15 mai, 2009
Mudanças climáticas – o debate (1)
Posted by: Darwinista In: Debate| Mudanças climáticas
Acabo de receber a primeira contribuição para nosso debate a respeito das mudanças climáticas, enviada pelo Pablo Villarnovo. É um artigo de Syun-Ichi Akasofu, pesquisador da University of Alaska Fairbanks.
Como combinado, segue o resumo do trabalho (por ora apenas em inglês) e o link para o artigo completo. Mas antes, um esclarecimento. Um comentário muito pertinente do André Monsores me levou a mudar a tag Aquecimento global para Mudanças climáticas. Realmente, é mais adequado.
Two Natural Components of the Recent Climate Change:
(1) The Recovery from the Little Ice Age
(A Possible Cause of Global Warming)
and
(2) The Multi-decadal Oscillation
(The Recent Halting of the Warming)
Syun-Ichi Akasofu
International Arctic Research Center
University of Alaska Fairbanks
Fairbanks, Alaska
Abstract
Two natural components of the currently progressing climate change are identified. The first one is an almost linear global temperature increase of about 0.5°C/100 years, which seems to have started in 1800–1850, at least one hundred years before 1946 when manmade CO2 in the atmosphere began to increase rapidly. This 150~200-year-long linear warming trend is likely to be a natural change. One possible cause of this linear increase may be the earth’s continuing recovery from the Little Ice Age (1400~1800); the recovery began in 1800~1850. This trend (0.5°C/100 years) should be subtracted from the temperature data during the last 100 years when estimating the manmade contribution to the present global warming trend. As a result, there is a possibility that only a small fraction of the present warming trend is attributable to the greenhouse effect resulting from human activities.
It is also shown that various cryosphere phenomena, including glaciers in many places in the world and sea ice in the Arctic Ocean that had developed during the Little Ice Age, began to recede after 1800 and are still receding; their recession is thus not a recent phenomenon.
The second one is oscillatory (positive/negative) changes, which are superposed on the linear change. One of them is the multi-decadal oscillation, which is a natural change. This particular natural change had a positive rate of change of about 0.15°C/10 years from about 1975 (positive from 1910 to 1940, negative from 1940 to 1975), and is thought by the IPCC to be a sure sign of the greenhouse effect of CO2. However, the positive trend from 1975 has stopped after 2000.
One possibility of the halting is that after reaching a peak in 2000, the multi-decadal oscillation has begun to overwhelm the linear increase, causing the IPCC prediction to fail as early as the first decade of the 21st century.
There is an urgent need to correctly identify natural changes and remove them from the present global warming/cooling trend, in order to accurately and correctly identify the contribution of the manmade greenhouse effect. Only then can the effects of CO2 be studied quantitatively. Arctic research should be able to contribute greatly to this endeavor.
Artigo completo em http://people.iarc.uaf.edu/~sakasofu/pdf/two_natural_components_recent_climate_change.pdf
