Benchmarking coupled climate‐carbon models against long‐term atmospheric CO₂ measurements

Abstract

[1] We evaluated three global models of the coupled carbon-climate system against atmospheric CO 2 concentration measured at a network of stations. These three models, HadCM3LC, IPSL-CM2-C, and IPSL-CM4-LOOP, participated in the C 4 MIP experiment and in various other simulations of the future climate impacts on the land and ocean carbon cycle. A new set of performance metrics is defined and applied to quantify each model's ability to reproduce the global growth rate, the seasonal cycle, the El Niño-Southern Oscillation (ENSO)-forced interannual variability of atmospheric CO 2 , and the sensitivity to climatic variations. Knowing that the uncertainty on the amplitude, in 2100, of the climate-carbon feedback is mainly due to the uncertainty of the response of the terrestrial biosphere to the climate change, our new metrics primarily target the evaluation of the land parameterization of the carbon cycle. The modeled fluxes are prescribed to the same global atmospheric transport model LMDZ4, and the simulated concentrations are compared to available observations. We found that the IPSL-CM4-LOOP model is best able to reproduce the phase and amplitude of the atmospheric CO 2 seasonal cycle in the Northern Hemisphere, while the other two models generally underestimate the seasonal amplitude. This points to some shortcomings in describing the vegetation phenology and heterotropic respiration response to climate. We also found that IPSL-CM2-C produces a climate-driven abnormal source of CO 2 to the atmosphere in response to El Niño anomalies. Here a good model performance rests upon a realistic simulation of ENSO-type climate variability and the subsequent tropical carbon cycle response. The three climate models underestimate the sea surface temperature warm anomaly during an El Niño, but HadCM3LC does best in reproducing the interannual CO 2 variability. More efforts are needed to further develop metrics for assessing the sensitivity of the carbon cycle to climate change, and this work should now be extended to assess ocean carbon models against observations.

Impact of aragonite saturation state changes on migratory pteropods

“…Imbedded in this climate system are modules for the terrestrial biosphere (ORCHI-DEE [30]) and the marine carbon cycle (PISCES [31]). More about the IPSL-CM4 Earth System Model and its validation can be found in Cadule et al [32,33].…”

Skill assessment of three earth system models with common marine biogeochemistry

“…The model is described in more detail in Marti et al (2010), but this version includes the marine carbon cycle model PISCES (detailed below). The IPSLCM4 is a fully coupled climate and carbon cycle model (Cadule et al 2010). Thus carbon sources and sinks over land and ocean are included.…”

A framework for benchmarking land models

“…The Coupled Carbon Cycle Climate Model Intercomparison Project (C4MIP) compared simulation of the climate-carbon cycle coupling among 11 models (Friedlingstein et al, 2006). Nevertheless, there have been a very few, if any, attempts to systematically evaluate land models against data from a range of observation networks and experiments in a comprehensive, objective and transparent manner (Cadule et al, 2010;Randerson et al, 2009).…”