CONTROL ID: 1792131

TITLE: Causes and Implications of Persistent Atmospheric Carbon Dioxide Biases in Earth System Models (Invited)

AUTHORS (FIRST NAME, LAST NAME): Forrest M Hoffman1, 2, James Tremper Randerson1, Vivek Arora3, Qing Bao4, Katharina D. Six5, Patricia Cadule6, Duoying Ji7, Chris D Jones8, Michio Kawamiya9, Samar Khatiwala10, Keith T Lindsay11, Atsushi Obata12, Elena Shevliakova13, Jerry F. Tjiputra14, Evgeny M. Volodin15, Tongwen Wu16

INSTITUTIONS (ALL): 1. Earth System Science, University of California, Irvine, CA, United States.
2. Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN, United States.
3. Canadian Centre for Climate Modelling and Analysis, Meteorological Service of Canada, Victoria, BC, Canada.
4. State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China.
5. Max Planck Institute for Meteorology, Hamburg, Germany.
6. Laboratoire des Sciences du Climat et de l’Environnement, Institut Pierre Simon Laplace, Gif sur Yvette Cedex, France.
7. State Key Laboratory of Earth Surface Processes and Resource Ecology, College of Global Change and Earth System Science, Beijing Normal University, Beijing, China.
8. Hadley Centre, U.K. Met Office, Exeter, United Kingdom.
9. Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokosuka-city, Kanagawa, Japan.
10. Lamont Doherty Earth Observatory, Columbia University, Palisades, NY, United States.
11. Climate & Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO, United States.
12. Meteorological Research Institute, Japan Meteorological Agency, Tsukuba-city, Ibaraki, Japan.
13. Geophysical Fluid Dynamics Laboratory, Princeton University, Princeton, NJ, United States.
14. Uni Climate, Uni Research, Bergen, Norway.
15. Institute of Numerical Mathematics, Russian Academy of Science, Moscow, Russian Federation.
16. Climate System Modeling Division, Beijing Climate Center, China Meteorological Administration, Beijing, China.

ABSTRACT BODY: The strength of feedbacks between a changing climate and future CO2 concentrations are uncertain and difficult to predict using Earth System Models (ESMs). We analyzed emission-driven simulations—in which atmospheric CO2 levels were computed prognostically—for historical (1850–2005) and future periods (RCP 8.5 for 2006–2100) produced by 15 ESMs for the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5). Comparison of ESM prognostic atmospheric CO2 over the historical period with observations indicated that ESMs, on average, had a small positive bias in predictions of contemporary atmospheric CO2. A key driver of this persistent bias was weak ocean carbon uptake exhibited by the majority of ESMs, based on comparisons with observations of ocean and atmosphere anthropogenic carbon inventories. We found a significant linear relationship between contemporary atmospheric CO2 biases and future CO2 levels for the multi-model ensemble. We used this relationship to create a contemporary CO2 tuned model (CCTM) estimate of the atmospheric CO2 trajectory for the 21st century. The CCTM yielded CO2 estimates of 600±14 ppm at 2060 and 947±35 ppm at 2100, which were 21 ppm and 32 ppm below the multi-model mean during these two time periods. Uncertainty estimates derived from this approach were almost 6 times smaller at 2060 and almost 5 times smaller at 2100 than those from the ESM ensemble. The CCTM also significantly narrowed the range of CO2-induced radiative forcing and temperature increases during the remainder of the 21st century. Because many processes contributing to contemporary carbon cycle biases persist over decadal timescales, our analysis suggests uncertainties in future climate scenarios may be considerably reduced by tuning models to the long-term time series of CO2 from Mauna Loa and other atmospheric monitoring stations.

KEYWORDS: 0428 BIOGEOSCIENCES Carbon cycling, 0365 ATMOSPHERIC COMPOSITION AND STRUCTURE Troposphere: composition and chemistry, 0426 BIOGEOSCIENCES Biosphere/atmosphere interactions, 4805 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL Biogeochemical cycles, processes, and modeling.
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Additional Details

Previously Presented Material: 50% of material previously presented at the 9th International Carbon Dioxide Conference (ICDC9) in Beijing, China.

Contact Details

CONTACT (NAME ONLY): Forrest Hoffman