Prior reconstructions have gone back further — in some cases back to 3 million years — but were less comprehensive or focused only on particular time periods. As part of her doctoral dissertation at Stanford University, Carolyn Snyder , now a climate policy official at the U.S. Environmental Protection Agency, created a continuous 2 million year temperature record, much longer than a previous 22,000 year record. “People can take this and improve upon it as more records become available in the future.”

Using a subset of the reconstructed temperature data, Snyder, who began the study while at Stanford University in Palo Alto, California, analysed the relationship between past temperatures and carbon dioxide (CO 2 ) levels estimated from Antarctic ice cores covering the past 800,000 years. But many of the same scientists said Snyder's estimate of future warming seems too high. But he adds that the question of how the planet will respond to atmospheric CO 2 over the long term requires more detailed analysis. In particular, the study fails to account for subtle changes in Earth’s orbit that affected global temperatures and helped to drive the expansion and retreat of glaciers throughout the time period covered by the analysis, says Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies in New York City. Credit: NASA

A new study paints a picture of an Earth that is warmer than it has been in about 120,000 years, and is locked into eventually hitting its hottest mark in more than 2 million years. The Intergovernmental Panel on Climate Change estimates that short-term climate sensitivity is around 3 °C of warming for a doubling of atmospheric CO 2 3. If that relationship were to hold up, it would suggest that the Earth is in store for even more warming in the future. Past and future polar amplification of climate change: climate model intercomparisons and ice-core constraints . “This is something that just needed to be done,” Shakun says.
A study published in Nature finds the Earth's surface is warmer than it has been in about 120,000 years, and is locked into eventually hitting its hottest mark in more than 2 million years.