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The year 2011 has been the 10th warmest year on record in spite of a strong La Nina, which has a relatively cooling influence. In the event of a La Nina, the sea surface temperature is lower than usual in the tropical Pacific Ocean. Also, in 2011, the extent of the Arctic sea ice was the second lowest on record, and its volume was the lowest, revealed a provisional statement by the World Meteorological Organization (WMO). The statement, released at the ongoing 17th Conference of Parties (CoP) at Durban, aimed at providing scientific knowledge to inform action by decision makers.
The statement presents a snapshot of weather and climate events and presents global temperature assessment as well. WMO estimated global combined sea surface and land surface air temperature for 2011 (January-October) at 0.41°C±0.11°C above the 1961-1990 annual average of 14°C. This is the 10th equal warmest year since record keeping began in 1850. Incidentally, the 13 warmest years have all occurred in the 15 years since 1997.
La Nina gave no respite from heat
The 2002-2011 period equals 2001-2010 as the warmest decade on record—0.46°C above the long-term average (the period from 1961 to 1990). This warming happened despite the strongest La Nina in 60 years, which was linked to extreme events such as drought in east Africa, islands in the central equatorial Pacific and in southern part of the United States, and flooding in southern Africa, eastern Australia and southern Asia. Strong La Nina years are typically 0.1°C to 0.15°C cooler than the years preceding and following them. But, 2011’s global temperatures were considerably warmer than the most recent moderate to strong La Nina years.
It is not clear, however, whether such events can be linked directly to climate change because La Nina is a natural variability event. “Science is still not advanced enough to isolate natural variability and anthropogenic-forced variability in quantitative terms and hence these events cannot be linked to climate change,” says K J Ramesh, adviser/scientist with the Ministry of Earth Sciences.
But the world suffered the impact of the extreme weather in 2011 nevertheless (see 'The year of extreme weather'). Surface air temperatures were above the long-term average in 2011 over most land areas of the world. The largest departures from average were over Russia, especially in northern Russia where January-October temperatures were about 4°C above average in places.
Ice-free passage in Arctic
There’s bad news from the Arctic sea region as well. The seasonal Arctic sea ice minimum was 35 per cent below the 1979-2009 average. Both the Northwest and Northeast Passages were ice-free during the 2011 summer. Sea ice volume was further below average and was estimated at a new record low of 4,200 cubic km, surpassing the record of 4,580 cubic km set in 2010, the statement said. These coincided with the above-average temperatures in most northern polar regions.
This year will also go on record for having among the most active tornado seasons in Canada. Parts of the Mississippi river experienced the worst floods since 1933, and there was also major flooding in the Missouri river and several Canadian rivers.
An updated report with the final figures for 2011 will be published in March 2012, the World Meteorological Organization has announced.