Humanity still has a chance, close to the last, to prevent the worst of climate change’s future harms, a top United Nations panel of scientists said Monday.

But doing so requires quickly slashing nearly two-thirds of carbon pollution by 2035, the Intergovernmental Panel on Climate Change said. The United Nations chief said it more bluntly, calling for an end to new fossil fuel exploration and for rich countries to quit coal, oil and gas by 2040.

“Humanity is on thin ice — and that ice is melting fast,” United Nations Secretary-General Antonio Guterres said. “Our world needs climate action on all fronts — everything, everywhere, all at once.”

Stepping up his pleas for action on fossil fuels, Guterres called for rich countries to accelerate their target for achieving net zero emissions to as early as 2040, and developing nations to aim for 2050 — about a decade earlier than most current targets. He also called for them to stop using coal by 2030 and 2040, respectively, and ensure carbon-free electricity generation in the developed world by 2035, meaning no gas-fired power plants either.

That date is key because nations soon have to come up with goals for pollution reduction by 2035, according to the Paris climate agreement. After contentious debate, the U.N. science report approved Sunday concluded that to stay under the warming limit set in Paris the world needs to cut 60% of its greenhouse gas emissions by 2035, compared with 2019, adding a new target not previously mentioned in six previous reports issued since 2018.

“The choices and actions implemented in this decade will have impacts for thousands of years,” the report said, calling climate change “a threat to human well-being and planetary health.”

“We are not on the right track but it’s not too late,” said report co-author and water scientist Aditi Mukherji. “Our intention is really a message of hope, and not that of doomsday.’’

With the world only a few tenths of a degree away from the globally accepted goal of limiting warming to 1.5 degrees Celsius since pre-industrial times, scientists stressed a sense of urgency. The goal was adopted as part of the 2015 Paris climate agreement and the world has already warmed 1.1 degrees Celsius.

This is likely the last warning the Nobel Peace Prize-winning collection of scientists will be able to make about the 1.5 mark because their next set of reports may well come after Earth has either passed the mark or is locked into exceeding it soon, several scientists, including report authors, told The Associated Press.

After 1.5 degrees “the risks are starting to pile on,” said report co-author Francis X. Johnson, a climate, land and policy scientist at the Stockholm Environment Institute. The report mentions “tipping points” around that temperature of species extinction, including coral reefs, irreversible melting of ice sheets and sea level rise of several meters.

“1.5 is a critical critical limit, particularly for small islands and mountain (communities) which depend on glaciers,” said Mukherji.

“The window is closing if emissions are not reduced as quickly as possible,” Johnson said in an interview. “Scientists are rather alarmed.”

Many scientists, including at least three co-authors, said hitting 1.5 degrees is inevitable.

“We are pretty much locked into 1.5,” said report co-author Malte Meinshausen, a climate scientist at the University of Melbourne in Australia. “There’s very little way we will be able to avoid crossing 1.5 C sometime in the 2030s ” but the big issue is whether the temperature keeps rising from there or stabilizes.

Guterres insisted “the 1.5-degree limit is achievable.” Science panel chief Hoesung Lee said so far the world is far off course.

If current consumption and production patterns continue, Lee said, “the global average 1.5 degrees temperature increase will be seen sometime in this decade.”

Scientists emphasize that the world or humanity won’t end suddenly if Earth passes the 1.5 degree mark. Mukherji said “it’s not as if it’s a cliff that we all fall off.” But an earlier IPCC report detailed how the harms — including even nastier extreme weather — are much worse beyond 1.5 degrees of warming.

“It is certainly prudent to be planning for a future that’s warmer than 1.5 degrees,” said IPCC report review editor Steven Rose, an economist at the Electric Power Research Institute in the United States.

If the world continues to use all the fossil fuel-powered infrastructure either existing now or proposed, Earth will warm at least 2 degrees Celsius since pre-industrial times, the report said.

Because the report is based on data from a few years ago, the calculations about fossil fuel projects already in the pipeline do not include the increase in coal and natural gas use after Russia’s invasion of Ukraine. It comes a week after the Biden Administration in the United States approved the huge Willow oil-drilling project in Alaska, which could produce up to 180,000 barrels of oil a day.