Stratospheric ozone during the Last Glacial Maximum

Abstract

Stratospheric ozone during the Last Glacial Maximum (LGM) is investigated in on‐line simulations with the GISS Global Climate/Middle Atmosphere Model 3. LGM boundary conditions and atmospheric concentrations are employed in three simulations: without interactive ozone, with ozone photochemistry appropriate for that time period and with the LGM climate but current atmospheric composition for chemistry. Results show stratospheric ozone increased during the LGM due to reduced NOy and chlorine, while warmer stratospheric temperatures (from reduced stratospheric CO2) decrease ozone with current photochemistry. The stratospheric residual circulation intensified in the lowermost stratosphere, increasing stratosphere/troposphere exchange at higher latitudes, although for most of the middle atmosphere the circulation decreased; the age of air in the Middle Atmosphere increased by up to one year. Compared with the vastly different LGM conditions, increase in stratospheric ozone of 2% by mass had little effect on atmospheric dynamics, and increased the global radiation balance by <0.1 Wm−2.