B22A-05
Improving the representation of photosynthesis in Earth system models
Tuesday, 15 December 2015: 11:20
2004 (Moscone West)
Alistair Rogers1, Belinda E Medlyn2, Jeffrey Dukes3, Gordon B Bonan4, Susanne von Caemmerer5, Michael Dietze6, Jens Kattge7, Andrew DB Leakey8, Lina M Mercado9, Ulo Niinemets10, Iain C Prentice11, Shawn Serbin1, Stephen Sitch9, Danielle A Way12 and Soenke Zaehle7, (1)Brookhaven National Laboratory, Upton, NY, United States, (2)Western Sydney University, Hawkesbury Institute for the Environment, Sydney, Australia, (3)Purdue University, Department of Forestry and Natural Resources, West Lafayette, IN, United States, (4)National Center for Atmospheric Research, Boulder, CO, United States, (5)Australian National University, Canberra, Australia, (6)Boston University, Boston, MA, United States, (7)Max Planck Institute for Biogeochemistry, Jena, Germany, (8)University of Illinois, Department of Plant Biology and Crop Sciences, Urbana, IL, United States, (9)University of Exeter, Exeter, United Kingdom, (10)Estonian University of Life Sciences, Tartu, Estonia, (11)AXA Chair of Biosphere and Climate Impacts, Grand Challenges in Ecosystems and the Environment and Grantham Institute, Climate Change and the Environment, Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot SL5, London, United Kingdom, (12)University of Western Ontario, London, ON, Canada
Abstract:
Continued use of fossil fuel drives an accelerating increase in atmospheric CO2 concentration ([CO2]) and is the principal cause of global climate change. Many of the observed and projected impacts of rising [CO2] portend increasing environmental and economic risk, yet the uncertainty surrounding the projection of our future climate by Earth System Models (ESMs) is unacceptably high. Improving confidence in our estimation of future [CO2] is essential if we seek to project global change with greater confidence. There are critical uncertainties over the long term response of terrestrial CO2 uptake to global change, more specifically, over the size of the terrestrial carbon sink and over its sensitivity to rising [CO2] and temperature. Reducing the uncertainty associated with model representation of the largest CO2 flux on the planet is therefore an essential part of improving confidence in projections of global change. Here we have examined model representation of photosynthesis in seven process models including several global models that underlie the representation of photosynthesis in the land surface model component of ESMs that were part of the recent Fifth Assessment Report from the IPCC. Our approach was to focus on how physiological responses are represented by these models, and to better understand how structural and parametric differences drive variation in model responses to light, CO2, nutrients, temperature, vapor pressure deficit and soil moisture. We challenged each model to produce leaf and canopy responses to these factors to help us identify areas in which current process knowledge and emerging data sets could be used to improve model skill, and also identify knowledge gaps in current understanding that directly impact model outputs. We hope this work will provide a roadmap for the scientific activity that is necessary to advance process representation, parameterization and scaling of photosynthesis in the next generation of Earth System Models.
