Natural processes in the Arctic? Real Climate clarifies

In their usual public-spirited way, Real Climate parses a confusion in a recent paper about Arctic heating: New rule: When declaring that climate models are misleading in a high profile paper, maybe looking at some model output first would be a good idea.

This is a reference to an otherwise interesting paper in Nature this week (Graversen et al) on the vertical structure of heating in the Arctic in recent decades. One of the key results is that during the summer, when temperatures near the surface are constrained to be close to zero by the presence of open water and sea ice, the troposphere heats up anyway. The mechanism for this heating is hypothesised to be related to changes in atmospheric heat transport. So far so good.

But towards the end, there is this curious line:

Our results do not imply that studies based on models forced by anticipated future CO₂ levels are misleading when they point to the importance of the snow and ice feedbacks. …. Much of the present warming, however, appears to be linked to other processes, such as atmospheric energy transports.

The clear implication is that climate models don't suggest that atmospheric heat transports will change and that all polar amplification in those possibly misleading models is driven by snow and ice feedbacks. But is this correct? Well, it's hard to tell from this paper because they don't look at any model results!

This didn't stop the AP from declaring the heat transports to be part of some "natural and cyclical increase"! For National Geographic it was just 'mysteriously occurring'….

But in order to see what models have to say, all one has to do is look. With the easy availability of the CMIP3 archive, it's not too difficult to do the analysis for all the IPCC AR4 simulations for this exact period. As a short cut (and just because there is an easy interface) you can also go to the GISS archive and to pull down the figure for the summertime (Jun-Aug) temperature changes in the "all forcings" run for the same time period (1979-2001). If you do so, you'll see that in the Arctic, the models also suggest that summer time surface changes are small and that there is heating aloft - similar to the analysis in this paper. The match to the ERA-40 analysis isn't perfect by any means (but the match between different analyses products is not that great either). More analysis would need to be done to work out what was forced and how large the weather noise is etc, but the basic phenomena seems to be quite universal and not mysterious at all.

The point is that this isn't difficult stuff, and it should be standard practice to at least give a cursory look at what models actually show before accusing them of being misleading.