A global perspective on CMIP5 climate model biases

  • 3 March 2014
  • Number of views: 4021

Researched funded by CPO’s MAPP program was published in Nature Climate Change on Feb. 23.  Scientists at NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML) led a new study to be published in Nature Climate Change, identifies a path forward to reduce or eliminate global sea surface temperature biases in the Intergovernmental Panel on Climate Change’s (IPCC) Assessments resulting in greater confidence in climate model projections.  

This study links regional ocean circulation processes to patterns of global sea surface temperature biases in the global climate models. Previously, the IPCC documented and accounted for these biases by increasing the uncertainty in model projections. Most models, have deficiencies and biases that raise large uncertainties in their products. Over the past several decades, a tremendous effort has been made to improve model performance in the simulation of special regions and aspects of the climate system.

 

a, The annual-mean SST bias averaged in 22 climate models. The SST bias is calculated by the SST difference between the model SST and extended reconstructed SST. The dots denote where at least 18 of 22 models (82%) have the same sign in the SST bias. The rectangles represent the focused regions. b,c, Spatial maps of SST bias and the AMOC for the first inter-model SVD mode (accounting for 45% of total covariance). d, Their corresponding coefficients. The x axis in d represents different models (Supplementary Table 1). The coefficients have been normalized by their own standard deviations. 

 

In the study, the authors show that biases or errors in special regions can be linked with others at far away locations. They found that in 22 climate models regional sea surface temperature (SST) biases are commonly linked with the Atlantic meridional overturning circulation (AMOC), which is characterized by the northward flow in the upper ocean and returning southward flow in the deep ocean. A simulated weak AMOC is associated with cold biases in the entire Northern Hemisphere with an atmospheric pattern that resembles the Northern Hemisphere annular mode. The AMOC weakening is also associated with a strengthening of Antarctic Bottom Water formation and warm SST biases in the Southern Ocean.

The study also showed that cold biases in the tropical North Atlantic and West African/Indian monsoon regions during the warm season in the Northern Hemisphere have interhemispheric links with warm SST biases in the tropical southeastern Pacific and Atlantic, respectively.

According to the researchers, the study results suggest that improving the simulation of regional processes may not suffice for overall better model performance, as the effects of remote biases may override them.

The study, was funded by NOAA’s Climate Program Office, was co-authored by the Cooperative Institute for Marine and Atmospheric Studies, and university partners in China.

To view the article online in Nature Climate Change, visit: www.nature.com/nclimate/journal/v4/n3/full/nclimate2118.html

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MAPP Program Director
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