We're Screwed: 11,000 Years' Worth of Climate Data
Prove It
The Atlantic
3 MAR 9 2013
New research takes the deepest dive ever into historic climate records.

Average global temperature over the last ~2,000 years. Note the massive
uptick on the far right side. (Science)
Back in 1999 Penn State climate scientist Michael Mann released the climate
change movement's most potent symbol: The "hockey stick," a line graph of
global temperature over the last 1,500 years that shows an unmistakable,
massive uptick in the twentieth century when humans began to dump large
amounts of greenhouse gases into the atmosphere. It's among the most
compelling bits of proof out there that human beings are behind global
warming, and as such has become a target on Mann's back for climate
denialists looking to draw a bead on scientists.

Now it's gotten a makeover: A study published in Science reconstructs global
temperatures further back than ever before -- a full 11,300 years. The new
analysis finds that the only problem with Mann's hockey stick was that its
handle was about 9,000 years too short.

Marcott's team used ocean records to reconstruct global climate further back
in time than ever before. (Science)
To be clear, the study finds that temperatures in about a fifth of this historical
period were higher than they are today. But the key, said lead author Shaun
Marcott of Oregon State University, is that temperatures are shooting
through the roof faster than we've ever seen.

"What we found is that temperatures increased in the last hundred years as
much as they had cooled in the last six or seven thousand," he said. "In
other words, the rate of change is much greater than anything we've seen in
the whole Holocene," referring to the current geologic time period, which
began around 11,500 years ago.

Previous historic climate reconstructions typically extended no further back
than 2,000 years, roughly as far back as you can go by examining climate
indicators from tree rings, as Mann did. To dig even deeper, Marcott's team
looked at objects collected from more than 70 sites worldwide, primarily
fossilized ocean shells that have been unearthed by oceanographers.
Existing research has shown that certain chemical tracers in the shells link
directly to temperature at the time they were created; by studying oxygen
isotopes in the fossilized plankton shown below, for example, scientists can
deduce that it formed its shell at a time when Greenland was fully without ice.
Marcott's task was to compile enough such samples to represent the whole
planet over his chosen timeframe.

Fossilized ocean organisms like this plankton, the size of a grain of sand,
keep a chemical snapshot of the climate at the time they first formed their
calcium-carbonate shells. (Jennifer McKay, Oregon State)
"There's been a lot of work that's gone into the calibrations, so we can be
dead certain [the shells] are recording the temperature we think they're
recording," he said.

Today's study should help debunk the common climate change denial
argument that recent warming is simply part of a long-term natural trend.
Indeed, Marcott says, the earth should be nearing the bottom of a
several-thousand year cool-off (the end-point of the rainbow arc in (B)
above), if natural factors like solar variability were the sole driving factors.
Instead, temperatures are rising rapidly.

Mann himself, who literally wrote the book on attacks on climate scientists,
said in an email to Climate Desk that he was "certain that professional
climate change deniers will attack the study and the authors, in an effort to
discredit this important work," especially given the close ties between the two
scientists' research. "It will therefore be looked at as a threat to vested
interests who continue to deny that human-changed climate change is a

Marcott admitted he was apprehensive about charging into the
fully-mobilized troll army, but said he was grateful scientists like Mann had
"gone through hell" before him to build a support network for harassed
climate scientists.

"When Michael came along there was a lot more skepticism about global
warming, but the public has come a long way," he said. "I'm curious to see
how the skeptics are going to take this paper."

This piece is by Tim McDonnell of The Climate Desk.
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