Published on 13 January 2024
NASA announced that 2023 was the hottest year on record, according to an analysis of annual global average temperatures by the Goddard Institute for Space Studies. Scientists who maintain the temperature record, which begins in 1880, calculate a global temperature anomaly each year to determine how much temperatures have changed compared to temperatures from 1951–1980.
Every month from June through December 2023 came in as the hottest month on record. July ranked as the hottest month ever recorded.
But what caused 2023, especially the second half of it, to be so hot? Scientists asked themselves this same question. Here is a breakdown of primary factors that scientists considered to explain the record-breaking heat.
The long-term rise in greenhouse gases is the primary driver.
For more than 100 years, humans have been burning fossil fuels such as coal, gas, and oil to power everything from lightbulbs and cars to factories and cities. These actions, along with changes in land use, have led to a rise in greenhouse gases in the atmosphere. Greenhouse gases act like a blanket trapping heat around the planet. The more of them you add, the thicker that blanket becomes, further heating Earth.
January 1 - December 31, 2021
In May 2023, carbon dioxide concentrations in the atmosphere peaked at 424 parts per million at NOAA’s Mauna Loa Observatory, Hawaii. The annual peak has been steadily rising since measurements began in 1958. (Other global carbon measurement projects showed similarly high numbers.) Extending the record back even further with ice cores, carbon dioxide concentrations are the highest they have been in at least 800,000 years.
“We’re going to continue to have records be broken because the baseline temperature is moving up all the time,” said Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies in New York City. “The cause of that warming trend over the last 50 to 60 years is dominated by our changes to greenhouse gases, particularly carbon dioxide and methane.”