a, The time series of the global-mean surface temperature (GMST) is nearly identical for the HadCRUT3, HadCRUT4 and GISTEMP data sets2,3. Here, the data are plotted as a departure (anomaly) from the average value of the GMST during the period 1981–2010. b, But when these data are modelled as trends (measured in monthly increments from 1998), the type of model used and small differences in the data give remarkably different results4. The year labels span the calendar year, with the tick marks corresponding to 1 January. Medhaug et al.1 reconcile these results and show that the climate-model projections and observed trends are consistent. c, GMST warming fluctuates about a longer-term average warming rate — the warming is sometimes faster than the average rate (red dashes) and at other times slower (blue dashes). Some interpretations of the periods of slower-than-average warming include a 'pause' in which the short-term trend is either not positive (no trend) or below the average long-term trend (a slow trend).