1 International Arctic Research Center, University of Alaska Fairbanks * To whom correspondence should be addressed. E-mail: sakasofu@iarc.uaf.edu

Natural Components of Climate Change During the Last Few Hundred Years

Syun-Ichi Akasofu1*

Global warming and climate change are a major issue in recent years. On the

basis of published reports and articles, two natural components are identified.

Climate change during the last few hundred years may be interpreted mainly in

terms of a combination of the recovery from the Little Ice Age (LIA) and the multi-

decadal oscillation, which are natural changes. Thus, there is a possibility that

only a small fraction of the warming between 1900 and 2000 may be attributed to

the greenhouse effect. In this view, the predicted temperature change in 2100 is

about 0.5°C ± 0.2°C.

Temperature changes from about 1900 and a little earlier have been the subject of intense

investigations in terms of global warming caused by the greenhouse effect of CO2 and

other gases. However, there has been little attention paid to the fact that the temperature

changes may be approximated, with a high confidence, by a linear change (1), together

with superposed fluctuations. In Fig. 1, the boxed portion illustrates this interpretation

using the temperature data (2). The rate of increase of temperature is about 0.5 C°/100

years.

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Fig.1 The figure shows that the linear trend between 1880 and 2000 is a continuation of

the recovery from the LIA. It shows also the predicted temperature rise (4°C ± 2°C) by

the IPCC after 2000. However, in this paper, it is suggested that the linear recovery from

the LIA from 1800-1850 would continue to 2100, together with the superposed multi-

decadal oscillation. This possibility can explain the halting of temperature rise after 2000

(as indicated by the red-dot line and green arrow).

One interesting question is how far back the linear line can be traced. There are a large

number of studies that the linearity can be extended to about 1800. For example, Figure

2 shows a compilation of proxy temperature data (3); a very similar compilation was

given made in (4). There is little doubt that the temperature began to rise fairly steadily

from about 1800-1850, although CO2 began to increase rapidly only after 1946.

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Fig 2. Reconstruction of large-scale surface temperature variations (Northern

Hemisphere mean or global mean) from seven different research teams (3).

Global sea level increased almost linearly from about 1800 to 2000 (5,6); see Fig. 3.

Glaciers (cf. Glacier Bay in Alaska, Franz Josef Glacier in New Zealand, Gangotri

Glacier in Himalaya, Mer de Glace Glacier in Alps) began to recede in about 1800-1850

(7-10). Freezing and break-up of major rivers in the Northern Hemisphere occurred fairly

steadily in later dates and early dates from 1845, respectively (11). The southern edge of

sea ice in the Norwegian Sea began to shift almost linearly northward in about 1800 (12).

There are many other data to indicate a fairly steady rise of the proxy temperatures from

1800-1850 to 2000.

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Fig. 3 Global sea level changes from 1700 to 2000 (6).

From these facts, it may be concluded that the warming trend until 2000 began in 1800-

1850, well before CO2 in the atmosphere began to increase rapidly in 1946, soon after the

end of WWII. Further, the temperature rise was fairly steady and thus the linear increase

from 1800 to 1850 is a reasonable first approximation.

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The above conclusion suggests that the period around 1800 and earlier was cooler than

the 20th century. The next question is how far back the cool period had lasted. There are a

large number of documents in which the authors suggest that the period between 1400

and 1800 was cool (cf. 8,13). This period is well known as the LIA. There was much

debate on the inferred temperature, but it seems to be about 1°C cooler than the 20th

century. Glaciers both in Alaska and the Alps advanced during this period. There have

been recent publications, indicating that the LIA was experienced in the Orient (cf.

14,15,16) as well, so that it was a worldwide phenomenon; they showed also that the

recovery was fairly steady.

From these facts, one possibility is that the continuous rise of the temperature during the

19th and 20th centuries may be considered to be the recovery from the LIA.

Then, the next obvious question is what is happening after 2000,namely the cause of the

halting of temperature rise after 2000. It is shown in Fig. 4 (17), which shows that the

temperature rise reached a plateau in about 2000.

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Fig 4. Global averaged temperature changes from 1975 (17).

Figure 1 shows the temperature changes during the 20th century may be approximated by

a linear increase with superposed fluctuations. Although the 100-year data is too short in

determining confidently their periodicity, it can be seen that there occurred a distinct

temperature rise from 1910 to 1940 (Fig. 1) without a prominent rise of CO2; actually,

this rise was as significant as the rise from 1975 to 2000. Then, the temperature actually

decreased from 1940 to 1975 although CO2 increased rapidly, and subsequently it

increased from 1975 to 2000. Thus, it is interesting to speculate that the situation in 2000

is similar to that in 1940. The spectral analysis conducted by Polyakov et al. (18)

confirmed the presence of the multi-decadal periodicity.

