result of which the planetary albedo of the
atmospheric transparency due to the propaga- Earth becomes higher. Because of the radiation
tion of volcanic eruption dust in it. Having diffusion by dust mainly in the direction of an
agreed to this point of view that is confirmed incident ray (Mie effect) the direct radiation
by many new data, it should be suggested that decreases with diffusion t o a greater extent
a decrease in radiation after 1940 could also than the total radiation does. Using the calcula-
depend on the increase of dust in the atmo- tion method developed by K. S. Shifrin and his
sphere due to man's activity. collaborators (K. S. Shifrin, I. N. Minin, 1957;
As can be seen from Fig. 1, the curves of sec- K. S. Shifrin, N. P. Pyatovskaya, 1959), one
uiar variations of temperature and radiation can estimate the ratio of decrease in total radia-
are more or less similar. tion to that in direct radiation.
To find out the dependence between the ra- Such a calculation shows that this ratio com-
diation change and that of temperature, let us puted for the average annual conditions changes
compare the radiation and thermal regimes of slightly with the change of latitude, and on an
the northern hemisphere for two thirty-year average for the Earth equals 0.15.
periods: 1888-1917 and 1918-1947. It follows Thus, the difference in total radiation for the
from the data given in Fig. 1 that the tempera- periods under consideration amounts to 0.30 %.
ture in the latter of these periods was by I n this case the ratio of temperature change to
Tellus XXI (1969), 5EFFECT OF SOLAR RADIATION VARIATIONS 613
the change of radiation turns out to be equal to and (2) the dependence of the Earth's mean
l.l"C per 1 % of radiation change. temperature on the value of solar radiation. I n
This value should be compared with the this case it turns out that the change of solar
values of similar ratio obtained as a result of radiation by l % , with the average for the
calculating the radiation influence on the ther- Earth value of cloudiness equal to 0.50 and
mal regime of the Earth. constant albedo equal to 0.33, causes the tem-
To determine the dependence of temperature perature change by 1.5'.
on solar radiation with the average relationship This result can be compared with similar
between temperature, air humidity and other estimate obtained from the work by Manabe
factors influencing the long-wave radiation, we and Wetherald from which it follows that with
used the results of calculations of monthly mean constant relative air humidity the mean tem-
values of radiation a t the outer boundary of the perature at the Earth's surface changes by 1.2"
atmosphere that were made when preparing solar radiation changes by 1%.
Atlas of the heat balance of the Earth (1963). It is clear that both of these values agree
On the basis of these data relating to each satisfactorily with the relation between changes
month for 260 stations an empirical formula in temperature and radiation that was obta.ined
was derived from observational data. One can believe that
some excess of the computed temperature chan-
I =a +BT -(a, + B,T)n (1) ges aa compared to observational data reflects
where I =outgoing radiation in kcal/cm2month, the thermal inertia effect of ocems the heating
or cooling of which smoothes the Earth's tem-
T =temperature a t the level of Earth's perature variations in comparison with the
surface in O C , computed values for stationary conditions.
n = cloudiness in fractions of unit, Thus, it seems probable that present changes
of the Earth's temperature are determined
the values of dimensional coefficients of which mainly by the atmosphere transparency varia-
equal: a = 14.0; B =0.14; a, =3.0; B , =0.10. tions that depend on the level of volcanic activ-
The root-mean-square deviation of the results ity.
of calculation by this formula from the initial If the present changes in volcanic activity
data accounts for less than 5 % of the radiation cause radiation variations by several tenths
values. of per cent and the planetary temperature varia-
Comparing formula (1) with similar depend- tions by several tenths of a degree, one can
ence that can be obtained from the work by believe that in the paat respective variations of
Manabe and Wetherald (1967), it is possible to radiation and temperature reached appreciably
conclude that they practically coincide for the larger values.
conditions of cloudless sky and differ in con- It is evident that the number of volcanic
sidering the cloudiness effect on radiation. eruptions for the given interval of time is dif-
For mean annual conditions, the equation of ferent with constant mean level of volcanic
the heat balance of the Earth-atmosphere activity for statistic reasons, these differences
system has the following form: being the greater, the longer general period of
time being considered. The standard of volcanic
Q(l - a ) - I = A (2) activity in different geological epochs is also
known to change noticeably in connection with
where Q =solar radiation coming to the outer
boundary of the atmosphere; the change of tectonic processes intensity.
