Some of the most prominent examples of extreme weather are misleading, and some weather events are becoming less extreme. Photo: Andrew Quilty
One of the most persistent claims in the climate debate is that global warming leads to more extreme weather. Green groups and even such respectable outlets as Scientific American say ''extreme weather is a product of climate change''. And the meme seems irresistible as a political short cut to action. President Barack Obama has explicitly linked a warming climate to ''more extreme droughts, floods, wildfires and hurricanes''. The White House warned this summer of ''increasingly frequent and severe extreme weather events that come with climate change''. Yet this is not supported by science.
''General statements about extremes are almost nowhere to be found in the literature but seem to abound in the popular media,'' climate scientist Gavin Smith of the NASA Goddard Institute for Space Studies said last month. ''It's this popular perception that global warming means all extremes have to increase all the time, even though if anyone thinks about that for 10 seconds they realise that's nonsense.''
Global warming is real. It is partly man-made. It will make some things worse and some things better. Overall, the long-run impact will be negative. But some of the most prominent examples of extreme weather are misleading, and some weather events are becoming less extreme.
The UN Intergovernmental Panel on Climate Change (IPCC) delivered a 600-page report on extreme weather in 2011. It got little attention because it is nuanced.
Global warming, in general, will mean higher temperatures. This causes more heatwaves, more extreme weather. But it also causes fewer cold waves, less extreme weather. More people die from excessive cold than excessive heat.
By mid-century, researchers estimated in 2006, that means about 1.4 million fewer deaths a year.
Moreover, global warming will mostly increase temperatures during winter, at night and in cold places, making temperature differences less extreme.
Global warming will also cause more heavy rain; this is clearly more extreme. But warming will also help alleviate water scarcity - about 1.2 billion fewer people are expected to live with water scarcity by the end of the century because of increased precipitation.
Drought is expected to increase in some regions while decreasing in others. Overall, the impact will probably be slightly more extreme. Likewise, sea levels will rise, meaning more flooding of coastal structures - more extreme. Total impact is likely to be less than 0.1 per cent of global economic output.
Hurricane wind speeds are likely to increase (more extreme), but the number of hurricanes is likely to decrease or hold steady (less extreme). The number of extra-tropical cyclones is likely to decline (less extreme).
Obama's examples of more extreme weather from droughts, floods, wildfires and hurricanes are weak examples for the US. Wildfire may be the only one of these indicators that is increasing in the US but to a large degree this is because fire suppression efforts have resulted in more material being available to burn.
The IPCC found that ''droughts have become less frequent, less intense, or shorter, for example, in central North America''. A scientific overview published in June in the Bulletin of the American Meteorological Society found that the severe drought of 2012, which at one point covered 39 per cent of the US, was still much less extreme than droughts in the 1930s (which covered 63 per cent) and the 1950s (50 per cent).
Damage from flooding in the US has declined from 0.2 per cent of gross domestic product in 1940 to less than 0.05 per cent today. And US hurricanes have not increased in frequency, intensity or normalised damage since at least 1900. It has been more than seven years since the country was hit by a category-three or stronger hurricane. That is the longest such hurricane drought since 1900.
A new paper in the journal Nature shows on a crucial measure that there is no increase in extremes.
Looking at temperature variability as one kind of extreme weather, the authors document that extreme weather globally has been constant since 1960. Moreover, the researchers found that extreme weather as temperature variability will decline in the future with higher levels of carbon dioxide.
They laconically conclude: ''Our findings contradict the view that a warming world will automatically be one of more overall climatic variation.''
It is understandable a lot of well-meaning people, wanting stronger action on global warming, have tried to use the meme of extreme weather to draw attention. But alarmism and panic are rarely the best way to achieve good policies. The argument that global warming generally creates more extreme weather needs to be retired.
The writer, an adjunct professor at the Copenhagen Business School, directs the Copenhagen Consensus Centre. He is the author of The Skeptical Environmentalist and, most recently, How Much Have Global Problems Cost the World? A Scorecard From 1900 to 2050.