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In addition, there are several recent reports that contain publicly available data and a

published paper, to suggest that the halting is not temporal or irregular changes, but is a

more subtle change. They are:

(1) The Pacific Decadal Oscillation (PDO) has a similar phase (19).

(2) The sea level rise stopped after 2005 (20).

(3) Heat content of the oceans began to decrease after 2005 (21).

(4) The Central Pacific Ocean is cooling (22).

(5) The area of sea ice in the Arctic Ocean has begun to recover after the drastic

reduction in 2007 (23).

Assuming that the main part of the fluctuations can be identified as the multi-decadal

oscillation, the amplitude of temperature changes is about 0.2°C and the period being 50-

60 years. Since the rate of change of the multi-decadal oscillation is 0.2°C/30 years

(0.07°C/10 years), while the recovery rate from the LIA is about 0.5°C/100 years

(0.05°C/10 years), it is possible that the multi-decadal oscillation can overwhelm the

recovery from the LIA; the situation may be similar to that during 1940 to 1975. This

may be the cause of the halting after 2000. This interpretation implies that the

temperature will decrease until 2025-2030 and also that the temperature rise due to the

recovery from the LIA, if it were to continue, will be 0.5°C in 2100; depending on the

phase of the multi-decadal oscillation, ±0.2°C may be added to the above value.

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This prediction differs greatly from that of the IPCC (4°C ± 2°C). The difference can be

understood by the IPCC statement: “Most of the observed increase in globally averaged

temperatures since the mid-20th century is very likely due to the observed increase in

anthropogenic greenhouse gas concentrations” (24); actually, the last temperature rise

began in 1975, not from “the mid-20th century”. The rise is shown by the thick red line in

Fig. 1. Since this rise was assumed to be mostly due to CO2 by the IPCC, there is no

choice for them but to extend the thick red line to 2100, since the amount of CO2 is

expected to rise continuously.

In conclusion, climate change during the last few hundred years may be interpreted

mainly in terms of a combination of the recovery effect and the multi-decadal oscillation.

These are natural changes. Thus, there is a possibility that only a small fraction of the

warming between 1900 and 2000 may be attributable to the greenhouse effect. In this

view, the predicted temperature change in 2100 is about 0.5°C ± 0.2°C.

Therefore, there is an urgent need to correctly identify natural changes and remove them

from the present temperature changes in order to accurately and correctly identify the

contribution of manmade greenhouse effect.

Acknowledgments

I would like to thank a large number of colleagues from many different fields of arctic

science. Otherwise, it would not have been possible to synthesize results from a great

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variety of subjects for the purpose of examining the recent climate change. This research

was conducted as part of the International Arctic Research Center.

References and Notes (1) E. Bryant, Climate Process and Change, Cambridge University Press (1997).

(2) P.D. Jones and R.S. Bradley, in Climate Since A.D.1500, R.S. Bradley and P.D.

Jones, Eds. (Routledge, London, 1992), pp. 246–268.

(3) “Surface temperature reconstructions for the last 2000 years” (National Research

Council of the National Academies, Washington, DC, 2006).

(4) A. Moberg, D.M. Sonechkin, K. Holmgren, N.M. Datsenko, and W. Karlen,

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(9) J. Kargel, “Earth Observatory Newsroom: New Images - Retreat of Gangotri

Glacier” (USGS, 2009).

(http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id

=16584).

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(10) R. Kwok and D.A. Rothrock, Geophys. Res. Lett. 36, L15501, doi:10.1029/2009GL

039035 (2009).

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(14) P.D. Nunn, Climate, Environment and Society in the Pacific during the last

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Research 39(4), 651–657 (2007).

(17) R.A. Kerr, Science 362, 28 (2009).

(18) I.V. Polyakov et al., Amer. Met. Soc., 16, 2067 (2003).

(19) University of Washington, http://jisao.washington.edu/pdo/ (2008)

(20) R. Nerem, D. Chambers, J. Choe, G. Mitchum, and J. Ries,

http://sealevel.jpl.nasa.gov/science/scientific-investigations-2008/nerem.html

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(21) R.A. Pielke, Sr., Physics Today, 94, Nov. (2008)

(22) JPL, http://www.nasa.gov/tropics/earth/features/2008/209.html (2008).

(23) International Arctic Research Center/JAXA, http://www.ijis.iarc.uaf.edu/jp/index.htm

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(24) “Climate Change 2007; The Physical Science Basis, Summary for Policy Makers”

(IPCC, 2007).

Supporting Online Material

http://people.iarc.uaf.edu/~sakasofu