The capacity of oceans and terrestrial ecosystems such as forests and grasslands to store carbon emissions is considered one of the primary ways the effects of climate change can be mitigated. Unfortunately, such natural carbon sinks may not be much help to Europe thanks to the continent's intensive land management practices, according to a new published online in Nature Geoscience.

The researchers from 17 European countries compiled the first comprehensive greenhouse gas balance of Europe, and made two independent estimates: one based on what the atmosphere sees and one based on what terrestrial ecosystems see. While the new bookkeeping effort confirmed the existence of a strong carbon sink of -305 Million tonnes of carbon per year--capable of absorbing 19% of the emissions from fossil fuel burning--it also found that agricultural land and drained peat-land are emitting carbon dioxide, which cancels part of this sink.

The resulting net carbon dioxide sink of the European continent is 274 Million tonnes of carbon per year - only 15% of the emissions from fossil fuel burning. But this balance is still incomplete, because all European ecosystems are managed and as a by-product of land management other powerful greenhouse gases are released - for example nitrous oxide from fertilizers applied to grassland and crops, and methane from ruminants and from peat-lands.

These previously neglected emissions of greenhouse gases from land-use cancel out almost the entire carbon sink, leaving the landscape offsetting only some 2% of the carbon dioxide emissions from households, transport and industry.

Compared to Europe as a whole, the situation is even worse for the 25 states of the European Union. Here, although forests and grasslands can compensate for 13% of the carbon dioxide emitted by fossil fuel burning, emission of powerful greenhouse gases from agricultural emissions and peat mining reduces the effectiveness of the land surface sink to 111 Million tonnes of carbon per year, which is only 11% of the carbon dioxide emitted by fossil fuels.

However, since the emissions of methane and nitrous oxide are relatively higher in the European Union the land surface emerges as a greenhouse gas source of 34 Million tonnes of carbon per year. This effectively increases the emissions from fossil fuel burning by another 3%.

Citation: E. D. Schulze, S. Luyssaert, P. Ciais, A. Freibauer, I. A. Janssens et al., 'Importance of methane and nitrous oxide for Europe's terrestrial greenhouse-gas balance', 2009, Nature Geoscience Online, doi:10.1038/ngeo686