Medieval warmth and English wine

— gavin @ 12 July 2006

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!

Comments (pop-up) (81)

81 Responses to “Medieval warmth and English wine”

1 2 Next »

1. 1

Spencer Weart says:

12 July 2006 at 10:12 AM

Winemaking is certainly a poor climate proxy. I have heard that wine is made in every

one of the 50 states. I have personally drunk wine on the spot which was made in what

are pehaps the most unexpected states — Alaska, Hawaii, and Arizona. As you might

expect, they were not particularly good. But they were drinkable by modern standards, let

alone medieval standards (when wine was less important as a gourmet experience than as

a good way to get sterilized fluids, and also a good way to preserve fruit calories for

winter consumption).

2. 2

pete best says:

12 July 2006 at 11:06 AM

Here in the UK the growing season appears to be getting shorter due to their being more

sunshine and heat. I have visited several vinyards in the south of england (below London)

and they have told me this. There are even reports of red wine grapes now being grown in

the south of the UK and they are suprisingly good. In addition to this a lot of the south of

the UK (which is chalky like Champagne in France is) has been a target for grape

growers from France and Calafornia. It would appear that UK sparking Wine is very

good and has won some top awards in the last few years.

therefore I would suggest that the UK is warming in realtion to grape growing. On

another related matter is butterflies, where in Europe the UK is often the most northern

range of their habitat. One particular butterfly, the comma has in recent decades extended

its range from Middle England into northern England and even Scotland and has been

successful in colonisation.

3. 3

Sean D says:

12 July 2006 at 11:11 AM

I like Gavin‘s synopsis of the twisted logic of people like Singer in the first paragraph. It

is useful to bring out in the open the (il)logic behind these types of distracting and mostly

irrelevant arguments about the existence of said vineyards. I‘m surprised no one has

suggested that global warming will be good because England will be able to produce

wine.. …I‘m sure someone will trot that one out soon enough.

4. 4

Don Baccus says:

12 July 2006 at 11:30 AM

Re: #2 ―Here in the UK the growing season appears to be getting shorter due to their

being more sunshine and heat. I have visited several vinyards in the south of england

(below London) and they have told me this.‖

In a fine coincidence, The Oregonian, my daily newspaper here in Portland, Oregon, ran

a piece a couple of days ago on the future of winemaking in the western United States.

Winemakers here in Oregon are reporting the same situation as you describe for the UK.

Oregon made its mark on the wine map for its decent pinot noir. Winemakers are already

making plans to switch to warmer-climate grapes like syrahs and the like. And attribute it

to global warming.

In fact, the article was based on a commissioned study which among other things predicts

that many areas in California that now produce grapes for cheap table wine will become

too hot to grow grapes by the end of the century. Again, attributed to global warming.

5. 5

Tom Fiddaman says:

12 July 2006 at 11:35 AM

French grape harvests have been explored as a proxy too:

Grape ripening as a past climate indicator

Nature, Vol. 432, 18 November 2004.

French records of grape-harvest dates in Burgundy were used to reconstruct spring-

summer temperatures from 1370 to 2003 using a process-based phenology model

developed for the Pinot Noir grape. Our results reveal that temperatures as high as those

reached in the 1990s have occurred several times in Burgundy since 1370. However, the

summer of 2003 appears to have been extraordinary, with temperatures that were

probably higher than in any other year since 1370.

6. 6

Dano says:

12 July 2006 at 11:39 AM

RE 4 (Baccus):

Here in the Seattle area, winemakers are crowing over the news – Walla Walla and

Yakima wine growers are very happy to hear that CA will be negatively affected by

AGW.

Another negative effect will be that, according to some UW scientists, it will be cloudier

in Western WA due to AGW, as the marine layer will move inland more often (can‘t hunt

down a ref now).

Best,

D

7. 7

Marlowe Johnson says:

12 July 2006 at 11:52 AM

Strangely enough the PNAS is also running a story on AGW and wine production

http://www.pnas.org/misc/news.shtml

―Future climate warming across the United States could reduce the areas suitable for

premium wine production by up to 81% by the end of this century, severely damaging an

important U.S. industry.‖

Now Gavin, is the timing of your post purely a coincidence or is there some kind all-out

PR offensive by the wine industry to get us to stockpile our wine cellars? Be honest :).

