Are We Headed for a “Year Without a Summer”?

The climate over the past few thousand years has been unusually stable, helping bring about the rise of modern civilization. However, ice core studies reveal that the “normal” climate for Earth is one of frequent extreme jumps – like a light switch flicking on and off. So it is incorrect to think that global warming will lead to a slow and steady increase in temperature that humans can readily adapt to. Global warming could push the climate system past a threshold where a sudden, irreversible climate shift would occur.

That outcome would most likely happen if the increased precipitation and glacial meltwater from global warming flood the North Atlantic with enough fresh water to slow down or even halt the Atlantic Meridional Overturning Circulation (AMOC), which transports warm, salty water from the tropics to the North Atlantic and sends cold water to the south along the ocean floor. The mighty Gulf Stream current forms the portion of the AMOC that runs along the U.S. East Coast.

If the AMOC were to shut down, the Gulf Stream would no longer pump warm, tropical water to the North Atlantic. Average temperatures would cool in Europe and North America by three degrees Celsius (5°F) or more in just a few years – not enough to trigger a full-fledged ice age, but enough cooling to bring snows in June and killing frosts in July and August to New England and northern Europe, such as occurred in the famed 1816 “year without a summer”. In addition, shifts in the jet stream pattern would bring about severe droughts and damaging floods in regions unaccustomed to such events, greatly straining global food and water supplies.

A study published in August 2021 looked at eight independent measures of the AMOC, and found that all eight showed early warning signs that the ocean current system may be nearing collapse. “The AMOC may have evolved from relatively stable conditions to a point close to a critical transition,” the authors wrote.

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