New maps of ancient warming reveal strong response to carbon dioxide | Ars Technica

he warming of the PETM was triggered by a geologically rapid release of CO2, primarily from a convulsion of magma in Earth’s mantle at the place where Iceland is now situated. The magma invaded oil-rich sediments in the North Atlantic, boiling off CO2 and methane. It took an already warm, high-CO2 climate and made it hotter for tens of thousands of years, driving some deep-sea creatures and some tropical plants to extinction. Mammals evolved smaller, and there were big migrations across continents; crocodiles, hippo-like creatures, and palm trees all thrived just 500 miles from the North Pole, and Antarctica was ice-free.

As our climate warms, scientists are increasingly looking at past climates for insights, but they are hampered by uncertainties in temperature, CO2 levels, and the exact timing of changes—prior work on the PETM had temperature uncertainties on the order of 8° to 10° C, for example. Now Tierney’s team has narrowed that uncertainty range to just 2.4° C, showing that the PETM warmed by 5.6° C, a refinement on the previous estimate of approximately 5° C.

“We were really able to narrow that estimate down over previous work,” said Tierney.

The researchers also calculated the CO2 levels before and during the PETM derived from isotopes of boron measured in fossil plankton shells. They found CO2 was about 1,120 ppm just before the PETM, rising to 2,020 ppm at its peak. For comparison, preindustrial CO2 was 280 ppm, and we’re currently at about 418 ppm. The team was able to use these new temperature and CO2 values to calculate how much the planet warmed in response to a doubling of CO2 values, or the “Equilibrium Climate Sensitivity” for the PETM.

New maps of ancient warming reveal strong response to carbon dioxide | Ars Technica