Coupled Model Errors in the Tropical Atlantic in CMIP5 and their impact on the reliability of climate projections.

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Many of the climate models that contributed to the third coupled model intercomparison project (CMIP3) which were extensively used in the IPCC 4th Assessment Report share common biases in the tropical Atlantic. These biases are characterised by a warm sea-surface temperature (SST) bias in the Eastern Tropical Atlantic and cold SST biases in the western tropical Atlantic and either side of the equator. These SST biases are associated with too strong north-easterly trade winds and too weak easterly flow on the equator. SSTs play a large role in determining regional weather systems including the monsoons, but are also partly determined by the regional circulation. Through the large-scale circulation of the atmosphere, sea surface temperatures in one region of the globe can also influence the weather remotely. The relationship between the SST biases and the wind biases is consistent with their development through a coupling between biases in the atmospheric and oceanic components of the model which reinforce each other, and as such it is difficult to determine the original source of the bias. In this project we propose to assess the quality of the models contributing to the latest model intercomparison project (CMIP5) which will be the main source of information to inform the 5th Assessment Report of the IPCC. We will use the contributions to the CMIP5 archive which have been initialized from the observed state of the atmosphere and ocean and run for 10 years to examine how these errors develop and identify those processes which contribute to the development of the biases to inform future model development. We will also identify the impact these biases have on our confidence in near term (next 10 -20 years) prediction of the climate, in particular in the regions around the tropical Atlantic (e.g. Africa and the Amazon) but also globally.