(I copy the article because it will not be available in a month)
Between 1978 and 2003, in England and Wales, the Earth released into the atmosphere an annual average of 13 million tonnes of CO2
As a result of global warming, soils release carbon
THE WORLD | 08.09.05 | 14:08 pm • Updated on 08.09.05/14/08 | XNUMX:XNUMX p.m.
A vicious circle. The process described by British researchers in the Thursday, September 8, edition of the journal Nature is cause for concern. It indicates that global warming leads, in certain ecosystems, to responses leading directly to its worsening. Pat Bellamy, Peter Loveland and three of their colleagues at the National Soil Resources Institute (University of Cranfield), measured the amounts of carbon dioxide (CO2) released from the soils of England and Wales between 1978 and 2003. Poor surprise: during this period and under the effect of climate change, approximately 13 million tonnes of carbon escaped annually and were released into the atmosphere.
The peril of reforestation of the tundra
As a result of warming, the vegetation cover of the arctic regions of Canada, Alaska and Russia is continuously increasing. As several studies have shown, this process involves, via the synthesis of new biomass, a significant storage of carbon. Studies published on Thursday September 7 in the Journal of Geophysical Research explore another aspect of these upheavals. According to this study, the accelerated growth of tundra shrubs changes the winter snow cover of these large areas. In return, the reflexivity index (or albedo) of these regions changes: they reflect less sunlight and absorb more energy. What upset a fragile energy balance, explain the authors of the study, and promote, even more, the growth of plants.
The excess energy absorbed by the tundra during the winter is also likely to release part of the carbon stored in the soil. Finally, the reduced snow cover of these regions could contribute to modifying the average albedo of the Earth and directly contributing to its warming.
Such carbon losses are "alarmingly large," write Annette Freibauer and Ernst-Detlef Schulze, biogeochemists at the Max Planck Institute, in a commentary published by Nature. By comparison, human activities in the UK generate around 150 million tonnes of carbon equivalent.
The CO2 released by the soil increases this balance. Worse still, according to researchers' estimates, these unrecognized losses correspond to "the totality of the CO2 emissions reductions achieved by the United Kingdom between 1990 and 2002". This reduces to nothing the effect of the measures taken across the Channel to reduce greenhouse gas emissions.
In addition, the Kyoto Protocol does not take into account changes in the stocks of organic carbon in the soil. In the light of the work presented, warn Ernst-Detlef Schulze and Annette Freibauer, "an effective climate policy must, in the future, take all carbon sources into account" while avoiding favoring the release into the atmosphere of stocks existing in the biosphere.
"PEAT ZONES"
Strikingly, the estimate put forward by British researchers is nevertheless deemed "very solid" by Dominique Arrouays, director of the Infosol unit of the National Institute for Agronomic Research (INRA). All the more, he explains, that "scientists suspected that one of the potential sources of carbon release from the soil was located in the countries of the northern hemisphere, in the peaty areas that are found even in circumpolar regions ".
According to the authors of the study, the main cause is the increase in temperature due to global warming. This accelerates the mineralization mechanisms which transform the organic carbon stored in soils into CO2.
The changes in land use and exploitation that have taken place over the past twenty-five years are, no doubt, also to blame. But researchers do not have sufficiently precise data on the evolution of agricultural practices (soil drainage, conversion to meadows, etc.) between 1978 and 2003 to give an opinion. "The drops in carbon content highlighted mainly concern meadows, peat and mid-mountain areas," says Arrouays, however. Cultivated areas are also affected, but to a lesser extent. "
Although limited to England and Wales, this work is nonetheless of crucial importance. On a global scale, in fact, soils conserve an amount estimated at 300 times the amount of carbon released each year by the combustion of fossil resources (oil, gas, coal). In the layer of earth close to the surface are indeed stored organic residues of plants, animals, etc., mainly composed of carbon.
The phenomenon highlighted in England and Wales cannot however be generalized to the whole planet. Far from it. "The soils studied, very peaty and particularly rich in carbon, are only found under climatic conditions of cold and humidity, says Mr. Arrouays. The land found in France or around the Mediterranean is, for example, much less rich in organic matter. " They are therefore much less likely to release excess CO2 into the atmosphere. "The trend is not unequivocal, adds Arrouays. In other areas, carbon stocks may be increased as a result of climate change."
6 SAMPLES
Extrapolating the situation encountered across the Channel to comparable soil regions is also perilous: the stability of the stored organic matter depends not only on the quality of the soil, but also on several factors such as the intensity of global warming measured locally, uses and agricultural practices, possible changes in rainfall regime, etc.
Measures comparable to those carried out by the National Soils Resources Institute cannot be carried out in all countries. They are, in fact, based on a dense network of territories. It is thanks to this network that the researchers were able to study the variations in the carbon content of 6 samples representative of the composition of the terrain. They then extrapolated their measurements to the entire territory.
Such a soil monitoring network is being deployed in France by a Scientific Interest Group (GIS) which brings together the Ministries of Ecology, of Agriculture, Ademe, the French Institute for environment (IFEN) and INRA. This network now covers 40% of the territory and is to be finalized in 2007. It will, once completed, monitor changes in carbon concentrations, but also the levels of heavy metals and various pollutants.
