Increased soil emissions of potent greenhouse gases under increased atmospheric CO ₂

Increasing concentrations of atmospheric carbon dioxide (CO ₂) can affect biotic and abiotic conditions in soil, such as microbial activity and water content. In turn, these changes might be expected to alter the production and consumption of the important greenhouse gases nitrous oxide (N ₂O) and methane (CH ₄) (refs 2, 3). However, studies on fluxes of N ₂O and CH ₄from soil under increased atmosphericCO ₂have not been quantitatively synthesized.Hereweshow, using meta-analysis, that increased CO ₂(ranging from 463 to 780 parts per million by volume) stimulates both N ₂O emissions from upland soils and CH ₄emissions from rice paddies and natural wetlands. Because enhanced greenhouse-gas emissions add to the radiative forcing of terrestrial ecosystems, these emissions are expected to negate at least 16.6 per cent of the climate change mitigation potential previously predicted froman increase in the terrestrial carbon sink under increased atmospheric CO ₂concentrations4. Our results therefore suggest that the capacity of land ecosystems to slow climate warming has been overestimated.