Scientific American: Scientists can study Earth's climate as far back as 800,000 years by drilling core samples from deep underneath the ice sheets of Greenland and Antarctica. Detailed information on air temperature and CO2 levels is trapped in these specimens. Current polar records show an intimate connection between atmospheric carbon dioxide and temperature in the natural world. In essence, when one goes up, the other one follows.
There is, however, still a degree of uncertainty about which came first--a spike...