Relationships between the sea-ice concentration, cloud cover and air moisture in the Arctic are analysed for the period 1989–2009 on the basis of the ERA-Interim reanalysis of the ECMWF. The reanalysis shows a significant increasing trend for the annual mean total water vapour (TWV) averaged over the polar cap north of 70° N, while for the cloud water content (CWC) the increasing trend is not statistically significant. Seasonally, the increasing trends for TWV are significant for summer (July–September; p < 0.05) and autumn (October–December; p < 0.01), and for CWC in autumn (p < 0.01). The TWV correlates with sea-ice concentration in every season, and CWC correlates with sea-ice concentration in every season except summer. In summer, CWC does not depend on sea-ice cover because of thermal decoupling, but the CWC correlates with the Arctic oscillation index (r = 0.68). The ERA-Interim-based results are qualitatively in agreement with satellite observations and in situ data on the atmospheric transmissivity for shortwave radiation. To find out the causal relationships, the time lags between anomalies in the air moisture, cloud cover and sea-ice concentration are analysed.