June 01, 2015
In the long run . . .
. . . we're all dead, as John Maynard Keynes famously observed. And by "we," I mean "everybody." When the Sun enters its red giant phase, this planet and everything on it will be vaporized.
Don't panic: that won't happen for 7.5 billion years. The problem is, the Sun is a fusion furnace and it's slowly but certainly running out of its primary fuel, hydrogen. As it does, the core shrinks a little and heats up a little.
In turn, the Earth's orbit widens a little. It all balances out--until it doesn't. Solar luminosity has been growing about 10 percent every billion years. But once helium fusion commences, the Sun will get way too hot way too fast.
|Courtesy Wikipedia Commons.|
Life will get uncomfortably warm long before that, in only a few hundred million years. Ironically, what will probably kill us first is the lack of carbon dioxide in the atmosphere.
That's right. Too little carbon dioxide. As plate tectonics slows down and the Sun heats up, continental erosion and ocean evaporation will accelerate carbonate formation, locking away more and more carbon dioxide.
So as the Sun slowly brightens, carbon dioxide is sequestered into limestone. Some 600 to 800 million years from now, atmospheric carbon dioxide concentrations should fall below 10 parts per million, a threshold where plants can no longer photosynthesize. This process might wipe out plants and the animals that depend on them.
Including us. Not to mention that no more green plants means no more oxygen. So forget about breathing. But hey, we've got a half-billion years to go! For once, we can definitely call it somebody's else's problem.