Weather Wise

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A BIG sigh of relief all round a few days ago, when it was announced that we would not, after all, be having a close encounter of the most unpleasant kind in October 2028.

But what would have happened if asteroid 1997XF11 had hit the Earth? This is not idle speculation. An object a few times larger than XF11 slammed into what is now Mexico only 65 million years ago, and managed to wipe out not only the dinosaurs, but pretty well all land animals larger than a labrador. This will happen again, sooner or later.

A major asteroid strike would throw a large spanner into the delicate workings of our climate. If it hit the ocean, a lump of space debris a mile across would be able to punch a hole clean into the sea floor, liquefying it. Shockwaves would generate huge tsunami, killing millions. Clouds of steam would be released into the upper atmosphere.

Water vapour is a powerful greenhouse gas, and it might be expected that the catastrophe could lead to runaway global warming. In fact, it would probably be more likely to cause something akin to a "nuclear winter", as the sunlight was blocked by planet-wide haze.

A land strike would be little better. Huge quantities of dust would be thrown into the stratosphere, blocking the sunlight for decades and causing global cooling. It is probably this that did for the dinosaurs.

It would be wise not to throw away all our nuclear bombs (our only realistic hope of deflecting one of these space monsters) just yet.