It’s been a year of extremes. Wildfires consumed vast areas of Australia, Siberia and the U.S. West. Flooding in Africa and southeast Asia pushed millions from their homes, while extreme heat and drought hit countries in South America. Cyclone Harold tore through the Pacific, and this year saw an exceptionally intense hurricane season in the Atlantic, including unprecedented back-to-back Category 4 hurricanes that devastated Central American countries in November. And in the Arctic, sea ice shrank back to its second-lowest extent ever recorded.
Wild weather, warming planet
In 2020, the fingerprints of climate change appeared around the world
For years, scientists have warned that climate change will cause increasingly chaotic and extreme weather, and studies are bearing that out. Advances in a field known as “event attribution science” mean researchers are able to assess whether climate change played a role in causing, or worsening, a specific weather event.
In determining that link, scientists run computer simulations of how weather systems might have behaved if people had never started pumping carbon dioxide into the air, and compare that with what is happening today. They also factor in weather measurements made over the last century or more.
“While all extreme events have multiple causes we’re increasingly seeing the fingerprints of climate change in our weather, including events that would be almost impossible to imagine happening without human-caused climate change,” said Friederike Otto, associate director of the Environmental Change Institute at the University of Oxford.
For example, when a new record temperature for the Arctic, 38°C (100.4°F), was recorded in the Russian town of Verkhoyansk on June 20, scientists took only days to conclude that the event was at least 600 times more likely to have occurred due to climate change. Heat continued to bake Siberian Russia through the summer, with average temperatures in the Arctic hitting exceptional highs into late November.
This year also saw the highest temperature ever reliably recorded, when a heat wave gripping California drove the temperature at Death Valley in the Mojave Desert up to 54.4°C (130°F). With 2020 on track to be one of the warmest years on record, scientists see climate change as a major culprit behind heatwaves, more violent storms, more intense fires, and the loss of sea ice.
The year began with devastating wildfires already raging across eastern Australia. Sparked in September 2019, the blazes burned through more than 37 million acres (15 million hectares) — an area around half the size of the United Kingdom — before they were snuffed out in March 2020.
Exceptionally hot and dry weather had turned swathes of territory into a tinderbox. Research published in January by the World Weather Attribution, an international scientific collective, found that climate change had made these fire-friendly conditions in Australia at least 30% more likely to occur.
Halfway around the world in the western United States, wildfires tore through forests and communities. Four of the five largest fires in California’s recorded history occurred in 2020, including the August Complex fire, which burned more than 1 million acres (405,000 hectares) in August. Colorado saw the largest wildfires in state history this year, as well.
In the U.S. West, long-term trends such as growing encroachment of urban areas into fire-prone areas, and reduced use of fire-suppression tactics such as controlled burns, were also factors. But scientists say climate change made the fires far more likely. Higher temperatures sapped the air of humidity and dried out forest and brush on land, creating perfect conditions for intense blazes.
The number of autumn days with ideal fire conditions has more than doubled since the early 1980s due to human-caused climate change, according to a paper published in August by Daniel Swain, a climate scientist at the University of California, and colleagues.
Climate change is also making cyclones and hurricanes more intense, with stronger winds and heavier rains. The last half-century has seen an increasing number of storms, powered by warmer ocean waters, develop into strong tropical cyclones. A study published by the National Academy of Sciences in June found that major tropical cyclones — category 3 and above on the Saffir-Simpson scale — were more likely to form with each passing decade.
Research also suggests that, with climate change, hurricanes overall are moving more slowly, meaning they can linger for longer over land, causing more damage. But researchers are still working to establish whether and how climate change might be affecting the frequency of hurricanes, with the number historically varying widely from year to year.
While this year saw a record 30 named Atlantic storms, the total number of storms globally in 2020 was actually below average — thanks to a quieter season in the Pacific. But the Pacific also served up the world’s strongest landfalling storm in recorded history this year. The deadly Super Typhoon Goni slammed the Philippines on Nov. 1 with wind speeds of up to 195 mph, according to the U.S. military’s Joint Typhoon Warning Center in Hawaii.
Central America was also hit hard. In November, two Category 4 hurricanes, Eta and Iota, slammed into Nicaragua in almost the same location a mere 13 days apart, damaging 44,000 homes and causing $740 million in damage, said Nicaraguan Finance Minister Ivan Acosta. Across the region, the hurricanes disrupted the lives of an estimated 7.3 million people, according to U.N. estimates.
Arctic sea ice
When the Arctic sea ice reached its annual minimum extent in September 2020, it was the second lowest in 42 years of satellite monitoring, according to the Boulder, Colorado-based National Snow and Ice Data Center. Scientists were watching closely because bright Arctic sea ice reflects sunlight, helping to keep polar regions cool. Less ice means the ocean will absorb more heat, leading to even warmer water.
To prevent the worst impacts of climate change, countries have pledged under the 2015 Paris Agreement to limit global warming to 2°C above pre-industrial levels. To do that, scientists say, the world will need to drastically curb its release of climate-warming emissions by 2030.
Instead, the world saw a new record level of emissions released in 2019. This year, as the coronavirus pandemic brought much of the global economy to a halt, greenhouse gas emissions fell by up to 17% in April — during the height of the pandemic lockdowns — compared with the same month a year earlier. It was the largest drop since World War Two.
The dramatic reductions turned out to be a temporary blip. Annual emissions are expected to be down 7% compared with 2019. In many areas, emissions have returned to where they were a year ago.
“Countries want to bring their economies back to normal as quickly as possible,” said Glen Peters, research director at the CICERO Center for International Climate Research in Norway. “But the type and speed of the recovery is really a choice.”
About the data
Each line in the global temperature chart shows the global monthly temperature relative to the global mean from 1980–2015. Global temperatures are warmest between May and September because most of the world’s land area is in the northern hemisphere. This chart uses the GISS Surface Temperature Analysis (GISTEMP v4).
Copernicus Climate Change Service, National Oceanic and Atmospheric Administration, NASA Fire Information for Resource Management System and the Global Carbon Project
Additional reporting by
Katy Daigle, Jon McClure and Nick Zieminski