Dr. Philipp Lengsfeld
Primary source: Rosenblum and Eisenman (2017) Sea Ice Trends in Climate Models Only Accurate in Runs with Biased Global Warming Journal of Climate, 30 6265-6278
The current greenhouse-gas anthropogenic global warming (GHG-AGW) hypothesis heavily relies on climate modelling. The recent fundamental work by Rosenblum and Eisenman highlights the grave issues for current modelling to accurately describe temperature and sea ice developments – two key factors for climate modelling.
The authors have worked extensively on sea ice modelling using standard climate models, e.g. CMIP3, CMIP5, CMIP6. Sea ice modelling is about doing prediction of the future evolution of sea ice extents in the Arctic and Antarctic. A key input parameter for this modelling is the temperature.
The scope of the above referenced work is to compare sea ice trends in the Artic and the Antarctic and the necessary temperature input to actually observed values returned by using the CMIP5 model. The work documents, that the observed correlation between the temperature and the Arctic sea ice extent is stronger than models imply while the observed temperature dependence of Antarctic sea ice extent is considerably weaker than modelled. This means that the modelling in fact does not work properly.
Rosenblum and Eisenberg papers states that the current models cannot capture the entirety of observations simultaneously. While the observed Arctic sea ice extent is decreasing, the Antarctic sea ice extent is actually increasing. This asymmetry is not captured by any of the models with any realistic temperature assumption: When accounting for the Arctic, a larger warming is needed in the CMIP5 model, when accurately displaying the Antarctic, less warming is needed. Reality needs to be force-fitted in with increasingly unrealistic assumptions.
To quote the authors:
“We find that simulated Arctic sea ice retreat is accurate only in runs that have far too much global warming (references to figures in the original manuscript). This suggests that the models may be getting the right Arctic sea ice retreat for the wrong reasons. Similarly, simulated periods with accurate Antarctic sea ice trends tend to have too little global warming, although these results are more equivocal (references to figures in the original manuscript). Relatedly, the simulations do not capture the observed asymmetry between Arctic and Antarctic sea ice trends (references to figures in the original manuscript).” (The original quote also contains references – for full text please refer to original manuscript).
Erica Rosenblum is currently working as an associate professor at Berkeley. The paper has been written when Eric Rosenblum and Ian Eisenman both were working for the Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California
This work puts a spotlight onto the weaknesses of current climate models. Written by respected experts from first class institutions their summary seems to be a pretty harsh judgment on the validity and or robustness of current climate modelling.
A deeper understanding of the evolution of overall climate is very important. The models and their underlying mechanistic assumptions must have the capacity to display changes such as sea ice extent accurately employing realistic temperature assumptions.
If they can’t, a better approach might be to start with local/regional changes instead of trying to solve the broad picture in one go. In any case, with such large gaps between modelling and reality the underlying mechanistic assumptions likely need to be challenged, reviewed and adapted.