8. 8

Rod Brick says:

12 July 2006 at 11:56 AM

There is no (or at least little/uncertain) connection between climate temperatures and

grape growing in medieval, but there is much joy in the Oregon vinewards over global

warming: is this not having AND eating our cake?

9. 9

S Molnar says:

12 July 2006 at 12:56 PM

Re #7: You messed up the link to the National Academy news page, but not to worry –

the National Academy messed up the link from the news page to the article.

A separate news account quoted one of the authors as saying that by 2100 Cape Cod will

be a good wine-growing location. He obviously hasn‘t been keeping up with Ice Sheets

and Sea Level Rise, or he would know that Cape Cod will be underwater by then!

10. 10

Tom Cecere says:

12 July 2006 at 2:23 PM

I think the logic trail is slightly mis-stated. There are another couple of links between iv)

therefore England was warmer back then, and v) therefore increasing greenhouse gases

have no radiative effect.

Link iv.1: therefore current warmth is not unprecedented

Link iv.2: therefore something other than man-made forcing can be responsible for this

level of warming

Link iv.3: therefore today‘s warming is more likely caused by something natural than by

man-made forcing.

It‘s still wrong, but most ―skeptics‖ amongst the general public get stuck at iv.2…if it‘s

possible that natural causes are responsible, and it‘s a hassle to remediate, then maybe we

should just wait for the weather to change back again, no?

11. 11

William Hyde says:

12 July 2006 at 2:41 PM

Gavin,

When you were in Halifax a decade ago we did our

best to shelter you from Nova Scotia wine, but

the industry does exist there, despite winters

much colder than Yorkshire generally sees – or

even experienced in the worst of the little ice

age – and generally cool summers.

The first favourable review of English wine that

I recall was well back in the 1970s. Somewhat

earlier Monty Python referred to a Welsh Claret,

but not by implication favourably.

Transportation issues alone would make the whole

issue moot, even if England produced no wine

at all today.

The English wine argument is not quite as silly as

the ―vast fields of greenland wheat‖ argument I

see from time to time, but it‘s up there.

William Hyde

[Response: I remember it well. As I recall, I was 'sheltered' by being forced to consume

copious amounts of Nova Scotian beer.... definitely did the trick. -gavin]

12. 12

Steve Sadlov says:

12 July 2006 at 3:18 PM

Gavin I am surprised that you do not undestand why knowledge of past climate

variability is important. Without knowledge of it, how can we do a good MSA of our

current data collection network and past networks? Without knowledge of it, how can we

assess the degree of current and projected abnormality versus which baselines, ―control

limits‖ and ―spec limits?‖ If we don‘t understand the innate ―natural capability of the

process‖ then we are hopeless in terms of understanding what might be deemed ―Green‖,

―Yellow‖ and ―Red‖ status. But of course, this is the true crux of the issue. To continue

the Six Sigma analogy, there are three camps. One camp would be those who want to

invest maximal effort ―fixing‖ all root causes, whether or not they are capable of

resulting in anything that is truly serious long term. The second camp, in which I reside,

says, determine the Cpk, determine control and spec limits, and consider excursions

beyond spec limits warnings and anything beyond the spec limits a disaster. Then of

course there is the third camp, who would say ―ship it‖ – I have to of course acknoledge

that yes, there are actual real world despoilers out there who really would destroy the

Earth. But to be in camp two, to me, is actually the best. Camp two is the most likely one

to be good stewards while not being ideologically charged overreacting maniacs.

[Response: Since I spend about half the time of my day job looking at natural variability

in the pre-anthropogenic period, I have no idea why you think that I don't understand its

value - try reading some of my papers: Schmidt et al (2004) for instance. - gavin]

13. 13

Steve Sadlov says:

12 July 2006 at 3:39 PM

RE: Gavin‘s response to #12 – Well then, why do you spend so much time trying to

downplay the MWP and when not doing that, trying to make the case that past variability

really does not matter? You appear to be in camp one. I base this on: ―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.‖ I beg to differ. I am

not arguing AGW yea or nay. I am arguing the significance of AGW. Even assuming that

ALL of whatever current and project abnormality is exclusively due to AGW (a suspect

assertion) what does it mean? Are we Green, Yellow, or Red? He who can firstly

determine the innate variability with sufficient confidence, and where we are and might

be versus that variability with equally good confidence, and then tell us the status, will be

a good candidate for a Nobel Prize.

