It’s always worse than expected in the world of climate research. But in the case of sea-level rise it’s the models that are turning out to be worse than expected, which means sea-level rise itself is likely to be less than expected. A recent study in Science Advances, for which our h/t tip goes to the new YouTube channel World Climate News (to which we recommend you subscribe), took note of the fact that climate models up to now have had a spatial resolution for oceans that was too coarse to properly model oceanic eddies, those large swirling circles in the water that control movements of vast amounts of heat, salinity, momentum and dissolved carbon around the world. But recently one model has been developed that can simulate ocean eddies more precisely, and as a result it does a better job of reproducing the lack of warming around the Antarctic. One big implication is that it predicts a lot less melting of Antarctic ice, which translates into 25 percent less sea-level rise over the coming century.
You can learn about eddies in this lesson from NASA’s Jet Propulsion Lab. Because they are relatively small and short-lived, you might think the behaviour of eddies wouldn’t matter for global models. And that’s been the silent hope up to now, namely that since the models could only operate at a large spatial scale and average everything out, fingers crossed that whatever we can’t model will conveniently turn out not to matter. (Need we mention again the guy who dropped his key by the door but is searching under the lamppost because the light is better?)
In the new study in Science Advances, the authors were able to run a model that has high resolution ocean dynamics, with a small enough spatial scale that eddies can be represented with something like physical accuracy rather than averages and loose estimates. The most notable result was that the simulated temperature trends around Antarctica were much lower than the old-fashioned low resolution models, and of all things much closer to actual observations of real-world data. And following from that, ice melting in the high resolution model around the Antarctic base was only about one-third that estimated in the low-resolution model, which translated into a global sea-level rise this century about 25 percent lower.
The authors lament that there is only one climate model with the higher resolution required to simulate eddies. And they say it still generates about as much global warming as the low resolution versions, but that same warming translates into less sea-level increase. Still, as more high resolution models become available maybe they’ll start shedding light on the general problem that climate models generate too much warming as well as too much sea-level rise.