Global (left) and European (right) annual average near-surface temperature anomalies relative to the pre-industrial period 1850-1900

The IPCC report on ‘Global warming of 1.5°C’ (https://www.ipcc.ch/sr15/) adopted an estimate of the global average temperature for 1850-1900 as an approximation for the pre-industrial temperature level. The rise in global average temperature over the industrial era was taken to be 0.63°C larger than the (less uncertain) rise in temperature above the 1981-2010 period. Our estimate was 0.05°C below that quoted in the IPCC report, i.e. we take the preindustrial era to be 0.68°C below the 1981-2010 average.

In the results presented, we use the updated 1991-2020 30-year reference period defined by the World Meteorological Organization (WMO) for calculating climatological averages. Therefore, each dataset shown in the graphs is aligned to have the same average temperature as ERA5 for 1991-2020 and a correction of 0.19°C difference between ERA5 averages for 1991-2020 and 1981-2010 is applied.  Additionally, an adjustment of 0.01°C was introduced for consistency with new estimates documented last year in the Sixth IPCC Assessment Report. Overall, the global average for the period 1850-1900 is found to be 0.88°C below the 1991-2020 average. These estimates were based on a different mix of datasets than used here.

IPCC estimates are not available for the all-land, European and Arctic regions for which C3S provides temperature indicators. For these cases, the changes from the 1850-1900 average shown in each graph are based on estimates of the differences between 1991-2020 and 1850-1900 averages derived from the Berkeley Earth, GISTEMPv4, HadCRUT5 and NOAAGlobalTempv5 datasets, which is found to be 1.47°C.

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