[Response: You don't seem to be following the point. I have no preference for any particular medieval temperature - the record is what it is. Explaining what was going on then is of interest regardless of what actually happened. What I object to is the use of the medieval period as if it meant something for current change attribution. It doesn't. And more importantly it doesn't affect by an iota the projections for the future.

To paraphrase your point, you seem to imply that the medieval period defines 'natural' variability. But 'natural' variability is made up of two components - internal variations and natural forcings (solar and volcanoes on this time scale). A globally warm medieval period could be a simple forced response to increased solar, in which case it doesn't imply any larger intrinsic variability than already assumed, and since solar has been pretty much constant over the last 50 years, improvements to our understanding of solar forced climate changes are irrelevant for the last few decades.

On the other hand if the medieval period was all intrinsic variability, that would be surprising, but similarly not much use for determining the forced response to increasing GHGs. Since it's some balance of the two (with an uncertain split) it is extremely difficult to simply use medieval temperatures to conclude much of anything. - gavin]

14. 14

Eric says:

12 July 2006 at 5:41 PM

Gavin, have you seen this link?

http://people.whitman.edu/~storchkh/clim.pdf It shows a pretty good

correlation of wine quality with temperature on average. Also I

remember from my wine tasting trip through Nova Scotia in the early

80‘s that the red wines were much worse than the whites, due mostly to

climate. Perhaps there is historical data of the ratios of red to

white which (disregarding cultural and taste preferences) could

correlate to climate?

15. 15

BG says:

12 July 2006 at 6:22 PM

Ok, so,

If a forest catches fire on a hot day, everything burns down. Voila, its done. It was a

NATURAL cause.

Later, me and my buddies decide to have a party at another forest. Somebody throws a

cigar on the leaves on the forest floor and we CREATE a fire. This is a MAN-MADE

fire.

Therefore, if there is a fire, it could be NATURAL, or MAN-MADE.

Now, lets assume that wine does correlate with temperatures (positive correlation.)

I think that Gavin‘s point is:

In the past these rises in temperature were NATURAL. Today, they could be (and lets

face it, they are) MAN-MADE.

Thus, you can provide all the evidence regarding wine and it means nothing in the

context of the causes of todays warming. The same way that if me and my buddies were

taken to court for lighting up the forest, we could provide ALL the evidence in the world

that forests fires occur naturally, but the fact that they occur naturally does not prove that

we did not cause that PARTICULAR fire.

BG

16. 16

cwmagee says:

12 July 2006 at 6:38 PM

Re 12, 13:

I know what red and white are, but what are these ―yellow‖ and ―green‖ types of wine?

17. 17

Steve Sadlov says:

12 July 2006 at 8:47 PM

Good debate Gavin, thanks. This is the type of constructive debate I enjoy. This rising

tide lifts all boats.

18. 18

Arun says:

12 July 2006 at 9:04 PM

I think the point being raised was that if the medieval warming by natural causes was not harmful, why would the modern warming by human causes be harmful?

19. 19

Wolfgang Flamme says:

12 July 2006 at 10:16 PM

With winter temperatures well below 0°C regularly in a wine region here at Mainz,

Germany the region has switched to growing much more red wine in the last decades. We

are growing a fig tree in our garden fine, requiring no care at all. Our neighbours are

growing a palm tree – they simply tie the leaves together in winter and shield it using a

plastic bag. My uncle grows an olive tree for fun (several hundred years old) – frost-

shielded by a tent in winter (which might not be neccessary since it has passed several

years of travel and adaption).

A (presumed) zero point something temperature increase just cannot account for all these

observed changes over the last decades. Climate here ist still very(!) far from becoming

mediterranean. So people, culture, tradition, lifestyle matter most. Nature following

indeed looks like a very poor and unreliable indicator to me.

20. 20

wayne davidson says:

12 July 2006 at 10:36 PM

There is the added component, of history, which surely must complement wine making in

the UK. Any study assigning a medieval warming just on wine making is a bit tipsy…

There are other periods when weather was remarked directly. For instance, when there

was ―no summer‖ after a volcanic eruption at about the 4th century CE. It would be good

to read about contemporaneous historical evidence to make this subject complete.