Since the volcanic activity variations caused
a =albedo; by tectonic factors are characterized by long
A =gain or loss of heat as a result of the periods of time to calculate the influence of
atmosphere and hydrosphere circula- radiation variations associated with them on
tion, including heat redistribution of the thermal regime, changes in the Earth's al-
phase water transformations. bedo should be taken into account that are due
to expansion or reduction of the area covered
Taking into account that for the Earth aa a with ice on the land and oceans.
whole A =0, we shall find from formulae (1) As observations from meteorological satellites
Tellua XXI (1969), 5614 M. I. BUDYKO
4
I
0
-2
-I
-6
-8
Fig. 2. The dependence of horizontal heat transfer upon temperature difference.
have shown (see Raschke, Moller, Bandeen, From formulae ( l ) , (2) and (3), taking into
1968), the albedo of the Earth-atmosphere sys- consideration that for the Earth as a whole
tem over areas with ice cover is greater than A =0, we obtain equations
that over ice-free areas, due to which fact the
change in area covered with ice increases the Q ( 1 -a) -a + a,n + PT,
radiation variation effect on thermal regime. T- (4)
B+B-B,n
To estimate the radiation variation influence
on the temperature of latitudinal zones, taking &,(I - a , ) - a + a , n
into account the indicated effect, one of numeri- T p= B-B,n (5)
cal models of the average latitudinal tempera-
ture distribution should be used. Since in this (where Q, and up are planetary values of radia-
case we are only interested in temperature tion and albedo) by which the average latitud-
distribution near the Earth's surface it is pos- inal annual mean temperatures were computed
sible to use, instead of existing comparatively for present climatic conditions of the northern
complicated models, a simple scheme based on hemisphere. The values of Q , Q, accepted in this
the solution of equations ( 1 ) and (2) to which the calculation correspond to the value of solar
relation should be added that characterizes the constant 1.92 cal/cm2min, the albedo, according
relationship between temperature distribution to observational data available, a t the latitudes
and horizontal heat transfer in the atmosphere of 0" to 60' is considered to be equal to 0.32, a t
and hydrosphere. the latitude of 70" to 0.50, at the latitude of
Such a relation can be obtained by comparing 80" to 0.62. I n the calculation, the influence of
the mean latitudinal values of term A calculated deviations of cloudiness values from its mean
from formula ( 1 ) with quantities T - T,,where planetary value equal to 0.50 on temperature is
T is annual mean temperaure a t a given lati- neglected.
tude, T, is the planetary mean temperature. The possibility of such an assumption results
The result of the above comparison is shown from the conclusion established in the calcula-
in Fig. 2 from which it follows that the cor- tions made using the above formulae concerning
responding dependence can be expressed in the a comparatively weak effect of cloudiness on
form of equation the mean indices of thermal regimewithin a
A =B(T - T,) (3) rather wide range of conditions. Such a con-
clusion drawn, taking into account the de-
where B = 0.235 kcal/cma month degree pendence of albedo on cloudiness, implies that
Tellus X X I (1969), 5EFFECT OF SOLAR RADIATION VARIATIONS 615
the effect of cloudiness on the change in ab-
sorbed radiation in a number of cases is com-
T°C
pensated for by its influence on the outgoing mt
long-wave radiation. The results of calculating
the contemporary average latitudinal distribu-
tion of temperature are presented in Fig. 3
where they correspond to line T o . As is seen,
these results are in good agreement with the
observed temperature a t different latitudes that
is represented in Fig. 3 by line T . Such an agree- '9"
ment allows us to use the scheme described for
evaluation of the radiation variation effect on
the Earth's thermal regime and glacltttions.
