LONDON (Reuters) - Rising temperatures are driving more frequent bouts of extreme weather which governments should heed with climate action even as the world economy teeters.
Global carbon emissions rose by a record amount last year rebounding on the heels of recession, showing the problem remains even when economies plummet.
Meanwhile a U.N. climate meeting which starts later this month in Durban, South Africa, will likely be one of the most uneventful yet in stalled talks to agree a global deal.
An early draft of a report on extreme weather events to be published by the Intergovernmental Panel on Climate Change (IPCC) on Friday makes only broad brush links with climate change.
It says that manmade climate change is “likely” responsible for hotter heatwaves worldwide, in findings which experts from 110 countries debated this week and may still change. In IPCC jargon, “likely” means a two-thirds chance or more.
The report should give more prominent weight to growing evidence for a link, however.
Summer mean temperatures, including data for 2011, have risen inexorably above the 1951-1980 average, unpublished research by NASA’s James Hansen shows.
Each year about a tenth of the world’s land area now experiences an “extremely hot” June-July-August, something all but unheard of just 60 years ago, Hansen says. (See Chart 1)
In a stark example, a Russian heatwave last July wiped out a quarter of the country’s grain crop and panicked world food markets.
It prompted President Dmitry Medvedev to acknowledge a climate threat which his predecessor, Vladimir Putin, had once joked about.
Hansen defined extremely hot summers as those exceeding three standard deviations from the average 1951-1980 climate.
One standard deviation captures about two thirds of observations compared with the seasonal summer average, and three standard deviations nearly 99.9 percent.
In other words, a summer more than three standard deviations from the average should barely ever happen.
Yet they are occurring, in Europe in 2003, in eastern Europe in 2007, Russia and the Middle East in 2010 and Texas in early 2011. (see the dark red areas in Chart 2)
The argument is that such increasing frequency can’t be explained only by natural variation in the weather.
And the problem is growing, with Hansen’s research showing average summer temperatures globally are up by 1 standard deviation since 2001 compared with 1951-1961 in a steadily rising trend. (Chart 3)
He forecasts by 2050, assuming present trends of growth in fossil fuel carbon emissions, “extremely hot” summers in 1951-1980 terms would become the norm.
His observations appear robust for global data but less so for regions: the recent trend in extremely hot U.S. summers, for example, appears similar to those of the 1930s. (See Chart 4)
Such “noise” from natural weather variation may be expected in local and regional data.
Global full-year mean temperatures reached a record in 2010 tied with 1998 and 2005, the World Meteorological Organisation (WMO) said. The past decade was the warmest since measurements began in the nineteenth century.
Linking particular extreme weather events to climate change remains a matter of probability rather than proof, given the chaotic events which drive natural patterns.
Researchers from Germany’s Potsdam Institute for Climate Impact Research used simulations with and without a warming trend to show that recently rising temperatures in Russia, especially since 1980, had increased the chance of last year’s heatwave.
They calculated an 80 percent probability that the heatwave was due to climate change, in a paper published last month in the Proceedings of the National Academy of Sciences.
Moscow temperatures were the highest since the beginning of modern records and exceeded the long-term average by 7.8 degrees Celsius, according to the WMO.
The WMO earlier this year said that it was “very likely” that human influence on climate had at least doubled the risk of a heatwave such as the one in Europe in 2003, blamed for 40,000-70,000 deaths, compared with pre-industrial times.
Climate change also explained roughly half the increased dryness of Mediterranean winters in a recent study by the U.S. National Oceanic and Atmospheric Administration (NOAA).
Higher sea surface temperatures helped explain how 10 of the 12 driest winters since 1902 had all been in the past 20 years, the authors said in the Journal of Climate.
Since the last major IPCC report in 2007 many studies have shown that climate change is adding to the frequency of heavy rain, even making individual flood events more likely, adding to the evidence which goes beyond mere caution calling for much steeper carbon cuts.
(Editing by Jason Neely)
Gerard Wynn is a Reuters market analyst. The views expressed are his own.