Research published in Nature explores the origins of the Antarctic ice sheet during the Oligocene transition, 33.5 to 34 million years ago. The formation of the sheet was apparently triggered by a drop in the atmospheric concentration of carbon dioxide (CO2) below a critical level. The researchers were able to estimate CO2 levels in this time period by examining boron isotope rations in fossils from Tanzania, an approach that was necessary since it is not possible to go so far back on the basis of data from ice core samples. The researchers estimate that the CO2 concentration during this transition period was about 760 parts per million (ppm). That is about twice the level of current atmospheric CO2 concentrations. If the world carries along on its current trajectory of greenhouse gas emissions, the atmospheric concentration of CO2 will be above 1000ppm by 2100.
The operation of the global climate is highly complex, with many significant inputs and internal feedbacks. The researchers specify that the ice sheet displays “a nonlinear response to climate forcing during melting.” Nonetheless, it is worrisome to think that we are on track to exceed the atmospheric CO2 concentration at which the Antarctic ice sheet started to form, and do so well before the end of this century. That being said, even if we do push the climate into a state where the serious or total melting of Antarctica becomes an inevitability, the process may take hundreds or thousands of years to occur. Such long-term impacts seriously complicate economical and ethical analysis of climate change.