See how hot 2023 was in two charts. Tip: Record hot.

The numbers are in and scientists can now confirm what month after month of extraordinary heat worldwide began signaling long ago. Last year was by far the warmest year on Earth in a century and a half.

Global temperatures started rising above records midway through the year and didn’t let up. First of all, June was the warmest June ever on Earth. Then July was the warmest July. And so on, throughout the month of December.

On average over the past year, global temperatures 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. That is considerably warmer than 2016, the previous warmest year.

To climate scientists, it is no surprise that unabated greenhouse gas emissions have caused global warming to reach new highs. What researchers are still trying to understand is whether 2023 portends many more years in which heat records will not only be broken, but broken. In other words, they wonder whether the numbers are a sign that planetary warming is accelerating.

“The extremes we have witnessed in recent months are dramatic evidence of how far we are now from the climate in which our civilization developed,” Carlo Buontempo, director of the EU’s Copernicus Climate Change Service, said in a statement.

Every tenth degree of global warming represents additional thermodynamic fuel that intensifies heat waves and storms, contributes to rising sea levels and accelerates the melting of glaciers and ice caps.

Those effects were visible last year. The warm weather baked Iran and China, Greece and Spain, Texas and the American South. Canada experienced by far its most devastating wildfire season on record, with more than 45 million hectares burned. Less sea ice formed around Antarctica’s coasts, in both summer and winter, than ever recorded.

NASA, the National Oceanic and Atmospheric Administration and the research group Berkeley Earth will release their own estimates of 2023 temperatures later this week. Each organization’s data sources and analytical methods are somewhat different, although the results rarely vary much.

Under the 2015 Paris Climate Agreement, countries agreed to limit long-term global warming to 2 degrees Celsius and, if possible, 1.5 degrees. At current greenhouse gas emissions, it will only take a few years before the 1.5 degree target is a lost cause, researchers say.

Carbon dioxide and other greenhouse gases are the main cause of global warming. But several other natural and human-related factors also contributed to increasing temperatures last year.

The 2022 eruption of an underwater volcano near the Pacific island of Tonga spewed huge amounts of water vapor into the atmosphere, trapping more heat near the Earth’s surface. Recent restrictions on sulfur pollution from ships have led to a decline in the amount of aerosols, small particles in the air that reflect solar radiation and help cool the planet.

Another factor was El Niño, the recurring shift in tropical weather patterns in the Pacific that began last year and is often associated with record warmth worldwide. And that comes with a warning of possibly worse this year.

The reason: In recent decades, very warm years have typically started in an El Niño state. But last year’s El Niño didn’t start until mid-year — indicating that El Niño wasn’t the main cause of the anomalous warmth at that time, says 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 year. “It’s very likely to be the top three, if not the record,” said Dr. Becker, referring to 2024.

Scientists warn that a single year, even one as extraordinary as 2023, can only tell us so much about how planetary warming could change in the long term. But other signs point to the world warming faster than before.

About 90 percent of the energy trapped by greenhouse gases accumulates in the oceans, and scientists have found that the absorption of heat by the oceans accelerated considerably since the 1990s. “If you look at that curve, it’s clearly not linear,” says 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 global warming – of the oceans, land, air and ice – has been accelerating since 1960. This is broadly consistent with the increase in carbon emissions and decrease in aerosols in recent decades.

But scientists will have to continue studying the data to understand whether other factors may also be at play, 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,” said Dr. von Schuckmann.