Wednesday, December 05, 2007
Deep history underfoot -- Part 2
If you followed my snowflake reflection yesterday, then the graph above -- from Maureen's web page -- will make a bit of sense. The bigger the number for oxygen-18 percentage in benthic (ocean-floor) sediments, the more ice on the continents. A warmer Earth is up; a cooler Earth is down. Click to enlarge.
You can see that the Earth began cooling significantly about 3 million years ago. For the past million years or so the climate has dipped in temperature every 100,000 years -- the ice ages. We are in a warmer, interglacial period now.
The 100,000-year cycle is well understood. It correlates with precisely calculable "wobbles" in the Earth's orbit that affect how much solar energy falls upon the planet's surface.
All other things being equal, we are sure to drop back into another ice age, with glaciers creeping down across the northern continents. But all things aren't equal. Human technology has the power to overwhelm the astronomical cycle and send the curve climbing back toward the top of the graph. Anthropogenic global warming.
But what set the whole thing cooling about 3 million years ago? There are various theories. One theory that has strong support is the "mountain uplift hypothesis," for which Maureen can take much of the credit. Mountain building means mountain weathering -- mountains go up, rain and erosion takes them down. The chemistry of rock weathering takes carbon dioxide out of the atmosphere. Carbon dioxide is a green house gas. Less CO2 in the air means less trapped solar energy and a cooler Earth.
The Himalayas rise, the Earth cools.
Of course, it takes a lot of planet-wide research to put it all together.
Drifting continents, mountains in Asia, ice in Canada, isotopic ratios on the ocean floor: All connected in one grand system into which a single species of life on Earth as become a planet-transforming geological force. We are clever enough to figure it out. Will we be clever enough to manage our interventions?
At least one of the leading candidates for president of the US believes the Earth is less than 6000 years old and that the end of the world is imminent. That doesn't bode well for American leadership in climate research and action.