A glacier in Half Moon Bay, Antarctica, on Feb. 18. (Alexandre Meneghini/Reuters)

SCIENTISTS HAVE given Antarctica a thorough physical exam. The results are grim. The continent is shedding weight at an astonishing and accelerating rate, and that is alarming news for anyone living near a major body of water — in other words, much of humanity.

A landmark study published last week in the journal Nature combined the work of 80 scientists from 42 institutions, including NASA, and found that, since 1992, Antarctica has lost nearly 3 trillion tons of ice, enough to raise sea levels by a little less than a centimeter. Forty percent of that ice loss occurred in the past five years. The ice-loss rate is now triple what it was a decade ago.

One should guard against assuming that trends will continue as they have in the immediate past. But there is more reason to fear that ice loss will worsen rather than abate. East Antarctica, once gaining mass, now appears to be losing it. And scientists warn of instability in major West Antarctic ice formations that could lead to catastrophic ice loss.

The paper took data from researchers who estimated Antarctic ice loss in 24 studies using three methods. These three methods resulted in parallel, wholly independent readings that largely matched up. Their combination produced findings that even the most circumspect critics of climate science should not be able to ignore.

As Antarctica melts, North America will take a particularly hard wallop. Melting ice shrinks Antarctica and, therefore, its gravitational field. Without as much mass pulling ocean water south, sea levels will rise farther north as the oceans redistribute. For every centimeter the seas rise, major East Coast cities will see a roughly 1.25-centimeter increase. Coastal cities need to start preparing, now.

Yet even though evidence continues to mount about the direct and dangerous disruptions humans are imposing on the climate system, the federal government’s highest leadership refuses to acknowledge the problem, let alone do anything about it. This month brought the first anniversary of the Trump administration’s pullout from the Paris climate agreement, an international accord that took decades to strike and that offered the best hope of getting every nation to reduce greenhouse-gas emissions together. At the time, President Trump said he would be open to renegotiating U.S. participation in the agreement, but the administration has hardly tried. The United States is now the only country on the planet not party to the agreement.

Closer to home, embattled Environmental Protection Agency Administrator Scott Pruitt is allowed to continue “serving” despite countless ethical failings, seemingly because he has aggressively advanced Mr. Trump’s know-nothing environmental regulatory rollback. Key Obama-era rules — such as one that would have demanded better vehicle fuel efficiency and another that would have required existing power plants to cut their greenhouse-gas emissions — are on the chopping block, while Mr. Pruitt waters down the EPA’s ability to use peer-reviewed science in its decision-making.

Better leaders will return. Unfortunately, the planet’s systems will not cease changing in the meantime.