'Global warming on, despite recent cool off' - Times of India

NEW DELHI: That average global temperatures have hardly shown an increase in the past 15 years (1998-2012), is often used by climate change sceptics as proof that human-induced global warming threat is exaggerated. The IPCC's Summary for Policymakers report addresses the question directly, arguing that the current slowdown in global warming will not affect long-term rise in temperatures.

Global temperatures have on average risen by 0.12 degrees Celsius per decade since 1951 but the warming rate in the 1998-2012 period is considerably lower at 0.05 degrees C.

The report attributes a number of reasons for this slowdown. One, it says, 15 years is too short a period for making generalizations. "Due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends," it says.

"If you take away the first year — 1998, which was exceptionally hot because of a strong El Nino — the graph looks very different," says Krishna AchutaRao of IIT Delhi, one of the lead authors of a forthcoming IPCC report.

The report says the slowdown in warming since 1998 could be due to two factors. One, the Earth retained less heat during this period primarily due to volcanic eruptions and a downward phase in the 11-year solar cycle. And two, much of the energy generated by global warming went into the ocean.

The report admits there is "low confidence" in the first reason and only "medium confidence" in the second. It also admits that some climate models could have "overestimated the response to increasing greenhouse gas and other anthropogenic forcing".

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