Scientists are issuing a stark warning about the changing climate after the planet reached a key warming benchmark in 2024. Newly released data from the European Union’s Copernicus Climate Change Service showed last week that the world’s average surface temperature was more than 1.5 degrees Celsius (2.7 degrees Fahrenheit) warmer on average last year than it had been prior to industrialization.  U.S. data showed the world was just shy of the 1.5-degree threshold. Scientists have said that in order to avoid some of the worst and most irreversible impacts of climate change, policymakers should try to limit warming to that benchmark. The 1.5-degree benchmark was enshrined in the Paris Agreement, in which most global nations pledged to work to keep the world from crossing it in an effort to protect against those effects. The Earth hitting the 1.5-degree threshold for just one year does not necessarily mean it has warmed that much permanently. Nevertheless, the data is a glaring reminder that the planet is inching closer to irreversible damage. “In some ways, it’s certainly a very important and a very sad milestone for the world, and it’s just a real wake-up call that the climate crisis is here,” said Laurie Geller, an atmospheric scientist who directs the peer review science office at the Natural Resources Defense Council, an environment advocacy group.  However, she added, “in other ways, though, I think it’s less of a line than some people think it is.” When scientists and the global Paris Agreement talk about limiting global warming to 1.5 degrees, they typically mean for longer than a single year. “Monthly and annual breaches of 1.5°C do not mean that the world has failed to achieve the Paris Agreement’s temperature goal, which refers to a long-term temperature increase over decades, not individual months or years,” the United Nations’s website states. However, Alex Ruane, co-director of the climate impacts group at NASA’s Goddard Institute for Space Studies, pointed out that in general, the years have been getting warmer, not cooler.  “We keep having 10-year periods that are much warmer than the previous 10-year periods. So we don’t really see a lot of room for temperature to come back down unless policies change,” said Ruane, who is also a research scientist at Columbia University and has worked on the United Nations’s latest climate report.  “In that sense, crossing this threshold suggests that we’re going to be living in a warmer-than-1.5-degree environment for a while,” he added.  The planet’s 10 warmest years since recordkeeping began in 1850 have all occurred in the past decade, according to U.S. data. Last year’s grim milestone comes as wildfires raging in California highlight the dangers that come with warming. Climate change has made the Western U.S. more susceptible to raging wildfires because when the temperature is hotter, the air demands more moisture and makes vegetation drier. This dry vegetation can be fuel that exacerbates a fire.  One reason scientists are urging the global community to try to limit warming is to avoid crossing “tipping points” — extreme environmental damage caused by climate change that is difficult to reverse. This includes the potential for the Greenland ice sheet to melt, the Amazon rainforest to decline significantly and the collapse of Atlantic Ocean currents that help regulate global temperature.  Breaching 1.5 degrees on a more sustained basis would bring the world closer to some of these points. A study has estimated, for example, that the Greenland ice sheet could see abrupt melting once warming has reached between 1.7 and 2.3  degrees Celsius (3.1 and 4.1 degrees Fahrenheit). “Some of these global tipping points are big, active areas of research, but they’re not magically or directly connected to that 1.5 alone,” Ruane said.  “The warmer the world gets, the closer we get to these types of tipping points,” he added.  But, scientists say, every increment of additional warming also matters.  “This is just a kind of another step along the way where, you know, 1.5 is worse than 1.49, but so is 1.51 worse than 1.5,” Ruane said.  Gisela Winckler, a climate professor at Columbia University, added that every increase in temperature means additional harms to people and the planet.  “It means a whole list of impacts that we are seeing,” Winckler said, adding that this includes “the increase in extreme weather events, be it drought on the one hand, but also extreme precipitation events … by increasing the water vapor in the atmosphere as the result of the global warming.”