The top 10 global weather and climate change events of 2021

 

https://yaleclimateconnections.org/2022/01/the-top-10-global-weather-and-climate-change-events-of-2021/

 

 by Jeff Masters January 11, 2022

The year 2021 made an indelible mark in the annals of weather history. Not only did it feature the most extreme heat wave in history – the late June heat wave over western North America that smashed all-time records by unprecedented margins – it was also the first year to record four weather mega-disasters costing over $20 billion

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A total of eight extreme weather events were ranked in the top ten; in addition, there were two concerning climate change discoveries that may presage serious future challenges. Below is a list of the top-10 weather and climate change events of 2021, as rated by the impacts on humans and/or meteorological significance.
1. The most extreme heat wave in world history

Never in the century-plus history of world weather observation have so many all-time heat records fallen by such a large margin than in the historic late-June 2021 heat wave in western North America. The intense heat wave was the second-deadliest weather disaster of the year, with 1,037 deaths: 808 in western Canada and 229 in the northwestern U.S. The only deadlier weather disaster of 2021 was summer monsoon flooding in India that claimed 1,292 lives, according to insurance broker Aon.

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6. July 2021: Earth’s warmest month in recorded history

July 2021 was Earth’s hottest July since global record-keeping began in 1880, 0.93 degrees Celsius (1.67°F) above the 20th-century average, NOAA’s National Centers for Environmental Information reported. Since July is also the hottest month of the seasonal cycle, that meant that July 2021 was “more likely than not the warmest month on record for the globe since 1880,” NOAA said. July 2021 was just 0.01 degree Celsius hotter than July of 2016, 2019, and 2020, so these months can be considered to be in a statistical tie for Earth’s hottest month on record.

The record July warmth was particularly remarkable since there was a moderate La Niña event in the Eastern Pacific that ended in May 2021. La Niña events typically cause global cooling of about 0.1 degree Celsius; the peak cooling occurs five months after the La Niña peak, on average. July 2021 temperatures would have been even warmer had a La Niña event not occurred earlier in the year.

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7. Danger signs: a key Atlantic Ocean current system is near collapse

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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