2020 rivals hottest year on record, pushing Earth closer to a critical climate threshold

Only the "super" El Niño year of 2016 appears to have been slightly hotter in the era of reliable measurements dating to the late 1800s, according to the results from NASA, the National Oceanic and Atmospheric Administration, the United Kingdom's Met Office and Berkeley Earth. NASA finds that 2020 edged out 2016 by less than a hundredth of a degree Celsius, while the other three groups say it fell shy by a mere .01 to .02 degrees Celsius (.02 to .04 degrees Fahrenheit).

"The last seven years have been the seven warmest on record," said Ahira Sánchez-Lugo, a climate expert with NOAA's National Centers for Environmental Information. "And the 10 warmest years have now occurred since 2005."

Experts said that another year as hot as 2016 coming so soon suggests a swift step up the climate escalator. And it implies that a momentous new temperature record - breaching the critical 1.5 degrees Celsius (2.7 degrees Fahrenheit) warming threshold for the first time - could occur as soon as later this decade.

Particularly striking is the unassuming way that 2020 joined the ranks of the very hottest years. Unlike 2016, it did so without any substantial boost from an El Niño. The El Niño phenomenon, part of a natural climate cycle with global consequences, spreads unusually warm waters across the tropical Pacific Ocean and generally unleashes hotter temperatures as a result.

But 2020 was the opposite: A La Niña developed later in the year. La Niña years tend to be relatively cool in comparison with El Niño years. Except, perhaps, when the planet is changing so quickly.

"It is somewhat shocking to me how fast the warming seems to be proceeding," said Andrew Dessler, a climate scientist at Texas A&M University, in an email.

And those very high temperatures had sweeping consequences across the globe.

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2020 was characterized by some of the biggest wildfires on record in Siberia, Australia, the Western United States and the Pantanal, a vast, carbon-rich wetlands ecosystem in South America. In most of these cases, climate change played a key role, according to scientific studies.

"It truly was the year of global fire. From the devastating fires in Australia . . . to the fires in the largest wetlands in South America to the coastline of California, the fires that occurred in 2020 responded to very dry conditions and warm temperatures on several continents," said Merritt Turetsky, a climate scientist at the University of Colorado Boulder.

The year began with severe fires in eastern Australia that devastated some of the nation's most biologically productive landscapes. As many as 3 billion animals, including species such as the koala and kangaroo, perished. The fires were so intense they lofted smoke high into the stratosphere, and the smoke is still swirling aloft a year later.

In the western United States, the 2020 wildfire season was devastating and deadly, with a total of about $16 billion in losses, and Colorado and California saw their largest blazes in state history. Five of the six largest wildfires in California history occurred in 2020, including the biggest blaze, known as the August Complex. That fire alone burned more than 1 million acres, becoming the state's first "gigafire." The region was smothered in noxious smoke for months, a severe assault on people's lungs even as they hunkered down because of the coronavirus pandemic.

In California as well as Australia, climate change has meant hotter, drier weather, with faster-spreading blazes and fires that burn more intensely. California had its hottest fall on record, following an unusually hot and dry summer, which primed the region for firestorms. Los Angeles hit an record high of 121 degrees Fahrenheit (49.4 degrees Celsius) on Sept. 6, which came during one of a series of scorching heat waves that ratcheted up the fire threat.

Some of 2020's most extreme climate conditions were focused in northern Siberia and parts of the Arctic, with annual average temperatures between 3 and 6 degrees Celsius (5.4 to 10.8 degrees Fahrenheit) above normal. In certain months, these anomalies topped 8 degrees Celsius (14.4 degrees Fahrenheit). Even after a somewhat cooler December compared with previous months, Siberia stands out on 2020 temperature maps as a large red splotch of unusually hot conditions. The Arctic as a whole is warming at about three times the rate of the rest of the globe.

In the remote Siberian town of Verkhoyansk, about 3,000 miles east of Moscow, the mercury climbed to 100.4 degrees Fahrenheit (38 degrees Celsius) on June 20, the highest temperature recorded north of the Arctic Circle since record-keeping began in 1885.

The warmer-than-usual conditions had cascading consequences. Wildfires in the Siberian Arctic began early, in May, and continued later than average, through October. These blazes set a record for the amount of carbon dioxide released north of the Arctic Circle.

"These extreme events are happening in the context of continuing impacts on Arctic communities who are dealing with the hazards of ground collapse from permafrost thaw, loss of land and sea ice, and, overall, an increasingly unfrozen Arctic," said Sue Natali, Arctic program director at the Woodwell Climate Research Center. "And this is what we're seeing at [an approximately] 1 C global temperature increase, so 1.5 C or more is very much a concern."

