Art Viterito
One of the most important questions in geophysical science is whether the system of North Atlantic currents, collectively known as the Atlantic Meridian Cycle, or AMOC, has strengthened or weakened in recent years. recent years.
Opinions vary widely, but there is a strong consensus among climate modelers that the AMOC has weakened in the past and will continue to weaken in the future. A slowdown in AMOC could have profound effects on global climate, from cooling northern Europe and the Arctic to accelerating trade winds in the Pacific.
In contrast, recent empirical studies have challenged the “weakening” hypothesis. Getting the argument “right” is vitally important, as enhanced AMOC will raise temperatures in the Arctic. This will lead to a decrease in ice cover in the Arctic Ocean, the retreat of permafrost, the expansion of undersea forests, and the shrinking of the Eurasian and North American tundra. Three recent studies clearly illustrate this important epistemological divide.
In a 2018 modeling study by Caesar, et al., (Observable handprints of a waning Atlantic circulation reversal | Nature), the authors conclude that AMOC has been on the decline since the mid-twentieth century. Direct quote from the study:
“This weakening is revealed by the characteristic seasonal and spatial ‘fingerprints’ of sea surface temperatures — including a cooling pattern in the subpolar Atlantic and warming in the Gulf Stream region — and calibrated through a group of simulation models from the CMIP5 project. We find this fingerprint both in high-resolution climate models in response to increasing concentrations of carbon dioxide in the atmosphere and in temperature trends observed since the late nineteenth century. This pattern can be explained by the decline of AMOC and decrease in heat transport from the north…. “
In contrast, a 2021 experimental study by Oziel et al. (Faster Atlantic currents promote polar expansion of temperate phytoplankton in the Arctic Ocean | Nature Communications) largely contradicts this finding. In their study of North Atlantic currents, the authors demonstrate that the Northern Branch of the Gulf Stream has doubled in speed since 1995. Using satellite data and phytoplankton , they conclude:
“The Arctic marine biome, which shrinks as temperatures rise and sea ice recedes, is closely connected to lower latitudes across the North Atlantic. By flowing north through Europe’s Arctic Corridor (the main gateway to the Arctic, where 80% of the flow goes in and out), the North Atlantic Waters transport most of the ocean’s heat, but both nutrients and plankton towards the Arctic Ocean. Using satellite altimeter observations, we detect an increase, up to twofold, in the North Atlantic current surface velocity over the past 24 years. “
The third study, which combined modeled results with a range of experimental inputs, corroborates Oziel et al. findings. As the authors said in Heat Loss in the Nordic Sea, Atlantic Current and Arctic Sea Ice Cover in the Last Century – Smedsrud – 2022 – Review of Geophysics – Wiley Online Library:
“The Arctic Ocean, including the Nordic and Barents Seas, has warmed since the 1970s. This warming is accompanied by increased ocean heat transport and loss of sea ice and has contributed to into the retreat of sea-terminating glaciers on Greenland. “
Press release on this study by the Bjerknes Center for Climate Research (Gulf flows have increased steadily over the past century (uib.no)) Statuses:
“Heat transport into the Nordic seas has steadily increased in volume and temperature over the past century…”
Bjerknes’ press release goes on to say:
“It is surprising to find such consistent results showing a steady increase, followed by the expansion of the Gulf Stream into the reinforced Nordic Sea…. With a surprising increase in volume, the total amount of heat transported has increased… 30 percent. “
Notable in these comments is that the researchers (who were 17 in the group) were “surprised” by the enhancement. This is without a doubt a response to the large number of modeling studies that have concluded to the contrary. Clearly, climate science has become deeply committed to numerical modeling with a gradual reduction in interest in experimental inputs.
Rooted in the long tradition of the scientific method, we should never overlook the value of observation. Furthermore, we must stop being so dependent on the “regulating” algorithmic structures of our world, as their products have been used to create far-reaching policies that affect the way we operate. We evaluate and use our resources. Empiricism should always be the foundation for understanding climate. Modelers might think differently about this, but the temperate phytoplankton that recently migrated to the Arctic would certainly be different.
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