The 2020 global wildfire season brought extreme fire activity to the western U.S., Australia, the Arctic, and Brazil, making it the fifth most expensive year for wildfire losses on record.

The year began with an unprecedented fire event in Australia, where wildfire smoke in the capital city of Canberra registered the worst air quality readings in the world on January 1. The Canberra Times reported that smoke billowing through the city exceeded the “hazardous” threshold by over a factor of 20.

Australia in 2019 had experienced its hottest and driest year on record, which helped drive fires that burned an astonishing 46 million acres – an area larger than the state of Florida – during the 2019-2020 fire season. While larger areas of the nation have burnt in at least four previous years, the 2019-2020 wildfires affected a larger share of forested and populated areas than previous fires did, resulting in far more impacts to people and ecosystems.

According to insurance broker Aon, the 2019-2020 wildfires were Australia’s most expensive on record, with damages of $4.5 billion (including physical damage and impacts to timber, agriculture, infrastructure, and direct business interruption). EM-DAT, the international disaster database, lists the “Black Saturday” wildfire season of 2009 as Australia’s second-most expensive wildfire season, with $1.6 billion (2020 dollars) in damages.

On December 31, 2019, one of the most intense wildfire events in world history affected southeast Australia, generating a massive fire-induced thunderstorm cloud called a pyrocumulonimbus (pyroCb). The fires were so intense that they created a spinning bubble of heat and smoke 1,000 kilometers (621 miles) in diameter; the smoke penetrated into the stratosphere and persisted for more than 13 weeks, circling the globe. Chemical reactions within the bubble created a mini-ozone hole that depleted stratospheric ozone by up to 100 Dobson units (over 30% of the total) at its center.

The fires injected enough ash into the stratosphere to rival the impact of a moderate-sized volcanic eruption, and they were the largest source of aerosol particles to the stratosphere since the 1991 eruption of the Philippines’ Mt. Pinatubo, according to a September 2020 study led by Sergey Khaykin, a scientist at the Laboratory of Atmospheric Research and Satellite Observations at Sorbonne University in France.

The previous record-breaking wildfire, a 2017 pyroCb event in western Canada, was more than three times smaller in its impact to the stratosphere. PyroCbs infuse the stratosphere with gases from combustion and dark-colored smoke particles such as black carbon, which absorb sunlight and heat the surrounding air. The heat makes the air more buoyant, allowing the particles to persist in the stratosphere longer. There, the particles block sunlight from reaching the surface, and the December 31, 2019 pyroCb event was strong enough to produce several months of slight global cooling. During January, February, and March 2020, the sunlight-blocking impact of the New Year’s Eve Australian pyroCb event was similar to the impact of a moderate-sized volcanic eruption, scientists said.

PyroCb events intense enough to cause global perturbations to climate are new to science, and are a concern. In a December 2020 interview with the Washington Post, Khaykin said, “It has only been recently that the role of moderate volcanic eruptions on the global stratosphere has been recognized and evaluated. Now we have a newcomer, which is wildfires. What is going to happen if we have stronger wildfires and a strong volcanic eruption at the same time? It’s quite scary because we realize we know quite little.”

An attribution study released in March 2020 found that human-caused climate change made the conditions for Australia’s unprecedented 2019-20 bushfires at least 30% more likely. An October 2020 report by the Australian Royal Commission into National Natural Disaster Arrangements concluded that “more dangerous weather conditions for bushfires are very likely to occur throughout Australia in the future due to a warming climate.”

A record fire season in the Arctic

In the Arctic, active fires first detected by satellite in May increased in intensity and number from early June onwards, the Copernicus Atmosphere Monitoring Service reported. All-time record heat in Siberia during June led to the Arctic’s first-ever 38.0°C (100.4°F) temperature, measured at Verkhoyansk on June 20, helping drive massive wildfires for the remainder of the summer. More Arctic wildfire activity was measured in June-October 2020 than in the same period in any year since satellite records began in 2003. Arctic fires released a record amount of carbon dioxide in 2020: 244 megatons, beating the previous record of 181 megatons in 2019.

According to an attribution study done by the World Weather Attribution group, the Siberian heat wave of 2020 would have been “almost impossible without climate change.”

