President Trump's decision to yank the United States from the Paris climate agreement spurred a rallying cry from environmentalists committed to meeting the accord's goals anyway.
Too late, say the researchers behind a pair of studies published yesterday in Nature Climate Change.
Climate modeling and observational data suggest the world is already on track to reach dangerous levels of warming by the end of the century, according to the two papers.
There's only a 5 percent chance of limiting warming to less than 2 degrees Celsius, according to a forecast drawn from a statistical analysis of 150 countries' population and economic growth.
Two degrees of warming marks the likely threshold for widespread ecological problems, including coral reef collapse, markedly higher sea-level rise and crop failures, according to NASA.
The median forecast suggests 3.2 C of warming by 2100, with a likely range of between 2 and 4.9 C.
Even if all human emissions immediately ceased, the atmosphere probably contains enough carbon to push up temperatures by about 1.3 C by the end of the century, according to the second study.
And that might understate the effect of today's greenhouse gases.
The amount of warming caused by CO2 might have been masked over the years by accompanying aerosol emissions. So as emissions fall — and aerosols wash out of the air — we might find ourselves on track for even more warming than we realized, said Robert Pincus, a scientist with the University of Colorado, Boulder, and NOAA's Physical Sciences Division.
Pincus authored the analysis of committed warming, along with Thorsten Mauritsen of the Max Planck Institute for Meteorology.
The ocean's ability to absorb heat and carbon could reduce the warming already in the pipeline by 0.2 to 0.3 C, they wrote.
The findings are dire, but they should inspire action rather than hopelessness, said Adrian Raftery, a professor of statistics and sociology at the University of Washington and author of the study on temperature forecasts.
"The consequences of not [acting] are even higher with these results than they were before, when we could think about 1.5 degrees as being in the realm of possibility — which I think, realistically, it's not," he said, urging more investments in research, a tax on carbon and other established paths to emissions reductions.
Raftery's forecasts align with the middle-of-the-road scenarios put forward by the Intergovernmental Panel on Climate Change.
His study found population growth will likely play a small role in climate change, because the areas with the highest growth — like Africa — have a small carbon footprint.
Some uncertainty remains around how much Africa's emissions will grow over the coming century, he said, but relative to the United States, it's a question of whether Africa's per capita emissions will be "lower or much, much lower."
Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.