Impact of the El Niño–Southern Oscillation on upper-tropospheric water vapor

The majority of present-day and future global warming is related to various positive feedbacks in the climate system that tend to amplify the initial radiative forcing from increasing greenhouse gases in the atmosphere. One essential positive feedback is the rise in upper tropospheric water vapor (UTWV) or the specific humidity (SH) that acts as an intense greenhouse gas trapping in additional heat released from the Earth's surface. In this paper we expand on previous studies showing that the interannual variability of UTWV in the tropical and extratropical climates is strongly linked with the El Nino-Southern Oscillation (ENSO). We have expanded on previous studies by looking at the response of the long-term UTWV concentrations to the ENSO over a 41-year period (1979–2019) using the ERA5 reanalysis data. For the first time we look at the physical mechanism for the El Nino and La Nina connections to UTWV that is shown to be related to changes in deep convection over the central and eastern Pacific Ocean. In agreement with previous studies, we find that El Nino years have positive anomalies in UTWV, while in La Nina years there are negative anomalies in UTWV (±10%).