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Global warming may be less than IPCC predicts

30.12.2010
30.12.2010 17:40 Age: 3 yrs
Category: Climate change
By: Leon Clifford

Global warming during the twenty first century may be significantly less than that forecast by the Intergovernmental Panel on Climate Change (IPCC), according to a new paper.

Click to enlarge. Diverging predictions of temperature rise from the IPCC and from Akisofu's hypothesis of continuing natural recovery from the Little Ice Age with multi-decadal oscillations superposed. (Picture credit: Natural Science).

Physicist and Arctic research expert Syun-Ichi Akasofu of the International Arctic Research Center at the University of Alaska Fairbanks in the US predicts that the temperature in 2100 will be 0.5C ± 0.2C higher than today, rather than the 4.0C± 2.0C predicted by the IPCC.

Akasofu is an acknowledged climate change sceptic – although he prefers the term critic - and his prediction is based on an attempt to separate out the effects of naturally-driven warming from man-made greenhouse warming. Akasofu states that the warming trend recorded during the nineteenth and twentieth century may be a combination of a natural recovery from the so called Little Ice Age mixed in with greenhouse warming.

Linear warming of 0.5C per century

Akasofu's paper, “On the recovery from the Little Ice Age”, has been published in Natural Science. During the Little Ice Age global temperatures are believed to have been around 1C lower than today. The Little Ice Age is thought to have begun around 1200 and to have ended in the period between 1800 and 1850. Since then, global temperatures have been recovering at a linear rate of around 0.5C per century with the effects of multi-decadal oscillations superposed, according to Akasofu.

Crucially, Akasofu believes that the recovery from the Little Ice Age is still ongoing and is in part responsible for recent warming. He suggests that the effects of multi-decadal oscillations have halted the current warming and were also responsible for a flattening in warming seen between 1940 and 1975.

As much as 0.5C of the 0.6C rise recorded in the last century may be due to the natural recovery from the Little Ice Age, according to Akasofu. He bases this on the fact that there has been an underlying linear warming since the early nineteenth century where as carbon dioxide levels only started to increase significantly from around 1946.

Understanding the relative contribution of man-made changes to global warming is important as it enables climate scientists to accurately assess the sensitivity of the climate to increases in the levels of atmospheric carbon dioxide.

Diverging predictions

The accompanying diagram, from the paper, shows that the linear temperature trend between 1880 and 2000 is a continuation of the recovery from the Little Ice Age, together with the superposed multi-decadal oscillation. It also shows the predicted temperature rise by the IPCC after 2000. It has been suggested by the IPCC that the thick blue line portion was caused mostly by the greenhouse effect, so the future IPCC prediction is a sort of extension of the blue line, according to Akasofu. The diagram assumes that the recovery from the Little Ice Age continues to 2100, together with the superposed multi-decadal oscillation, which would suggest a further 0.5C warming. This view could explain the apparent halting of the warming after 2000 as a result of the impact of multi-decadal oscillations. The observed temperature in 2008 is shown by a red dot with a green arrow.

The implication is that over the next ten years or so there will be a significant and measurable divergence between the IPCC prediction and the the prediction generated by Akasoku's hypothesis of recovery from the Little Ice Age.

Key points in the conclusion to Akasofu's paper:

1) The Earth experienced the Little Ice Age (LIA) between 1200-1400 and 1800-1850. The temperature during the LIA is expected to be 1C lower than the pre-sent temperature. The solar irradiance was relatively low during the LIA.

2) The gradual recovery from 1800-1850 was ap-proximately linear, the recovery (warming) rate was about 0.5°C/100 years. The same linear change contin-ued from 1800-1850 to 2000. In this period, the solar irradiance began to recover from its low value during the LIA.

3) The recovery from the LIA is still continuing today.

4) The multi-decadal oscillation is superposed on the linear change. The multi-decadal oscillation peaked in about 1940 and also in 2000, causing the temporal halting of the recovery from the LIA.

5) The negative trend after the peak in 1940 and 2000 overwhelmed the linear trend of the recovery, causing the cooling or halting of warming.

6)The view presented in this paper predicts the temperature increase in 2100 to be 0.5C ± 0.2C, rather than 4C ± 2.0C predicted by the IPCC

Citation

"On the recovery from the Little Ice Age" by Syun-Ichi Akasofu see here.

Natural Science Vol.2, No.11, 1211-1224 (2010) doi:10.4236/ns.2010.211149

Source

Also see Akasofu's guest post on Roger Pielke Sr's Climate Science website here


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