Below is the text of an article by William Barbat, in the second issue of his CO2 Newsletter, published in December 1979. I’ve added hyperlinks and references.
How fast can the ocean waters and other natural sinks take up the CO2 produced by man? This question has been the center of heated controversy which occupied a large share of the Dahlem (Berlin) Conference on ‘Global Chemical Cycles’ in 1976 and ERDA’s Miami Beach Workshop on the ‘Global Effects of Carbon Dioxide from Fossil Fuels Combustion’ in 1977.
One school of thought holds that man-created CO2 would be removed from the atmosphere at a rapid rate – possibly as high as 6% per year – once man’s outpourings of CO2 have ceased. If so, any legacy of a CO2-induced climate change would be short-lived except possibly for any destruction of icecaps that has taken place before a CO2~induced warming ended. Natural uptake of CO2 this fast would essentially relegate the CO2 problem to a reversible status similar in certain respects to smoke pollution and acid rain. Also, the contributions to the CO2 build-up due to fossil-fuel consumption by people in the United States (which comprise 5% of the world’s total population) in such a case figures to be 12% of the overall atmospheric build-up rather than 24%.
The leading advocate of this rapid-uptake hypothesis is biologist George Woodwell of Woods Hole. Woodwell’s position is based on his estimate that the cutting and burning of forests (essentially for farm-clearing in the tropics) is currently a major source of CO2 – possibly as much as 20 to 100 percent of that released by the burning of fossil fuels. Woodwell’s estimate of the deforestation rate is not based on hard data, but is projected from very limited statistical samplings, which statistics have also been interpreted by some others as showing a slight increase in forest biomass.
The opposing school of thought holds that uptake by the oceans is very slow and depends on the turnover rate of undersaturated deep ocean waters, which is of the order of 1000 years. If true, then as man’s cumulative output of CO2 exceeds certain threshold values to cause impacts such as a decrease in agricultural productivity, a decrease in marine habitat cause icecaps to become unstable, these impacts would become irreversible for many generations to come. Also the slow uptake carries the implication that the highly industrialized nations bear most of the responsibility for the CO2 buildup rather than sharing it almost equally with farmers in the tropics.
The slow uptake view is shared by the geophysicists, geochemists and ocean scientists who have made extensive studies of the world’s overall carbon budget. Notable among this group are Wallace S. Broecker, Taro Takahashi, and associates of Lamont Doherty Geological Observatory and Columbia University, C.D. Keeling and associates of Scripps Institution of Oceanography, Minze Stuiver of University of Washington, and H. Oeschger and U. Siegenthaler of Switzerland.
An article published in Science 26 October 1979 by Broecker and his associates notes that “several versions of recent atmosphere-ocean models appear to give reliable and mutually consistent estimates for carbon dioxide uptake by the oceans calling for a modest increase in the size of the terrestrial biosphere order to achieve a balance in the carbon budget.” These workers further provide hard data on the distribution of carbon isotopes between various carbon reservoirs which provide constraints on the size of the known carbon reservoirs. The authors also note that Woodwell rapid uptake hypothesis and deforestation estimate demands that between one third and one-half of all the tropical forest would have disappeared in the last two decades, which should be more readily apparent if true. (Projected at a constant rate per year rather than at the exponential rate of growth exhibited by the CO2 buildup, one notes that Woodwell’s hypothesized deforestation rate would result in complete elimination of’ tropical forest cover in two or three more decades.) In resolving the apparent carbon budget contradiction, Broeckerl’s group concluded that “regrowths of previously cut forests and enhancement of forest growth resulting from excess CO2 the atmosphere have probably roughly balanced the rate of forest destruction during the past few decades.”
While the controversy over deforestation and ocean uptake is not yet settled to everyone’s satisfaction, majority scientific opinion seems to strongly favor the slow-uptake school of thought. With slow uptake by oceans, there is no safe allowable rate of CO2 output which could prevent temperature thresholds from being reached. Rather every single contribution of CO2 is likely to have a long-lasting effect. Acceptance of the slow uptake theory shifts the social concern from slowing the rate of CO2 production to limiting the total amount of CO2 produced from the combustion of fossil fuels.
Citation: Barbat, W. 1979. Will impacts remain for one generation or thirty? ‘Tropical Deforestation’ issue seeks the answer. CO2 Newsletter, Vol 1. No. 2 p. 3
Annotations:
This is vintage Barbat – the ability to synthesise a large amount of information, summarise ongoing scientific debates in clear and judicious language. It looks easy, but then playing tennis like Roger Federer looks easy.
The Broecker article is Fate of Fossil Fuel Carbon Dioxide and the Global Carbon Budget | Science
W S Broecker, T Takahashi, H J Simpson, T H Peng. 1979. Fate of fossil fuel carbon dioxide and the global carbon budget Oct 26;206(4417):409-18. doi: 10.1126/science.206.4417.409.
The Dahlem Conference was this – Global chemical cycles and their alterations by man : report of the Dahlem Workshop on Global Chemical Cycles and their Alterations by Man, Berlin 1976, November 15-19
