Art Viterito
One of the most important questions in the geophysical sciences is whether the system of currents of the North Atlantic, collectively referred to as the Atlantic Meridional Overturning Circulation, or AMOC, has strengthened or weakened in recent years.
Opinions vary widely, but there’s a strong consensus among climate modelers that the AMOC has weakened in the past and will continue to weaken going forward. A slowing AMOC could have profound impacts on the global climate, ranging from cooling in Northern Europe and the Arctic to accelerated trade winds in the Pacific.
By contrast, recent empirical studies have challenged the “weakening” hypothesis. Getting the argument “right” is critically important, as a strengthened AMOC would increase Arctic temperatures. This would result in diminished ice cover in the Arctic Ocean, permafrost retreat, expansion of the boreal forests, and shrinkage of the Eurasian and North American tundra. Three recent studies clearly illustrate this critical epistemological divide.
In a 2018 modeling study by Caesar, et al., (Observed fingerprint of a weakening Atlantic Ocean overturning circulation Nature), the authors conclude that the AMOC has been weakening since the mid-twentieth century. To quote directly from the study:
“This weakening is revealed by a characteristic spatial and seasonal sea-surface temperature ‘fingerprint’—consisting of a pattern of cooling in the subpolar Atlantic Ocean and warming in the Gulf Stream region—and is calibrated through an ensemble of model simulations from the CMIP5 project. We find this fingerprint both in a high-resolution climate model in response to increasing atmospheric carbon dioxide concentrations, and in the temperature trends observed since the late nineteenth century. The pattern can be explained by a slowdown in the AMOC and reduced northward heat transport….”
By contrast, a 2021 empirical study by Oziel, et al. (Faster Atlantic currents drive poleward expansion of temperate phytoplankton in the Arctic Ocean
