- Bishop Hill blog

One of the things I've noticed about climatologists is that once they get each generation of models out into the open they spend the following few years producing papers that analyse some aspect of the model output. This is no doubt an easy way of making an impact on the research evaluation exercises to which all academics are subjected. And if the papers are accompanied by bloodcurdling headlines about future disaster are no doubt good for promotion, salary increases and invitations to speak to the United Nations.

This paper (via Leo Hickman's Twitter feed) looks to be from the same drawer. Here's the abstract:

Trends of Arctic September sea ice area (SSIA) are investigated through analysis of Coupled Model Intercomparison Project phase 5 (CMIP5) data. The large range across models is reduced by weighting them according to how they match nine observed parameters. Calibration of this refined SSIA projection to observations of different 5 year averages suggests that nearly ice-free conditions, where ice area is less than 1 × 10⁶ km², will likely occur between 2039 and 2045, not accounting for internal variability. When adding internal variability, we demonstrate that ice-free conditions could occur as early as 2032. The 2013 rebound in ice extent has little effect on these projections. We also identify that our refined projection displays a change in the variability of SSIA, indicating a possible change in regime.

So far so bloodcurdling. However, it seems to me that the authors, and indeed the climatological community as a whole, have a problem. We know that the aerosol forcing figures in the CMIP5 models are far greater than the best observational evidence would suggest. This being the case the models will necessarily run too hot. This presumably makes the claim that the Arctic ice will be gone by 2032 just a weeny bit shaky.

Aren't they going to have to sort the aerosols out before they can start to make predictions?