21. 21

JohnLopresti says:

13 July 2006 at 12:10 AM

I am glad to locate this picturesque discussion, having read of the PNAS report‘s

publication in our local Sonoma County, CA, Alexander Valley AVA ridgetop location‘s

nearby press outlet on the first page yesterday in a decent article by the viticulture writer.

Even that media is skipping some of the science which will help correlate with climate

change science. I look forward to exploring the ASEV site with respect to the enological

view. For my own part, I will proffer here some rudimentary Vitis vinifera data, then

complete the full download, such as it is, in chapter aggregates.

Grape buds in order to produce viable and healthy leaves and clusters, need ultraviolet.

Overcast skies in the UK would mitigate against opting to grow grapes.

The ecclesiastical wines are a dual process product, often beginning with a low sugar

grape from a short growing season, fortified with more grape sugar during fermentation,

and then even cooked afterward with addition of more alcohol content. Typically dessert

or sacramental wines may originate in various climatic regions, but also are possible to

make by blending arts. Absent modern national governmental regulations, I would

imagine all manner of vinification took place.

Another aspect of suitability of a zone for viticulture, as the NAS report evidently

mentions, is grapevines‘ debilitation when there are excessive numbers of days warmer

than about 88 degrees F, though there is a ceiling in the mid 90s beyond which leaf

turgidity effects, wilt, and the like inflict damage on the vine. The Diffenbaugh report is

saying if global warming produces 35 heat peak days during summer in CA premium

viticultural lands, the wine will be inferior quality; that is right. Compare for example the

wines of the midi in France, where excessive warmth lends itself better to bulk wine

production rather than, as our host extolls, say, a Bordeaux. In this regard, this week I

heard a scientist describing heat peaks 18 degrees warmer than currently during 2070-

2100 in our region, a shift which would obliterate most premium grapes, absent an effort

to grasp the hockeystick, soon.

There are other seasonal parameters applicable to grapevines likely more readily

available from the experts more knowledgeable in this than I, the excellent viticulture and

and enology college at UC Davis; I am sure we will hear from them.

UCD several decades ago developed a heat summation formula for suitability of coastal

zones for wine growing, it is a complex calculation which counts number of days over 50

degrees Fahrenheit; and it intercalculates with the length of growing season from

budbreak to first frost. There are horticultural workarounds, whereby we have

microclimates which support vineyards in snowy climates. As the Diffenbaugh report

also mentions, grapevine and fruit resistance to a host of fungal disease, mildews, and the

like also affect suitability of a region for viticulture.

I will give this some study and return, when I have a moment, if some of this agricultural

enological view appears to inform the climatologic discussion more.

John Lopresti

———-

notes:

Local CA viticulture writer:

http://www1.pressdemocrat.com/apps/pbcs.dll/article?AID=/20060711/NEWS/60711001

/1033/NEWS01

National picture US region reconfiguration

http://www.alertnet.org/thenews/newsdesk/N10448932.htm

22. 22

Robin Johnson says:

13 July 2006 at 12:55 AM

I‘d like to add – who says that the Medieval Warm Period WASN‘T man made?

Human population in Northern Europe increased substantially from the 6th centuary

onward due to the invention of the advanced plow and yoke in the ―Dark Ages‖. This was

BEFORE any claimed warming. These vast numbers of additional humans cleared forests

increasing CO2, mined and burned lots of peat which is a fossil fuel, and increased

bovine herds substantially which raises methane levels. So maybe humans at least

contributed to the Medieval Warm Period or made it warmer. One could then argue this

warming was subsequently quashed by the Black Plague (1346 – 1380) and notably the

medieval high was in 1370 just as reforestation was taking place. So I question the

premise that the Medieval Warm period was definitely ―natural‖.

23. 23

Oliver Morton says:

13 July 2006 at 4:35 AM

Just to add a little modern day evidence, south facing chalky slopes along the downs and

into the weald are defintiely producing high quality ―champagnes‖; try Nyetimber

(already getting too pricey, I suspect) and the confusingly named range from Ridgeview.

