The world can't afford to build any more fossil fuel burning plants if it hopes to avoid catastrophic climate change, according to a new study in the journal Nature.
Carbon dioxide emissions from the power plants, factories, furnaces and vehicles the world has already built will warm the planet into dangerous territory, past the target set in the Paris climate agreement, the researchers find.
Any new plants -- and some older ones -- will either have to close early, before they are paid off, or install costly carbon-capture gear, the researchers say.
Greenhouse gas emissions from burning fossil fuels have already warmed the planet about 1 degree Celsius on average. Heat waves, droughts, wildfires and rainstorms have grown more intense, and sea levels are rising. Impacts will get worse as the planet warms, scientists say.
In Paris, negotiators agreed to keep global warming "well below" 2 degrees, and to aim for 1.5 degrees.
To meet that target, the world can produce at most another 580 gigatons of carbon dioxide, according to a U.N. Intergovernmental Panel on Climate Change estimate.
But the new study finds that existing fossil fuel infrastructure will produce more than that over its lifetime: about 658 gigatons total. (One gigaton equals a billion tons.)
Additional plants that are planned, permitted or under construction will add another 188 gigatons, putting the world about two-thirds of the way to 2 degrees.
"If we want to stay under one and a half degrees, we'd need to stop building new stuff immediately and retire a fair amount of our already existing stuff before the end of its operating lifetime," said study co-author Steve Davis, Earth science professor at the University of California, Irvine.
The study adds detail to an IPCC report last October, which said global emissions need to fall 45 percent by 2030 to keep below the 1.5 degree target.
There is some wiggle room in the estimates.
Another study earlier this year gave a 64 percent chance that the world would stay below 1.5 degrees of warming if all existing plants were phased out starting in 2018.
"The message is still consistent," said lead author Chris Smith, a climate researcher at the University of Leeds. "Basically, we need to transition away from fossil fuels as quickly as possible."
Both studies assume that no more fossil plants will be built. Davis calls that assumption "laughable."
"Research like this makes it obvious that we can't fight climate change and continue burning oil and gas at the same time," said Greenpeace USA Climate Campaign Director Janet Redman, "but the United States continues to expand drilling, fracking, and mining for fossil fuels."
The American Petroleum Institute, the main U.S. oil and gas industry trade group, said in a statement that the industry "is already driving emissions to 25-year lows—more than any nation on earth—made possible by the growing use of clean natural gas for power. The U.S. and the world can continue that progress, meet record consumer energy demand, and protect the environment by investing in modern natural gas and oil infrastructure.”
The new study is a follow-up to one Davis co-authored in 2010. It found that the world was on track for 1.3 degrees of warming, and "sources of the most threatening emissions have yet to be built."
That was before China went on a coal-plant building binge.
Today, the study finds, nearly half of the world's industrial and electricity generation emissions come from China.
As the cost of wind and solar energy plummet, however, "we have an opportunity to retire some of these things early, and it might not even be that far-fetched," Davis said. "That's the piece that is a little more hopeful."
With the cost of renewables declining and health care costs from fossil fuel air pollution mounting, "Many governments have recognized that the economics of coal power...make new coal power economically and socially unfavorable," said the World Resources Institute's Kelly Levin.
Nearly 31 gigawatts of coal-fired capacity was taken out of service worldwide in 2018, compared with about 2 gigawatts in 2006, according to Global Energy Monitor.
But early retirements will be expensive and hard to swallow, Davis acknowledged, even for those with good intentions.
Davis is working with the University of California's 10-campus system to meet its goal to be carbon neutral by 2025. The schools recognize that one of the biggest challenges will be replacing the seven on-campus natural gas combined heat and power plants.
"I've had conversations with the administrators where they say, 'Well, let's go ahead and make a plan for when this thing is fully paid for," he said.
"This is exactly what our paper gets at is, we can't just wait for the end of these things' lifetime to make a decision. We actually need to hasten that."