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 also had four weather mega-disasters costing over $20 billion each, tied with 2017 for the most such disasters on record.
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.
Two examples of the insane extremity of the heat wave:
• Canada broke its all-time national temperature record on three consecutive days at Lytton, British Columbia, which topped out at a stunning 49.6°C (121°F) on June 29 – a day before the town burned down in a ferocious wildfire fed by the extreme heat. The old Canadian heat record was 8°F cooler, 45.0°C (113°F) on July 5, 1937.
• Quillayute, Washington, broke its all-time high by a truly astonishing 11°F, after hitting 110°F on June 29 (old record: 99°F on August 9, 1981). Quillayute is located near the lush Hoh Rain Forest on the Olympic Peninsula, just three miles from the Pacific Ocean, and receives an average of 100 inches of precipitation per year.
“This was the most anomalous regional extreme heat event to occur anywhere on Earth since temperature records began. Nothing can compare,” said weather historian Christopher Burt, author of the book Extreme Weather, in an email. Pointing to Lytton, Canada, he added, “There has never been a national heat record in a country with an extensive period of record and a multitude of observation sites that was beaten by 7°F to 8°F.” International weather records researcher Maximiliano Herrera (@extremetemps) agreed. “What we are seeing now is totally unprecedented worldwide,” said Herrera, who tweeted on June 30, “It’s an endless waterfall of records being smashed.”
According to Herrera, more all-time heat records were broken by at least five degrees Celsius (9°F) during the heatwave than in the previous 85-plus years of world weather recordkeeping, going back to July 1936, when the hottest summer in U.S. history brought the previous most extreme heatwave in world history. It’s worth noting that the record North American heat of the 1930s, including 1936, was largely connected to the Dust Bowl, in which the effects of a multiyear drought were amplified by over-plowed, denuded soil across the Great Plains – an example of human-induced climate change itself, albeit temporary.
A rapid-response study from the World Weather Attribution program found that the daily high temperatures observed in a study area encompassing much of western Oregon, Washington, and British Columbia during June 2021 would have been “virtually impossible without human-caused climate change.” The study estimated it was roughly a 1-in-1000-year event in today’s climate, but in a world with 2 degrees Celsius of global warming (0.8 degree Celsius warmer than today, which, at current emission levels, would be reached as early as the 2040s), an event like this could occur roughly every five to 10 years.
2. Hurricane Ida: fifth-costliest weather disaster in world history ($65 billion)
Hurricane Ida made landfall at Port Fourchon, Louisiana, on August 29 as a category 4 storm with 150 mph winds. Ida moved up the U.S. East Coast and unleashed a devastating flood event over much of the mid-Atlantic and Northeast. Aon estimated Ida’s damages at $65 billion, making it the fifth-most expensive weather disaster in world history. NOAA’s estimate was $75 billion.
3. European summer floods: costliest weather disaster in European history ($43 billion)
Europe’s deadliest flood since 1985 struck western Germany and eastern Belgium July 12-18, when a stalled low-pressure system dumped torrential rains that killed 240 people and caused $43 billion in damage, according to Aon (note that EM-DAT had lower damages: $22 billion). The flood ranks as the costliest weather disaster in European history.
A rapid-response study from the World Weather Attribution program found that the likelihood of such an extreme one-day rainfall event has increased by a factor between 1.2 and 9 because of human-caused global warming.
4. Flooding in China: third-costliest weather disaster in Asian history ($30 billion)
An extreme rainfall event of nearly unimaginable intensity hit Zhengzhou, China, on July 20, which recorded an astonishing 644.6 mm (25.38 inches) of rain in 24 hours. This is literally more than a year’s worth of rain: Its average annual precipitation (1981-2010 climatology) is only 640.9 mm (25.23 inches).
Flooding in China during the June-through-September rainy season killed 347 people, damaged or destroyed 1.4 million homes and businesses, and did $30 billion in damage, according to Aon and EM-DAT. EM-DAT ranks that total as the third-most expensive non-U.S. weather disaster since accurate records began in 1990 (adjusted for inflation), behind 1998 flooding in China ($48 billion) and 2011 flooding in Thailand ($47 billion).
In a September 2020 study published in the Bulletin of the American Meteorological Society, “Each 0.5°C of Warming Increases Annual Flood Losses in China by More than US$60 Billion,” researchers found that annual average flood losses in China during the period 1984-2018 were $19.2 billion (2015 dollars), which was 0.5% of China’s GDP. Annual flood losses increased to $25.3 billion annually during the period 2006-2018. The study authors predicted that each additional 0.5 degree Celsius of global warming will increase China flood losses by $60 billion per year.
