Where we are now in global warming
You would have to go back at least 15 million years to find carbon dioxide levels on Earth as high as they are today, a UCLA scientist and colleagues report Oct. 8 in the online edition of the journal Science.
“The last time carbon dioxide levels were apparently as high as they are today — and were sustained at those levels — global temperatures were 5 to 10 degrees Fahrenheit higher than they are today, the sea level was approximately 75 to 120 feet higher than today, there was no permanent sea ice cap in the Arctic and very little ice on Antarctica and Greenland,” said the paper’s lead author, Aradhna Tripati, a UCLA assistant professor in the department of Earth and space sciences and the department of atmospheric and oceanic sciences.
“Carbon dioxide is a potent greenhouse gas, and geological observations that we now have for the last 20 million years lend strong support to the idea that carbon dioxide is an important agent for driving climate change throughout Earth’s history,” she said.
Yes, pumping more and more CO2 into the air is a very bad idea, as this news release from UCLA on a major new study makes clear. The study itself, “Coupling of CO2 and Ice Sheet Stability Over Major Climate Transitions of the Last 20 Million Years,” (subs. req’d) was released by Science earlier this month.
The study notes importantly, “This work may support a relatively high climate sensitivity to pCO2” [the partial pressure of CO2], which is the same conclusion that a number of major studies looking at paleoclimate data have come to:
Scientists analyzed data from a major expedition to retrieve deep marine sediments beneath the Arctic to understand the Paleocene Eocene thermal maximum, a brief period some 55 million years ago of “widespread, extreme climatic warming that was associated with massive atmospheric greenhouse gas input.” This 2006 study, published in Nature (subs. req’d), found Arctic temperatures almost beyond imagination–above 23°C (74°F)–temperatures more than 18°F warmer than current climate models had predicted when applied to this period. The three dozen authors conclude that existing climate models are missing crucial feedbacks that can significantly amplify polar warming.
A second study, published in Geophysical Research Letters (subs. req’d), looked at temperature and atmospheric changes during the Middle Ages. This 2006 study found that the effect of amplifying feedbacks in the climate system–where global warming boosts atmospheric CO2 levels–”will promote warming by an extra 15 percent to 78 percent on a century-scale” compared to typical estimates by the U.N.’s Intergovernmental Panel on Climate Change. The study notes these results may even be “conservative” because they ignore other greenhouse gases such as methane, whose levels will likely be boosted as temperatures warm.
The third study, published in Geophysical Research Letters (subs. req’d), looked at temperature and atmospheric changes during the past 400,000 years. This study found evidence for significant increases in both CO2 and methane (CH4) levels as temperatures rise. The conclusion: If our current climate models correctly accounted for such “missing feedbacks,” then “we would be predicting a significantly greater increase in global warming than is currently forecast over the next century and beyond”–as much as 1.5°C warmer this century alone.
So we need to keep atmospheric concentrations of CO2 as low as possible — and if we do go above 450 ppm, we need to get back to under 350 ppm as rapidly as possible, preferably by century’s end, though that would be no easy feat.
Here’s more on this important study: …
