Arctic warming will cost trillions of dollars to the global economy over time as the permafrost thaws and the sea ice melts—how many trillions depends on how much the climate warms, and even a half a degree makes a difference, according to a new study.

If nations don’t choose more ambitious emission controls, the eventual damage may approach $70 trillion, it concluded.

For tens of thousands of years, grasses, other plants and dead animals have become frozen in the Arctic ground, building a carbon storeroom in the permafrost that’s waiting to be unleashed as that ground thaws.

It’s considered one of the big tipping points in climate change: as the permafrost thaws, the methane and CO2 it releases will trigger more global warming, which will trigger more thawing. The impacts aren’t constrained to the Arctic—the additional warming will also fuel sea level rise, extreme weather, drought, wildfires and more.

In a study published Tuesday in the journal Nature Communications, a team of scientists for the first time is putting a long-term price on the climate impacts caused by the rapidly increasing temperatures in the Arctic. The authors—a mix of economists and climate scientists—looked at the costs across various future scenarios, including those with limited global warming (for which the calculations include the costs of mitigating climate change) and those with far higher temperatures.

Even if the goals of the Paris climate agreement are achieved—if the world keeps warming below 2°C from pre-industrial temperatures, or ideally below 1.5°C—the costs will be significant. At 1.5°C of warming, thawing permafrost and loss of sea ice will have cost the global economy an estimated $24.8 trillion in today’s dollars by the year 2300. At 2°C, that climbs to $33.8 trillion.

If countries only meet their current pledges under the Paris Agreement, the cost will rise to $66.9 trillion.

Those figures represent only a fraction of the total cost of climate change, somewhere between and 4 and 5 percent, said lead author Dmitry Yumashev, but they send an important message to policymakers: namely, that the costs associated with keeping global warming to 1.5°C are less than the costs of the impacts associated with letting warming go to 2°C or higher.

“The clear message is that the lower emissions scenarios are the safest option, based on the cost estimates we presented here,” Yumashev said.

Permafrost Feedback Loop Worsens Over Time

The authors were able to determine the costs associated with Arctic warming by running various scenarios through a complex computer model that takes the myriad impacts of climate change into account.

These models provide the basis for a significant body of scientific literature around climate change, but perhaps the most widely respected published work—the Intergovernmental Panel on Climate Change’s Fifth Assessment Report, which provided a scientific basis for the Paris climate agreement—did not adequately account for the impacts of permafrost when it modeled what’s at stake with climate change. The science on permafrost at that point was too preliminary.

What models now show—and what is reflected in this most recent work—is that the problematic permafrost feedback becomes increasingly worse as the temperature climbs.

Helping Policymakers Understand the Impact

While the idea of tipping points isn’t new, the assignment of costs to specific feedback loops is, said Paul Ekins, an energy and climate economist who was not involved in the new study.

“They come up with some pretty startling results in terms of extra damages we can expect if and when these tipping points are triggered,” he said. “I think it very much is a question of ‘when’ unless we get a grip on climate change very quickly.”

Ekins said he hopes that quantifying the economic risks might help motivate policymakers to act more decisively.

Kevin Schaefer, a coauthor of the study who specializes in permafrost carbon feedback at the National Snow and Ice Data Center, shares that hope. “What we’re talking about is a set of tools that we’re hoping we can put into the hands of policymakers on how to proceed by knowing a realistic estimate of economic impacts,” he said.