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Including the Stratosphere in Models of Global Climate Change

Marsh, D.R., Mills, M.J., Kinnison, D.E., Lamarque, J.-F., Calvo, N., and Polvani, L.M. 2013. Climate change from 1850 to 2005 simulated in CESM1(WACCM). Journal of Climate 26: 7372-7391.
Noting that "it is becoming increasingly recognized that resolving the stratosphere and modeling its variability are necessary to correctly simulate tropospheric weather and climate," Marsh et al. (2013) write the U.S. National Center for Atmospheric Research's Earth System Model (CESM) "now includes an atmospheric component that extends in altitude to the lower thermosphere," and they say this model, "known as the Whole Atmosphere Community Climate Model (WACCM), includes fully interactive chemistry, allowing, for example, a self-consistent representation of the development and recovery of the stratospheric ozone hole and its effect on the troposphere." As their contribution to the topic, the authors set out to conduct a study that "focuses on analysis of an ensemble of transient simulations using CESM1 (WACCM), covering the period from the preindustrial era to present day [1850-2005], conducted as part of phase 5 of the Coupled Model Intercomparison Project [CMIP5]."

The six scientists report that "in comparison of tropospheric climate predictions with those from a version of CESM that does not fully resolve the stratosphere, the global-mean temperature trends are indistinguishable," which suggests no improvement in the new model over the old model. However, they state "systematic differences do exist in other climate variables, particularly in the extratropics." And they state "the magnitude of the difference can be as large as the climate change response itself."

Marsh et al. additionally report "both models overestimate the short-term cooling following large volcanic eruptions." And they note "WACCM predicts significantly larger changes in precipitation over Europe, the Mediterranean, and northern Africa," once again stating "the differences in predicted changes between the two models can be larger than the magnitude of the climate change prediction itself." And in regard to this unsettling fact that keeps popping up, they conclude, "when quantifying uncertainty in past and future climate change predictions, it will be important to consider the systematic errors introduced by the choices made on how the upper atmosphere is represented in the model," which suggests the quest for the Holy Grail of climate modeling has yet to be satisfactorily consummated.

Archived 5 February 2014