Matt Ridley: Real possibility that "overall effect of climate change will be positive"

The IPCC's "fifth assessment report", to be published on September 27, will - quite like its predecessors - be presented as a portender of ominous happenings. However, as Matt Ridley points out, it is quite possible that the overall effect of global warming will be positive:

It is significant because it points to the very real possibility that, over the next several generations, the overall effect of climate change will be positive for humankind and the planet.--

Warming of up to 1.2 degrees Celsius over the next 70 years (0.8 degrees have already occurred), most of which is predicted to happen in cold areas in winter and at night, would extend the range of farming further north, improve crop yields, slightly increase rainfall (especially in arid areas), enhance forest growth and cut winter deaths (which far exceed summer deaths in most places). Increased carbon dioxide levels also have caused and will continue to cause an increase in the growth rates of crops and the greening of the Earth—because plants grow faster and need less water when carbon dioxide concentrations are higher.

Up to two degrees of warming, these benefits will generally outweigh the harmful effects, such as more extreme weather or rising sea levels, which even the IPCC concedes will be only about 1 to 3 feet during this period.

Yet these latest IPCC estimates of climate sensitivity may still be too high. They don't adequately reflect the latest rash of published papers estimating "equilibrium climate sensitivity" and "transient climate response" on the basis of observations, most of which are pointing to an even milder warming. This was already apparent last year with two papers—by scientists at the University of Illinois and Oslo University in Norway—finding a lower ECS than assumed by the models. Since then, three new papers conclude that ECS is well below the range assumed in the models. The most significant of these, published in Nature Geoscience by a team including 14 lead authors of the forthcoming IPCC scientific report, concluded that "the most likely value of equilibrium climate sensitivity based on the energy budget of the most recent decade is 2.0 degrees Celsius." --

Since the last IPCC report in 2007, much has changed. It is now more than 15 years since global average temperature rose significantly. Indeed, the IPCC chairman Rajendra Pachauri has conceded that the "pause" already may have lasted for 17 years, depending on which data set you look at. A recent study in Nature Climate Change by Francis Zwiers and colleagues of the University of Victoria, British Columbia, found that models have overestimated warming by 100% over the past 20 years.

Explaining this failure is now a cottage industry in climate science. At first, it was hoped that an underestimate of sulfate pollution from industry (which can cool the air by reflecting heat back into space) might explain the pause, but the science has gone the other way—reducing its estimate of sulfate cooling. Now a favorite explanation is that the heat is hiding in the deep ocean. Yet the data to support this thesis come from ocean buoys and deal in hundredths of a degree of temperature change, with a measurement error far larger than that. Moreover, ocean heat uptake has been slowing over the past eight years.

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