State of the Planet

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In Continuing Trend, 2021 Tied for 6th Warmest Year on Modern Record

Continuing the planet’s long-term warming trend, scientists at NASA’s Goddard Institute for Space Studies in New York say 2021 was tied with 2018 as the 6th warmest year on the modern record. Collectively, the data show that the past eight years are the warmest since modern record keeping began in 1880. Earth in 2021 was about 1.9 degrees Fahrenheit (about 1.1 degrees Celsius) warmer than the late 19th century average. NASA says that global temperatures in 2021 were 1.5 degrees Fahrenheit (0.85 degrees Celsius) above the 1951-1980 average, suggesting that the warming trend has sped up in recent decades.

Slightly different but similar measurements for 2021 have come from the the U.S. National Oceanic and Atmospheric Administration, the Japanese Meteorological Agency, Europe’s Copernicus Climate Change Service, and Berkeley Earth.

“The complexity of the various analyses doesn’t matter because the signals are so strong,” said Gavin Schmidt, director of Goddard, which is affiliated with Columbia University’s Earth Institute and School of Engineering and Applied Science. “The trends are all the same because the trends are so large.”

Scientists agree that global warming is due to human emissions of carbon dioxide and other greenhouse gases into the atmosphere. The planet is already seeing the effects of global warming: Arctic sea ice is declining, sea levels are rising, wildfires are becoming more severe and animal migration patterns are shifting.

While 2021 was not Earth’s warmest year yet, it was close. And many separate regions saw heat records surpassed by wide margins. Last year, parts of the United States and Canada experienced striking heat waves unlike anything seen before. And some 1.8 billion people in 25 Asian, African and Middle Eastern nations had their hottest years on record, including China, Nigeria, Bangladesh, Iran, Myanmar and South Korea, according to Berkeley Earth. The deep ocean, which soaks up much of Earth’s rising heat, also set a record for warmth in 2021, according to a separate new study.

Weather stations, ships and ocean buoys around the globe record temperatures at Earth’s surface throughout the year. These ground-based measurements of surface temperature are validated with satellite data from the Atmospheric Infrared Sounder (AIRS) on NASA’s Aqua satellite. Scientists analyze these measurements using computer algorithms to deal with uncertainties in the data to calculate the global average surface temperature difference for every year. The 1951-1980 baseline includes climate patterns and unusually hot or cold years due to other factors, ensuring that it encompasses natural variations in Earth’s temperature.

Many factors affect the average temperature any given year, including La Niña and El Niño climate patterns in the tropical Pacific Ocean. For example, 2021 was a La Niña year; NASA scientists estimate that it may have cooled global temperatures by about 0.06 degrees Fahrenheit (0.03 degrees Celsius) from what the average would have been.

A separate, independent analysis by the National Oceanic and Atmospheric Administration has also concluded that the global surface temperature for 2021 was the sixth highest since record keeping began in 1880. NOAA scientists use much of the same raw data, though they have a different baseline period (1901-2000) and methodology.

“Science leaves no room for doubt: Climate change is the existential threat of our time,” said NASA Administrator Bill Nelson. “Eight of the top 10 warmest years on our planet occurred in the last decade, an indisputable fact that underscores the need for bold action to safeguard the future of our country, and all of humanity.”

NASA’s full dataset of global surface temperatures for 2021, as well as details of how NASA scientists conducted the analysis, are publicly available.

Adapted from a press release by NASA, with additional information from the Associated Press.

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