The idea that melting ice from Greenland will disrupt the flow of water around the Atlantic is something that, thanks to The Day After Tomorrow, most people are aware of. But while the movie was (obviously) a Hollywood dramatization in which the effects happened at super-speed, the core idea is increasingly looking possible.
Case in point: a new study found that models are underestimating the risk of a slowdown and eventual stop of the Atlantic Meridional Overturning Circulation(AMOC). The paper is discussed in depth at RealClimate by AMOC expert Stefan Rahmstorf, who is uniquely qualified to talk about it as his past work was the starting point for this new study. That said, the paper is also dismissed out of hand by WUWT and Steve Milloy, whose qualifications include... blog posts and getting kicked off Fox News for shilling for tobacco, respectively.
Anyway, there are two main factors at play in the science of AMOC-- mixing and melting. First, current climate models seem to overestimate the stability of the AMOC based on how salt and fresh water mix. Present thinking is that if emissions/warming cease, the current will weaken but will eventually return to relative stability. However, this new study suggests that it is not so stable after all and claims that the way in which the current models deal with the mixing salinity of melting ice and seawater are misguided. After they make corrections, the study concludes that AMOC is projected to weaken considerably over time.
The other factor is the water from Greenland entering the current. As the ice continues to melt more rapidly than expected, its effects on the AMOC will be more quick and more immense than previously thought. The study claims that the models, then, need to incorporate this development and when they do, the AMOC becomes more unstable more quickly and permanently.
So despite denier accusations of over-hype and the occasional Hollywood dramatization, it seems that scientists have underestimated how easy it is for warming to make sensitive cycles run AMOC.
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