Overnight the big climate news has been the new paper by Chen and Tung, which seeks to explain the pause in surface temperature rise, now nearly 18 years old on some measures. Judith Curry has excerpts here, while a layman's summary is available at the Economist.
The story goes that much of the missing heat is to be found in the Atlantic, with a slow-moving current speeding up in recent times so that heat is drawn down into the deep-ocean. The theory seems to be that this process runs over a 60-year cycle, for half the time with the depths warming and the surface cooling and half the time the other way round. Chen and Tung conclude that we are currently in a surface cooling phase, so the pause could last another ten years or more.
The corollary is that the warming at the end of the last century was accelerated by the same process. Indeed, the press release notes that:
Rapid warming in the last three decades of the 20th century, they found, was roughly half due to global warming and half to the natural Atlantic Ocean cycle that kept more heat near the surface.
Strangely, this conclusion doesn't seem to have made it into the paper itself.
No doubt there will be a lot of banter on the subject today. Doug McNeall has opened up with a little jibe at us sceptics on Twitter:
If I was trying to counter the "pause" news, I'd also talk about post hoc rationalisation. Just a little tip there.
But it is inescapable that the climate models fail to capture this important process, if indeed it is real. This is understandable, given that Chen and Tung don't yet have an explanation for why the process changes.
Once again this brings us back to the thorny question of whether a GCM is a suitable tool to inform public policy.
Bishop Hill
Climatologist Gareth Jones notes that the Chen and Tung results are highly uncertain, although the failure of the authors to include error bars rather obscures this fact.