Global Warming and Anthropogenic Emissions of Water Vapor

The two major components of greenhouse gases, CO₂ and water, are indispensable for sustaining life on Earth. Water vapor is the most significant greenhouse gas that has provided the earth with an "atmospheric blanket" and prevented the surface of the earth from freezing. However, contemporary climate models largely consider the influence of water vapor as a factor within positive feedback loops, while the possibility of direct anthropogenic emissions of water vapor as primary drivers of global warming remains underexplored. In particular, a common assumption has been that the global atmospheric water vapor will increase by about 6 to 7% in response to each 1 °C of warming caused by the nonaqueous greenhouse gases in accordance with the Clausius-Clapeyron equation, and this increased moisture content will lead to an increased greenhouse gas effect. However, the Clausius-Clapeyron equation is based on two-phase equilibrium, and there is no a priori physical basis that it can be applied to the earth's climate for which the water vapor does not always coexist with a condensed phase. Here, we utilized global specific humidity data from the NCEP/NCAR reanalysis data set to examine whether the Clausius-Clapeyron equation can form a basis for such positive feedback commonly assumed in the contemporary climate models. Our results show (1) qualitiatively, the linear nature of the Clausius-Clapeyron equation demonstrates a significant level of consistency when averaged over expansive regions like specific latitudes around the globe, (2) this consistency does not extend to individual locations where a plot of (ln P_v) vs (1/T) becomes nonlinear, indicating substantial undersaturation that varies with time, (3) quantitatively, the discrepancies between the observed and the expected values of the slopes are wide-ranging, and (4) the absolute amount of water vapor increased substantially above the population centers and the agricultural areas in the Northern Hemisphere between 1960 and 2020. Human activities appear to have substantial impacts on the local water vapor content in the atmosphere. Once we assume that anthropogenic emissions of water vapor are the source of local water vapor content in the atmosphere, it can, together with the air circulation patterns (Hadler, Ferrel and polar), provide an explanation for the observations that Arctic ice has been melting at a much more accelerated rate than Antarctic ice.