Ancient Global Warming Episode Holds Clues To Future Climate

Over millions of years, these materials pile up and build climate archives that tell stories about Earth's history. Today, scientists recover those archives during ocean drilling expeditions aboard research vessels such as the JOIDES Resolution (see Figure).

Now a team of scientists, led by Richard Zeebe of the University of Hawai'i at Manoa's School of Ocean and Earth Science and Technology, has examined data from sediment cores from around the world to study an ancient global warming episode, known as the Paleocene-Eocene Thermal Maximum. This warming event occurred about 55 million years ago and provides important clues about what the future may hold. By studying the past, the researchers contribute to better forecasting the future – a principle once expressed by the English historian Edward Gibbon: "I know no way of judging of the future but by the past."

There is little doubt among scientists that the Earth is warming because of carbon dioxide emissions from human activities. But exactly how much the Earth will warm – say until the end of the 21st century – is still uncertain. In their study published in the journal Nature Geoscience, Zeebe and his team help to resolve the question by studying a possible analog in the past. Using sediment archives and theoretical tools, they provide estimates of the amount of carbon dioxide in the atmosphere during the warming episode 55 million years ago.

The team had to go back that far in time because this event may be the only one during the past 55 million years of similar scale and pace as the current human disruption. At that time, global surface temperatures rose by 5