Last month wasn’t only the hottest June by far in the observed temperature record, but marked the first-ever 12-month stretch of the Earth’s average temperature exceeding 1.5 degrees Celsius of temperature rise above the pre-industrial baseline against which human-caused warming is measured.

“This is more than a statistical oddity and it highlights a large and continuing shift in our climate,” said Carlo Buontempo, director of the Copernicus Climate Change Service, which released its monthly update Monday. The report showed that, over the past 12 months, the planet’s average temperature was 1.64 degrees Celsius above the 1850-1900 reference period.

Even when the current string of extremes ends at some point, Buontempo added, “more records will be broken … This is inevitable, unless we stop adding [greenhouse gases] into the atmosphere and the oceans.”

Some other global temperature datasets show the same 12-month streak, while others have yet to be finalized, and differences of a few tenths of a degree shouldn’t distract from the fact that global heating is “continuing apace,” said Gavin Schmidt, director of the NASA Goddard Institute for Space Studies in New York.

But the milestone isn’t as significant as it might appear, he said, because there is a range of 0.1 to 0.2 degrees Celsius uncertainty about the exact pre-industrial baseline temperature. “So while the exact point in these records at which we first cross 1.5 degrees Celsius may be exciting, it’s not really very important nor does it have much climate significance,” he added.

The 1850-1900 period is used as the reference point for conditions before human emissions of greenhouse gases started having a noticeable impact on the climate, and it was also chosen by the Intergovernmental Panel on Climate Change because that’s when direct measurements of air temperature and ocean surface temperature started to become available routinely from various parts of the globe, said Julien Nicolas, a senior climate scientist with Copernicus.

Under the 2015 climate pact, 196 countries pledged to limit human-caused warming to well below 2 degrees Celsius, and to pursue efforts to prevent warming more 1.5 degrees Celsius above that baseline, and the current stretch of 12 months with a temperature anomaly of more than 1.5C above the baseline doesn’t mean that the global average temperature has breached the climate target set by the Paris Agreement, he said. 

“It must be stressed that the 1.5 and 2 degree limits set in the Paris Agreement are targets for the average temperature of the planet over a twenty or thirty-year period,” Nicolas said.

Just a month after the Paris accord was signed, Earth’s average monthly temperature went above the 1.5 threshold for the first time, reaching 1.51 degrees Celsius in January 2016 and staying above 1.5 through March of that year, making it the now second-longest such streak, Nicolas said. 

The three months with the greatest absolute warming anomaly above the 1.5-degree mark were all last winter; November 2023 at 1.74C, February 2024 at 1.77C and December 2023 at 1.78C, edging closer to the Paris Agreement’s highest allowable temperature limit of 2 degrees Celsius of warming.

The new report from Copernicus shows how close world leaders are to a failure in addressing the climate crisis. Despite the promises made in Paris, current policies mean the world is currently on track to warm about 2.7 degrees Celsius by 2100, a level at which parts of modern civilization could start to unravel, according to climate scientists who study tipping points.

Already Past 1.5?

Former NASA climate scientist James Hansen said the current debate about crossing the 1.5 degree Celsius threshold shows that mainstream climate institutions like the IPCC “have lost sight of what is of practical importance.”

“If IPCC doodles for another 10 years before it admits that we have reached more than 1.5 degrees of warming, we will be far above that level by that time,” he said. The slow process by which the IPCC assesses thousands of studies isn’t keeping pace with the rate of warming, which has jumped to .32 degrees Celsius per decade since 2010, up from 0.18 per decade in the 1970 to 2010 period, he added.

“The current excursion above 1.5, to about 1.6, is driven in part by the recent El Niño,” he said, referring to a warming and cooling cycle in the tropical Pacific Ocean that affects global temperatures. “However, the rapid leap from about 1.2 to 1.6 degrees Celsius is too large to have been driven by the moderate El Nino, or any El Nino of record.” 

Hansen led recent research suggesting that the past few years’ sharp reduction of industrial aerosol pollution that reflects some solar radiation, and the heat that accompanies it, away from the planet was a big factor in the recent string of monthly temperature records.

“If IPCC doodles for another 10 years before it admits that we have reached more than 1.5 degrees of warming, we will be far above that level by that time.”

He said the next few months will tell a lot more about how big the effect of the currently ending El Niño really was.

“The decline of global temperature following a moderate El Nino should only be about 0.2C,” he said. “So for all practical purposes, the world has now reached the 1.5C level, as the average of El Niño and La Niña conditions.” He said he expects the global average temperature anomaly to drop back down to 1.4 degrees Celsius as the current El Niño ends.

That temporary slowdown of warming has already started, added climate scientist Michael Mann, director of the University of Pennsylvania’s Center for Science, Sustainability & the Media. He noted that the global average sea surface temperature recently dropped below the record levels that have persisted for more than a year.

“As we head into La Niña now, we will see the anomalous short-term spike of the past year disappear,” he said. “What will remain is the steady long-term warming that will continue as long as human-generated carbon emissions continue. That’s what the focus should be on.”

And the relief of the fading El Niño will likely pale in comparison to the other factors turning up the heat. Given the current pace of warming, Hansen has said previously that the ongoing buildup of greenhouse gases and the continued reduction of industrial aerosols could push global heating to more than 2 degrees by 2050.

Kevin Trenberth, a climate scientist in New Zealand, said the 12-month streak with temperatures more than 1.5 degrees Celsius above the pre-industrial level is “not meaningful for science but it is meaningful societally and because of the Paris Agreement. It’s not unexpected and it will get worse.”

He said that June 2024 will probably be the last month in this series breaking the 1.5 degree mark, but the odds are high that 2024 will end up as the warmest year on record, and he expects temperatures to permanently cross the 1.5 degree threshold by about 2030.World Meteorological Organization Secretary-General Celeste Saulo said that, even if the Paris limits haven’t been crossed yet, the latest Copernicus report “unfortunately highlights that we will be exceeding the 1.5 degree Celsius level on a temporary basis with increasing frequency, on a monthly basis.”