Fearsome climate prospect. Will Trump administration suppress a major federal climate change report?

OVER THE next week or so, the Trump administration must decide whether to approve or suppress a major federal climate change report. Though scientists have signed off on its findings, including that the average U.S. temperature has spiked in the past several decades and that humans have almost certainly played a predominant role, President Trump and Environmental Protection Agency Administrator Scott Pruitt have indicated they simply do not believe the experts.

Even as the federal climate assessment has been under review, the warnings have grown starker.

A paper published last week in Nature Climate Change offered a harrowing view. International negotiators committed in Paris to keeping global temperature rise below 2 degrees Celsius, the point past which experts warn warming could be very dangerous. Analysts from the University of Washington and the University of California at Santa Barbara found that there is only a 5 percent chance the world will achieve that goal.

Instead of predicting how technology or policy might change, the researchers looked at how nations have done until now and inferred from those trends what will happen in the future. As economies expand, they emit more planet-warming carbon dioxide into the air. Fortunately, over time economies also produce more efficiently, using less fuel and therefore emitting less carbon dioxide for every widget assembled or mile driven. By projecting population growth, economic expansion and carbon efficiency into the future, the analysts came up with a rough guide to where the global temperature will be at the end of the century.

They found that there is a 90 percent chance the world will warm between 2 degrees and 4.9 degrees Celsius, with a median of 3.2 degrees. Though this avoids the most alarming scenarios scientists have previously considered, it also excludes the least concerning, finding virtually no chance the Earth will keep warming below the desirable level of 1.5 degrees Celsius.

How does this translate into the real world? Some other new research provides answers. Experts at the Massachusetts Institute of Technology and Loyola Marymount University in Los Angeles found that at 4.5 degrees of temperature rise by 2100, highly populated and impoverished swaths of South Asia would experience heat waves so extreme that human beings would not be able to survive without protection. At 2.25 degrees of warming, heat-wave temperatures in the region would be dangerous but not as deadly. Another new analysis from European Union researchers warned that deaths due to extreme weather across Europe could increase from about 3,000 per year to 152,000 annually if the Earth warmed 3 degrees by century’s end.

Each of these studies comes with caveats. For example, much of the risk would be averted with a strong global commitment to cutting carbon dioxide emissions, particularly if green technology became significantly cheaper, making it easier to decarbonize than in the past. Yet even if the breakthroughs do not come, or do not come fast enough, the latest research suggests it is neither unrealistic nor pointless to aim for the low end of the range of possible climate outcomes, even over 2 degrees, to at least limit the damage to the planet’s habitability. That path, however, requires leaders to admit there is a problem.