Ice from Mendenhall Glacier spills alongside sediment and rocks in Juneau, Alaska, on Feb. 15. (Becky Bohrer/Associated Press)

“I JUST think we have much bigger risks,” Donald Trump told us last week. We had asked the Republican presidential candidate about human-caused climate change, a phenomenon in which he said he is “not a big believer.” Don’t good business leaders hedge against risks, spending something now to avoid potentially negative outcomes later? “I think our biggest form of climate change we should worry about is nuclear weapons,” he responded.

Mr. Trump is not alone among Republicans in citing other scary problems to illogically ignore the danger of a warming world. Sen. Ted Cruz (Tex.) and Ohio Gov. John Kasich both mention terrorism — “the real problem that faces us today,” Mr. Kasich said — when criticizing President Obama’s efforts to slow climate change.

Meanwhile, in the world of facts, evidence and science, the dangers of climate change look ever more frightening.

The latest news comes courtesy of a shocking paper in the journal Nature about how Antarctic ice sheets might respond to warmer air and ocean temperatures. Scientists from the University of Massachusetts at Amherst and Pennsylvania State University examined previous eras in which the planet was only a bit warmer yet seas were much higher. Previous modeling did not match these foreboding historical phenomena, so the scientists used insights into the physics of how the continent’s massive ice formations melt to improve the models. The result is downright scary: “Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 15 metres by 2500, if emissions continue unabated.” With that additional melting from Antarctica, seas could rise some 6 feet by 2100. This would result in humanitarian catastrophe, swamping coastal cities all over the world and forcing massive inland migrations.

In separate research, highlighted last week by The Post’s Chris Mooney, scientists found strong evidence that a layer of permafrost across the frozen north is thawing, which could lead to massive stocks of organic matter breaking down, which would release more planet-warming greenhouse emissions. This feedback loop could significantly worsen global warming over time.

Perhaps warmer Arctic temperatures will also lead to large-scale plant growth, canceling out some of the greenhouse gases emitted during the thaw? A group of researchers asked 98 experts on the Arctic about this possibility, and the results were not encouraging. Models predicting large offsetting effects, for example, failed to account for changes in the region’s water resources. All in all, the chance that the Arctic will become an increasingly large source of greenhouse emissions this century appears to be significant, if humanity does not act to arrest warming.

The interlocking effects of the Earth’s various systems remain complex and difficult to predict. What is beyond question is that we face significant risk. The prudent response would be to mitigate the threat, instead of waiting to discover that scientists’ warnings were on target — or even understated — after the damage has been done.