Carbon Dioxide and Temperature: Who Has Led Whom?

As I wrote in my new book, The Moon in the Nautilus Shell, given the scientific complexities, one can only be rather agnostic about the role that human actions have played and are playing in climate change.  A new, important paper in the journal Science casts some fascinating light on the question of whether carbon dioxide change precedes temperature change, and therefore is a likely cause of the temperature change, or whether temperature change precedes carbon dioxide change, casting doubt on the role of the greenhouse gas in climate change.  Rather than continue the discussion as a morality play about who is on the right side of the debate, it is time to return the discussion to the fundamental scientific questions — and at the same time, not lose track of all the other important environmental issues that continue to confront us: deforestation; overfishing; air and water pollution with directly toxic chemicals; invasive species; illegal harvesting of threatened and endangered species; and other direct threats to biological diversity.

The who-led-whom question — carbon dioxide or temperature — became widely discussed after several scientific papers, including a 2003 paper in the journal Science, showed that for the past 800,000 years, temperature change preceded carbon dioxide changes in the Antarctic ice cores by an average of 800 years.  (For those who are interested, one of the key scientific papers is Caillon, et al, "Timing of Atmospheric CO2 and Antarctic Temperature Changes Across Termination Ill." Science, 2003. 299: 1728–1731.)

This was a striking and surprising finding, for which there are two possible explanations:  Either the lag is the result of natural physical and chemical processes, or there is a measurement or scientific error in interpretation of the data. Natural causes of a CO2 lag include the long time it takes ocean waters around the world to warm up following an atmospheric warming; a warmer ocean stores less carbon dioxide than a cooler one. It could also result from a lag in the way that forest trees responded to warming climates, or the way sea ice responded.

The new paper just published in Science shows that much of the lag could be the result of a problem in analyzing the ice cores from Antarctic. (For those interested, the paper is: Parrenin, et. al., “Synchronous Change of Atmospheric CO2 and Antarctic Temperature During the Last Deglacial Warming,” Science, 2013. 339: p. 1060.)  The chemistry is complicated, highly sophisticated, and indirect.  You don’t just stick a thermometer into the ice core to determine what the atmospheric temperature was 800,000 years ago.

Who appears to have lagged whom depends on assumptions about the timing of carbon dioxide storage in air pockets in ice cores compared to the timing of factors used to reconstruct temperature. The new paper in Science presents new ways of analyzing those events, yielding results that greatly reduce the time gap between rising temperature and rising carbon dioxide.  The lag could still be there but much shorter — perhaps only as long as 130 years.  Or it might not exist at all.

The new Science  paper is objective and open, and very careful, allowing for a variety of interpretations, even the previous much longer lags. This is the way that the entire discussion of climate change should be going on.

What, then, should an ordinary citizen who doesn’t have the training to evaluate these complex methods do?  As I said in The Moon in the Nautilus Shell, the key is to take actions that help solve here-and-now environmental problems and are at the same time either also beneficial to reducing greenhouse gas concentrations in the atmosphere or neutral.  Examples include:

• continuing to move away from fossil fuels — such as shale gas, so popular now — and moving to alternative energy;
• stopping deforestation, which is happening widely around the world, and improving forest management, not just abroad but in the United States;
• helping to conserve biological diversity by direct actions, such as halting the illegal killing of African elephants for their ivory;
• reducing the release of toxic chemicals into our air and waters;
• conserving the world’s supply of fresh water.

Then stay tuned as the scientists doing excellent research continue, and let them do so independent of the blame game fashioned by the climate-change morality play.