1. Small Impact of Stratospheric Dynamics and Chemistry on the Surface Temperature of the Last Glacial Maximum in CESM2(WACCM6ma).
- Author
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Zhu, Jiang, Otto‐Bliesner, Bette L., Garcia, Rolando, Brady, Esther C., Mills, Mike, Kinnison, Douglas, and Lamarque, Jean‐Francois
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LAST Glacial Maximum , *STRATOSPHERIC chemistry , *SURFACE chemistry , *SURFACE temperature , *OZONE layer , *EARTH'S orbit - Abstract
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. Plain Language Summary: The Last Glacial Maximum (LGM), the peak of the last ice age about 20,000 years ago, has been used frequently to calculate the Earth's climate sensitivity and to evaluate Earth System Models (ESM). These applications of the LGM climate rely on an accurate understanding of the LGM temperature and its relationship with changes in Earth's orbits and the subsequent physical, chemical, and biological interactions in the system. How the changes in stratospheric dynamics and chemistry impact the LGM temperature is important but not well studied. Here we address this question using a state‐of‐the‐art ESM that can simulate explicitly stratospheric dynamics and chemistry. A comparison with parallel simulations using the same ESM but without the capability of stratospheric dynamics and chemistry shows that stratospheric processes exert only a minor impact on the changes in the LGM surface temperature (approximately −0.21°C in global annual mean, or about <5% of the total change). Our results, if confirmed by other ESMs, suggest that stratospheric dynamics and chemistry do not affect much glacial‐interglacial climate change, and that ESMs without stratospheric dynamics and chemistry are sufficient for climate sensitivity and model evaluation studies using the LGM. Key Points: We present coupled Last Glacial Maximum (LGM) simulations using CESM2(WACCM6ma) with a high‐top atmosphere and compare them with parallel low‐top simulationsThe high‐top LGM simulations show weaker stratospheric circulation and substantial ozone changes in the troposphere and lower stratosphereThe active stratospheric dynamics and chemistry in CESM2(WACCM6ma) cause little change (<5%) in LGM surface and tropospheric temperatures [ABSTRACT FROM AUTHOR]
- Published
- 2022
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