The southern boundary of the existing ice
cover on the sem and 1an.d in the Arctic cor-
responds to the mean latitude of 72" N. Let us
consider that with a decrease in solar radiation Fig. 3. The average latitudinal temperature distri-
the surface of ice cover expands in accordance bution.
with the extension of the surface area with tem-
perature equal to or lower than the temperature where TI, is the existing mean temperature of
observed now at 72'N. In this case let us as- the Earth.
sume that albedo on the ice-covered area is Using this formula and considering the de-
equal to 0.62 and at the southern boundary of pendence of values Q and S on latitude, one can
this ice cover to 0.50. compute the position of glaciation boundary
It follows from the above values of albedo for different values of AQp/Qp.By this formula
that with the change of ice cover area the mean it is also possible to calculate the distributions
albedo of the Earth changes by value 0 . 3 0 s of temperature at different latitudes that cor-
where coefficient 0.30 corresponds to the differ- respond to these values. The results of such a
ence of albedo values with the presence and calculation are shown in Fig. 4, where lines
absence of ice cover, and quantity S =lq, (1 = and correspond to temperature distri-
the ratio of ice area change to the whole area butions with the decrease in radiation income
of the Earth, q =the ra.tio of mean radiation in by 1.0% and 1.5% respectively. In the above-
the same zone of ice area change to the mean mentioned calculation the interrelationship
value of radiation for the Earth as a whole). between the thermal regimes of the northern
To take into account the influence of the and southern hemispheres is neglected (which
glaciation area change on the annual mean tem- assumption is reasonable with the similar change
perature of the Earth, we shall use formula of thermal regime in both hemispheres). It is
assumed in calculation that the relative de-
ATp = ~
B -QBpi n [""
~
QD
(1-aD - 0.30s)- 0 . 3 0 5
I
(6)
crease in radiation at different latitudes is the
same.
Fig. 5 represents the values obtained from
this calculation for the mean planetary tem-
perature T pand mean latitude to which glacia-
which is obtained from formulae (1) and (2), tion extends po depending on relative radiation
where ATp is the Earth's temperature change changes. As is seen from this figure, the radia-
with the change of mean radiation Qp by value tion variation effect on thermal regime con-
AQp* siderably increases as a result of glaciation deve-
From (11, ( 2 ) , (3), (6) we shall deduce a for- lopment, the corresponding dependence becom-
mula for temperature at some latitude ing nonlinear.
T=
'p=
-a+a,n+fiTi+
fi + B - B,n
I (7)
Tellus XXI (1969), 6616 M. I. BUDYKO
T" of tho Earth with the present value of solar
30r constant was mentioned in the author's works
(Budyko, 1961, 1966).
Thus, the present thermal regime and glacia-
tions of the Earth prove to be characterized by
high instability. Comparatively small changes
of radiation-only by 1.0-1.5 %-are sufficient
for the development of ice cover on the land
and oceans that reaches temperate latitudes.
It should be noted that such changes in radia-
tion are only several times as great as its varia-
-fLl -
tions observed due to the changeability of vol-
canic activity in the last century.
-20- Taking into consideration that according to
the data of geological investigations the level
of volcanic activity for long periods of time in
Fig. 4. The dependence of temperature distribution the past changed by a factor of several times
on radiation amount. (see Ronov, 1959), one can believe that the
influence of long-period variations of volcanic
If with the decrease in radiation by 1 % the activity is a probable factor of glaciation deve-
mean temperature of the Earth drops by 5", lopment.
then with the decrease in radiation by 1.5% This conclusion is confirmed by the fact,
such a drop reaches 9". Simultaneously with established by Fuchs and Patterson, of cor-
the above temperature drop the glaciation respondence between the main epochs of qua-
displacement 1Q-18" to the south takes place, ternary glaciations and the periods of consider-
i .e. the distancw approximately corresponding able increase in volcanic activity in a number
to the expansion of quaternary glaciations. of regions of low latitudes (1947).
When radiation decreasm by 1.6% the ice cover Though in this paper the author has no pos-
reachas the mean latitude of about 50°, after sibility to discuss numerous other hypotheses
that it starts shifting towards lower latitudes as to be causes of quaternary glaciations, never-
up to the equator as a result of self-develop- theless it is necessary to dwell upon popular idea
ment. At the same time the planetary tempera- concerning the influence of changes of the
ture drops sharply and reaches the value of Earth's orbit elements on glaciations.
several tens of degrees below zero. Such a conception substantiated by Milan-
A conclusion on the possibility of complete kovich (1930 and others) and other authors is
glaciation of the Earth after ice cover reaches shared by many specialists studying quaternary
some critical latitude follows from the calcula- glaciations.
