Unevenly distributed CO2 and its impacts on surface energy balance

Atmospheric carbon dioxide (CO2) has affected global surface and atmospheric energy balance since the In-dustrial Revolution. The spatial distribution of CO2 concentrations derived from satellite observation are introduced into the coupled Beijing Normal University Earth System Model (BNU-ESM) to study the responses of temperature and surface energy balance to non-uniform CO2 distribution under the Representative Concentration Pathway 8.5 scenario to 2100. Global annual mean atmospheric CO2 concentrations are set to equal those specified in the standard uniform CO2 simulations with differences in spatial pattern and seasonal cycles amounting to tens of ppm. Relative to the uniform CO2 simulation, global annual mean surface air temperature increases by 0.44 +/- 0.03 degrees C over 2071-2100 when forced with non-uniformly distributed CO2, in the Arctic by 1.63 +/- 0.28 degrees C and by 0.67 +/- 0.08 degrees C in northern midlatitudes. The non-uniform CO2 simulation increases global surface energy by 0.68 +/- 0.06 W m(-2), principally due to a 0.73 +/- 0.08 W m(-2) increase in net downward surface longwave flux. Surface energy balance increases by 0.33 +/- 0.11 W m(-2) (7.4%) averaged over oceans indicting a significant increase in ocean heat uptake. Surface energy budget averaged over the Arctic summer increases by 0.91 +/- 0.68 W m(-2) in the non-uniform CO2 simulation, which would have impact on sea ice extent and land ice melt rates with associated feedbacks. The increased surface energy fluxes and temperatures imply reduced time and emission space for greenhouse gases before running into scientific and politically flagged temperature limits.