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Let's look a little more closely at the evidence that the climate has warmed up over the past century. Warming cycles have happened before but climate scientists want to know more about how this current trend is different. Now a research team says they have some answers. They've put together a record of global temperatures going back to the end of the last ice age, about 11,000 years ago. As NPR's Christopher Joyce reports, their study confirms that what we are seeing now is unprecedented.

CHRISTOPHER JOYCE, BYLINE: Climate scientists are, in a sense, time travelers. They peer into the past. Ice cores from polar regions show what temperatures were over hundreds of thousands of years - but only for those regions, not the whole planet. Tree rings give a more global record of temperatures, but only back about 2,000 years. Now a team from Oregon State University and Harvard has done something new. They've got a global temperature record back to the last ice age, when mammoths and saber-tooth cats roamed the planet. Geologist Shaun Marcott says what they found is...

SHAUN MARCOTT: Global temperatures are warmer than about 75 percent of anything we've seen over the last 11,000 years or so.

JOYCE: The other way to look at it is 25 percent of the time since the last ice age it's been warmer than now. So what's to worry about, you might think. But Marcott, who's at Oregon State University, says the record shows just how unusual our current warming is.

MARCOTT: It's really the rates of change here that's amazing and atypical.

It's warming up super-fast. Here's what happened before. After the end of the Ice Age, the planet got warmer. Then about 5,000 years ago it started to get cooler - but really slowly. In all, it cooled 1.3 degrees Fahrenheit, up until the last century or so. Then the temperature shot up.

Temperatures now have gone from that cold period to the warm period in just 100 years.

JOYCE: That's right. It's taken just 100 years for the average temperature to change by 1.3 degrees, when it took 5,000 years to do that before. The research team tracks temperature by studying chemicals in the shells of tiny fossilized sea creatures called foraminifera. Their temperature record matches other techniques that look back 2,000 years, which supports the validity of their much longer record. Climate scientists predict the current warming will continue, given the amount of greenhouse gases going up into the atmosphere. Gavin Schmidt is at NASA's Goddard Institute of Space Studies.

GAVIN SCHMIDT: So the climate changes to come are going to be larger than anything that human civilization and agriculture has seen in its entire existence. And that is quite a sobering thought.

JOYCE: The research appears in the journal Science. Christopher Joyce, NPR News.

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