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Climatology

Emitting More, Absorbing Less

Carbon dioxide spillage into the Earth's atmosphere is set to spiral far higher than hitherto forecast, while the earth's natural capacity to partially absorb CO2 emissions is weakening. This alarming conclusion arises from two separate recent international studies, both involving CNRS researchers.

An international team of economists and carbon cycle and emissions experts found that almost eight billion tons of CO2 from burnt fossil fuels were expended into the atmosphere in 2005, compared with six billion tons in 1995. “There has been no other comparable scientific assessment of global emissions during recent years,” says Philippe Ciais from LSCE,1 who co-authored the study published earlier this year.2

Based on a detailed trawl of national statistics worldwide, the study found that a previously declining global trend in the carbon intensity3 of Gross Domestic Product (GDP) was reversed as of 2000. “Emissions now surpass the Kyoto Protocol objectives by 30%,” says Ciais. “We estimate that fossil fuel emissions will account for 11 billion tons of atmospheric CO2 by 2020.”

Through the 1990s, the average yearly global increase of CO2 emissions to the atmosphere from the burning of fossil fuels was a steady 1.1%. The new research found that from 2000 to 2004, that yearly increase jumped to 3%.

While the growth rate of emissions is highest among developing countries, developed nations are currently among the most polluting; average carbon emissions per capita in China in 2005 was less than one ton, compared with five in the United States. But developing nations such as China and India, with growing populations and increasing per-capita GDP, are set on an expansive course of intensive fossil fuel burning which may only peak in several decades.

Until recently, the equivalent of some 50% of manmade CO2 emissions was each year absorbed by forests and oceans, known as CO2 sinks. This absorption rate has been historically consistent, whatever the atmospheric quantity of CO2. Now, an international team of scientists, specialized in the observation and modeling of oceanic and atmospheric carbon cycles, found that one major CO2 sink, the Southern Ocean, is gradually failing.4 This research is all the more significant because the absence of any neighboring land mass allowed precise measurement of the capacity of the ocean alone to absorb CO2. Until now, the waters situated below 45°S accounted for the yearly disappearance of some 15% of manmade CO2 emissions, in a process by which the surface layer 'swallows' the gas before it eventually sinks to the ocean's depths. But changes in atmospheric circulation–caused by greenhouse gases and ozone depletion–have accelerated the parallel and contrary easterly and westerly winds that sweep the ocean. The increasing pull on the surface has caused deep, CO2-rich water to rise to the top, bringing the sink to saturation point. “The narrowing difference between CO2 quantities in the water and air means that the ocean is unable to absorb as much atmospheric CO2 as before,” explains Nicolas Metzl from LOCEAN.5 “The question now,” adds fellow co-author of the study Michel Ramonet, from LSCE, “is whether this same phenomenon is repeated in other key ocean sinks, notably the North Atlantic, and whether it is reversible.”

 

Graham Tearse

Notes :

1. Laboratoire des sciences du climat et de l'environnement (CNRS / CEA / Université Versailles Saint-Quentin).
2. M. Raupach et al., “Global and regional drivers of CO2 emissions,” PNAS. 104(24): 10288-93. 2007.
3. Ratio of carbon emissions to various economic activities.
4. C. Le Quéré et al., “Saturation of the Southern Ocean CO2 sink due to recent climate change,” Science. (316)5832: 1735-1738. 2007.
5. Laboratoire d'océanographie et du climat: expérimentations et approches numériques (CNRS / Université Paris VI / MNHN / IRD).

Contacts :

> Philippe Ciais, LSCE, Gif-sur-Yvette.
philippe.ciais@cea.fr
> Nicolas Metzl, LOCEAN, Paris.
metzl@ccr.jussieu.fr
> Michel Ramonet, LSCE, Gif-sur-Yvette.
Michel.Ramonet@lsce.ipsl.fr


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