News from the Arctic, and it's bad
I was just directed to a recent paper in Nature called "The central role of diminishing sea ice in recent Arctic temperature amplification" by Screen & Simmonds [LINK]. The title doesn't quite do justice to the paper. Maybe a better title would be something like, "Staring into the face of polar amplification and knowing fear." To summarize, they use a new "renalysis" dataset called ERA-Interim to show that there is detectable polar amplification over the past twenty years. Renalysis just means a model that is guided by observations, and this one is a more sophisticated one than the more popular ERA-40 or NCEP/NCAR ones. They look at the northern high latitudes and find substantial warming, mostly confined near the surface. The rate of warming is faster than the global mean, and that is the definition of polar amplification. The fact that it is mostly near the surface implicates near-surface processes, and that is actually the key point for arctic researchers because this has recently been a bone of contention. Some previous work suggested that the extra warming was distributed through the atmosphere, leading to the conclusion that changes in atmospheric circulation were most important for the warming. This new paper reaches the conclusion that the mechanism most responsible for the polar amplification is temperature-ice interactions, which many of us like to lump into "ice-albedo feedback." They consider other mechanisms, but the evidence points toward decreasing sea ice being strongly tied to the warming. An implication of the work is that positive feedbacks are already evident in observations, and positive feedbacks destabilizing to the system and can lead to abrupt changes. Insert the phrase "tipping point" somewhere into this discussion, since that is really what we're talking about. The question now is just how far the Arctic can be pushed before things get scary. It is an open question, but clearly needs to be answered soon!