An astonishing seven consecutive months of record-breaking warmth have culminated in a grim milestone for humanity: 2023 was, officially, Earth’s hottest year on record.
That assessment, announced Tuesday by the European Union’s Copernicus Climate Change Service, follows a year in which extreme heat smothered multiple continents simultaneously, pushed ocean temperatures to alarming highs and spurred dire warnings about the worsening effects of climate change.
“2023 was an exceptional year with climate records tumbling like dominoes,†read a statement from Samantha Burgess, deputy director of Copernicus. “Not only is 2023 the warmest year on record, it is also the first year with all days over 1 degree Celsius warmer than the preindustrial period. Temperatures during 2023 likely exceed those of any period in at least the last 100,000 years.â€
With a global average temperature of 58.96 degrees, last year was about 0.31 of a degree warmer than the previous hottest year on record, 2016, according to data from Copernicus. December was also the warmest on record globally, as were all the months from June through November.
Official record-keeping of global temperatures began in 1850, or shortly after the end of the Industrial Revolution. Analysis of those records reveal that 2023 was 2.67 degrees warmer than the preindustrial period — or just shy of the 2.7-degree limit (1.5 degrees Celsius) established under the 2015 Paris climate agreement, an internationally recognized tipping point for the worst effects of climate change.
Nearly half the days last year reached at least 2.7 degrees over preindustrial levels, Burgess said.
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While global average temperature is an abstract concept for many people — nobody actually lives in a climate that is constantly 59 degrees — the effects of extreme heat were felt by the vast majority of Earth’s inhabitants last year.
In July — Earth’s hottest month on record — 81% of people on the planet experienced soaring temperatures made more likely by climate change, according to an analysis from Climate Central, a nonprofit news organization that reports on the effects of climate change. Heat waves roiled parts of China, Europe, North Africa, South America and South Asia.
That same month, Phoenix experienced 31 consecutive days of temperatures of 110 degrees or hotter — conditions so stifling that airplanes were grounded and sidewalks caused second-degree burns.
Off the coast of Florida, the Atlantic soared to 101 degrees — the temperature of a hot tub.
And in Death Valley, the mercury skyrocketed to 128 degrees, a near world record.
Experts say much of the heat was supercharged by the June arrival of El Niño, a climate pattern associated with warmer global temperatures.
Read all of our coverage about how California is neglecting the climate threat posed by extreme heat.
Still, the primary cause of increasing global temperatures remains human-caused climate change driven by fossil fuel emissions. The 10 warmest years on record have all occurred since 2010.
“We know for sure that the two main reasons 2023 was warm were an El Niño event on top of long-term climate change,†said Zeke Hausfather, a climate scientist with Berkeley Earth. “The long-term warming is the basis on which any of these records are set, necessarily.â€
The latest El Niño arrived on the heels of a rare three consecutive years of La Niña, its cooler counterpart, which may have had a masking effect on the heat, Hausfather said.
“When you flip from temperatures being suppressed to temperatures being enhanced, you might see a bigger effect this year than, say, comparable El Niño events where you went from neutral conditions,†he said.
The first winter outlook from the National Oceanic and Atmospheric Administration predicts that a strong El Niño will remain in place through at least the spring, bringing warm, wet conditions to California and large swaths of the U.S.
There are other variables that may have contributed to 2023’s runaway warmth, including the eruption of the Hunga Tonga volcano in the South Pacific the year prior, which shot record amounts of heat-trapping water vapor into the stratosphere.
Reductions in aerosol emissions have also contributed about a tenth of a degree of warming over the last two decades, as sulfate and other aerosols in the atmosphere can reflect sunlight away from the Earth, Hausfather said.
Additionally, solar activity is ramping up as part of an 11-year oscillation known as the solar cycle, which periodically heightens the amount of energy reaching Earth from the sun and may have contributed a couple hundredths of a degree of warming last year.
