Idealized climate change experiments from the CMIP5 archive
Abstract
Comprehensive climate models represent myriad processes across scales, and by including everything they are our most complete tools for studying climate change. This complexity, however, can impede understanding fundamental processes within the model (and hopefully the climate system). Given the spread of climate sensitivity among current climate models, it is useful to ask whether idealized experiments can help to shed light on the processes and phenomena that underlie climate sensitivity. In this work, we analyze idealized climate change experiments from the CMIP5 archive. These experiments use fixed sea-surface temperature in either a realistic Earth configuration using observed sea-surface temperatures over 30 years, or a further idealized aquaplanet configuration with an analytic surface temperature distribution. Uniform 4K sea-surface temperature warming is applied to examine the atmospheric response to warming. Separate simulations quadruple atmospheric carbon dioxide, allowing a direct measure of the tropospheric adjustment. Comparing the aquaplanet and Earth-like experiments exposes the role of asymmetries for processes affecting climate change. We find that most models have similar sensitivity and cloud changes in the two configurations, implying the importance of accurately representing shallow cumulus clouds over the tropical oceans. Several models have inconsistent responses between the configurations, and we show that this can occur because of zonally asymmetric responses in the Earth-like configuration or due to reorganization of the tropical circulation in the aquaplanet. This study confirms the utility of idealized experiments for understanding climate sensitivity, bolstering the ideal of a hierarchy of climate models. Understanding the similarities and differences among model configurations points toward processes and biases that may have physical constraints that can be observed and lead to model improvement and more confident projections of future climate change.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.A12A..05M
- Keywords:
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- 0321 ATMOSPHERIC COMPOSITION AND STRUCTURE Cloud/radiation interaction;
- 1626 GLOBAL CHANGE Global climate models;
- 1610 GLOBAL CHANGE Atmosphere;
- 3310 ATMOSPHERIC PROCESSES Clouds and cloud feedbacks