Earth is becoming so hot that temperatures in about a decade will probably blow past a level of warming that world leaders have sought to prevent, according to a report released Monday that the United Nations called a "code red for humanity."
"It's just guaranteed that it's going to get worse," said report co-author Linda Mearns, a senior climate scientist at the U.S. National Center for Atmospheric Research. "Nowhere to run, nowhere to hide."
But scientists also eased back a bit on the likelihood of the absolute worst climate catastrophes.
The authoritative Intergovernmental Panel on Climate Change report, which calls climate change clearly human-caused and "unequivocal" and "an established fact," makes more precise and warmer forecasts for the 21st century than it did the last time it was issued in 2013.
Each of five scenarios for the future, based on how much carbon emissions are cut, passes the more stringent of two thresholds set in the 2015 Paris climate agreement. World leaders agreed then to try to limit warming to 2.7 degrees Fahrenheit above levels in the late 19th century because problems mount quickly after that. The world has already warmed nearly 2 degrees since then.
Under each scenario, the report said, the world will cross the 2.7degrees warming mark in the 2030s, earlier than some past predictions. Warming has ramped up in recent years, data shows.
"Our report shows that we need to be prepared for going into that level of warming in the coming decades. But we can avoid further levels of warming by acting on greenhouse gas emissions," said report co-chair Valerie Masson-Delmotte, a climate scientist at France's Laboratory of Climate and Environment Sciences at the University of Paris-Saclay.
In three scenarios, the world will also likely exceed 3.6 degrees over pre-industrial times -- the less stringent Paris goal -- with far worse heat waves, droughts and flood-inducing downpours unless there are deep emissions cuts, the report said.
"This report tells us that recent changes in the climate are widespread, rapid and intensifying, unprecedented in thousands of years," said report Vice Chair Ko Barrett, senior climate adviser for the U.S. National Oceanic and Atmospheric Administration.
With crucial international climate negotiations coming up in Scotland in November, world leaders said the report is causing them to try harder to cut carbon pollution. U.S. Secretary of State Anthony Blinken called it "a stark reminder."
The 3,000-plus-page report from 234 scientists said warming is already accelerating sea level rise and worsening extremes such as heat waves, droughts, floods and storms. Tropical cyclones are getting stronger and wetter, while Arctic sea ice is dwindling in the summer and permafrost is thawing. According to the report, all of these trends will get worse.
For example, the kind of heat wave that used to happen once every 50 years now happens once a decade, and if the world warms another 1.8 degrees, it will happen twice every seven years, the report said.
As the planet warms, places will get hit more not just by extreme weather but by multiple climate disasters at once, the report said. That's like what's now happening in the Western U.S., where heat waves, drought and wildfires compound the damage, Mearns said. Extreme heat is also driving massive fires in Greece and Turkey.
Some harm from climate change -- dwindling ice sheets, rising sea levels and changes in the oceans as they lose oxygen and become more acidic -- is "irreversible for centuries to millennia," the report said.
The world is "locked in" to 6 to 12 inches of sea level rise by midcentury, said report co-author Bob Kopp of Rutgers University.
Scientists have issued this message for more than three decades, but the world hasn't listened, said U.N. Environment Program Executive Director Inger Andersen.