14 October 2014

Impact of Large-Scale Climate Extremes on Biospheric Carbon Fluxes


The role of climate extremes and understanding their impact on the carbon (C) cycle is increasingly a focus of Earth system science research. Droughts, heat waves, or heavy rain/snow can cause substantial changes in terrestrial C fluxes. And extreme climate conditions often drive extreme changes in C fluxes. Researchers, including Department of Energy scientists from Pacific Northwest National Laboratory analyzed how temperature and precipitation extremes and extreme changes in terrestrial C fluxes are related to each other in outputs from 10 state-of-the-art terrestrial biosphere models, all driven by the same climate forcing and environmental factors provided by the North American Carbon Program Multi-scale Synthesis and Terrestrial Model Intercomparison Project (MsTMIP). Through a global-scale analysis, the research showed that both droughts and heat waves translate into anomalous net CO2 releases from the land surface via different mechanisms. At the global scale, droughts and heat waves lead to large temporary net carbon release or decrease in C sink, while colder and wetter periods lead to a comparably smaller net carbon uptake or increase in C sink. The analysis revealed that extreme changes in gross primary production and total respiration (TR) are often caused by strong shifts in water availability, but extremes in TR shifts in temperature are also important. Extremes in net CO2 exchange are equally strongly driven by deviations in temperature and precipitation. Models mostly agree on the sign of the C flux response to climate extremes, but the model spread is large. In tropical forests, C cycle extremes are driven by water availability, whereas in boreal forests temperature plays a more important role. Models are particularly uncertain about the C flux response to extreme heat in boreal forests.

Jakob Zscheischler
Zscheischler, J, AM Michalak, C Schwalm, MD Mahecha, DN Huntzinger, M Reichstein, G Berthier, P Ciais, RB Cook, B El-Masri, M Huang, A Ito, A Jain, A King, H Lei, C Lu, J Mao, S Peng, B Poulter, D Ricciuto, X Shi, B Tao, H Tian, N Viovy, W Wang, Y Wei, J Yang, and N Zeng.  2014.  "Impact of Large-scale Climate Extremes on Biospheric Carbon Fluxes: An Intercomparison Based on MsTMIP Data."  Global Biogeochemical Cycles 28(6): 585-600, doi:10.1002/2014GB004826.