I recently wrote about Ashenfelter et al., 1995.   In an effort to reproduce the results of the paper, I tracked down Global Historical Climate Network data for Bordeaux-Merignac and compared it to the weather reported in Ashenfelter’s paper. The problem with the GHCN data for Bordeaux is that it ends in 1999.   There happens to be another source of data provided by the NCDC, called the Global Summary of Day, and it too contains Bordeaux daily weather data up to today.

56 Years of Bordeaux Temperature Data

56 Years of Bordeaux Temperature Data

The graph shows three time series of 3 sources of data:

1) Ashentemp – Temperature data averaged between April and September for each year shown.  This is the data as reported by the original paper

2) GHCN Temp – Average temperature between April and September for each year shown from the Global Historical Climate Network.   The average is the average of “daily average temperate” for each day in the year.   Daily Average temperature is the average of the reported daily maximum and daily minimum temperature.

3) GSOD Temp – Average temperature between April and September for each year shown from the Global Summary of the Day.

When I look at this graph one thought comes to mind.     Something happened in 1987 that drastically changed the climate as reported by the Bordeaux-Merignac weather station.     Much has been written about potential impacts of climate on the wine industry, but I don’t believe the signal shown is related to climate change.    The change is too sudden.   Up to 1987, the average temperature is approximately 16.5 oC, where as after 1987 is about 18.5 oC.   The graph indicates a less than gradual change.
Even more interesting,  the standard deviation of temperature from 1952 to 1988 is 0.63 oC.    So, the change in temperature of 2 oC is much greater than the natural variability of climate.

What happened?   I believe the station was moved .   There was a time when I was a participant in the Weather Derivatives industry, in which a contract pays out based on what happens with weather at specific airport locations.   That industry has put significant effort into documenting known and unknown station moves.    Believe it or not,  but moving a weather station from one side of an airport to another can cause significant changes in the reported weather and therefore its climatology.

I’ll develop an analysis of this station, but I don’t know yet if I have enough data to make a statement about a station move.  There are probably records of what happened to the station, but they are held by Meteo France, meaning I’ll never get them.    If the station was moved and it explains this temperature change,  the results of the Ashenfelter paper need to be reevaluated relative to the change in the reported climate.   In general,  I expect the variability of temperature to remain essentially unchanged, but the mean temperatures may change.   This is important because the perceived quality of post-1987 vintages could be misrepresented (think 1990) after recalibrating the model.

Ah,  much analysis to come.   Who would have though a blog about Albemarle County Wine and it Terroir would have spend so much blog space discussing Bordeaux.   Unfortunately, I need to sort this issue out as the paper provides an excellent framework to evaluate the quality of wines in Virginia and the rest of the world.