From the New York Times, an interesting concession from researchers that claim the world is at its hottest in the past 4,000 years. (The fact that Michael Mann seems supportive of the overall findings should give you pause, though, given his links to blacklisting scientists that disagreed with global warming, and credible allegations that he manufactured the infamous "hockey stick" graph). Anyway, from the article:
Though the paper is the most complete reconstruction of global temperature, it is roughly consistent with previous work on a regional scale. It suggests that changes in the amount and distribution of incoming sunlight, caused by wobbles in the earth’s orbit, contributed to a sharp temperature rise in the early Holocene.
The climate then stabilized at relatively warm temperatures about 10,000 years ago, hitting a plateau that lasted for roughly 5,000 years, the paper shows. After that, shifts of incoming sunshine prompted a long, slow cooling trend.
The cooling was interrupted, at least in the Northern Hemisphere, by a fairly brief spike during the Middle Ages, known as the Medieval Warm Period. (It was then that the Vikings settled Greenland, dying out there when the climate cooled again.)
Scientists say that if natural factors were still governing the climate, the Northern Hemisphere would probably be destined to freeze over again in several thousand years. “We were on this downward slope, presumably going back toward another ice age,” Dr. Marcott said.
Instead, scientists believe the enormous increase in greenhouse gases caused by industrialization will almost certainly prevent that.