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Bridging climate science, citizens, and policy

Ancient Greenhouse Climates Had Similar CO2 Concentrations As Predicted for 2100

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New research into past climates with elevated CO2 concentrations demonstrates the absolute folly of refusing to reduce our greenhouse gas pollution.

A favorite talking point of climate change deniers has been that past CO2 concentrations swung wildly up and down by thousands of ppmV (parts per million by volume).  When the concentrations were very high, greenhouse climates were found on Earth.  When they were low, ice sheets were able to cover large swaths of the planet.

Like other talking points by the deniers, this one has now been proven to be false.  CO2 concentrations did not, in fact, fluctuate by large amounts.  It turns out that previously assumed soil CO2 concentrations during carbonate formation (which removes atmospheric CO2, albeit very slowly) were too high.  Using more accurate constraints, past greenhouse climates were accompanied by concentrations similar to those projected for the end of this century.

This news is stunning in its implications.

We have to decide what kind of planet we want to try to live on: a planet with a climate similar to that of the past 100,000 years, or a planet with a climate reminiscent of Permian and Mesozoic greenhouse times.  During these prehistoric eras, concentrations previously assumed to range from ~1,000-3,000 ppmV instead “did not persist above 1,500 ppmV in the past 400 million years”.

If we continue along the business-as-usual path (increasing greenhouse emissions year after year), CO2 concentrations by the end of this century will be near 1,000 ppmV.  Whether it’s 600 or 750 or 800 or 1,000, it is becoming clearer that large concentrations have been associated with much warmer climates than what we experience today.  The concentration in Dec. 2009 was ~387ppm.  The average concentration in all of 2009 was also ~387ppm, with a high of 390ppm in May.  All those numbers represent the highest concentrations measured in modern times.  They’re all higher than concentrations have been for at least the past 20 million years

The authors of this latest study finish with the following [emphasis mine]:

Comparison of projected future [CO2]atm (2) with results from the recalibrated CO2 paleobarometer (Fig. 2 B) indicate atmospheric CO2 may reach levels similar to those prevailing during the vegetated Earth’s hottest greenhouse episodes by A.D. 2100. The abrupt increase in [CO2]atm during the Early Permian is similar in magnitude to that possible for the next century in the absence of CO2 mitigation (Fig. 2 B). Given that the Early Permian CO2 increase may have caused the termination of the Late Paleozoic Ice Age (7, 8, Fig. 2 D), the only known icehouse-greenhouse transition on a vegetated Earth, the effects that unmitigated CO2 increases may have on future climate warrant careful consideration.

This is about as close as most papers (scientists) get to policy recommendations.  Their recommendation is absolutely critical: without CO2 mitigation, we could witness the abrupt switch from an icehouse (glaciated poles) to a greenhouse – for only the second time in our planet’s history.

Switching gears to modern policy initiatives, I will make note again that Brazil has already signed their pledges made at the 2009 Copenhagen Climate Summit into law.  Germany is in the process of pushing very aggressive goals into a domestic (i.e. not international) legally binding vehicle.  The U.S. House has passed H.R. 2454 and are waiting on the U.S. Senate to begin serious consideration of their own version of a climate/energy bill.  Dirty Energy Corporations watched the health insurance battle last year with great interest.  They will likely employ similar measures as health care reform obstructionists did to continue discrediting scientists and science-based policies.  At 387ppm, we simply don’t have the time to push this issue down the road any more.  Action will be much cheaper and more efficient if done today.

Cross-posted at SquareState.

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