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.
Of the Domesday vineyards, all appear to lie below a line from Ely (Cambridgeshire) to Gloucestershire. Since the Book covers all of England up to the river Tees (north of Yorkshire), there is therefore reason to think that there weren’t many vineyards north of that line. Lamb reports two vineyards to the north (Lincoln and Leeds, Yorkshire) at some point between 1000 and 1300 AD, and Selley even reports a Scottish vineyard operating in the 12th Century. However, it’s probably not sensible to rely too much on these single reports since they don’t necessarily come with evidence for successful or sustained wine production. Indeed, there is one lone vineyard reported in Derbyshire (further north than any Domesday vineyard) in the 16th Century when all other reports were restricted to the South-east of England.
Wine making never completely died out in England, there were always a few die-hard viticulturists willing to give it a go, but production clearly declined after the 13th Century, had a brief resurgence in the 17th and 18th Centuries, only to decline to historic lows in the 19th Century when only 8 vineyards are recorded. Contemporary popular sentiment towards English (and Welsh) wine can be well judged by a comment in ‘Punch’ (a satirical magazine) that the wine would require 4 people to drink it – one victim, two to hold him down, and one other to pour the wine down his throat.
Unremarked by most oenophiles though, English and Welsh wine production started to have a renaissance in the 1950s. By 1977, there were 124 reasonable-sized vineyards in production – more than at any other time over the previous millennium. This resurgence was also unremarked upon by Lamb, who wrote in that same year that the English climate (the average of 1921-1950 to be precise) remained about a degree too cold for wine production. Thus the myth of the non-existant English wine industry was born and thrust headlong into the climate change debate…
Since 1977, a further 200 or so vineyards have opened (currently 400 and counting) and they cover a much more extensive area than the recorded medieval vineyards, extending out to Cornwall, and up to Lancashire and Yorkshire where the (currently) most northerly commercial vineyard sits. So with the sole exception of one ‘rather improbably’ located 12th Century Scottish vineyard (and strictly speaking that doesn’t count, it not being in England ‘n’ all…), English vineyards have almost certainly exceeded the extent of medieval cultivation. And I hear (from normally reliable sources) they are actually producing a pretty decent selection of white wines.
So what should one conclude from this? Well, one shouldn’t be too dogmatic that English temperatures are now obviously above a medieval peak – the impact of confounding factors in wine production precludes such a clear conclusion (and I am pretty agnostic with regards to the rest of the evidence of whether northern Europe was warmer 1000 years than today). However, one can conclude that those who are using the medieval English vineyards as a ‘counter-proof’ to the idea of present day global warming are just blowing smoke (or possibly drinking too much Californian). If they are a good proxy, then England is warmer now, and if they are not…. well, why talk about them in this context at all?
There is a bigger issue of course. For the sake of argument, let’s accept that medieval times were as warm in England as they are today, and even that global temperatures were similar (that’s a much bigger leap, but no mind). What would that imply for our attribution of current climate changes to human causes? ……. Nothing. Nowt. Zero. Zip.
Why? Well, warm periods have occured in the past, and if not the medieval period, then probably the last interglacial (120,000 years ago), certainly the Pliocene (3 million years ago), without question the (Eocene 50 million years), and in particular the Paleocene-Eocene Thermal Maximum (55 million years ago), and so on. Current theories of climate change do not rely on whether today’s temperatures are ‘unprecedented’. Instead they examine the physical causes of climate change and match up what we know about their physical effects and time history and see which of the multiple drivers or combination can best explain the observations. For the last few decades, that is quite clearly the rise in greenhouse gases, punctuated by the occasional volcano and mitigated slightly by the concomittant rise in particulate pollution.
Understanding past climate changes are of course also very interesting – they provide test cases for climate models and can have profound implications for the history of human society. However, uncertainties (as recently outlined in the NAS report) increase as you go back in time, and that applies to our knowledge of the climate drivers as well as to temperatures. So much so that even a medieval period a couple of tenths of a degree warmer than today would still be consistent with what we know about solar forcing and climate sensitivity within the commonly accepted uncertainties.
My oenological research project has not then lead me to any profound insights into climate change in the past, but it has given me a little more respect for the dedication of my winemaking compatriots. So next time I’m in the area, I’ll drink to that!