Some energy and climate projections may have been distorted by inflated estimates of available coal, a new study shows.

Since the 1990s, climate and energy models have assumed we’d use the entirety of the world’s coal reserves, but it has become clear in recent decades that only about a third of all coal deposits can feasibly be recovered.

But, researchers warn, changing those assumptions doesn’t alter the forcasts of the lowest-emission—but still risky—climate scenario.

The mismatch in coal usage estimates and actual availability results surprised researchers Justin Ritchie and Hadi Dowlatabadi, of the University of British Columbia, who published their findings last month. Coal had once been assumed to be essentially unlimited (for the purposes of modeling), and their new estimates severely constrained the potential supply—so much so that the worst case climate scenario put forth by the Intergovernmental Panel on Climate Change, which assumes an increase in future coal use, may not be possible. At least not in the way scientists thought.

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When Ritchie and Dowlatabadi adjusted their model to account for the lower coal estimates, they substituted natural gas or renewable energy for additional coal use in coal’s place. When natural gas picked up the slack, emissions fell by 15%, and when renewable energy filled the gap, emissions estimates fell by 30%.

Eric Roston, reporting for Bloomberg:

The discovery that there’s a whole lot less coal to burn would seem a gift to skeptics of climate change and opponents of climate policy. But Ritchie’s paper is a double-edged sword. The same finding that shrinks CO2 emissions may also lower the cost of dealing with global warming, making the Paris Agreement that addresses climate change easier to achieve.

Although the study may lead to more well-informed models, it doesn’t necessarily indicate a brighter future for climate. Even low-end scenarios—in which emissions drop enough to limit warming to 3.6˚ F—would bring drastic changes to the climate system.