Thursday, September 19, 2013

On the 60% Larger Arctic Ice Cap Year-Over-Year and on the Recent Global Warming Hiatus

I am not an atmospheric scientist. But I thought I could introduce some explanations about the recent measurements that are seemingly contradictory to the IPCC reports (AR4 and upcoming AR5).

First, does this year's Arctic ice cap that is reportedly 60% larger than the last year's mean climate is cooling? Not so. It is just a symptom of the so-called 'regression toward the mean' bias.
Let's look at the measurement data. The 60% increase in 2013 is just due to the record-contraction of the Arctic ice cap in 2012 (Meier, 2012). The downward trend is still valid.

Source: National Snow & Ice Data Center.

Second, does the hiatus of global warming since 1998 mean that the IPCC's forecasts are outright wrong? Not so. Their models were found wrong in that they couldn't predict the anomaly (How much the models were wrong can be found at Fyfe et al., (2013)). However, the overall global warming is happening exactly as the IPCC has been telling the world.
A Nature paper published today (Kosaka & Xie, 2013) clarifies what is really happening on the Earth. If their analysis is correct (Their explanation corresponds to 97% of temperature changes during 1970-2012.), the former climate models underestimated the natural variation known as "La-NiƱa-like decadal cooling." Their conclusion is,
"Although similar decadal hiatus events may occur in the future, the multi-decadal warming trend is very likely to continue with greenhouse gas increase."
(The IPCC report use the term "very likely" when the probability of a predicted outcome is greater than 90%.)
I think this study is a good answer to the so-called confusion between the short-term noise and the long-term change.


Fyfe, J. C., Gillett, N. P., & Zwiers, F. W. (2013). Overestimated global warming over the past 20 years. Nature Climate Change, 3(9), 767-769. [Full-text at]

Kosaka, Y., & Xie, S.-P. (2013). Recent global-warming hiatus tied to equatorial Pacific surface cooling. Nature, 501, 403-407. [Full-text at] (If you don't have a permission to read this article, just open the following link.

Meier, W. (2012). Record Low Arctic Sea Ice Extent in 2012: An exclamation point on a long-term declining trend [PowerPoint slides]. Boulder, CO: National Snow & Ice Data Center. [Slides at]

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