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A New, much Longer Version of the Hockey Stick

March 7, 2013; 6:08 PM ET

Scientists from Oregon State University (OSU) and Harvard university have been able to reconstruct the Earth's temperature history going back to the end of the last ice age and have determined that the Earth is warmer today than 70-80 percent of the entire period going back 11,300 years.

Below image courtesy of Science/AAAS

Previous studies on past global temperature change mostly focused on the last 2,000 years from tree ring data.

This study was recently posted in the journal Science.

The OSU/Harvard team used fossilized ocean shell data from 73 sites across the globe to construct the long-term temperature trend.

Over the past 5,000 years, the Earth on average cooled 1.3 degrees F. until the last 100 years when it warmed 1.3 degrees F. The largest increase was in the northern hemisphere where there is much more land and human population compared to the southern hemisphere.

Key excerpts from the EurekAlert report on the study....

"When you just look at one part of the world, the temperature history can be affected by regional climate processes like El Niño or monsoon variations," noted Peter Clark, an OSU paleoclimatologist and co-author of the study. "But when you combine the data from sites all around the world, you can average out those regional anomalies and get a clear sense of the Earth's global temperature history."

Over the past 5,000 years, the Earth on average cooled about 1.3 degrees (Fahrenheit) - until the past 100 years, when it warmed ̴ 1.3 degrees (F). The largest changes were in the northern hemisphere, where there are more land masses and greater human populations.

"During the warmest period of the Holocene, the Earth was positioned such that Northern Hemisphere summers warmed more," said lead author Shaun Marcott, a post-doctoral researcher in Oregon State's College of Earth, Ocean, and Atmospheric Sciences. "As the Earth's orientation changed, Northern Hemisphere summers became cooler, and we should now be near the bottom of this long-term cooling trend - but obviously, we are not."

"The Earth's climate is complex and responds to multiple forcings, including CO2 and solar insolation," Marcott said. "Both of those changed very slowly over the past 11,000 years. But in the last 100 years, the increase in CO2 through increased emissions from human activities has been significant. It is the only variable that can best explain the rapid increase in global temperatures."

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