tion, using the above formulae, of the values of
decrease in radiation necessary for further mo-
vement of ice to the equator. Such a calculation
shows that to the south of critical latitude ice
will move to the equator with the decrease in
radiation by less than 1.6%, and a t lower lati-
tudes ice will move in the indicated direction
with the existing values of radiation and even o -m V
with its values exceeding those in the present 1
I
QP
epoch. I
-ID -40 I
It should be noted that similar conclusion U
E
from other considerations was drawn previously
by Opik (1953, et al.)who considered, however, -20 30
that for glaciating the Earth a considerable
decrease in solar constant is necessary. The Fig. 5. The dependence of the Earth's temperature
possibility of existence of complete glaciation and ice cover boundary on radiation variations.
Tellus XXI (1969), 5EFFECT OF SOLAR RADIATION VARIATIONS 617
As is known, the effect of changes in the
Earth's orbit eloments leads to appreciable re-
distribution of radiation amount coming to dif -
ferent latitudes. Considering these changes and
using the model of latitudinal temperature
distribution suggested by him, Milankovich
concluded that with the changes of orbit ele-
ments a t temperate and high latitudes consider-
able changes in temperature occur that can
result in glaciation.
It should be mentioned that the model of
temperature distribution suggested by Milan-
kovich did not take into account horizontal
heat transfer in the atmosphere and hydro-
sphere due to which it had to overestimate con- -20 1
siderably the influence of changes in radiation
fig^. 6. Ice cover effect on temperature distribution.
in a given latitudinal zone on the thermal regime
of the same zone.
To verify the hypothesis of Milankovich,there caused weakening of water circulation in the
were calculated, using the above-mentioned oceans between low and high latitudes.
scheme, changes in thermal regime and glacia- It was ascertained long ago (Budyko, 1948,
tions for the case of considerable change of the et al.) that the heat transfer between the equator
Earth's orbit elements 22 thousand years ago and the poles in the hydrosphere is a consider-
which is usually associated with the last glacia- able portion of the corresponding transfer in the
tion. The calculations made have shown that atmosphere, in connection with which the chan-
though the variations of orbit elements influence ges in water circulation in the oceans should
in ~1definite way the thermal regime and glacia- influence essentially the thermal regime a t high
tion, this influence is comparatively small and and temperature latitudes.
corresponds to possible displacement of the To clear up this question, temperature distri-
glaciation boundary by a little less than lo of bution was calculated using the above-men-
latitude. It should be borne in mind that such tioned scheme for the case of absence of ice a t
a calculation allows for the change in annual high latitudes.
radiation totals. According to Milankovich, the The results of such calculations are shown in
main influence on the glaciation is exerted by Fig. 6 where line Torepresents the present-day
the variations of the summer radiation values temperature distribution, and line T, tempera-
that at latitudes 65-75' are 2 to 3 times as ture distribution with the absence of polar
large as the variations of annual values. Empha- glaciations. I n these calculations the albedo a t
sizing the necessity of further study of the pro- high latitudes is accepted to be equal to the
blem on the effect of annual radiation variation albedo of ice-free areas and the coefficient /? is
on the glaciation, it should be noted that the considered t o be equal to its value accepted
above-obtained result casts some doubt on the above.
hypothesis that the effect of the Earth's orbit As is seen from Fig. 6, the polar ice changing
changes is sufficient for the explanation of the little the temperature a t low latitudes consider-
quaternary glaciations. ably decreases the temperature at high latitudes.
Now we shall proceed to the question of why As a result, the mean difference in temperature
the volcanic activity variations, that occured between the pole and the equator decreases and
during the whole history of the Earth, did not the annual mean temperature in polar zone
result in the development of glaciations during turns out to be equal to several degrees below
hundreds of millions of years previous to the zero.
quaternary period. One can believe that with ice-free regime the
It has been established in geological investiga- meridional heat transfer in the polar ocean will
tions that in the pre-quaternary time the gra- increase as compared to present conditions
dual rise of continents level took place. This since this ocean, that is now isolated from the
Tellus XXI (1969), 5618 M. I. BWDYKO
atmosphere by ice, will give off a considerable as its present mean value for the ice-free areas,
amount of heat to the atmosphere through then according to the calculations by the above
turbulent heat exchange. formulae, the annual mean temperature in the
If to consider that with the absence of ice the Arctic reached lo", which fact excluded the
Arctic Ocean receives additionally an amount possibility of glaciation even with appreciable
of heat equal to the mean value coming now to anomalies of radiation.
