The keys to understanding future climate change may be locked in rocks and sediments that act as records of conditions millions or billions of years ago, the National Academy of Sciences said yesterday.

Without steep cuts to the world's greenhouse gas output, the amount of carbon dioxide in the atmosphere could soar by the end of the century to a level not seen for 34 million years.

Understanding how that would affect the climate will require going beyond historical records of climate change, or even the information encoded in tree rings or ice cores, to what scientists call "deep time" records of conditions on Earth, according to a new NAS analysis.

"It is our only window into how our Earth system operates in a high-CO2 world," said Isabel Montañez, a paleoclimatologist at the University of California, Davis, who led the committee that wrote the report. "We are there already. We haven't seen these levels since, minimally, 3.5 million years ago. ... It is really a matter of time until the climate changes dramatically."

Examining "deep time" records in rocks and sediments would help scientists understand how fast and how extensive future changes might be, Montañez said. The analysis recommends a concerted international effort to drill sediment cores in the ocean and on land to reconstruct climatic conditions ranging back millions of years.

Climate change speeding up the clock
Making a concerted effort to expand the "deep time" climate record is especially important because climate models have been constructed and refined using information on conditions over the past several hundred years, the report says.

"As Earth continues to warm, it may be approaching a critical climate threshold beyond which rapid and potentially permanent -- at least on a human time-scale -- changes not anticipated by climate models tuned to modern conditions may occur," the report says.

Those changes may include the loss of Arctic summer sea ice, the collapse of ice sheets in Greenland and western Antarctica, dieback of the Amazon rainforest and changes in the jet stream and the pattern of El Niño and La Niña weather cycles.

Montañez said that scientists are concerned that some aspects of the climate behave very differently in a high-CO2 world.

"We see processes that operate in the climate system that either don't operate in glacial times we've seen in the last 2 million years, or they operate very differently," she said, citing the behavior of ice sheets as an example.

"We tend to think that ice sheets will melt or respond to increases in temperature on hundreds- or thousands-of-year time scales," Montañez said. But in a high-CO2 world, that response -- increased melting or even collapse -- could occur in a matter of decades.

The National Science Foundation, the U.S. Geological Survey and Chevron Corp. sponsored the report.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500