Not summers, but winters that are warmer
On September 25, Frédérique Bec from Théma (University of Cergy-Pontoise), Anders Rahbek (University of Copenhagen) and myself organized a workshop in our ESSEC campus in La Défense.
Among the presenters, who were mostly working on theoretical models for time series, Jesus Gonzalo (Universidad Carlos III, Madrid) showed us some interesting results based on a series of daily temperature recordings in a station in Oxfordshire, UK.
The interesting feature of this temperature series is that it is consistent: measurements have been performed using a similar technique since the 18th Century. This is great as often, studies on long term temperatures face issues dealing with data compatibility over time.
One of the conclusion of Jesus Gonzalo's work (joint with Lola Gadea, from the University of Zaragoza) working on the evolution of the annual distribution of temperatures is that it is not the higher range of temperatures that have changed, but rather the lower end of the distribution, i.e. winters are warming up, not summers (at least in the UK). This result is interesting in that it could explain why polar caps are melting progressively.
Yet, more analysis is warranted, in particular, I wonder whether the fact that over this period there hasn't been massive volcanic eruptions (which project ashes in the upper atmosphere, thus temporarily and partially blinding the sun, which in turn may induce a reduction in global temperatures for a few years) may have had an effect.