Greenhouse gases are rising so fast that it could soon be "game over" for the climate, a leading scientist warned in response to a new study published Wednesday that finds the planet could be heading for more than 7°C warming within a lifetime.

The study, published in the journal Science Advances, reported that the United Nations' most accurate estimates on the "business as usual" rate of global warming may actually be vastly underestimated.

The U.N.'s Intergovernmental Panel on Climate Change (IPCC) recently estimated that continuing to use fossil fuels at current rates would put the Earth on track for an average temperature rise of 2.6°C to 4.8°C above pre-industrial levels by 2100.

But the authors, a team of climate researchers and scientists at the University of Hawaii at Manoa, the University of Washington, the University of Albany, and the Potsdam Institute for Climate Impact Research, say the range for that same time period is actually  4.78°C to 7.36°C. That's because the climate has "substantially higher sensitivity" to greenhouse gases during warm phases, they write—which ultimately means that "within the 21st century, global mean temperatures will very likely exceed maximum levels reconstructed for the last 784,000 years."

The results correspond with other recent data that finds, despite all the pledges made in the landmark Paris climate agreement, the planet is still on track for at least a 3°C global temperature rise. Scientists have long warned that catastrophic, irreversible damage would come at 2°C.

President-elect Donald Trump, who has denied that climate change exists, has vowed to withdraw from the Paris agreement, and his transition team is rife with fellow deniers and fossil fuel industry lobbyists. Green groups on Wednesday reacted to his win by calling on people around the world to mobilize against his anti-environmental policies "for the sake of our brothers and sisters around the world and for all future generations."