a, 15-year trends; b, 62-year trends. Thin coloured lines show individual models as diagnosed previously35; if multiple realizations were available for a model, then the ensemble average of the individual diagnosed ERF time series for that model was given35 and is shown here. The thick red line shows the ensemble average over all models. The thick black line shows the best estimate from AR546, including, for illustration, the 5–95% uncertainty range for the periods 1984–1998 (a) and 1951–2011 (b), taken from fig. 8.19 in ref. 46. These uncertainty ranges, both of which are around 0.2 W m−2 per decade, do not take into account observational biases such as those diagnosed in ref. 48. Despite the scatter of the CMIP5 ensemble trends, the ensemble mean is in good agreement with the AR5 best estimate for almost all start years. The AR5 best-estimate ERF sums time series of forcing across individual forcing terms. Individual time series of AR5 ERF were derived in different ways. Greenhouse gas concentrations (observed or inferred), stratospheric aerosol optical depth and total solar irradiance were used to derive estimates of radiative forcing using simple formulae. Surface albedo forcing was derived from estimated anthropogenic vegetation trends. Ozone and aerosol forcings were derived from chemical transport model results with aspects of the forcing constrained by other modelling approaches or observations, or both. ERF sums rapid adjustments with traditional radiative forcings. Most time series in AR5 were based on traditional radiative forcings, and only CO 2 and aerosol forcings included an assessment of the rapid adjustment. In other cases ERF and radiative forcings were assumed to be the same. The AR5 ERF for the most recent 2000–2011 period included updated estimates of volcanic and solar forcing, taking into account the broader 2008–2009 solar minimum and post-2000 volcanic activity46. These two cooling influences are not included in the CMIP5 ERF; it is hence surprising and unexplained why the CMIP5 ensemble-mean of 15-year ERF trends lies below the best-estimate AR5 ERF trend for the latest start years in a.