For the second year in a row, Earth will almost certainly be the hottest it's ever been. And for the first time, the globe this year reached more than 1.5 degrees Celsius of warming compared to the pre-industrial average, the European climate agency Copernicus said Thursday. 

“It's this relentless nature of the warming that I think is worrying,” said Carlo Buontempo, director of Copernicus. 

Buontempo said the data clearly shows the planet would not see such a long sequence of record-breaking temperatures without the constant increase of greenhouse gases in the atmosphere driving global warming.

He cited other factors that contribute to exceptionally warm years like last year and this one. They include El Nino — the temporary warming of parts of the Pacific that changes weather worldwide — as well as volcanic eruptions that spew water vapour into the air and variations in energy from the sun. But he and other scientists say the long-term increase in temperatures beyond fluctuations like El Nino is a bad sign. 

“A very strong El Nino event is a sneak peek into what the new normal will be about a decade from now,” said Zeke Hausfather, a research scientist with the nonprofit Berkeley Earth.

Buontempo pointed out that going over the 1.5 degree Celsius (2.7 degrees Fahrenheit) threshold of warming for a single year is different from the goal adopted in the 2015 Paris Agreement. That goal was meant to try to cap warming at 1.5 degrees Celsius (2.7 degrees Fahrenheit) since pre-industrial times on average, over 20 or 30 years. 

A United Nations report this year said that since the mid-1800s on average, the world has already heated up 1.3 degrees Celsius (2.3 degrees Fahrenheit) — up from previous estimates of 1.1 degrees (2 degrees Fahrenheit) or 1.2 degrees (2.2 degrees Fahrenheit). That's of concern because the U.N. says the greenhouse gas emission reduction goals of the world's nations still aren't nearly ambitious enough to keep the 1.5 degree Celsius target on track.

The target was chosen to try to stave off the worst effects of climate change on humanity, including extreme weather. “The heat waves, storm damage, and droughts that we are experiencing now are just the tip of the iceberg,” said Natalie Mahowald, chair of Earth and Atmospheric Sciences at Cornell University.

Going over that number in 2024 doesn't mean the overall trend line of global warming has, but “in the absence of concerted action, it soon will,” said University of Pennsylvania climate scientist Michael Mann. 

Stanford University climate scientist Rob Jackson put it in starker terms. “I think we have missed the 1.5 degree window,” said Jackson, who chairs the Global Carbon Project, a group of scientists who track countries' carbon dioxide emissions. “There's too much warming.”

Indiana state climatologist Beth Hall said she isn't surprised by the latest report from Copernicus, but emphasised that people should remember climate is a global issue beyond their local experiences with changing weather. “We tend to be siloed in our own individual world,” she said. Reports like this one “are taking into account lots and lots of locations that aren't in our backyard.”

Buontempo stressed the importance of global observations, bolstered by international cooperation, that allow scientists to have confidence in the new report's finding: Copernicus gets its results from billions of measurements from satellites, ships, aircraft and weather stations around the world.

He said that going over the 1.5 degree Celsius (2.7 degrees Fahrenheit) benchmark this year is “psychologically important” as nations make decisions internally and approach negotiations at the annual U.N. climate change summit Nov. 11-22 in Azerbaijan. 

“The decision, clearly, is ours. It's of each and every one of us. And it's the decision of our society and our policymakers as a consequence of that,” he said. “But I believe these decisions are better made if they are based on evidence and facts.”