But now, researchers estimate in a new paper published Thursday that number has been cut in half — thanks to three years of high emissions and new scientific understanding of how air pollution particles, known as aerosols, will affect the climate.
“This is unprecedented,” Piers Forster, one of the paper’s authors and a climate scientist at the University of Leeds, told a news conference in Bonn, Germany.
The shift is due in part to the fact that, despite a brief drop in emissions during the coronavirus pandemic, carbon dioxide emissions from burning coal, oil and gas remain high — and even rose slightly last year.
At the same time, researchers also updated their climate models to take into account new scientific findings. As the world phases out fossil fuels, aerosol pollution has already begun to decline. That’s good for air quality and human health – but aerosols also cool the planet slightly by reflecting sunlight. Scientists updating climate models to account for this fact have realized that the planet may have a much smaller carbon budget than originally expected.
“We have a fairly significant update of the remaining budget by 1.5 degrees,” Joeri Rogelj, one of the paper’s authors, at a press conference. “There is only 250 gigatons of CO2 left.”
Other experts say it is very possible that the remaining carbon budget has been reduced to almost nothing.
“It’s possible — perhaps likely — that we’ve already exhausted much of the remaining 1.5C carbon budget,” Rob Jackson, a professor of Earth system science at Stanford University who was not involved in the study, said in an email. “The earth is warmer today than it was five years ago, and we are heading for 1.5C with no sign of reducing greenhouse gas emissions.”
It’s important to note that 1.5 degrees Celsius has always been a very ambitious climate goal – at the beginning, some scientists questioned whether it was even possible to phase out fossil fuels fast enough to achieve it. But in the past five years it has become a key focus of climate activism, even as some experts have warned that it is now essentially out of reach. Scientists now estimate that the world is likely to exceed that temperature mark sometime in the next 10 years.
Researchers don’t think catastrophic tipping points will be triggered exactly at 1.5 degrees Celsius, but they do know that every tenth of a degree worsens warming and the damage it causes.
The new document shows that progress towards the 2 degree Celsius target has also been affected. Over the past three years, the researchers estimated, the carbon budget for 2C has decreased by about 15 percent. And temperatures are already 1 degree Celsius higher than in pre-industrial times.
