Medieval warmth and English wine

Never let it be said that we at RealClimate don’t work for our readers. Since a commenter mentioned the medieval vineyards in England, I’ve been engaged on a quixotic quest to discover the truth about the oft-cited, but seldom thought through, claim that the existence of said vineyards a thousand years ago implies that a ‘Medieval Warm Period‘ was obviously warmer than the current climate (and by implication that human-caused global warming is not occuring). This claim comes up pretty frequently, and examples come from many of the usual suspects e.g. Singer (2005), and Baliunas (in 2003). The basic idea is that i) vineyards are a good proxy for temperature, ii) there were vineyards in England in medieval times, iii) everyone knows you don’t get English wine these days, iv) therefore England was warmer back then, and v) therefore increasing greenhouse gases have no radiative effect. I’ll examine each of these propositions in turn (but I’ll admit the logic of the last step escapes me). I’ll use two principle sources, the excellent (and cheap) “Winelands of Britain” by geologist Richard C. Selley and the website of the English Wine Producers.

Are vineyards a good temperature proxy? While climate clearly does impact viticulture through the the amount of sunshine, rainfall amounts, the number of frost free days in the spring and fall, etc., there a number of confounding factors that make it less than ideal as a long term proxy. These range from changing agricultural practices, changing grape varieties, changing social factors and the wider trade environment. For instance, much early winemaking in England was conducted in Benedictine monasteries for religious purposes – changing rites and the treatment of the monasteries by the crown (Henry VIII in particular) clearly impacted wine production there. Societal factors range from the devastating (the Black Death) to the trivial (working class preferences for beer over wine). The wider trade environment is also a big factor i.e. how easy was it to get better, cheaper wine from the continent? The marriage of Eleanor of Aquitaine and the English King in 1152 apparently allowed better access to the vineyards of Bordeaux, and however good medieval English wine was, it probably wasn’t a match for that!

However, for the sake of argument, let’s assume that climate is actually the dominant control – so what does the history of English vineyards show?

The earliest documentation that is better than anecdotal is from the Domesday Book (1087) – an early census that the new Norman king commissioned to assess his new English dominions, including the size of farms, population etc. Being relatively ‘frenchified’, the Normans (who had originally come from Viking stock) were quite keen on wine drinking (rather than mead or ale) and so made special note of existing vineyards and where the many new vines were being planted. Sources differ a little on how many vineyards are included in the book: Selley quotes Unwin (J. Wine Research, 1990 (subscription)) who records 46 vineyards across Southern England (42 unambiguous sites, 4 less direct), but other claims (unsourced) range up to 52. Lamb’s 1977 book has a few more from other various sources and anecdotally there are more still, and so clearly this is a minimum number.

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