A streak of record-setting heat that began last summer has now persisted for an entire year across the globe, researchers announced Wednesday, pushing Earth closer to a dangerous threshold that the world's nations have pledged not to cross.
The data released by European climate scientists showed May was the 12th consecutive month during which average global temperatures surpassed all observations since 1850, and probably any extended period for more than 100,000 years. Over the past year, according to the European Union's Copernicus Climate Change Service, global temperatures averaged 1.6 degrees Celsius (2.9 degrees Fahrenheit) above preindustrial levels.
Under the landmark 2015 Paris agreement, the world's leaders pledged to limit Earth's temperature rise to 1.5 degrees C (2.7 degrees F) over preindustrial levels, to avert some of the worst effects of global warming. The fact that the planet surpassed this mark for one year does not amount to a permanent shift, but it comes as scientists are warning that it is likely to happen again - within a few years.
The World Meteorological Organization said that it is highly likely that, for at least one calendar year in the next five, temperatures will exceed 1.5 degrees C above preindustrial levels once more.
This unprecedented stretch of warmth, which has astonished scientists, prompted an urgent call by the United Nations to ban fossil fuel companies from advertising and encourage the public to stop using their products.
"For the past year, every turn of the calendar has turned up the heat," U.N. Secretary General António Guterres said in a special address in New York. "Our planet is trying to tell us something. But we don't seem to be listening."
Researchers have linked the rise in temperatures to the El Niño climate pattern and decades of global heating from human emissions of greenhouse gases.
A decade ago, scientists had estimated that the chances of the planet warming 1.5 degrees C by 2020 were nearly zero. Now, the probability of that happening by 2028 is an estimated 8 in 10.
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A year-long surge of record heat
Global temperature records have been broken by significant margins since last June, as a burgeoning El Niño began releasing vast stores of heat from the Pacific Ocean. During the periodic climate pattern, warmer-than-average waters pool along the equator in the central and eastern Pacific, transferring warmth and moisture into the atmosphere and triggering extreme heat waves, floods and droughts around the world.
In July, temperatures rose above the 1.5-degree C warming benchmark for an entire month, the first time that had happened.
That warming trend then continued largely unabated. Global surface-air temperatures last month averaged 1.5 degrees C higher than the 1850-1900 global average, according to Copernicus.
Carlo Buontempo, the Copernicus director, said that as remarkable as the trend is, "this string of hottest months will be remembered as comparatively cold" without action to reverse it.
Emissions of carbon dioxide and other greenhouse gases from burning fossil fuels like coal, oil and gas act to trap heat within the atmosphere, preventing it from escaping into space.
A separate study published by a group of 57 scientists on Wednesday found that human activities were responsible for 92 percent of the warming observed in 2023, the planet's hottest calendar year on record. It said the rate of warming in the past decade is "unprecedented in the instrumental record."
Data on global temperature records come from direct observations from ground sensors dating back nearly two centuries, satellite observations in more recent decades, and evidence from historical records and geologic analyses that go further back in time.
While this data may not allow scientists to determine how hot it was on a single day or over a period of months many thousands of years ago, it does give confidence that the planet has not experienced such rapid and sustained warming since the end of the last ice age about 125,000 years ago.
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Accelerating predictions of global warming
As warming has surged, projections of Earth's temperature trajectory have accelerated.
The latest version of a periodic report on near-term warming, also released Wednesday, shows it has become nearly a certainty that global temperatures will continue to cross into dangerous territory. At a sustained average of 1.5 degrees C above preindustrial levels, the U.N. Intergovernmental Panel on Climate Change has warned that weather will become so extreme, many people will struggle to adapt to it.
"The difference between 1.5 and 2 degrees could be the difference between extinction and survival for some small island states and coastal communities," Guterres said.
Many climate scientists say that the Paris agreement's target of no more than 1.5 C is already out of reach, though they stress that a single year above that level of warming does not mean the goal is lost.
Scientists now estimate an 86 percent chance that at least one of the next five years also surpasses the record average annual temperature observed across the globe in 2023.
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An increasingly dire call to action
Guterres used the data to stress the urgency of climate action ahead of a June meeting in Italy of the Group of Seven - the world's wealthiest democracies - where matters of war and global trade are expected to take center stage.
He repeated past calls for countries to stop investing in new coal power generation, and for developed countries to increase investment in clean energy and extreme weather adaptation, especially in poorer countries that have done the least to contribute to climate change and are feeling some of its worst effects.
And Guterres is now demanding all countries ban advertising from fossil fuel companies, and media and tech companies stop taking those companies' ad dollars.
Several cities and one country have already banned some fossil fuel advertising. Last month, the city council of Edinburgh, Scotland, voted to ban advertisements for fossil fuels as well as ads for SUVs and aviation. Amsterdam similarly has prohibited advertisements of gas-powered cars and airplane trips in the city's center and subway stations.
And after French President Emmanuel Macron asked 150 ordinary citizens to help with climate policymaking, his nation banned advertisements for coal, petroleum and hydrogen made from fossil fuels in 2022, though fossil fuel companies can still sponsor events.
"We are playing Russian roulette with our planet," Guterres said. "We need an exit ramp off the highway to climate hell."
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Shannon Osaka contributed to this report.
