Volume 5, Number 50: 11 December 2002
A long succession of climate models has consistently suggested that CO2-induced global warming should be amplified in earth's polar regions and that the first signs of man's predicted impact on the world's weather should thus be manifest there. Many people have consequently accepted recently-reported high temperatures from various parts of the Arctic as evidence of the validity of contemporary climate model predictions and an indisputable sign that the dreaded climatic effects of mankind's CO2 emissions have in very fact arrived at the world's doorstep. Actual temperature data, however, tell a vastly different story.
Following the recent release of Russian meteorological observations poleward of 62°N, Polyakov et al. (2002) created an Arctic-wide temperature history that runs from 1875 to 2001, based on data obtained from 75 land meteorological stations. Over this 126-year period, their record depicts two major intervals of warming, each of approximately 15 years duration. When annual temperatures are expressed as six-year running means, the first of these warmings starts at about 1922 and the other at about 1985. The initial warming is by far the more dramatic of the two, with temperatures rising by nearly 2°C, while temperatures rise by not quite 1°C in the second. In addition, the most recent six-year mean temperature is 0.2°C less than the peak analogous temperature achieved at the end of the first warming. So what is one to conclude from these observations?
First of all, as we have long claimed for the entire world [see our Editorial of 1 July 2000: There Has Been No Global Warming for the Past 70 Years], the Arctic - which according to essentially all climate models is supposed to be the harbinger of things to come for the rest of the world - is not yet as warm as it was in the late 1930s and early 1940s. In fact, because temperatures were so high for so long back then, the authors report that linear regression trends calculated from the 1920s to the present show a small but statistically significant cooling tendency.
Starting all the way back at beginning of the 20th century, however - at the time when Mann et al. (1999) claim the great "unprecedented" warming of the past millennium began - Polyakov et al.'s Arctic temperature data do produce a subsequent warming. However, for the period 1901 to 1997, they note that the upward temperature trend of the Arctic calculated from their data is "statistically indistinguishable" from the upward temperature trend of the entire Northern Hemisphere calculated from the data of Jones et al. (1999). Hence, as they most appropriately note, this similarity "does not support amplified warming in polar regions predicted by models (IPCC, 2001)," and especially does it not support a polar warming that is amplified by a factor of two to three, as most models predict.
So why have the world's best climate models erred so egregiously in this most common of their predictions? Polyakov et al. suggest that the models' missing of the mark may be due to the insignificance of what their creators ironically suggest is the cause of the supposed polar warming amplification, i.e., strong positive feedback induced by the melting of snow and sea ice. They note, for example, that in addition to analyzing temperature records they examined long-term records of observations of fast-ice thickness and ice extent from the Kara, Laptev, East Siberian and Chukchi Seas, finding that "long-term trends are small and generally statistically insignificant, while trends for shorter records are not indicative of the long-term tendencies, in agreement with the trends of air temperature."
In concluding their brief review, Polyakov et al. remark that "if long-term trends are accepted as a valid measure of climate change" - and, we wonder, what else could possibly qualify as an alternative? - "then the air temperature and ice data do not support the proposed polar amplification of global warming." They also note there are some other independent indications that "the importance of the ice- and snow-albedo feedbacks may be exaggerated (Robock, 1983), which may explain why the amplification of global warming is not found in the Arctic."
Clearly, as Polyakov et al. suggest in summation, "the Arctic poses severe challenges to generating credible model-based projections of climate change," and until there are models that can pass its reality check, there would appear to be little reason to give them any credence.
|Sherwood, Keith and Craig Idso|
Intergovernmental Panel on Climate Change. 2001. Climate Change 2001, The Scientific Basis. Contribution of Working Group 1 to the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), edited by J.T. Houghton, Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, and D. Xiaosu. Cambridge University Press, Cambridge, UK.
Jones, P.D., New, M., Parker, D.E., Martin, S. and Rigor, I.G. 1999. Surface air temperature and its changes over the past 150 years. Reviews of Geophysics 37: 173-199.
Mann, M.E., Bradley, R.S. and Hughes, M.K. 1999. Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophysical Research Letters 26: 759-762.
Polyakov, I., Akasofu, S-I., Bhatt, U., Colony, R., Ikeda, M., Makshtas, A., Swingley, C., Walsh, D. and Walsh, J. 2002. Trends and variations in Arctic climate system. EOS, Transactions, American Geophysical Union 83: 547-548.
Robock, A. 1983. Ice and snow feedbacks and the latitudinal and seasonal distribution of climate sensitivity. Journal of the Atmospheric Sciences 40: 986-997.