Via Climate Progress:

Drop in CO2 Levels Led to Antarctic Ice Sheet, Study Finds

Posted: 04 Dec 2011 09:23 AM PST

 

Upwelling seawater along parts of Pine Island Glacier Ice Shelf has carved out caves in the ice. A new study links CO2 and Antarctica glaciation.

The news release for a new Science study, “The Role of Carbon Dioxide During the Onset of Antarctic Glaciation” (subs. req’d), explains:

A drop in carbon dioxide appears to be the driving force that led to the Antarctic ice sheet’s formation, according to a recent study led by scientists at Yale and Purdue universities of molecules from ancient algae found in deep-sea core samples.The key role of the greenhouse gas in one of the biggest climate events in Earth’s history supports carbon dioxide’s importance in past climate change and implicates it as a significant force in present and future climate….

“The evidence falls in line with what we would expect if carbon dioxide is the main dial that governs global climate; if we crank it up or down there are dramatic changes,” [co-author Matthew} Huber said. "We went from a warm world without ice to a cooler world with an ice sheet overnight, in geologic terms, because of fluctuations in carbon dioxide levels."

We know from earlier study this year led by the Jet Propulsion Laboratory that polar ice sheet mass loss is speeding up and on pace for 1 foot sea level rise by 2050:

The Greenland and Antarctic ice sheets are losing mass at an accelerating pace, according to a new NASA-funded satellite study. The findings of the study — the longest to date of changes in polar ice sheet mass — suggest these ice sheets are overtaking ice loss from Earth’s mountain glaciers and ice caps to become the dominant contributor to global sea level rise, much sooner than model forecasts have predicted.

Recent modeling work suggests we are approaching the tipping point for irreversible melting of the Greenland ice sheet, which would, ultimately, represent 20 feet of sea level rise (see New study of Greenland under “more realistic forcings” concludes “collapse of the ice-sheet was found to occur between 400 and 560 ppm” of CO2).
And we know from paleoclimate studies that the Antarctic ice sheet (which contains 90% of the ice on the planet) is vulnerable to modest warming from current levels, particularly the West Antarctic Ice Sheet (see Science: CO2 levels haven’t been this high for 15 million years, when it was 5° to 10°F warmer and seas were 75 to 120 feet higher -- “We have shown that this dramatic rise in sea level is associated with an increase in CO2 levels of about 100 ppm”).

While the new study  firms up our understanding that CO2 is the "main dial that governs global climate," it does not appear to tell us what the tipping point is for full deglaciation:

The team found the tipping point in atmospheric carbon dioxide levels for cooling that initiates ice sheet formation is about 600 parts per million. Prior to the levels dropping this low, it was too warm for the ice sheet to form. At the Earth's current level of around 390 parts per million, the environment is such that an ice sheet remains, but carbon dioxide levels and temperatures are increasing. The world will likely reach levels between 550 and 1,000 parts per million by 2100. Melting an ice sheet is a different process than its initiation, and it is not known what level would cause the ice sheet to melt away completely, Huber said.
"The system is not linear and there may be a different threshold for melting the ice sheet, but if we continue on our current path of warming we will eventually reach that tipping point," he said. "Of course after we cross that threshold it will still take many thousands of years to melt an ice sheet."

It would no doubt take a long time to fully melt an ice sheet, but we are headed toward some serious polar warming (see M.I.T. doubles its 2095 warming projection to 10°F — with 866 ppm and Arctic warming of 20°F).  That study projects some 13°F warming over Antarctica in the 2090s.

And a study from earlier this year suggests we are headed toward far higher warming post-2100 (see Science: On our current emissions path, CO2 levels in 2100 will hit levels last seen when the Earth was 29°F (16°C) hotter; Paleoclimate data suggests CO2 “may have at least twice the effect on global temperatures than currently projected by computer models”).

Back in October, Climate Progress interviewed Rice University oceanographer John Anderson, a leading expert on sea level rise with more than 200 publications, (see Flood-Gate: Perry Officials Try to Hide Sea Level Rise from Texans with “Clear-Cut Unadulterated Censorship”).

Anderson explained that he's been working in Antarctica for 4 decades, that they've found unprecedented warming in the Antarctic Peninsula, and that "I am quite concerned about the potential of catastrophic contribution to  sea level rise from ice sheet collapse."

Indeed, he said "if people say that ice sheets react slowly, they are not familiar with what we know about ice sheets. There is clear evidence that that ice sheets behave catastrophically."
He was specifically worried about the "weak underbelly" of the West Antarctic Ice Sheet, the Pine Island Glacier.  For two recent discussions of PIG, see

• Large Antarctic glacier thinning 4 times faster than it was 10 years ago: “Nothing in the natural world is lost at an accelerating exponential rate like this glacier.”
• Ocean Currents Speed Melting of Antarctic Ice, as “Seawater Appear[s] to Boil on the Surface Like a Kettle on the Stove”

That’s why so many leading experts on the subject agree with the recent scientific literature that as long as we stay anywhere near our current emissions path, we are headed toward a meter or more of sea level rise by century’s end — and then 6+ inches of sea level rise a decade for a long, long time.
Related Posts:

• Eight Must-Have Charts Summarize the Evidence for a “Human Fingerprint” on Recent Climate Change
• 10 indicators of a human fingerprint on climate change
• In must-see AGU video, Richard Alley explains “The Biggest Control Knob: Carbon Dioxide in Earth’s Climate History”
• How carbon dioxide controls earth’s temperature — NASA’s Lacis: “There is no viable alternative to counteract global warming except through direct human effort to reduce the atmospheric CO2 level.”