CGD scientists completed 20^th Century Runs of the CESM-BGC version 1.5:

• Coupled climate-carbon experiments have been completed with an updated version of CESM. Compared to previous versions of CESM, the bias in CO2 uptake by the land model was significantly reduced, while the bias in CO2 uptake by the ocean did not change much.
  
  
• Within a large set of climate models, Antarctic sea ice and SSTs exhibit a 2-timescale response to SAM variability, with initial cooling and ice increases followed by warming and ice decline.
  
  
• Late 20th century Antarctic sea ice trends in CMIP5 simulations are related in part to different modeled responses to SAM variability acting on different time-varying transient SAM conditions.

As new parameterizations of eddy mixing are developed there is a need for quantitative guidance from observations and high-resolution modeling to first validate the parameterization, and second to guide the choice of free parameters. A recently developed technique for computing the global distribution of the eddy diffusivity tensor from passive tracer simulations with high-resolution global ocean models was used to develop estimates of the spatial dependence and degree of anisotropy of mixing by mesoscale eddies. These estimates were used to constrain the range of values used in simulations with prototype versions of CESM that incorporate a new anisotropic form of the Gent-McWilliams parameterization.