In this November 2016 photo provided by ARC Center of Excellence for Coral Reef Studies, dead staghorn coral killed by bleaching appears drab on the northern Great Barrier Reef, Australia. (Greg Torda/ASSOCIATED PRESS)

THE MEASURED warming of the planet is not hypothetical. Nor are its effects, which are happening now, not decades from now. An ecological catastrophe is unfolding off Australia’s coast: Humans are killing the Great Barrier Reef, one of the world’s greatest natural wonders, and there’s nothing Australians on their own can do about it. We are all responsible.

An ocean water temperature spike last year caused a massive “bleaching” event, in which colorful corals turned an antiseptic, sickly white. Scientists believe that the reef will never be the same.

“The chances of the northern Great Barrier Reef returning to its pre-bleaching assemblage structure are slim given the scale of damage that occurred in 2016 and the likelihood of a fourth bleaching event occurring within the next decade or two as global temperatures continue to rise,” a major new study in the journal Nature reported last week.

Alarmingly, but perhaps not surprisingly, the Australian government reports that sections of the reef are getting slammed again this year.

Corals are polyp creatures that build their iconic limestone structures in cooperation with photosynthesizing algae. When ocean temperatures increase, the algae emit poisons. The corals then reject their symbiotic partners and succumb to disease and death. This occurred across a vast section of the northern Great Barrier Reef last year.

Under normal conditions, corals can often recover from big bleaching shocks, but conditions are no longer normal. Higher background ocean temperatures mean that dangerous spikes are more likely. Corals decades of years old may be replaced by “weedier,” faster-growing species — or by none at all.

There is little doubt that temperature is the culprit. Reefs far away from human runoff and other local risks are suffering. Corals in pristine water bleached just like those in dirty water. The Nature study quantified a relationship between exposure to warm water and the severity of observed bleaching.

“Immediate global action to curb future warming is essential to secure a future for coral reefs,” the study warned. “Water quality and fishing pressure had minimal effect on the unprecedented bleaching in 2016, suggesting that local protection of reefs affords little or no resistance to extreme heat. Similarly, past exposure to bleaching in 1998 and 2002 did not lessen the severity of bleaching in 2016.”

Also last week, the Trump administration proposed deep cuts for the Environmental Protection Agency, singling out climate programs, as well as the National Oceanic and Atmospheric Administration, which monitors Earth’s seas and skies. President Trump also began what will no doubt be a broad rollback of Obama administration climate rules. Meanwhile, the president is still thinking about pulling the country out of the landmark Paris climate deal, which took decades to strike. The administration has offered no sense that it has any alternative emissions-cutting strategy in mind.

In the long run, the planet will change enough — hurting enough people in the process — that even Republicans will have to admit the issue must be addressed. The question is what price the nation and the world will pay, in dollars, lives and ecological catastrophe, because our leaders were negligent in the meantime.