Today, NASA and The National Oceanic and Atmospheric Administration (NOAA) has dropped its annual analysis of global temperatures: Last year was tied to 2018 as the sixth hottest on record, but colder than 2020. Good sign, right? Yes No. never.
“It’s easy to focus on this year-to-year variability,” says Bridget Segers, an oceanographer at NASA. “But it’s important to look at the trend: The past eight years have been the hottest on record.”
To calculate global temperatures, the two agencies pull data from weather stations around the world, as well as measurements from ships and buoys in the ocean. Other groups like Berkeley Earth, a nonprofit research organization, do the same with their somewhat different methodology. But the analyzes are almost identical in their findings. As you can see in the chart below, which compares results from Berkeley Earth, NOAA, NASA and two other groups in Europe, the average global temperature may have been lower in 2021 than in 2020, but it’s still rising.
One of the reasons for the cooler temperatures in 2021 was the La Niña, a body of cold water in the Pacific Ocean. It’s the product of strong ocean trade winds, pushing the upper layer of water toward Asia, causing deeper, colder waters to rush to the surface to fill the void. This in turn affects the atmosphere, for example changing the jet stream over the US resulting in more hurricanes in the Atlantic. The sea itself cools things down by absorbing heat from the atmosphere.
The Covid-19 pandemic may have an additional effect, but not in the way you might think. As the world shuts down in 2020, fewer emissions have gone into the sky, including aerosols that normally reflect some of the sun’s energy back into space. “If you take it away, you make the air cleaner, that’s a slight warming effect on the climate,” Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, said during a press conference Thursday to announce the results. But with economic activity picking up again in 2021, aerosol pollution also increased, again contributing to this cooling effect. Schmidt said the temperature drop in 2021 “may be due to the resumption of activity that produces aerosols in the atmosphere.”
(The epidemic-induced decline in carbon dioxide production had no cooling effect. Human civilization produces so many greenhouse gases each year, and they persist for so long in the atmosphere, that the epidemic is not even recorded as a flash.)