Global warming triggers the notable rise in water vapour: implications for global climate change

Among all greenhouse gases (GHGs), atmospheric water vapour is the most abundant and has huge influence on the Earth’s radiation budget, and plays decisive role in regional weather processes. Unlike other GHGs, which are controlled by emissions, atmospheric water vapour is influenced by the surface temperature. Here, we examine the long-term changes in global and regional water vapour using satellite and reanalysis datasets. The annual mean water vapour shows very high values in tropics and low values in the polar and high terrain regions. A clear seasonal cycle is observed in the water vapour, with high values in summer (25–65 kg/m²) and small values in winter (5–20 kg/m²), except in the tropics. The high values in summer is maily due to the enhanced evapotranpiration driven by surface air temperature, and water vapour transport by winds. There is a significant rise in annual mean global water vapour, driven by global warming, about 0.025–0.1 kg/m²/yr for the period 1980–2020. Furthermore, higher positive trends in water vapour is also observed in arid regions (Sahara, Arabian and Thar desert), Indian subcontinent and the Arctic. The higher values of water vapour trends in the Arctic is due to the significant rise in temperature there. Similarly, the increase in water vapour in desert regions is due to water vapour transport from nearby oceans. The associated radiative effects on short-wave at the surface varies from -5 to -70 W/m² over the tropical radiosonde stations, and the smallest of about -5– -10 W/m² in the polar regions. This study, therefore,  shows that there is significant rise in water vapour across the latitudes, which could further increase the global temperature through positive feedback mechamism and thus, change global and regional climate.

Keywords: Water Vapour, Evapotranspiration, Global Warming, Arctic, Desert; Radiative Effects