Small Impact of Stratospheric Dynamics and Chemistry on the Surface Temperature of the Last Glacial Maximum in CESM2(WACCM6ma)

Stratospheric dynamics and chemistry can impact the tropospheric climate through changing radiatively active atmospheric constituents and stratosphere-troposphere interactions. The impact of stratospheric dynamics and chemistry on the Last Glacial Maximum (LGM) climate is not well-studied and remains an uncertain aspect of glacial-interglacial climate change. Here we perform coupled LGM simulations using the Community Earth System Model version 2 (CESM2), with a high-top atmosphere—the Whole Atmosphere Community Climate Model version 6 with a middle atmosphere chemistry mechanism (WACCM6ma). The CESM2(WACCM6ma) LGM simulations show a weaker stratospheric circulation than the preindustrial, 10%–35% less tropospheric ozone and 10%–50% more ozone in the lower stratosphere. These dynamical and chemical changes cause slightly more cooling (<5%) in LGM surface and tropospheric temperatures than parallel simulations using a low-top atmosphere without active chemistry. Results from our model suggest that stratospheric dynamics and chemistry may have little direct effect on the glacial-interglacial climate change.