Skewness of Temperature Data Implies an Abrupt Change in the Climate
System between 1985 and 1991
Instrumental records of mean annual temperature extend back to the
seventeenth and eighteenth centuries at multiple sites in Europe. For
such long time series, we expect and find that histograms of mean annual
temperature data become skewed towards higher temperatures with time
because of global warming. However, we also find that skewness changed
abruptly and started increasing between 1985 and 1991 (95% confidence)
at 17 sites. We argue that this finding may imply an abrupt change in
the climate system affecting Europe which probably occurred at this
time. One possible cause is a climate tipping point having been passed.
Of known tipping elements, we find Arctic sea ice loss, potentially
linked to reduced sulfate aerosol emissions and coupled to temperature
by an albedo feedback mechanism, a likely candidate. This is based on
good correlations of sea ice extent and sulfate aerosol emissions with
skewness of mean annual temperature data.