Abstract: Change of water vapor may serve as the largest feedback that influences the climate sensitivity, i.e., amplifies the warming effects due to increases of other greenhouse gases (GHGs) such as atmospheric CO2 concentration. Such positive feedback very likely leads to more frequent extreme weather and climate events. It is essential to analyze the spatio-temporal distribution and long-term trend of atmospheric humidity and water vapor to assess the regional effect of the water vapor feedback to regional climate warming and to understand the mechanism of regional climate response to global warming. Summarizing latest studies, we can confirm that water vapor feedback is a strong positive feedback which could accelerate global warming by one time, and have estimated its range basically although this estimation has large uncertainty. Observational and re-analysis data of water vapor have become more abundant with the development of satellite and radiosonde techniques, but their consistency and homogeneity are far from perfect. Latest climate models could simulate the water vapor feedback in general, but advances in this area are not optimistic. In China, the observation and research in water vapor and its feedback have progressed much during last decades. Water vapor feedback in China is positive for surface temperature in consensus but has large uncertainty for precipitation due to regional climate changes.

Key words: atmospheric water vapor, water vapor feedback, climate effect