ClimateWire: Scientists trying to determine how the Earth might change as temperatures rise often look back in time to a period around 3.6 million years ago called the middle Pliocene, when concentrations of carbon dioxide ranged from about 380 to 450 parts per million. (Today they are nearing 400.)
A study published yesterday in the journal Science analyzed the longest land-based sediment core ever taken in the Arctic and found that during this period, from 3.6 million to 2.2 million years ago, the area around...