Ashley Ballantyne at the University of Colorado, Boulder, and colleagues analysed 4-million-year-old Pliocene peat samples from Ellesmere Island in the Arctic archipelago to find out what the climate was like when the peat formed.
At that time, CO2 levels are thought to have been close to current levels – around 390 parts per million – but global temperatures were around 2 to 3 °C warmer than today. It was the last warm period before the onset of the Pleistocene glaciation, and is used by climate researchers as a model for our future climate.
Previous studies using computer models have suggested that the Pliocene Arctic was also warmer than it is today – up to 10 °C warmer. A little warming can trigger a lot more in the Arctic because the loss of light-reflecting sea ice and the spread of plants across the land increase the amount of solar energy that is absorbed.
Ballantyne's team estimated the temperature of the period at which the peat formed by measuring three things that are affected by temperature: the concentration of various chemical compounds, levels of a certain isotope in tree rings and the amount and types of fossilised vegetation.
The group's analysis suggests the samples formed when average local temperatures were about -0.5 °C. That is 19 °C warmer than temperatures today – more than the previous computer models had estimated.
"These results should be alarming," says Ballantyne. Although it could take centuries for current global temperatures to respond to rising CO2 levels, we can expect the Arctic to warm much more than the rest of the planet, he says.
Polistra was named after the original townsite of Manhattan (the one in Kansas). When I was growing up in Manhattan, I spent a lot of time exploring by foot, bike, and car. I discovered the ruins of an old mill along Wildcat Creek, and decided (inaccurately) that it was the remains of the original site of Polistra. Accurate or not, I've always liked the name, with its echoes of Poland (an under-appreciated friend of freedom) and stars. ==== The title icon is explained here. ==== Switchover: This 2007 entry marks a sharp change in worldview from neocon to pure populist. ===== The long illustrated story of Polistra's Dream is a time-travel fable, attempting to answer the dangerous revision of New Deal history propagated by Amity Shlaes. The Dream has 8 episodes, linked in a chain from the first. This entry explains the Shlaes connection.