They are well to the north of traditional French winemaking areas doing similar things,

but they benefit from proximity to the channel giving mild winters and modern

winemaking techniques. That said, at an english winemaking event I attended last year

(well, a wine drinking event really)there was unanimous belief in climate change as a

factor in widening the envelope of the possible, with a number of producers eyeing the

possibility of reds in a way they never would have ten years ago.

24. 24

pete best says:

13 July 2006 at 5:00 AM

RE #22 Yep Nyetimber and Ridgeview now make award winning wines along with

Breaky Bottom and a couple of others. UK sparklers are getting expensive but they do

taste good, almost as good as a good champagne. Not all of the wine growing slopes are

south facing either.

25. 25

Jose de Freitas / Portugal says:

13 July 2006 at 8:50 AM

cwmagee asked: I know what red and white are, but what are these ―yellow‖ and ―green‖

types of wine?

I can‘t really speak for ―yellow‖ but ―green‖, at least in Portugal, is a sparkling wine

made with ―green‖ grapes, meaning not yet completely ripened. It‘s slightly less

alcoholic than your average white or red (it‘s between 11º and 12,50º), to be drunk

very fresh. Generally a summer drink for seafood or late afternoon meals, doesn‘t age

very well (2-3years is what you normally get) and doesn‘t travel very well either. It‘s

actually great, and comes mostly in ―dry‖ flavors and ―fruity‖ or slightly sweety taste.

More confusingly, it can be made with either white grapes (very common) and red grapes

(much more uncommon), giving rise to Red Green and White Green, which tends to

befuddle foreigners. :-)

I would suppose ―yellow‖ is something along these lines too.

Best

26. 26

tom root says:

13 July 2006 at 9:27 AM

Re: comment #19

―So people, culture, tradition, lifestyle matter most. Nature following indeed looks like a

very poor and unreliable indicator to me.‖

It would seem that besides climate, micro-climate (of the type for grape growing) dictates

whether or not suitable grapes can be grown in a particular location. As climate changes,

so do the many micro climates in a region. So a hillside vineyard that was favorable for

the past, say, 100 years may suddenly not produce many of the desired grapes. Growers

skills at finding suitable micro climates, that will work for as many years as it takes to

cultivate a vineyard, have increased remarkably (I presume) over the past 1000 years.

Wolfgang‘s conclusion seems to hold.

27. 27

chris says:

13 July 2006 at 12:19 PM

Re: comment 22

…and the suggestion that these periods (MWP) had significant man-made influence with

respect to atmospheric CO2 production from forest and peat burning.

The ice core record seems to rule out that suggestion I would have thought. I‘m looking

at data from Ethridge et al (1996) ―Natural and anthropogenic changes in atmospheric

CO2 over the last 1000 years from air in Antarctic ice and firn‖ [J. Geophys. Res. 101,

4115-4128 (1996)].

The atmospheric CO2 levels were 279.4 ppm in 1006; 280.3 in 1046; 282.4 in 1096;

283.8 in 1146; 283.9 in 1196; 281.7 in 1246; 283.4 in 1327; 280.4 in 1387; 281.7 in 1446

etc. etc.

In other words surely insignificant changes with respect to the Earths temperature…at

least one would hope so or we‘re in a whole lot of trouble!

They do go down a bit (to the mid 270‘s ppm) right through 1600 and 1700‘s so these

tiny changes do seem to correlate a bit with the warm and cool periods possibly. But

changes in these levels might well be responses to other factors rather than being cause of

the temperature variation.

The other factor of course is the extent to which wine growing in England in the so-called

MWP was an indication of a warmer Earth during this period or a small shift in the

temperature distribution of the Earth due to ocean circulation patterns and suchlike. In

other words not an indication of global warming at all!