Record drought and wildfires in Brazil

Severe drought gripped significant portions of Brazil in 2020, causing a devastating fire season and heavy agricultural losses. The drought contributed to record wildfires in the Pantanal rainforest – the world’s largest tropical wetland. About a quarter of this subtropical area south of the Amazon burned in 2020, surpassing the previous record set in 2005. Total damage from the Brazilian drought was estimated at $3 billion. According to EM-DAT, the 2020 drought is the third most expensive drought in Brazil’s history, behind droughts in 1978 and 2014.

An apocalyptic western U.S. wildfire season

A veritable witch’s brew seemed to conspire in 2020 to lead to an apocalyptic western U.S. wildfire season: The hottest August through October period in western U.S. history; the fourth-highest levels of October drought on record; an unusual dry lightning event caused by the remnants of an August Northeast Pacific tropical storm; and a once-in-a-generation offshore wind event in September.

The National Interagency Fire Center reported that U.S. wildfires burned 10.27 million acres as of December 31, 2020 – the highest yearly total since accurate records began in 1983. The previous record was 10.13 million acres in 2015. As opposed to the 2015 record, which was more than 50% the result of wildfires in Alaska, over 98% of the acreage burned in 2020 was in the contiguous U.S.

In California alone, nearly 4.2 million acres burned, more than double the previous record of 1.67 million acres in 2018. Five out of six of California’s largest fires on record occurred in 2020, including the largest in state history – the 1.03-milllion acre August Complex fire. That one was the largest wildfire in the continental U.S. since the Great Fire of 1910, which burned over three million acres in Idaho and Montana. Beyond California, Washington experienced its largest wildfire on record in 2020, and Colorado had its three largest wildfires on record.

U.S. wildfire damages in 2020 totalled $16.5 billion, ranking it as the third-costliest year on record, behind 2017 ($24 billion) and 2018 ($22 billion). Three separate fires in California and one in Oregon generated over $1 billion in losses; 12 additional fires in California, Oregon, Colorado, and Washington each caused over $100 million in direct losses. The indirect costs were much higher: A 2020 study estimated that the direct plus indirect costs of the 2018 wildfire season in California were nearly $150 billion.

The direct death toll from the western U.S. fires in 2020 was at least 43, but the indirect death toll due to inhalation of wildfire smoke was likely in the thousands, researchers at Stanford University reported in a September 11 study. Their research estimated that between 1,200 and 3,000 excess deaths occurred in California among people 65 and older between August 1 and September 10 from wildfire smoke-related causes. “This is likely a substantial lower bound,” the researchers wrote, since “Oregon and Washington are being hit very hard right now too, and non-elderly are also surely affected. These overall effects can be in large part attributable to climate change, which has dramatically increased the likelihood and severity of wildfire.” In an October 2020 article, the authors explained that wildfire smoke likely is responsible for 5,000 to 15,000 deaths in an average year in the U.S., but more smoky years like 2018 or 2020 will have a much higher death toll.

Climate change and ‘once-in-50-year’ wind event that drove western U.S. fires

A 2016 study found that a warming and drying climate has increased the intensity and duration of western U.S. fire seasons in recent years, and human-caused climate change has nearly doubled the area burned in the region since 1984. But the western U.S. wildfires of 2020 were exacerbated not only by heat and drought: An early September strong offshore wind event, partially attributed to climate change, also was a key factor.

With an extreme distortion of the jet stream, a record-intensity ridge of high pressure set up over the western U.S. during the first week of September, along with an unusually strong trough of low pressure over Rocky Mountain states. The ridge over the western U.S. brought all-time record heat and intense wildfire activity to many locations in California September 5-6.

The Rocky Mountain trough helped bring about what may be a world record for weather whiplash (for the fastest transition from 100-degree temperatures to measurable snow). According to climatologist Brian Brettshneider, Rapid City, South Dakota, was 102°F on September 5, and had measurable snow on September 7. This two-day gap between 100°F and measurable snow breaks the U.S. record for any station. The difference was even more extreme in Ordway, Colorado, which went from 104°F to 3.9 inches of snow in two days.

