Carbon Dioxide and Climate

While I'm on the subject of odd objections, LM, in the comments, said CO2 is "irrelevant." Now while that wouldn't sound too strange coming from a young Earth creationist, it is genuinely weird coming from somebody supposedly educated in physics. Not quite G&T strange (see previous post), but damn strange, since CO2 is clearly one of the principle actors in Earth's climate, not to mention the climates of the other planets. The misnamed greenhouse effect was discovered by the mathematician and physicist Fourier almost 200 years ago, but didn't create much of a stir for quite some time.

Maybe the first big caution signal was sounded when the hellish temperatures at the surface of Venus were discovered. That was a big surprise, since Venus is such shiny planet that it absorbs less sunlight than Earth, despite being only about 2/3 as far from the Sun. When it was realized that it was the greenhouse effect of thick carbon dioxide atmosphere of Venus that was responsible, greenhouse effects were studied everywhere. Mars and Earth, with much less CO2 in the atmosphere, also exhibit substantial effects, though in the case of Earth, water vapor is the biggest player.

Astronomy and geology cooperate to give us the next big clue to the centrality of CO2 in our climate history. The young Sun was a lot dimmer than its present self. Replace our present Sun with it and our planet would promptly freeze solid, but in fact, our young planet had lots of running water. How could this be? The present oxygen rich atmosphere is a relatively new invention, on Earth - "only" six hundred or so million years old. In the earliest Earth, much of the oxygen was locked up in CO2, and it provided enough of a greenhouse effect to keep the oceans liquid.

These are only two of the many threads which confirm that CO2 and the carbon cycle have played a pivotal role in the world's climate history. Over the long run CO2 is a regulator of climate, with a strong negative feedback, but that long run is millions of years. In the short run, its feedback is opposite.

CO2 will mostly be a bystander in the planet's finale, though. Eventually, the Earth's ability to sequester CO2 will be overcome by the increasingly hot Sun. At that point, the oceans evaporate and the atmosphere becomes too hot for rain to form. Water vapor is ionized into hydrogen and oxygen and the hydrogen is lost to space. The oxygen will combine to form CO2 and other gases and Earth will become another Venus like furnace. With luck, we should have another billion years or so.