March 9, 2013
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.
In Fallen Angels, environmentalists managed to stop the greenhouse emissions and an ice age ensued. Thank goodness they were less effective in real life.
UPDATE: Jim Bennett emails that this may bring new meaning to the term “Carbon Credit:”
If the Fallen Angels scenario becomes proven, perhaps the EPA will start establishing minimum quotas of carbon emissions that must be produced, with extra carbon credits for surplus.