What global climate models say and don’t say

There seems to be a widespread perception that global climate models capture all the important factors that will determine the future of the global climate. The previous post showed how changes in the underlying assumptions can cause the models to indicate less change, at least in the short term. But it is also relatively easy to show how things could be much worse than any model can currently capture.

What if the global system is now so stressed that major system shocks are triggered in much shorter timescales than we are currently expecting. What might they be?

Consider the following thought experiment. According to the scientific press, Antarctic temperature trends are uneven, with warming concentrated on the Antarctic Peninsula. If this causes more ice to melt in Western Antarctica than the rest of the continent, the resulting weight change could conceivably set off volcanic activity, earthquakes or even tectonic plate shifts, with potentially far-reaching effects. This is plausible since Antarctica sits on its own tectonic plate and is surrounded by earthquake and volcanic activity. Imagine something roughly similar to the 2004 Sumatra-Andaman subduction earthquake, not all that far from Antarctica, which was concentrated around a tectonic micro-plate and resulted in substantial sea floor uplift.

The sequence might go like this. As Western Antarctic ice gradually melts, the shifting weight distribution triggers a surge of volcanic activity below the ice. A substantial mass of Antarctic ice then melts asymmetrically and sets up more extreme stresses along subsea tectonic plate boundaries. This in turn leads to a massive earthquake and seabed uplift in the region of the unstable Shackleton Fracture Zone in the small gap between the tip of South America and the tip of the Antarctic Peninsula. The raised sea floor substantially blocks the Antarctic Circumpolar Current, a critical ring of interconnection for the world’s ocean currents. The ocean current system is forced to change and the whole global climate pattern is suddenly altered in ways not anticipated in the global climate models. This is a massive system shock with enduring worldwide consequences.

My point is not to argue that this specific event will happen or to be alarmist – but to illustrate the kind of thing that cannot be captured by existing detailed global modeling. The total planetary biogeochemical system almost certainly has many more feedback pathways and modes of response than we currently imagine, and we would do well to keep this in mind, both on the upside and the downside.