We are all familiar with this scene from the ridiculously loony “Great Global Warming Swindle” movie so favoured by wilfully ignorant and scientifically illiterate denialists. The suggestion is, and it is one their favourite catchcries, that “CO2 lags temperature!” To put it perhaps a little more scientifically, they are suggesting that because the Vostok ice core data from the last deglaciation shows a lag between temperature rise and CO2 concentration increase, this is evidence that CO2 does not drive climate. This is of course wrong because it is built on a false premise. The simplest explanation given by climate scientists is that Milankovitch cycles initiated the warming, and as things warmed up, CO2 previously locked away in permafrost and from vegetation being inundated by rising sea levels slowly increased to a level where it took over.
The problem as I see it is that the story has never been complete. Using a single data point such as the Vostok ice core is really only good for telling the story of what happened in that particular area. A new study published in Nature today goes along way to filling in the gaps. Here is its abstract…
Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation
Jeremy D Shakun, Peter U Clark, Feng He, Shaun A Marcott, Alan C Mix, Zhengyu Liu, Bette Otto-Bliesner, Andreas Schmittner & Edouard Bard
The covariation of carbon dioxide (CO2) concentration and temperature in Antarctic ice-core records suggests a close link between CO2 and climate during the Pleistocene ice ages. The role and relative importance of CO2 in producing these climate changes remains unclear, however, in part because the ice-core deuterium record reflects local rather than global temperature. Here we construct a record of global surface temperature from 80 proxy records and show that temperature is correlated with and generally lags CO2 during the last (that is, the most recent) deglaciation. Differences between the respective temperature changes of the Northern Hemisphere and Southern Hemisphere parallel variations in the strength of the Atlantic meridional overturning circulation recorded in marine sediments. These observations, together with transient global climate model simulations, support the conclusion that an antiphased hemispheric temperature response to ocean circulation changes superimposed on globally in-phase warming driven by increasing CO2 concentrations is an explanation for much of the temperature change at the end of the most recent ice age.
For the scientifically challenged, what this paper reports is the result of analysis of 80 proxy temperature records from around the globe from a variety of latitudes. The seven proxies used included oxygen isotopes from ice cores, pollen from lake mud sediment and marine microfossils. The results paint a global picture of temperature change and when related back to the CO2 record indicate very strongly that the Vostok result was in fact a localised condition and that globally, temperature generally lagged CO2, the opposite of what the deniers would have the gullible believe.
One by one, the denialists’ simplistic, deceitful and woefully unscientific arguments are being demonstrably savaged by actual evidence. How long before they pull their heads out of their collective arses and start seeing reason? Only time, an ice free arctic, continued loss of species and rising sealevels will tell.