With two weeks to run to the Copenhagen Summit on climate change (COP 15), which will be attended by 64 heads of state, a new report has presented detailed estimates of carbon fluxes in the European Union (Nature Geoscience, 22 November 2009). The figures included in the report are not limited to greenhouse gas emissions caused by industry, transport, and residential dwellings, but also cover exchanges of carbon between land, vegetation and the atmosphere, which, on land, mainly result from photosynthesis and respiration. These natural fluxes are important because forests, grasslands and peat bogs have the capacity—just as oceans do—to act as sinks for CO2 which accumulates in the atmosphere and contributes to global warming.

Whereas exchanges in most parts of the world result in the sequestration of a proportion of anthropogenic CO2, the report shows that in Europe, emissions of nitrous oxide (N2O) and methane (CH4)—two powerful greenhouse gases—produced by the cultivation of crops and the raising of livestock exceed the CO2 sink capacity of forests and grasslands in the region. Nitrous oxide is produced by the interaction of chemical fertilizers and bacteria, while methane is generated by the digestive systems and excrement of livestock. The prevalence of these gases has meant that the EU's terrestrial ecosystems now produce more CO2 than they are able to absorb. In fact, they add 3% of "carbon dioxide equivalent" to emissions caused by fossil fuels— and there is hardly any improvement in this balance elsewhere on the continent in countries like Turkey, Ukraine and Belarus.

The need to improve CO2 sequestration capacity

As a result, the European Union has one of the lowest rankings for CO2 sequestration of any political entity. In most regions of the planet, half of the greenhouse gases emitted by human activity are absorbed by marine and terrestrial ecosystems. In the United States, ecosystems perform significantly better than they do in the EU, sequestrating almost 25% of anthropogenic CO2 (0.4 billion tonnes of carbon are sequestrated for every 1.7 billion tonnes of carbon emitted).

The main lesson of the report concerns the implementation of climate change policy in the EU, which should not be limited to the reduction of emissions from fossil fuels used by industry and transport, but must also take into account and improve ecosystem CO2 sequestration capacity. Europe has significant room for manoeuvre in this field. "If we want natural environments to also contribute to the reduction of greenhouse gases, we will have to learn how to better manage agricultural methane and nitrous oxide emissions," explains Detlef Schmulze, of the Max Planck Institute in Jena, Germany, which led the team writing the report.

Intensive agriculture to blame

Already criticized for its impact on health and the environment, intensive agriculture has now been targeted for its role in global warming, along with intensive timber production, which limits the sequestration capacity of forests. Two thousand researchers participated in the five-year project to draft the report, which required the processing of massive amounts of statistical data and the collection of numerous field and atmospheric measurements. The work, which was conducted within the framework of CarboEurope programme, was funded to the tune of 16.3 million euros by the European Commission, with an additional 30 millions euros sourced from different national governments within the EU.

Numerous questions remain about the additional 50% in carbon fluxes in our terrestrial ecosystems that result from emissions of methane and nitrous oxide, explains Philippe Ciais of the Laboratory of Climate Sciences, one of the co-authors of the study. "Significant progress has been made, and the EU is the only entity with the capacity to produce data on these extremely complex processes." The development of a dense network of atmosphere stations and flux measurement sites will enable us to reduce this uncertainty and to study the different regions in Europe."