The end of the world as we may know it

Opinion editor's note: Editorials represent the opinions of the Star Tribune Editorial Board, which operates independently from the newsroom.

•••

It's bad enough to know that the world will one day come to an end. Those of us who are prone to worry about such things have grown accustomed to the idea that, in the far future, our sun would expand beyond Earth's orbit. That eventuality, thought to be 7 billion or so years off, was comfortably remote; surely by that time our descendants would be living in colonies on other planets, and the Vikings might have won the Super Bowl once or twice.

But now comes word that our species — and others, too — may be gone long before the sun gets around to swallowing our planet. A team of scientists in England has calculated that the class of animals known as mammals — including us — may have used up about half of its time on Earth. After 225 million years of bearing fur (or hair) and producing milk for our young, we could now be at the beginning of our long downward slide to extinction.

The likely culprit in our demise? Global warming, of course — but to a degree that would make our current climate struggles seem quaint.

The scientists suggest that, 250 million years from now, tectonic forces will return the continents to their former, single land mass. The land will have a vast interior far away from the worldwide ocean and thus be more susceptible to extreme heat. Not only that, by then the sun will actually be producing more energy. That will speed evaporation, putting more water vapor into the atmosphere, which in turn will trap more heat.

It won't mean the end of all life on Earth, or at least not necessarily. Just that land areas will be too hot to sustain the human lifestyle. Reptiles might do better.

So there's hope — but no reason to be overconfident. After all, existential threats are a more or less constant feature of our environment. Bennu, the asteroid from which NASA has just returned a sample, might strike earth in 2182. The Doomsday Clock maintained by the Bulletin of the Atomic Scientists stands at 90 seconds to midnight, suggesting that nuclear Armageddon is closer than it has ever been.

Any number of short-term crises could snowball into extinction events, but they are avoidable. Or they may be avoidable. At least, it's wise to think so.

"Answer me one question," demands Ebenezer Scrooge in Charles Dickens' classic "A Christmas Carol." "Are these the shadows of the things that Will be, or are they shadows of the things that May be, only?"

"Still the Ghost pointed downward to the grave by which it stood," wrote Dickens.