We describe the development and validation of a new near-global gridded marine humidity monitoring product, HadISDH.marine, from air temperature and dew point temperature reported by ships. Erroneous data, biases, and inhomogeneities have been removed where possible through checks for outliers, supersaturated values, repeated values, and adjustments for known biases in non-aspirated instruments and ship heights. We have also estimated uncertainty in the data at the grid box and regional level.

Using a sub-daily dataset of in situ observations, we have performed a study to see how the distributions of temperatures and wind speeds have changed over the last 45 years. Changes in the location or shape of these distributions show how extreme temperatures or wind speeds have changed. Our results show that cool extremes are warming more rapidly than warm ones in high latitudes but that in other parts of the world the opposite is true.

Measurements of sub-daily (e.g. hourly) rainfall totals are essential if we are to understand short, intense bursts of rainfall that cause flash floods. We might expect the intensity of such events to increase in a warming climate but these are poorly realised in projections of future climate change. The INTENSE project is collating a global dataset of hourly rainfall measurements and linking with new developments in climate models to understand the characteristics and causes of these events.

We compare the latest observations of relative and specific humidity with those from climate models. The climate models do not accurately reproduce the observed humidity behaviour for the last 15–20 years. We use the temporal, spatial and trend information to contrast the patterns exhibited by the observations and models. The temporal behaviour of the observations has previously been documented and is consistent with faster warming rates over land compared to oceans.

Observational data sets contain uncertainties, e.g. from the instrument accuracy, as well as from the fact that usually only a single method is used in processing. We have performed an assessment of the size of the uncertainties associated with choices in the method used. The largest effects come from changes which affect the station network or the gridding method used. However, for the temperature indices in places with many stations, these changes have little effect on the long-term behaviour.