Climate change scientists have consistently predicted that increasing greenhouse gas concentrations will increase global average precipitation levels. At the same time, many areas will see increased drought. 2010 shows early evidence for this forecast. The US National Climate Data Centre said earlier this week that the year equalled the hottest on record and this finding reached some of the newspapers. Less noticed was NCDC’s calculation that global rainfall levels were the highest since at least 1900. This year's anomaly (variance from the average) was over 50 millimetres, up significantly on the two previous peaks of about 45 millimetres. (For a sense of scale, Oxford's rainfall averages between 600 and 750 millimetres a year.)
This information probably doesn’t surprise any of us. In mid January 2011 we are seeing very serious flooding in Brazil, Sri Lanka and Australia. And the list of countries that suffered extreme rainfall in 2010 is a long one. So although UK residents – who have just been through the coldest December in living memory – have increasingly little faith that climate is warming, they may more easily believe that rainfall is increasingly heavy.
NCDC explicitly links some of the main flooding events in 2010 with the concurrent high temperatures. Importantly, it says that the unprecedented Pakistan floods (affecting 20 million people) were connected to the extremely hot air masses holding temperatures over Russia at high levels in summer of last year.
But global weather patterns are never consistent. Although Pakistan had catastrophic floods, Bangladesh has the driest monsoon season for fifteen years. Some parts of Brazil and Peru, including the vital Amazon region, were also very dry. The UK had less rain in the first half of the year than in any comparable period for half a century. Ontario had very little spring snow and Canada as whole had its driest winter since national records began in 1948.
One of the most troubling things I experienced during 2010 was delivering talks about climate change, mentioning the risks of extreme rainfall such as in Pakistan and being told by sceptics in the audience that the cause of floods is not high levels of rain but poor agricultural practices or increased urbanisation speeding the rate of water runoff. Both of these two explanations have a grain of truth but I hope that the increasingly obvious global threat from high levels of rainfall, and the increasing intensity of that precipitation, gets people to reconsider whether climate change is causing more floods.