2020 was the hottest year on record, tied with 2016, NASA and NOAA announced in a teleconference on Thursday at the 101st American Meteorological Society Annual Meeting. Last year was about 1.02°C (0.84°F) warmer than the baseline mean temperatures from 1951-1980.
More broadly, the period from 2010 to 2020 was also the hottest decade in the 140 year history of modern temperature record-keeping, and continues the alarming pattern in which each consecutive decade since the 1960s has been warmer than the last.
“This is the warmest decade in the historical record without any question whatsoever,” said Gavin Schmidt, director of NASA Goddard Institute for Space Studies, at the briefing. “There's perhaps a hint of an acceleration happening, but it's unclear whether that is a persistent signal or whether that will be simply some kind of decadal noise.”
Temperatures in 2016 were boosted by an El Niño event, a factor that was absent in 2020, suggesting a continuation of a trend in which each successive year breaks the temperature records of its predecessor. 2021, in contrast, may be slightly cooler due to an ongoing La Niña event that may chill global temperatures.
The culprit is clear: climate change during the past half-century is almost entirely driven by greenhouse gases, especially carbon dioxide, emitted by the fossil fuel industry.
The Paris Agreement and the Intergovernmental Panel on Climate Change have set goals to limit the rise in global temperatures ideally to 1.5°C, with an upper cap of 2°C, above pre-industrial levels by 2100.
Hitting this target will require rapid decarbonization of the global energy system by transitioning from fossil fuels to renewable power sources such as solar, wind, and hydro. At this point, the effort to decarbonize the world’s power supply is not happening fast enough to meet the objectives set out by the Paris Agreement.
People have been experiencing the deleterious effects of climate change for decades, especially in vulnerable regions such as the Arctic, but 2020 was a particularly sobering year that brought the myriad human and ecological costs of the climate crisis to the fore. Devastating wildfires broke out across the world: Australia experienced a “black summer” of bushfires that burned 21 percent of its broadleaf forests; a record-breaking heatwave in Siberia fueled unusually intense Arctic wildfires for a second year in a row; the Pantanal wetlands in of Brazil were consumed by flames; and California suffered its worst wildfire season ever.
Meanwhile, a record-breaking 30 storms were spawned during the Atlantic hurricane season, while extreme weather events menaced communities around the world. For instance, the summer monsoon season brought record-breaking floods to eastern China; a rare derecho tore through the US Midwest in August; and one of the strongest tropical cyclones on record battered the Philippines in November.
While individual weather events can not be directly linked to climate change writ large, there is plenty of evidence to suggest that the intensity, frequency, and duration of these disasters is generally amplified by warmer temperatures.
Climate scientists are particularly worried that rising temperatures will kick off feedback loops that could destabilize the global climate even if nations meet their climate targets.
Take the precipitous decline in Arctic sea ice: the reduced ice cover has not only disrupted communities and ecosystems, it has also reduced the overall reflectivity of the region since ice bounces more sunlight back into space than seawater. As a result, the Arctic is absorbing more heat, a process that further exacerbates its ice loss. Likewise, wildfires are belching unprecedented quantities of greenhouse gases into the atmosphere, which contributes to global warming and fans the flames of future fires.
“The planet’s closing in on the 1.5°C of warming discussed in the Paris Agreement,” said Russell Vose, chief of the analysis and synthesis branch of NOAA’s National Centers for Environmental Information, in the briefing.
“It's certainly warmer now than at any time in the past 2000 years at least, and probably much longer,” he concluded, “and there's a pretty good chance that the rate of increase in the past 60 years is faster than any time in the past two millennia.”