Increase in Tropospheric Water Vapor Amplifies Global Warming and Climate Change

Abstract

Among the greenhouse gases (GHGs), atmospheric water vapor is the most abundant, has a large influence on the radiation budget of Earth, and plays a decisive role in regional weather processes. We investigate the long-term (1980–2020) changes in global tropospheric water vapor using satellite, radiosonde, and reanalysis data and assess the impact of changes in water vapor on regional and global climate with respect to its radiative feedback. The annual climatology of global tropospheric water vapor varies from 5 to 60 kg/m 2 across different regions. Except in the tropics, there is a strong seasonal cycle in both the southern and northern hemispheres, with the highest values in summer (25 to 65 kg/m 2 ) and smallest values in winter (5 to 20 kg/m 2 ). Most regions show positive trends in the annual mean tropospheric water vapor, at about 0.025 to 0.1 kg/m 2 /year, for the period of 1980–2020, with a notable increase in the Arctic because of the high rise in temperature there. Throughout the troposphere (except 200 hPa), the annual mean specific humidity shows significant positive trends over both land and oceans, with the highest values of approximately 0.015 g/kg/year at 1000 hPa in the tropics. The associated radiative effects on shortwaves at the surface vary from −5 to −70 W/m 2 , with the highest values at Manaus, Porto, and Hanty–Mawsijsk (tropical stations) and the smallest values of about −5 to −10 W/m 2 in the polar regions. The model projections for future high-emission scenarios show a large increase in atmospheric water vapor, approximately twice the current value in the polar latitudes by the end of the 21st century. This is a great concern for global and regional climate, as the rise in water vapor would further augment global warming and phenomena, such as the Arctic amplification. Therefore, this study cautions that there is a significant rise in tropospheric water vapor across latitudes and altitudes, which could further increase the global temperature and, thus, accelerate global climate change.