Part one of this article discussed James Hansen’s demonstration that a relatively small increase in global average temperature – under 1°C – has already produced a significant increase in the frequency and intensity of extremely hot weather. Heat waves that were very rare in 1951-1980 became ten times more likely in 1981-2010. As one of Hansen’s associates pointed out, this was not speculation about a possible future, but actual experience: “this is not based on models or predictions, just on a straightforward statistical analysis of measured temperature data.”
Other studies, using other methods, have come to the same conclusion.
A 2012 paper examined the “exceptionally large number of record-breaking and destructive heatwaves” in the first decade of this century. The authors found that, “many lines of evidence – statistical analysis of observed data, climate modelling and physical reasoning – strongly indicate that some types of extreme event, most notably heatwaves and precipitation extremes, will greatly increase in a warming climate and have already done so…. The evidence is strong that anthropogenic, unprecedented heat and rainfall extremes are here – and are causing intense human suffering.”
A study of extreme weather events between 1997 and 2012 concluded that “the available evidence suggests that the most ‘extreme’ extremes show the greatest change. This is particularly relevant for climate change impacts, as changes in the warmest temperature extremes over land are of the most relevance to human health, agriculture, ecosystems and infrastructure.”
Others have found that global warming made the 2012-2014 California drought significantly worse than it would have otherwise been, and that in Australia, where hot and cold records used to be set in about equal numbers, all-time hot weather records now outnumber cold records by 12 to 1.
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