More Notes on Global Warming

Abstract

I was puzzled when I read the exchange of letters on global warming in the January 2005 issue of Physics Today, (page 13). George Smith suggested that the recent carbon dioxide increase could be the result of a century of global warming—in particular, by the degassing of the ocean. Spencer Weart answered (correctly, but see below) that scientists with the Intergovernmental Panel on Climate Change (IPCC) have calculated the budget between the carbon input with the sinks in different reservoirs of the carbon cycle: ocean, forest, soil, and so forthBesides technicalities implying that the global CO2 budget still has second-order uncertainties, I’m surprised Weart didn’t cite first-order proofs demonstrating that the recent CO2 increase cannot be due to ocean warming. Those killing proofs are well-known in the climatology community—for example, in the IPCC—but it is crucial to emphasize them again for a wider audience.The recent CO2 increase—280 to 380 parts per million by volume between 1800 and 2005—is accompanied by three phenomena that completely rule out ocean warming as the main cause: ▸ Parallel decline of the 14C/12C ratio of atmospheric CO2. Strictly speaking, this is the “Suess effect,” first observed, and correctly interpreted, by Hans Suess of the University of California, San Diego, in the early 1950s. The Suess effect occurs because fossil fuels do not contain 14C precisely because they are fossil—much older than 10 half-lives of 14C.▸ Parallel decline of the 13C/12C ratio of atmospheric CO2. This phenomenon is linked to the fact that fossil fuels, forests, and soil carbon come from photosynthetic carbon, which is strongly depleted in 13C.▸ Parallel decline in the oxygen concentration of the atmosphere, which is the inescapable signature of an oxidation of carbon. If ocean warming were responsible for the CO2 increase, we should also observe an increase in atmospheric O2. Nonspecialists will not easily be impressed by model calculations and complex budgets that contain often large uncertainties. Moreover, I have seen dishonest skeptics using “old hat” arguments such as ocean CO2 outgassing to refute the responsibility of human activities in the recent CO2 increase and the forthcoming large global warming. One crucial note about the global budget of inputs and outputs that Weart should have stated: Known CO2 emissions from fossil fuels and deforestation largely exceed (by about a factor of two) what remains in the atmosphere. Hence, if warming were the cause of the CO2 increase, how would we account for the hundreds of gigatons of carbon generated by human activity?© 2005 American Institute of Physics.