Tamino helpfully linked the underlying paper in his first comment: https://www.frontiersin.org/articles/10.3389/fpls.2016.00069/full https://www.frontiersin.org

Tamino helpfully linked the underlying paper in his first comment: https://www.frontiersin.org/articles/10.3389/fpls.2016.00069/full https://www.frontiersin.org/articles/10.3389/fpls.2016.00069.... It's a clear and well written paper. While I assume its main conclusions are true (temperatures are hotter today and grape harvests are earlier than the historical average) there is a big hole in the logic used to show causality. Figure 5 and Table 1 show the main issue. As I understand it (and I applaud the authors for the clarity of their explanation) the original data from the 1600's shows a harvest date about 7 days earlier than the 1700 and 1800's. The decided that this didn't agree with records for neighboring regions where such records existed, so they "homogenized" the data by pretending the actual recorded harvest dates were 7 days later. Their justification for this is a one-time change in winemaking practice in Burgundy. Oh, by the way, according to the original records the difference harvest between the 1600's and today would otherwise have been just over 7 days. Lest I seem that I exaggerate, here it is in their words (Section 2.6): In the perspective of reconstructing past spring–summer temperatures, this bias must be taken into account. Otherwise it would have mean April-to-July GHD temperature-based reconstructions with maxima and minima ca. 1 ∘C warmer before 1718 than afterwards on the decadal scale, even though temperature measurements available in France since 1658 do not provide any evidence of such a warming during the period 1658–1718. To homogenise the Beaune GHD series we have then added 7 d to raw data prior to 1718. The Pearson correlation with April-to-July mean temperature in Paris for the period 1658–2018 is stronger with the homogenised Beaune GHD time series (r=0.76) than with the non-homogenised one (r=0.74). Anthropogenic changes in winemaking are the most likely explanation. They aren't necessarily wrong to make an adjustment here, but it completely undermines the causal argument they are making (or at least, that Tamino is making). While it is unlikely that there were no changes in winemaking in the last 650 year, assuming that there was one and only one major change and that it can be dealt with by uniform change to a single period of the data is fantasy. The raw data shows an early harvest, they change it to a later one, and then go on to argue that harvests are happening earlier than ever! Again, I presume their general conclusions are correct: recent temperatures are warmer, and recent harvests are getting earlier. But this paper really doesn't do a good job of showing the extent to which this is true, and it makes almost no effort to convince the reader that other cultural changes (which are almost certain to have occurred) didn't have effects of similar magnitude in unknown directions.