Dan Drollette Jr
When it comes to tipping points, one of the greatest worries is the status of what is known as the Atlantic Meridional Overturning Circulation, or AMOC—a key player in making the northern part of Europe habitable. The AMOC has been described as a sort of conveyor belt, that uses currents such as the Gulf Stream to circulate saltwater and heat from south to north and back again in a long cycle within the Atlantic Ocean, warming up the land masses it passes on its northward journey in the process—and with effects on the rest of the globe as well.
To very loosely paraphrase the words of one observer, if this heat-transporting mechanism was to go out of business, then raising crops in Great Britain would be like trying to grow potatoes in northern Norway (near the Arctic Circle).
Fortunately, this oceanic circulatory system was generally regarded as more-or-less stable.
But new methods of data-collecting and computer-modelling have revealed that the AMOC has been unstable in the past, and its earlier collapses led to some of the most dramatic and abrupt climate shifts ever known. These days, melting ice in the North Atlantic—caused by increased global warming—has steadily caused more freshwater to be introduced into the system, changing its salinity and further pushing it toward collapse. At some point, this steady diet of change might no longer produce effects in a neat linear fashion but reach that moment of critical mass—an abrupt threshold, or tipping point—beyond which there could be large, accelerating, and possibly irreversible changes in the system and change its salinity and further pushing it toward collapse (or, at least irreversible changes within the span of a human lifetime).
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