The direction measurements of rising atmospheric CO2 since the 1950s is lower than the contributions from estimated emissions because both land and oceans continue to take up a portion of the atmospheric CO2 from human activities. The “CO2 fertilization effect” is the enhanced uptake of CO2 per unit land area caused by rising CO2 which is greater than could be expected from plant regrowth and stimulation by increased nutrient availability. Global analysis suggests that CO2 fertilization is responsible for up to 60% of the overall land sink but persistence of these benefits into the future is highly uncertain. As part of the 2nd State of the Carbon Cycle Report the team carried out a review of existing evidence for a terrestrial CO2 fertillization effect; I present the draft key findings for terrestrial systems here as an introduction to this organized oral session.
Results/Conclusions
There have been documented direct and indirect effects of rising atmospheric CO2 on terrestrial and oceanic systems and processes for different regions of North America and the globe, but the capacity of these systems to continue to act as carbon sinks is not certain. On land, different biomes and regions likely have different responses to rising CO2. In terrestrial ecosystems, increased atmospheric CO2 causes enhanced photosynthesis, growth, and increased water-use efficiency. This may change vegetation composition and carbon storage, and influence terrestrial hydrology and biogeochemical cycling. Additional consequences expected for human populations include more changes to ecosystem services, or benefits, that terrestrial and ocean systems provide to humans. Ocean and terrestrial effects are contingent on, and feed back to, global climate change.