the ice-free areas of the oceans at high latitudes, During the Tertiary period the isolation of
the mean air temperature in the Arctic must be polar basin from the tropic regions of ocean
somewhat higher than the above value, i.e. close gradually developed, which caused the tem-
to zero. perature decrease near the pole and approaching
This result is in agreement with the conclu- of temperature distribution to the values charac-
sions drawn using other methods in previous teristic of inter-ice epochs.
works by the author (Budyko, 1961,1962, 1966), It follows from the above considerations that
L. R. Rakipova (1962, 1966), D o ~ & S h a w the present epoch is a part of glacial period
(1966), and others. It confirms once more the since any noticeable increase in volcanic activity
possibility of existence of ice-free regime in the should lead to new glaciation development.
polar basin in the present epoch and a t the same Moreover, it seems probable that one of the
time indicates high instability of such a regime. following glaciers expansion could reach the
It is evident that with the annual mean critical latitude after which the complete glacia-
temperature in the Central Arctic close to water tion of the Earth would set in. Such a possibility
freezing point comparatively small anomalies was on the point of being realized in the period
of radiation income may lead to ice restoration. of maximum quaternary glaciation when the
Thus, with the present distribution of con- temperature of the Earth and the position of ice
tinents and oceans the existence of two climatic cover corresponded to dots plotted on lines T,
regimes is possible one of which is characterized and v0 in Fig. 5 .
by the presence of polar ice and large thermal As is seen from this figure, the ice cover under
contrast between the pole and the equator, these conditions has moved about 0.8 of the
and the other by the absence of glaciation and way from the present ice boundary to the critical
small meridional mean gradient of temperature. latitude.
Both of these regimes are unstable since even From such a viewpoint the Quaternary His-
small variations of solar radiation income could tory of the Earth seems to be the period of com-
be sufficient either for freezing of the ice-free ing climatic catastrophe due to which the exi-
polar ocean or melting of the existing ice. Such stence of higher forms of organic life on our planet
a peculiarity of climatic regime seems to deter- may be exterminated.
mine the main features of climate variations When estimating the probability of such a
in the Quaternary period. catastrophe being realized in future, the charac-
I n the periods of decreased volcanic activity ter of man's activity should be taken into ac-
the temperature distribution corresponded to count which influences to some extent the cli-
ice-free regime which characterizes the climate mate a t present. Without touching upon the
of comparatively warm inter-ice epochs. When possibility of implementing in futiire some pro-
volcanic activity increased, ice formed firstly jects of active influence on the climate which
in the arctic seas, and then greater or smaller could affect the glaciation development, ever in-
glaciations were developed on the land. creasing influence of man's activity on the ener-
As it was mentioned in the author's work gy budget of thc Earth should be mentioned.
(Budyko, 1968), in the mesozoic era and in the All the energy used by man is transformed
paleogene the northern polar basin was con- into heat, the main portion of this energy being
nected with the oceans of low latitudes with an additional source of heat as compared to the
much wider straits as compared to the Quater- present radiation gain. Simple calculations show
nary period. I n this case the heat income to the (Budyko, 1961) that with the present rate of
polar basin as a result of activity of sea cur- growth of using energy the heat produced by
rents seemed to exceed those values that are man in less than two hundred years will be
observed a t high latitudes under present condi- comparable with the energy coming from the
tions. If this income was 1.5 to 2 times as great sun. Since glaciations are greatly influenced by
Tellus XXI (1969), 5EFFECT OF SOLAR RADIATION VARIATIONS 619
the changes i n energy budget which are a small It should be mentioned that the conclusions
part of solar radiation income then i t is probable stated i n this paper o n the effect of changes i n
that in the comparatively near future the possi- solar radiation on climate h a v e besn drawn as a
bility of glaciation expansion will be excluded result of using a strongly schematized model of
and there will a.ppear the reverse one of polar the Earth's thermal regime. It is considered
ice melting on the land and oceans with all the desirable to make similar calculations with the
changes i n the Earth's climate that are asso- use of more general models.
ciated with it.
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