The Copernicus Climate Change Service that is being implemented by ECMWF on behalf of the European Commission has tracked a period of record global warmth in the temperature summaries it has published monthly since August 2015.
The globally averaged surface air temperature usually peaks in July, when the land masses of the northern hemisphere are generally at their warmest. It varies by more than 3°C over the course of each year. The largest recent deviation from this annual cycle occurred in February 2016, when the global temperature was more than 0.8°C higher than the 1981–2010 average for February. The differences have since narrowed, but July 2016 was still more than 0.5°C warmer than the corresponding average for July. This was sufficient to make July 2016 the warmest month on record in absolute terms. August 2016 was not quite as warm as July 2016 but still ended up as the second warmest month on record.
The global temperature for each of the twelve months from October 2015 to September 2016 exceeded the highest value previously recorded for that particular month. This came close to happening earlier, for the months from October 1997 to September 1998. Both twelve-month periods were characterised by pronounced El Niño events. The earlier event was for the most part a little stronger over the tropical Pacific Ocean, but air temperatures were generally higher during the latest event because of the overall progression of global warming. Lower Arctic sea-ice extent in 2016 was also a factor behind the larger temperature differences seen during the northern winter months.
The values published by the Copernicus Climate Change Service are based on ECMWF’s ERA-Interim reanalysis, which runs from 1979 onwards. They are in essence confirmed by values derived from the Japan Meteorological Agency’s JRA-55 reanalysis. Early results from ERA5, a new ECMWF/Copernicus reanalysis that is currently in production, show local improvements over ERA-Interim but similar global averages. Longer-term context is provided by conventional analyses such as HadCRUT4, produced collaboratively by the Met Office and the Climatic Research Unit of the University of East Anglia. Extending back to 1850, HadCRUT4 shows no month prior to 1979 that was as anomalously warm globally as the months from 1997 onwards.