Study: Earth Was Once Hot, CO2-Rich

Sept. 28, 2006 — If humans burn all the fossil fuels available, carbon dioxide and global temperatures could rise to levels not seen since 49 million years ago. In those days, there were tropical crocodiles in Canada.

New research shows that from 49 million to 56 million years ago the atmosphere contained more than 1,125 parts per million (ppm) of the greenhouse gas carbon dioxide (CO₂) — and it was an exceptionally warm time. If humans keep burning fossil fuels, carbon dioxide levels could reach 1,000 ppm, according to some studies.

If the past is any indicator of the future and the climate models are correct, that could make for a drastically different planet than the one we live in today.

"Well into Canada there were palm trees," said Tim Lowenstein of the State University of New York at Binghamton, referring to what's called the early Eocene climatic optimum. Lowenstein and Robert Demicco have published a paper in the Sept. 29 issue of Science reporting their mineral evidence for the ancient carbon dioxide levels.

"The Earth was very different (50 million years ago)," explained Lowenstein. There was no glacial ice on the planet, and places as far north as Sweden and Alaska were tropical.

"It was really warm, and the atmospheric CO₂ was really high," Lowenstein said.

In fact, 1,125 ppm is about four times the 280 ppm carbon dioxide level before the Industrial Revolution, when fossil fuels came into widespread use. Today the level is about 380 ppm, and rising.

The researchers discovered the high carbon dioxide levels in the early Eocene epoch by analyzing carbon-containing minerals that formed in ancient salt lakes. The minerals reflect the amount of carbon in the atmosphere at the time, as well as the water temperatures.

Current carbon dioxide levels cause a mineral called trona to crystallize and drop to the bottom of salt lakes when the temperature exceeds 77 degrees F (25 C). Another mineral, natron, crystallizes at lower temperatures. Yet another, called nahcolite, is rare because it is thought to crystallize only under a very high-carbon dioxide atmosphere.

In the Piceance Creek Basin in Colorado, an almost 1,000-foot-thick layer of nahcolite and halite (table salt) — a deposit left behind by a large salt lake in the early Eocene.

Laboratory experiments show that for those elements to have crystallized at the estimated 68 to 95 degrees F (20-35 C) seasonal temperature range of that latitude in the early Eocene, the atmosphere must have held 1,125 ppm to 2,985 ppm of carbon dioxide.

These new findings underline the conclusions of other researchers who only a week ago reported that Earth's current global temperatures are flirting with million-year records, and that human carbon dioxide emissions are the cause.

"We cannot afford to burn all the fossil fuel," said James Hansen of NASA's Goddard Institute of Space Studies. "We have to start now," he said of cutting back on fossil fuel use and carbon emissions. "We had better start this decade."