The mean temperature globally last year was 1.1 to 1.2 degrees Celsius (2 to 2.2 degrees Fahrenheit) higher than they were before industrialization led humans to begin pumping large quantities of carbon dioxide into the air.
The year was fifth warmest by a slight margin over 2015 and 2018, by Copernicus’s ranking. The hottest years on record are 2016 and 2020, in a virtual tie.
The steady warming corresponds with the scientific consensus that increasing levels of greenhouse gases in the atmosphere are causing long-lasting changes in the global climate. Copernicus said its preliminary analysis of satellite measurements had found that concentrations of heat-trapping gases continued to rise last year, helped by 1,850 megatons of carbon emissions from wildfires worldwide.
One big reason for 2021’s lower mean temperature was the presence during the early part of the year of La Niña conditions, a recurring climate pattern characterized by lower surface temperatures in the Pacific Ocean. (La Niña has returned in recent months, which could presage a drier winter in the Southern United States but wetter conditions in the Pacific Northwest.)
Those effects were offset in the 2021 average, however, by higher temperatures in many parts of the world between June and October, Copernicus said.
“When we think about climate change, it’s not just a single progression, year after year after year being the warmest,” said Robert Rohde, the lead scientist at Berkeley Earth, an independent environmental research group.
“The preponderance of evidence — which comes from looking at ocean temperatures, land temperatures, upper atmospheric temperatures, glaciers melting, sea ice changes — are telling us a coherent story about changes in the earth system which points to warming overall,” Dr. Rohde said. “Slight variations up or down, a year or two at a time, don’t change that picture.”
Berkeley Earth is expected to issue its own analysis of 2021 temperatures this month, as are two U.S. government agencies: NASA and the National Oceanic and Atmospheric Administration.
Unlike those groups, Copernicus uses a method called re-analysis, which produces a portrait of global weather conditions using a computer model that fills in the gaps between temperature measurements. Even so, the different groups’ conclusions usually line up quite closely.
As ever, higher average temperatures were not observed uniformly across the planet last year. Most of Australia and parts of Antarctica experienced below-normal temperatures in 2021, as did areas in western Siberia.
Europe’s summer last year was the warmest on record, though 2010 and 2018 were not far behind, according to Copernicus. Severe rainfall and flooding caused destruction and death in Belgium, Germany, Luxembourg and the Netherlands. Heat and dryness set the stage for wildfires that ravaged Greece and other places around the Mediterranean.
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