Global climate models for agricultural impact research
Global climate models (GCMs) have become increasingly important for climate change science and provide the basis for most impact studies. Since impact models are highly sensitive to input climate data, GCM skill is crucial for getting better short-, medium- and long-term outlooks for agricultural production and food security. The Coupled Model Intercomparison Project (CMIP) phase 5 ensemble is likely to underpin the majority of climate impact assessments over the next few years. We assess 24 CMIP3 and 26 CMIP5 simulations of present climate against climate observations for five tropical regions, as well as regional improvements in model skill and, through literature review, the sensitivities of impact estimates to model error. Climatological means of seasonal mean temperatures depict mean errors between 1 and 18°C (2–130% with respect to mean), whereas seasonal precipitation and wet-day frequency depict larger errors, often offsetting observed means and variability beyond 100%. Simulated interannual climate variability in GCMs warrants particular attention, given that no single GCM matches observations in more than 30% of the areas for monthly precipitation and wet-day frequency, 50% for diurnal range and 70% for mean temperatures. We report improvements in mean climate skill of 5–15% for climatological mean temperatures, 3–5% for diurnal range and 1–2% in precipitation. At these improvement rates, we estimate that at least 5–30 years of CMIP work is required to improve regional temperature simulations and at least 30–50 years for precipitation simulations, for these to be directly input into impact models.
Pour ceux qui se sont perdus dans le jargon scientifique, je résume l’étude… On a utilisé les modèles climatiques du GIEC (CMIP) pour vérifier s’ils étaient en mesure de « prédire » le climat observé dans le passé.
Les conclusions? Les modèles sont terriblement imprécis. Les chercheurs estiment qu’il faudra entre 5 & 50 ans pour avoir des prédictions fiables de température et entre 30 & 50 ans pour avoir des prédictions fiables de précipitation.
Et on ose nous dire que le débat est clos…