SCIENTISTS HAVE a good sense of what the Earth’s climate has been like over the past handful of centuries. But what about many thousands of years back? In a recent article in the journal Science, researchers at Oregon State University and Harvard explained how they used marine fossils to piece together a rough temperature record going back 11,300 years to the most recent ice age. That record indicates that the Earth warmed as it emerged from the ice age, followed by a long-term cooling trend. The cooling continued until the industrial revolution, when humans began burning fossil fuels in earnest — and pumping heat-trapping greenhouse gases such as carbon dioxide into the atmosphere. Then the temperature spiked. With the amount of carbon dioxide already in the atmosphere, models suggest, the Earth’s average temperature in 2100 will surpass that detectable in any of the millennia studied.
The most dramatic implication of the study is not the magnitude of the current warming but its extremely rapid pace.
With data from 73 ice and sediment core monitoring sites around the world, scientists have reconstructed Earth's temperature history back to the end of the last Ice Age. The analysis reveals that the planet today is warmer than it's been during 70 to 80 percent of the last 11,300 years. Results of the study, by researchers at Oregon State University (OSU) and Harvard University, are published this week in a paper in the journal Science. Lead paper author Shaun Marcott of OSU says that previous research on past global temperature change has largely focused on the last 2,000 years. Extending the reconstruction of global temperatures back to the end of the last Ice Age puts today's climate into a larger context.
"We already knew that on a global scale, Earth is warmer today than it was over much of the past 2,000 years," Marcott says. "Now we know that it is warmer than most of the past 11,300 years."
"The last century stands out as the anomaly in this record of global temperature since the end of the last ice age," says Candace Major, program director in the National Science Foundation's (NSF) Division of Ocean Sciences...
"This research shows that we've experienced almost the same range of temperature change since the beginning of the industrial revolution," says Major, "as over the previous 11,000 years of Earth history--but this change happened a lot more quickly."
Of concern are projections of global temperature for the year 2100, when climate models evaluated by the Intergovernmental Panel on Climate Change show that temperatures will exceed the warmest temperatures during the 11,300-year period known as the Holocene under all plausible greenhouse gas emission scenarios.