Adding Copernicus

I’ve added the Copernicus ‘ERA-Interim’ global temperature series to all of the global temperature plots. (You may need a browser refresh to see the latest versions.)

Copernicus is the new name for the European Union’s earth observation programme. The climate component, Copernicus Climate Change Service is run by European Centre for Medium-Range Weather Forecasts, operators of the world-leading global weather model that we call ECMWF. Starting in late 2014, much of the climate change program’s emphasis has been on reanalysis.



Reanalysis is the stuff of re-assimilating historical weather data into a global weather model to produce a fine-scale, time-varying representation of the system across the full length of the data record. That’s essentially just a data tracking model, but at extraordinary sophistication. ERA-Interim, published in 2009, is what ECMWF calls a fourth-generation reanalysis product. (Meteorologists have been at this thing for a while; Copernicus has now started publishing its fifth-generation product.) has this summary:

ERA-Interim was originally planned as an ‘interim’ reanalysis in preparation for the next-generation extended reanalysis to replace ERA-40. It uses a December 2006 version of the ECMWF Integrated Forecast Model (IFS Cy31r2). It originally covered dates from 1 Jan 1989 but an additional decade, from 1 January 1979, was added later. ERA-Interim is being continued in real time. The spectral resolution is T255 (about 80 km) and there are 60 vertical levels, with the model top at 0.1 hPa (about 64 km). The data assimilation is based on a 12-hourly four-dimensional variational analysis (4D-Var) with adaptive estimation of biases in satellite radiance data (VarBC). With some exceptions, ERA-Interim uses input observations prepared for ERA-40 until 2002, and data from ECMWF’s operational archive thereafter.

The strong advantage of reanalysis for estimating global temperature is that the answer is full-coverage; there is no need for crude or clever statistical approaches to estimating temperature change across data-poor regions. A secondary advantage is that temperatures are estimated directly as absolute values. They do not have to be estimated as differences (‘anomalies’), as they are in all of the popular instrumental series. A major disadvantage, for products as sophisticated as ERA-Interim, is that the data needs limit coverage to the satellite era — 1979 onwards.

The ‘Copernicus ERA-Interim’ published surface temperature field (and its regional and global averages) is not just the 2 m temperature from all the ECMWF runs; there is adjustment for sea surface temperature and sea ice coverage biases.



The published Copernicus global monthly temperature time series is expressed as anomalies relative to the 1981-2010 baseline, as are several others that I plot. Others use 1961-1990 (HadCRUT), 1951-1980 (GISTEMP), 1971-2000 (NOAA, JMA), etc etc. To rationalise and simplify rebasing for plotting I’ve now adopted the following:

  1. If a series is not stated to be 1981-2010 based, it is rebased to that using the difference between the (generally 30-year) all-months mean across its baseline and its all-months mean across 1981-2010. (Rebasing is annual not separately by months, and is intrinsic — it does not depend at all on other series.)
  2. All of the anomaly series are then rebased from 1981-2010 to ‘pre-industrial’ by adding a uniform 0.7 °C, following the plotting approach Copernicus itself has now adopted, for which they cite support from Hawkins et al 2017.



I have written before that reanalysis offers potentially the best estimates of global temperature. The new Copernicus series may well be that — for the satellite era. But in the overall scheme of things all of these estimation approaches give the same dreadful answer:

Simplistic global temperature extrapolations



  1. Hawkins, Ed, Pablo Ortega, Emma Suckling, Andrew Schurer, Gabi Hegerl, Phil Jones, Manoj Joshi et al. “Estimating changes in global temperature since the pre-industrial period.” Bulletin of the American Meteorological Society 2017 (2017).

2 comments to Adding Copernicus

  • You know this, I know this and most sensible educated people in the world know this. Somehow we have to band together to get the numskulls amongst our political power class to find a way to take appropriate action. Kill coal and petroleum products as energy sources. Combined with world population increase even if the average mineral energy use per person remain constant, which it is not as more and more people want to live like us, we are turning this planet into a shit planet in the space of a few hundred years after hundreds of thousands of years or even millions of years of human existence. We must be cleverer than this.