Simultaneity of Increased CO₂ Concentration and Temperature Increase Confirmed. (March 1, 2013)

 The Australian Science Media Centre (AusSMC) reports that analysis of Antarctic ice cores in the journal Science today has found that temperatures and atmospheric carbon dioxide amounts increased simultaneously during the last major warming period, some 20,000 to 10,000 years ago. The results clarify a long running argument that rises in CO₂ after the last Ice Age occurred after rather than before temperature increases and help dispel the notion that climate warming could not have been caused by increasing concentrations of atmospheric CO₂. This study uses alternative methods to confirm findings by Australian scientists released in July last year. Lead author of last year’s Australian study comments below.

Dr Joel Pedro Honorary Research Fellow at the Antarctic Climate & Ecosystems CRC, University of Tasmania makes the following observations:

The take home message from this paper is that temperature and CO₂ increased in lock step during the warming out of the last glacial period.

We came to the same conclusion using independent methods and different ice cores last year in a paper published in Climate of the Past (http://www.clim-past.net/8/1213/2012/cp-8-1213-2012.pdf). In terms of advancing the science this is good, we now have two studies by different groups of authors using different methods and several different ice cores coming to the same key result: that Antarctic temperature and atmospheric CO2 increased essentially in synchrony as the Earth warmed out of the most recent glacial period.

It is still a big challenge to pinpoint exactly what natural processes were responsible for such a tight feedback process at this time. Scientists in the carbon cycle and climate modelling communities working on this problem should be aided by the improved observations from the ice cores.

To provide a little more detail and background. A technical barrier confronting studies like Parrenin et al and ours from last year is that there is an inbuilt time offset in all ice cores between the CO2 and temperature record. The offset arises because temperature information is encoded at the surface in the composition of the water molecules in the snow itself, whereas the CO₂ is captured at around 60-120m deep as the pores in the snow close off. This size of the offset, which we call ‘delta-age’, depends on snowfall and temperature and can range from a few decades to over a thousand years. We must correct for delta-age in order to provide an accurate assessment of the real past time relationship between temperature and CO₂. For many cores the reported uncertainties in delta age were previously so large as to swamp results on the temperature and CO₂ relationship. In Pedro et al we worked around this problem by using high snowfall ice cores from close to the Antarctic coast for which the delta age is much smaller. Parrenin et al use cores from central Antarctica with larger delta age, but use a completely new method that appears to greatly reduce uncertainties for those cores, and correct an earlier bias which consistently overestimated it.

Finally, it is important to point out that coupled rise in temperature and CO₂ that marked the end of the glacial period occurred gradually, over about 8000 years. In contrast what we have seen since the start of the industrial revolution is a similar CO₂ increase occurring over only a few hundred years. This is way faster than anything in the ice core record and it’s clearly human-caused. Just as the steady increase in CO₂ helped to melt the ice caps and warm the Earth out of the glacial, the rapid increase now in CO₂ is also driving up temperatures, only at a much faster rate.”