Data from NASA shows that since 1970, the Arctic has warmed by an average of 2.94 degrees Celsius, or 5.29 degrees Fahrenheit, compared with the global average of 0.95 Celsius, or 1.71 degrees Fahrenheit, during the same period. Scientists call the phenomenon "Arctic amplification."

Researchers studying global warming's role in extreme events found that the Siberian heat wave, including the 100-degree temperature and January-to-June average temperatures, would not have occurred without human-caused global warming.

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Last week, the Copernicus Climate Change Service in Europe also pronounced that 2020 tied with 2016 for the title of warmest year. The group's data showed the gap between the two at just under .01 degrees Celsius (.02 degrees Fahrenheit).

Overall, the final 2020 result represents a "photo finish," said Zeke Hausfather, a climate expert at the Breakthrough Institute who works on the Berkeley Earth temperature database. "For most of the records, 2020 will be effectively tied with 2016, within the uncertainty of our estimates."

2020's extreme heat means that the planet last year (and in 2016) was roughly 1.2 degrees Celsius, or 2.16 degrees Fahrenheit, warmer than it was in the late 1800s, which climate researchers dub the preindustrial period. The United Kingdom's Met Office puts that figure even higher, at just shy of 1.3 degrees Celsius (2.34 degrees Fahrenheit) of warming, when compared with the preindustrial period from 1850 to 1900.

It all has scientists concerned that a very momentous climate record could be coming quite soon: We could see a year that breaches, for the first time, the 1.5 degrees Celsius (2.7 degrees Fahrenheit) temperature threshold.

The logic is simple: Lately the Earth has been warming at slightly over 0.2 degrees Celsius (0.36 degrees Fahrenheit) per decade, explained NASA's Gavin Schmidt, who directs the Goddard Institute for Space Studies, which maintains one of the major temperature data sets.

Meanwhile, individual years can vary in temperature by more than 0.1 degrees Celsius (0.18 degrees Fahrenheit) because of natural factors that shape the climate, such as the El Niño and La Niña cycle in the Pacific.

What this effectively means is that, while every year won't be warmer than the last, records will occur at regular intervals. And although no one can say precisely when it will occur, a first leap over 1.5 degrees Celsius could soon be among them.

"I think it will happen by 2030 perhaps," Schmidt said. "But then, being permanently over that won't happen for another decade."

Scientists have become increasingly concerned that if the planet holds a temperature at or above 1.5 degrees Celsius of warming for long, there could be severe impacts, such as the loss of most of the globe's coral reefs, increasing risks of a nearly ice-free Arctic Ocean in the summer and further destabilization of the polar ice sheets, locking in large-scale sea-level rise.

The 2015 Paris climate agreement set an aspirational global warming limit of 1.5 degrees Celsius. That agreement, which the incoming Biden administration intends to rejoin after the Trump administration walked away from it, set a more firm limit of "well below" 2 degrees Celsius, or 3.6 Fahrenheit, of warming.

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It wasn't just wildfires: 2020 featured the busiest Atlantic hurricane season on record, with the most named storms to make landfall in a single season in U.S. history. Two hurricanes struck within 14 miles of each other along the western Louisiana coast, devastating the city of Lake Charles. With warmer-than-average water temperatures throughout the Atlantic basin, many storms rapidly intensified, a trend tied to climate change.

In all, 30 named storms with top winds of at least 39 mph developed in the Atlantic basin, of which 13 became hurricanes (top winds of 74 mph or greater). Six of those storms became major hurricanes of Category 3 intensity or greater. This eclipsed the record season of 2005, when 28 named storms formed, and was only the second year forecasters were forced to dip into the Greek alphabet for names.

Globally, 2020 tied 2018's record for the most named tropical cyclones observed: 103 of them, according to the NOAA's Sanchez-Lugo. That's far above the average of around 80.

Overall, climate scientists say the disasters of 2020 are but a preview of what's to come if greenhouse gas emissions are not quickly curtailed.

"What keeps us climate scientists up in the dead of night is wondering what we don't know about the self-reinforcing or vicious cycles in the Earth's climate system," said Katharine Hayhoe, a professor at Texas Tech University, in an email. "The further and faster we push it beyond anything experienced in the history of human civilization on this planet, the greater the risk of serious and even dangerous consequences. And this year, we've seen that in spades.

"It's no longer a question of when the impacts of climate change will manifest themselves: They are already here and now. The only question remaining is how much worse it will get. And the answer to that question is up to us."