Carbon residence time dominates uncertainty in terrestrial vegetation responses to future climate and atmospheric CO 2

• DOI: 10.1073/pnas.1222477110
• Publication Date: 2013-12-17T02:44:35Z
• Authors: Andrew D. Friend; Wolfgang Lucht; Tim T. Rademacher; Rozenn Keribin; Richard Betts; Patricia Cadule; Philippe Ciais; Douglas B. Clark; Rutger Dankers; Pete D. Falloon; Akihiko Ito; Ron Kahana; Axel Kleidon; Mark R. Lomas; Kazuya Nishina; Sebastian Ostberg; Ryan Pavlick; Philippe Peylin; Sibyll Schaphoff; Nicolas Vuichard; Lila Warszawski; Andy Wiltshire; F. Ian Woodward
• Keywords: NPP; Time Factors; Climate Change; 01 natural sciences; Carbon Cycle; Computer Simulation; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment; 0105 earth and related environmental sciences; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; [SDU.OCEAN] Sciences of the Universe [physics]/Ocean, Atmosphere; Atmosphere; turnover; Uncertainty; ISI-MIP; Carbon Dioxide; Models, Theoretical; Plants; 15. Life on land; [SDU.ENVI] Sciences of the Universe [physics]/Continental interfaces, environment; Carbon; GVM; DGVM; 13. Climate action; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; Forecasting

Future climate change and increasing atmospheric CO 2 are expected to cause major changes in vegetation structure and function over large fractions of the global land surface. Seven global vegetation models are used to analyze possible responses to future climate simulated by a range of general circulation models run under all four representative concentration pathway scenarios of changing concentrations of greenhouse gases. All 110 simulations predict an increase in global vegetation carbon to 2100, but with substantial variation between vegetation models. For example, at 4 °C of global land surface warming (510–758 ppm of CO 2 ), vegetation carbon increases by 52–477 Pg C (224 Pg C mean), mainly due to CO 2 fertilization of photosynthesis. Simulations agree on large regional increases across much of the boreal forest, western Amazonia, central Africa, western China, and southeast Asia, with reductions across southwestern North America, central South America, southern Mediterranean areas, southwestern Africa, and southwestern Australia. Four vegetation models display discontinuities across 4 °C of warming, indicating global thresholds in the balance of positive and negative influences on productivity and biomass. In contrast to previous global vegetation model studies, we emphasize the importance of uncertainties in projected changes in carbon residence times. We find, when all seven models are considered for one representative concentration pathway × general circulation model combination, such uncertainties explain 30% more variation in modeled vegetation carbon change than responses of net primary productivity alone, increasing to 151% for non-HYBRID4 models. A change in research priorities away from production and toward structural dynamics and demographic processes is recommended.