The unusual distortion of the jet stream created a huge pressure difference that drove extreme offshore winds beginning on September 7. Climate scientist Daniel Swain called it a once-in-50-year event. The winds fanned fires that cloaked much of the western U.S. in clouds of choking smoke, resulting in the worst air quality anywhere in the world for multiple weeks, and skies that looked like those in the movie Bladerunner. The direct damages from Oregon’s Beachie Creek Fire alone totaled $1.6 billion, making it Oregon’s costliest fire on record.

Connecting the September western U.S. wind event to a Korean typhoon

The roots of the western U.S. wind event were in the Northwest Pacific Ocean, in the form of near-record warm ocean waters that a week earlier had helped fuel an unusually strong typhoon. As category 2 Typhoon Maysak plowed northwards towards Korea during early September, it was able to maintain its intensity unusually far to the north because of hot ocean waters created by one of the greatest heat waves in east Asian history. This heat wave was made more likely by global warming of a planet virtually tied in 2020 with 2016 as the warmest year on record.

Ocean temperatures in late August south of Korea were 30 degrees Celsius (86°F) – more than two degrees Celsius (3.6°F) above average. The intense heat wave that helped create these unusually warm ocean waters also brought Japan its hottest day in recorded history: on August 17, 2020, Hamamatsu, Japan, tied the record set in 2018 for hottest temperature ever measured in Japan, with 41.1 degrees Celsius (106°F). The extreme 2020 heat carried over into the first week of September, with Sanjo, Japan, setting the nation’s all-time September heat record on September 3, with 40.4 degrees Celsius (105°F).

Supercharged by the remarkable late-summer ocean heat, Typhoon Maysak was able to make landfall in South Korea on September 2 as one of only five category 2 or stronger typhoons on record (since 1945) to hit the nation.

After Maysak transitioned to a powerful extratropical storm, it merged with the jet stream on September 2-3. The extratropical version of Maysak was turbocharged with a tremendous amount of moisture and energy, which it injected into the jet stream, helping accelerate the winds of that mighty river of air to nearly 200 mph – a wind speed nearly five standard deviations above average. As shown in the tweet by Dr. Philippe Papin of the National Hurricane Center (click this link to animate and see the full explanation), the jet stream responded by contorting into a series of amplified ridges and troughs downstream from east Asia.

As explained in a 2014 paper by Kossin et al., “The poleward migration of the location of tropical cyclone maximum intensity,” typhoons and hurricanes have been growing more intense farther to the north in recent decades, and this effect can be plausibly linked to the changes in global circulation that are causing an expansion of the tropics, which is thought to have a significant link to human-caused global warming.

Thus, the unusual jet stream behavior that drove the 2020 western U.S. wind event may plausibly be linked to a climate change-enhanced typhoon in the Pacific. A December 2020 study led by Jacob Stuivenvolt Allen of Utah State University, titled “Three western pacific typhoons strengthened fire weather in the recent northwest U.S. conflagration” found that Typhoon Maysak combined with two other typhoons that hit Korea within a 12-day period in late August and early September to perturb the jet stream, contributing to the extreme wind event over the western U.S. 

But human-caused climate change may have also contributed to the unusual jet stream behavior via Arctic sea ice loss (though this is an area of active research – see the excellent June 2020 summary at Carbon Brief). Coverage of sea ice in the Arctic reached its second-lowest minimum on record in 2020, behind only 2012, according to the National Snow and Ice Data Center.

Overall, 2020 was below-average in wildfire activity, but extremely costly

Despite the record 2020 wildfire activity in Australia, the Arctic, Brazil, and U.S., very low levels of wildfire activity in Canada and tropical Africa resulted in a below-average year for global fire-related emissions of carbon to the atmosphere, according to the Copernicus Atmosphere Monitoring Service. However, the record wildfires in the U.S. made for a very expensive year: the global direct cost of wildfires in 2020 was $17 billion, said insurance broker Aon. This ranked as the fifth-costliest year for the peril behind 2017, 2018, 2015 (major Indonesian fires), and 2010 (major Russian fires).

Also see: Climate change is worsening California’s hellish wildfires

Bob Henson contributed to this post.

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