The Economist is read by all the most Important People (what, you say you don’t read it? Well…), so what they say about GW matters (even if they sometimes talk twaddle it still matters). What they are currently saying under the byline “Climate change may be happening more slowly than scientists thought. But the world still needs to deal with it” is
some scientists are arguing that man-made climate change is not quite so bad a threat as it appeared to be a few years ago… “climate sensitivity”… may not be as high as was previously thought. The most obvious reason is that, despite a marked warming over the course of the 20th century, temperatures have not really risen over the past ten years. It is not clear why climate change has “plateaued” (see article). It could be because of greater natural variability in the climate, because clouds dampen warming or because of some other little-understood mechanism in the almost infinitely complex climate system. But whatever the reason, some of the really ghastly scenarios—where the planet heated up by 4°C or more this century—are coming to look mercifully unlikely. Does that mean the world no longer has to worry?
No, for two reasons. The first is uncertainty. The science that points towards a sensitivity lower than models have previously predicted is still tentative… The risk of severe warming—an increase of 3°C, say—though diminished, remains real. There is also uncertainty over what that warming will actually do to the planet. The sharp reduction in Arctic ice is not something scientists expected would happen at today’s temperatures. What other effects of even modest temperature rise remain unknown?
The second reason is more practical. If the world had based its climate policies on previous predictions of a high sensitivity, then there would be a case for relaxing those policies… But although climate rhetoric has been based on fears of high sensitivity, climate policy has not been…
So, that’s all pretty good, even if you don’t like “plateau”.
The linked article sources Ed Hawkins pic. And apparently Work by Julia Hargreaves of the Research Institute for Global Change in Yokohama, which was published in 2012, suggests a 90% chance of the actual change being in the range of 0.5-4.0°C, with a mean of 2.3°C. Nic Lewis gets a mention for an unpublished paper. And then my eyes rather glazed over, because it was more of the same old stuff, ending up with
So what does all this amount to? … a small reduction in estimates of climate sensitivity would seem to be justified: a downwards nudge on various best estimates from 3°C to 2.5°C, perhaps; a lower ceiling (around 4.5°C), certainly… global temperatures rise by about 1.5°C for each trillion tonnes of carbon put into the atmosphere… At current rates, the next half-trillion tonnes will be emitted by 2045; the one after that before 2080… this could increase temperatures compared with pre-industrial levels by around 2°C even with a lower sensitivity and perhaps nearer to 4°C at the top end of the estimates. Despite all the work on sensitivity, no one really knows how the climate would react if temperatures rose by as much as 4°C. Hardly reassuring.