Multimodel assessment of the upper troposphere and lower stratosphere: Tropics and global trends

The models simulate continued decreases in tropopause pressure in the 21st century, along with ~1K increases per century in cold point tropopause temperature and 0.5-1 ppmv per century increases in water vapor above the tropical tropopause. TTL water vapor increases below the cold point. In two models, these trends are associated with 35% increases in TTL cloud fraction.

These changes indicate significant perturbations to TTL processes, specifically to deep convective heating and humidity transport. Ozone in the extratropical lowermost stratosphere has significant and hemispheric asymmetric trends. O3 is projected to increase by nearly 30% due to ozone recovery in the Southern Hemisphere (SH) and due to enhancements in the stratospheric circulation.

These UTLS ozone trends may have significant effects in the TTL and the troposphere.