Climate change is a serious threat to human society. But even the most extreme worst-case future scenario wouldn't wipe out humanity instantly. There's only one thing that might do that — a major asteroid or comet impact.
Big asteroid strikes are very rare, of course, but if one were to come along, we would all be dead in a matter of months — and while a small one wouldn't be so bad, it could still cause devastating losses. It sounds a bit silly, but there is a very strong case for the American government to set up a planetary asteroid defense system. It wouldn't cost much — just a few satellites and telescopes to keep track of all potential threats, and developing some collision or gravity-based techniques to deflect them if necessary.
The New Yorker recently published a fascinating profile of a paleontologist named Robert DePalma who has discovered what appears to be fossils of animals who died in the Cretaceous-Paleogene extinction event. It has been widely accepted that a big asteroid impact in Mexico probably caused the extinction, but until DePalma's discoveries in the Hell Creek Formation in North Dakota, nobody had found dinosaur fossils very close to the Cretaceous-Paleogene geological boundary layer (suggesting that perhaps they died out earlier than the impact). If DePalma is right, it will be a landmark finding for the field.
Pretty cool science! But the article also has a harrowing description of what happened when the Chicxulub impactor (a comet or asteroid, perhaps 11-81 kilometers wide) smashed into the Yucatan Peninsula 66 million years ago, creating a crater 93 miles in diameter. First came fire, as the kinetic energy released by the impact scorched everything in a 1,500-mile radius, and red-hot ejecta landed all around the world. Continent-wide firestorms burned up about 70 percent of all the world's forests, and huge tsunamis tore up the Gulf of Mexico. Then it got a lot worse:
The dust and soot from the impact and the conflagrations prevented all sunlight from reaching the planet’s surface for months. Photosynthesis all but stopped, killing most of the plant life, extinguishing the phytoplankton in the oceans, and causing the amount of oxygen in the atmosphere to plummet. After the fires died down, Earth plunged into a period of cold, perhaps even a deep freeze. Earth’s two essential food chains, in the sea and on land, collapsed. About 75 percent of all species went extinct. More than 99.9999 per cent of all living organisms on Earth died, and the carbon cycle came to a halt. [The New Yorker]
Big land animals fared particularly poorly — virtually everything weighing more than 5 kilograms was wiped out. Mammals at that time were mostly small, so the ones that survived were able to evolve into larger species after the ecosystem began to recover.
In the history of our planet, that's almost as bad as it gets (only the Permian-Triassic extinction was worse). But it's worth noting that even a small asteroid can cause enormous damage. In 2013, one only about 66-feet wide exploded in the sky near Chelyabinsk Oblast in Russia, shattering windows across the city and causing about 1,500 injuries. The explosion was as powerful as a large nuclear weapon — a direct hit on a major city would have killed millions.
So what do we do? The first thing is to track and record all the near-Earth objects, which is already underway with many projects across the globe and in space. Years ago, Congress required NASA to track 90 percent of objects one kilometer and over, which was accomplished as of 2011 — but smaller ones are still being racked up by the thousands. All told, nearly 20,000 near-Earth objects have been found at time of writing. Meanwhile, NASA's Jet Propulsion Laboratory has an automated system to detect which objects are a threat.
Then once every threatening object is tracked, we just need a way to deflect them. Laser light might exert enough pressure if it was caught early enough, as you'd only have to change the trajectory by a tiny bit. (This calls for extreme accuracy, as you don't want to accidentally deflect something into the planet.) You could accomplish the same thing with a probe's gravity — or you could crash the probe into it at high speed. Indeed, NASA is planning to launch a test probe for just this purpose in 2020 or 2021.
All the ingredients are there. But there is a distinct lack of urgency here. The best way to view asteroids and comets is with a space telescope. But NASA is using a repurposed old one that was meant to be turned off in 2011, and canceled their funding of a different one in 2015. If planetary defense were treated with the urgency it clearly requires, we wouldn't be screwing around with elderly equipment that was designed for a different purpose, or testing just one method of asteroid deflection every few years. We'd be doing it all as fast as possible.
Luckily, a fresh telescope or three, and full-throttle research on all deflection techniques would only take a few hundred million dollars in total — much less than the $2.5 billion President Trump wants to spend on his goofy "Space Force" alone. It's simply a matter of responsible government.