The media are bellowing about how April in Germany was the “all-time warmest ever recorded”, and so it has to be a clear sign of global warming (suddenly the colder than normal March and February have been forgotten).
Europe enjoyed a balmy April this year. Chart: NCEP.
What does the unusually warm Central European April mean for the rest of the summer, if anything?
It turns out that it very well might mean something. Schneefan (snow fan) at wobleibtdieerderwaermung.de here reports that statistically the chances of a cool summer following for the continent are much higher than average.
He wrote that when one compares the seven warmest Aprils in Germany since 1961 to the respective summers that followed, one sees that the summers were awfully cool.
Schneefan looked at the hot Aprils of the years 1961, 1993, 2000, 2007, 2009 , 2011 and 2014 and their respective summers that followed. He calculated the average June-August temperature for the seven summers and compared the figure to the WMO 1981-2010 mean summer temperature. Here’s the result, according to NOAA data:
The NOAA-Reanalysis shows the average 2m temperature deviation for the seven June-August summers that followed warm Aprils in Europe since 1961. Source: NOAA reanalysis.
Clearly when Aprils in Central Europe are warm, summers that follow very much tend to be cooler than normal across Europe (except Scandinavia).
By comparison Schneefan’s statistical outlook into the future from April 11, 2018, using different years follows:
Here an NOAA reanalysis shows the average temperature deviation of the summers (June-August) of the years in Europe he chose (1984, 1985, 1986, 1996, 2006, and 2013) with respect to the WMO 1981-2010 mean for the summer months. While far northern Europe showed above average temperatures, the large bulk of part of Europe was cooler than normal.
Here we see the stunning similarity in Europe between both analyses using entirely different selection criteria.
We can only hope that the statistical trend does not get reaffirmed, especially during the time of the World Cup. The cool global conditions also remain unchanged as the La Niña: is expected to persist.