Current state of the water vapour feedback

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The CO2 - water vapour positive climate feedback is real and active. The figure below is showing the meridional-vertical cross-section of the zonally-averaged specific humidity increase based between 1980 and 2018 for ERA5 reanalyses of the European Centre for Medium-range Weather Forecasts (ECMWF). The yearly-average specific humidity at certain grid point was computed for every year between 1980 to 2018 to estimate the linear trend and the difference between the trendline values are plotted.

specific humidity increase

The specific humidity increase is in line with the rising tropospheric temperature, taking into account the approximate exponential decrease of specific humidity with height. Thus, the increase is largest in the tropical mid-troposphere and in the lower-troposphere of northern extratropics.

temperature rise