by The numbers are in, and scientists can now confirm what month after month of extraordinary heat around the world began to signal long ago. Last year was by far the warmest on Earth in a century and a half.
Global temperatures began breaking records in the middle of the year and haven’t stopped. First, June was the warmest June ever recorded on the planet. So July was the warmest July. And so on until December.
On average over the past year, temperatures around the world were 1.48 degrees Celsius or 2.66 Fahrenheit, higher than in the second half of the 19th century, the European Union’s climate monitor announced Tuesday. This is much warmer than 2016, the previous warmest year.
For climate scientists, it is no surprise that relentless greenhouse gas emissions have caused global warming to reach new highs. What researchers are still trying to understand is whether 2023 predicts many more years in which heat records will not only be broken, but destroyed. In other words, they wonder if the numbers are a sign that global warming is accelerating.
When scientists combine their satellite readings with geological evidence about the climate’s distant past, 2023 also appears to be among the warmest years in at least 100,000 years, said Carlo Buontempo, director of the European Union’s Copernicus Climate Change Service, in a press conference. “There were simply no cities, no books, no agriculture, no domesticated animals on this planet the last time the temperature was this high,” he said.
Every tenth of a degree of global warming represents additional thermodynamic fuel that intensifies heat waves and storms, increases sea level rise, and accelerates the melting of glaciers and ice sheets.
These effects became evident last year. The warm climate cooked Iran and China, Greece and Spain, Texas and the southern United States. Canada had by far the most destructive wildfire season in its history, with more than 45 million acres burned. Less sea ice formed around the coasts of Antarctica, both in summer and winter, than has ever been measured.
NASA, the National Oceanic and Atmospheric Administration and the Berkeley Earth research group plan to release their own estimates of 2023 temperatures later this week. Each organization’s data sources and analytical methods are somewhat different, although their results rarely differ much.
Under the 2015 Paris Agreement, nations agreed to limit long-term global warming to 2 degrees Celsius and, if possible, 1.5 degrees. At current rates of greenhouse gas emissions, it will only be a few years before the 1.5 degree goal is a lost cause, researchers say.
Carbon dioxide and other greenhouse gases are the main driver of global warming. But last year, several other natural and human factors also contributed to rising temperatures.
The 2022 eruption of an underwater volcano off the Pacific island nation of Tonga spewed large amounts of water vapor into the atmosphere, helping to trap more heat near the Earth’s surface. Recent limits on sulfur pollution from ships reduced levels of aerosols, or small particles in the air that reflect solar radiation and help cool the planet.
Another factor was El Niño, the recurring change in tropical Pacific weather patterns that began last year and is often linked to record heat around the world. And that contains a warning that the worst is yet to come this year.
The reason: In recent decades, the very warm years have typically been those that began in an El Niño state. But last year, El Niño didn’t start until mid-year, suggesting that El Niño wasn’t the main driver of the abnormal heat at that time, said Emily J. Becker, a climate scientist at the University of Miami.
It’s also a strong sign that this year could be hotter than last. “It’s very, very likely to be in the top three, if not the record,” Dr. Becker said, referring to 2024.
Scientists warn that a single year, even one as exceptional as 2023, can’t tell us much about how the planet’s long-term warming might be changing. But other signs suggest the world is warming more rapidly than before.
About 90 percent of the energy trapped by greenhouse gases accumulates in the oceans, and scientists have found that heat absorption by the oceans has increased significantly accelerated since the 1990s. “If you look at that curve, it’s clearly not linear,” said Sarah Purkey, an oceanographer at the Scripps Institution of Oceanography at the University of California, San Diego.
A group of researchers in France recently found that overall warming of the Earth (in oceans, land, air and ice) had been accelerating for even longer, since 1960. This broadly coincides with increases in carbon emissions and reductions of aerosols in recent decades.
But scientists will need to continue studying the data to understand whether other factors could also be playing a role, said one of the researchers, Karina von Schuckmann, an oceanographer at Mercator Ocean International in Toulouse, France. “Something unusual is happening that we don’t understand,” Dr. von Schuckmann said.