5. February cold wave in central U.S.: second-costliest winter weather disaster in world history ($23 billion)
A disastrous winter weather onslaught over the central U.S. brought heavy snow, freezing rain, and severe cold to Texas and surrounding states February 12-20, killing 246 people and causing $23 billion in damage. One result: the most expensive winter weather disaster in U.S. history (previous record: $10.1 billion in 2021 dollars from the 1993 “Storm of the Century” in the eastern U.S.). Globally, the only costlier winter weather disaster was a $26 billion event in 2008 in China.
Extreme cold has become less common as a result of global warming, so it’s reasonable to expect that disasters of this nature are growing less likely. As documented by meteorologist Guy Walton, record high maximum temperatures outpaced record low minimum temperatures by a ratio of nearly three to one in the U.S. in 2021.
Climate scientist Judah Cohen led a 2021 study demonstrating that the 2021 Texas freeze was a result of a stratospheric polar vortex disruption where it stretched like a rubber band or taffy. For the months of October through February, these stretched polar vortex events have roughly doubled since 1980. The increase has been attributed to reduced Arctic sea ice and increased snowfall across Siberia during the fall months – largely from human-caused climate change.
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.
During the month, Death Valley National Park’s Furnace Creek Visitor Center in California (U.S.) hit an astonishing 130.0 degrees Fahrenheit (54.4°C) on July 9, beating the previous all-time world record for hottest reliably measured temperature of 129.9 degrees Fahrenheit (54.4°C), set at the same location on August 16, 2020. As explained in our post on the record, the official world record remains 134 degrees Fahrenheit at Furnace Creek in 1913, but this record has been strongly disputed as invalid.
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.
8. A wild 2021 Atlantic hurricane season
The 2021 Atlantic hurricane season generated an extraordinary 21 named storms (third highest on record), seven hurricanes, four major hurricanes, and an accumulated cyclone energy (ACE) of 145. Those numbers compare with the 1991-2020 averages for an entire season of 14.4 named storms, 7.2 hurricanes, 3.2 major hurricanes, and an ACE index of 123. As documented by Brian McNoldy, Senior Research Associate at University of Miami’s Rosenstiel School of Marine and Atmospheric Science, 2021 marked the sixth consecutive year with an ACE index above 129: “this has never happened before, not during the satellite era, not since records began in 1851. This sustained level of tropical cyclone activity in the Atlantic is unprecedented even for four years, let alone six!”
Eight named storms made landfall in the contiguous U.S. in 2021, ranking as the third highest on record, behind 2020 (11) and 1916 (nine). The two-year period 2020-2021 had a truly astonishing 19 landfalls in the contiguous U.S., six times the average for a two-year period, and beating the previous two-year landfall record of 15, set in 2004-2005. From 1950 through 2020, the U.S. averaged just three landfalling tropical storms (with one a hurricane) per year.
9. Two unprecedented December U.S. tornado and severe weather outbreaks
A week of stunning record warmth in the U.S. Midwest in mid-December led to two unprecedented severe weather outbreaks. The first outbreak, on December 10, was the nation’s deadliest and most damaging on record for any December, with at least 90 fatalities and a record 69 confirmed tornadoes, chiefly across western and central Kentucky. Preliminary insured damage estimates are $3-$5 billion, and total economic damages will be much higher.
Then, on December 15, the record set just five days previously was smashed, as a massive cyclone whipped across the central U.S., spawning EF2 tornadoes as far north as Minnesota and Wisconsin – an outbreak unprecedented for December in its northward extent and in the total number of twisters confirmed (a total of 100, one of the largest one-day outbreaks on record for any time of year).
10. Bad news from a key glacier in Antarctica
Scientists from the International Thwaites Glacier Collaboration in December announced their discovery of cracks and fissures in the floating ice shelf buttressing West Antarctica’s Thwaites Glacier. They predicted that the ice shelf could fracture in as little as five years, allowing for accelerated melting of the Thwaites Glacier, which currently contributes four percent of annual global sea level rise.
In a worst-case scenario, fracturing of the ice shelf would allow part of Thwaites Glacier to triple in speed, increasing the glacier’s contribution to global sea level rise to 5% in the short term. In the long term, loss of the ice shelf buttressing the Thwaites Glacier could lead to its rapid disintegration over a period of decades or centuries, resulting in the loss of the entire West Antarctic Ice Sheet, and an increase in global sea levels of about 10 feet. However, the speed with which that disintegration might occur is highly uncertain.
Bob Henson contributed to this post.
Editor’s note: This post was updated on Jan. 11 to include a newer damage assessment from NOAA for Hurricane Ida ($75 billion instead of $65 billion), and to update Figure 2 with numbers from EM-DAT instead of Aon.
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