Yet 2023’s heat came as a surprise even to some scientists. Historical patterns indicate that global temperatures reach peak warmth in the year after El Niño’s arrival, as was the case in 2016 and 2020, the two previous hottest years on record.
That means there is a chance 2024 could be even hotter.
“I’d still probably give sightly better than even odds of 2024 being warmer,†Hausfather said. “It’s going to be up there, but it’s less clear-cut because 2023 was so weird.â€
Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, said similarly in a post on X that there is a 55% chance of another record-warm year in 2024 because of the ongoing El Niño event, but that less confidence is warranted “given the exceptional nature of 2023.â€
The year was so exceptional that dozens of records were broken, according to Copernicus. June through August marked the Northern Hemisphere’s hottest summer on record, while sea surface temperatures remained persistently and unusually high, reaching record levels from April through December. Marine heat waves struck parts of the Mediterranean, Gulf of Mexico, Caribbean, Indian Ocean, North Pacific and North Atlantic.
Last year also saw Antarctic sea ice extents reach record lows for the time of year in eight months, including all-time daily and monthly lows in February. Arctic sea ice ranked among the four lowest on record at its peak in March.
Two degrees Celsius — or 3.6 degrees Fahrenheit — is the internationally agreed upon upper limit of warming established by the 2015 Paris climate agreement.
“The extremes we have observed over the last few months provide a dramatic testimony of how far we now are from the climate in which our civilization developed,†read a statement from Carlo Buontempo, director of Copernicus. “This has profound consequences for the Paris Agreement and all human endeavors. If we want to successfully manage our climate risk portfolio, we need to urgently decarbonize our economy whilst using climate data and knowledge to prepare for the future.â€
Despite such warnings, greenhouse gas emissions continued to soar in 2023. Carbon dioxide concentrations climbed to a record 419 parts per million — 2.4 parts per million higher than in 2022, according to Copernicus. Methane concentrations rose to a record 1,902 parts per billion — 11 parts per billion higher than the year prior — although methane’s rate of increase was lower than in the last three years.
Experts say the changing climate is exacerbating extreme events across the globe, including worsening heat waves, floods, droughts and wildfires. In 2023, the United States alone experienced a record 28 weather and climate disasters where damage estimates reached or exceeded $1 billion, according to the National Oceanic and Atmospheric Administration.
The average annual temperature of the contiguous U.S. last year was 54.4 degrees, or 2.4 degrees above the 20th century average, ranking as the fifth warmest on record, NOAA officials said in a separate report released Tuesday.
Despite the records, Buontempo said current trajectories indicate that in a few years, 2023 may well be remembered as a cold year.
“Our cities, our roads, our monuments, our farms — in practice, all human activities — never had to cope with a climate this warm,†he told reporters Tuesday. “There were simply no cities, no books, agriculture, or domesticated animals on this planet last time the temperature was so high. This calls for a fundamental rethink of the way in which we assess our environmental risk, as our history is no longer a good proxy for the unprecedented climate we are already experiencing.â€
The data make it clear the 1.5-degree Celsius benchmark is slipping away. In fact, the planet briefly surpassed 2 degrees Celsius of warming globally — the upper limit of the Paris agreement — for the first time ever on Nov. 17 and 18, according to data from Copernicus.
That same month, world leaders gathered in Dubai for COP28, an annual United Nations climate conference, where nearly 200 countries agreed for the first time to move away from planet-warming fossil fuels.
Hausfather said hope is still warranted as these and other efforts can make a difference, but “we should be cautious as we push the Earth further and further from the climate that it’s had for the past few million years.â€
“If we want to minimize the risks to both ourselves and future generations, we need to get our act together and start more rapidly reducing emissions,†he said. “It’s probably too late at this point to limit warming to 1.5 degrees without passing it along the way. But we certainly have a good chance, if we speed up the energy transition, to limit warming below 2 degrees.â€
