A team of scientists has nailed down the average global temperature at the peak of the last ice age, a time known as the Last Glacial Maximum, to about 46 degrees Fahrenheit (8 degrees Celsius). The research helps climate scientists to better understand today's relationship between rising atmospheric levels of carbon dioxide—a major greenhouse gas—and warming temperatures.

The Last Glacial Maximum, which occurred about 20,000 years ago, was a frigid period when glaciers covered large parts of the world's land surface and plants and animals thrived if they were adapted to the cold. The new study shows that temperatures at the time averaged 11°F (6°C) cooler than the present day.

The research also provides an important data point for scientists using the latest generation of global climate models. It indicates that, for every doubling of carbon dioxide in the atmosphere, average global temperature can be expected to increase by 3.4°C (6.1°F). That's in the middle of the range predicted by the latest generation of climate models (1.8°-5.6°C).

"Knowing precisely the global temperature in the Last Glacial Maximum is very important for us to understand how the climate system responds to changes in atmospheric carbon dioxide, as well as to evaluate how well the climate models match the real-world data," said Jiang Zhu, a scientist at the National Center for Atmospheric Research (NCAR) and co-author of the study.

The scientists used the NCAR-based Community Earth System Model, which offers the capability of simulating water isotopes.This enabled them to directly combine fossil data about past temperatures with climate model simulations and to create maps that showed how temperatures varied in specific regions around the globe.

The study, led by Jessica Tierney of the University of Arizona, was published this week in Nature. For more, see the University of Arizona news release.

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