The United States faces a choice between manageable warming and unmanageable catastrophe, according to a leaked draft report by scientists from 13 federal agencies.
The report’s “higher emissions” scenario projects a devastating 8°F to 10°F warming over the interior of this country–and, unimaginably, upwards of 18°F over in the Arctic–by 2071 to 2100. In that case, global sea levels could rise as much as 8 feet, inundating every major coastal city in this country and around the world.
The report was published by the New York Times, which noted that it “directly contradicts claims by President Trump and members of his cabinet who say that the human contribution to climate change is uncertain, and that the ability to predict the effects is limited.”
The draft, a special science section of the Congressionally-mandated quadrennial National Climate Assessment (NCA), has been given to Trump’s political appointees for review. It was reportedly leaked to the media out of concern that the report may be censored or watered down by the administration the way other climate documents have been.
The NCA is the definitive statement of current and future impacts of carbon pollution on the United States. The last one was from 2014, and it made crystal clear we were running out of time to avoid catastrophe.
“This latest report indicates that a path of inaction will truly lead to disastrous climate change impacts,” leading climatologist Michael Mann told ThinkProgress in an email. “Sadly, the Trump presidency has steered the U.S. toward this path.”
To get to the more manageable “lower emissions” scenario, the nation and the world must far exceed the emissions reduction goals agreed to in Paris in December 2015. Leaving the Paris accord and failing to meet our commitment–as Trump intends–puts the world on track for a “higher emissions” scenario that leads to unimaginable impacts.
“Emerging science regarding Antarctic ice sheet stability suggests that, for high emission scenarios, a GMSL [global mean sea level] rise exceeding 8 feet (2.4 m) by 2100 is physically possible, although the probability of such an extreme outcome cannot currently be assessed,” the report says.“For almost all future GMSL rise scenarios, RSL rise is likely to be greater than the global average in the U.S. Northeast and the western Gulf of Mexico,” and “for high GMSL rise scenarios, RSL rise is likely to be higher than the global average along all U.S. coastlines outside Alaska.”
We hold our future in our hands, as the report makes clear: “Choices made today will determine the magnitude of climate change risks beyond the next few decades.”
The bad news is that “the observed increase in global carbon emissions over the past 15-20 years has been consistent with higher scenarios.” The (somewhat) good news is that “in 2014 and 2015, emission growth rates slowed as economic growth has become less carbon-intensive. But even if this new trend continues, “it is not yet at a rate that would meet the long-term temperature goal of the Paris Agreement of holding the increase in the global average temperature to well below 3.6°F (2°C) above preindustrial levels.”
Deep in the report, the scientists spell out the choices we face concerning the Paris climate pledges, the Intended Nationally Determined Contributions (INDCs). The chart below, from the report, looks at probabilistic temperature outcomes for “emission scenarios following no policy, current policy, meeting the INDCs with no increased future ambition and meeting the INDCs with continually increasing ambition.”
As the chart makes clear, if we want a high probability of staying below the 2°C (3.6°F) threshold, beyond which scientists project impacts rapidly shift from dangerous to catastrophic, we will have to adopt policies that are considerably more ambitious than Paris–and we need to do that as soon as possible.
With the policies President Trump has embraced–where we don’t even meet the initial Paris targets and we return to promoting fossil fuels–then we face the very realistic prospect that total warming will be 4°C (7°F) or higher. And that, as the scientific literature makes clear, would be the end of modern civilization as we know it.
Furthermore, the report says that “climate models are more likely to underestimate than to overestimate the amount of long-term future change,” so there is a greater chance things will be worse than the report lays out than they will be better.
This post has been updated.