The role of earth: sink or source ?

Precise predictions regarding the future of terrestrial climate requires accurate understanding of the CO2 dynamics on both local and international scale. This is very difficult. But there are progress recently made:

One key to accurately predicting future levels of atmospheric carbon dioxide (CO₂) is understanding how land and atmosphere exchange CO₂. Each year, photosynthesizing land plants remove (fix) one in eight molecules of atmospheric CO₂, and respiring land plants and soil organisms return a similar number. This exchange determines whether terrestrial ecosystems are a net carbon sink or source. Two papers in this issue contribute to understanding the land-atmosphere exchange by elegantly analyzing rich data sets on CO₂ fluxes from a global network of monitoring sites. On page 834, Beer et al. (1) estimate total annual terrestrial gross primary production (GPP) in an approach more solidly based on data than previous simple approximations. On page 838, Mahecha et al. (2) assess how ecosystem respiration (R) is related to temperature over short (week-to-month) and long (annual) time scales, and find a potentially important but difficult-to-interpret relationship.

REPORTS
Terrestrial Gross Carbon Dioxide Uptake: Global Distribution and Covariation with Climate

Christian Beer, Markus Reichstein, Enrico Tomelleri, Philippe Ciais, Martin Jung, Nuno Carvalhais, Christian Rödenbeck, M. Altaf Arain, Dennis Baldocchi, Gordon B. Bonan, Alberte Bondeau, Alessandro Cescatti, Gitta Lasslop, Anders Lindroth, Mark Lomas, Sebastiaan Luyssaert, Hank Margolis, Keith W. Oleson, Olivier Roupsard, Elmar Veenendaal, Nicolas Viovy, Christopher Williams, F. Ian Woodward, and Dario Papale (13 August 2010)
Science 329 (5993), 834. [DOI: 10.1126/science.1184984]

REPORTS
Global Convergence in the Temperature Sensitivity of Respiration at Ecosystem Level

Miguel D. Mahecha, Markus Reichstein, Nuno Carvalhais, Gitta Lasslop, Holger Lange, Sonia I. Seneviratne, Rodrigo Vargas, Christof Ammann, M. Altaf Arain, Alessandro Cescatti, Ivan A. Janssens, Mirco Migliavacca, Leonardo Montagnani, and Andrew D. Richardson (13 August 2010)
Science 329 (5993), 838. [DOI: 10.1126/science.1189587]