Hayhoe: "We have, through human emissions of carbon dioxide and other heat-trapping gases, indefinitely delayed the onset of the next ice age and are now heading into an unknown future where humans control the thermostat of the planet"

Seth Borenstein:  Recent heat spike unlike anything in 11,000 years

WASHINGTON (AP) — A new study looking at 11,000 years of climate temperatures shows the world in the middle of a dramatic U-turn, lurching from near-record cooling to a heat spike.
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Marcott's data indicates that it took 4,000 years for the world to warm about 1.25 degrees from the end of the ice age to about 7,000 years ago. The same fossil-based data suggest a similar level of warming occurring in just one generation: from the 1920s to the 1940s. Actual thermometer records don't show the rise from the 1920s to the 1940s was quite that big and Marcott said for such recent time periods it is better to use actual thermometer readings than his proxies.
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The study shows the recent heat spike "has no precedent as far back as we can go with any confidence, 11,000 years arguably," said Pennsylvania State University professor Michael Mann, who wrote the original hockey stick study but wasn't part of this research. He said scientists may have to go back 125,000 years to find warmer temperatures potentially rivaling today's.

However, another outside scientist, Jeff Severinghaus of the Scripps Institution of Oceanography thinks temperatures may have been notably warmer just 12,000 years ago, at least in Greenland based on research by some of his colleagues.
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Marcott said the general downward trend of temperatures that reversed 100 years ago seemed to indicate the Earth was heading either toward another ice age or little ice age from about 1550 to 1850. Or it was continuing to cool naturally until greenhouse gases from the burning of fossil fuels changed everything.
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"We have, through human emissions of carbon dioxide and other heat-trapping gases, indefinitely delayed the onset of the next ice age and are now heading into an unknown future where humans control the thermostat of the planet," said Katharine Hayhoe, an atmospheric scientist at Texas Tech University, responding in an email.