28. 28

Lynn Vincentnathan says:

13 July 2006 at 2:59 PM

Everyone knows the best wine grapes are grown in cool, not hot climates — so that

Medieval period must have been a period of cooling :)

29. 29

Jim says:

13 July 2006 at 3:00 PM

Thank you for this post, this is another claim that is endlessly repeated. A letter to the

editor in today‘s San Francisco Chronicle:

http://www.sfgate.com/cgi-

bin/article.cgi?file=/chronicle/archive/2006/07/13/EDGOBIPUTR1.DTL

Editor — So, now we are to fear that our beloved wine industry could be destroyed by

climate change (―Now‘s the time to cellar wine,‖ July 11)? Never mind that the dire

predictions of scorched vineyards are based on models that climate scientists say ―aren‘t

yet good enough to predict effects (of global warming) on future agriculture.‖

By the way, which Bush policy was it that caused temperature fluctuations in the 1500s

to wipe out vineyards in England? Just wondering …

SANDRA SERBICKI

Sonoma

30. 30

Steve Sadlov says:

13 July 2006 at 3:51 PM

# 21 – if temps above 85 are such a problem then what about places like Paso Robles,

Calistoga, Livermore and misc Lake County locations, in terms of premium locations,

and of course, the San Joaquin Valley in terms of 2nd tier? All of those places have

routinely exceeded the century mark for days at a time, nearly every summer. And this is

hardly anything new. This has been the case for many decades.

31. 31

Mike Jacobs says:

13 July 2006 at 4:01 PM

According to Al Gore, by 2050, the Napa Valley, California‘s premier wine growing

area, will at best a saltwater estuary and at worst a deep water port. The wine growing

regions will definitely be lost. As for me, I‘ll have California ocean front property.

[Response: Sorry to put the damper on your soon-to-be-beach-front home idea, but

neither Al Gore, nor anyone else has suggested that sea level rise will be that fast. -

gavin]

32. 32

Robin Johnson says:

13 July 2006 at 4:36 PM

Chris-

Yes. I know that the CO2 concentrations from 1006 to 1800 seem to be 280 +/-10. And

so that is a valid point. But my understanding was that levels were lower in the 600 AD –

1000 AD time frame (when the bulk of the land clearing occurred). The additional

methane has to be considered important as well. So I would think the CO2 ppm post land

clearing is not a good proxy. But my real point is that it cannot be said that MWP was

definitely not man-made until a natural explanation other than ―natural variability‖

becomes the accepted scientific explanation. ―Natural variability‖ is another way of

saying ―we don‘t know‖. And possibly we may never.

33. 33

cat black says:

13 July 2006 at 4:40 PM

#30: I have lived in or around Calistoga and Lake County. It can become quite hot in

those areas of an afternoon, but my experience is that this is almost always bracketed

morning and evening by cooling breezes from the sea. As an indication, I‘ve never lived

with air conditioning in these areas, which in other parts of California is essentially

impossible. I suspect (from observation only and no direct experience in the vineyards)

that the grapes are able to integrate the heat over the day. Other places I have lived, like

Butte County, also have a few novelty vineyards but the heat there is entirely more

oppressive. Which is why I no longer choose to live there! I like ―grape country‖ for

similar reasons as the grapevines, I suspect.

34. 34

chris says:

13 July 2006 at 5:28 PM

Robin – (re comments 22, 27, 32)

that begs the question what the atmospheric CO2 levels (and methane too) were between

600 and 1000. I‘d love to know! presumably the data is there somewhere??? [maybe the

experts at this blog will tell us where to look!] So you may well be correct.

however the implication is that either (i) that the CO2 levels would have had to be rather

significantly below 270-ish ppm, or (ii) that the Earths temperature is really very

sensitive to CO2 levels indeed. In the latter case that would indicate that we have a whole

lot of warming in the pipeline from the raised levels that we‘ve generated at the present

time!

At least in my researching there is a bit of a chasm between the fine-grained CO2 data

that goes back to around 1000 AD and the ice core data that covers the 100‘s of

thousands of years before now [e.g. Siegenthaler et al. (2005) Science 310, 1313-1317

(2005)].

I‘m sure there‘s something in your suggestion of land-clearances. But is it enough to

cause significant climate change during these periods? I do think we need the CO2 levels

to be sure. I‘m still inclined to think that subtle changes in ocean circulation patterns,

with resulting local effects on climate, are more likley to be responsible.

For example, with all this talk on wine, has anyone mentioned the fact (apparently) that

they were growing grapes in Greenland during the MWP? I can‘t help thinking that some

strengthening of the Gulf Stream, carrying greater volumes of warm water to Greenland

and N.W. Europe, might be a better explanation of the MWP. But the atmospheric CO2

levels between 600-1000 might answer the question as to which is the dominant effect.

Hopefully someone will point us in the right direction!

35. 35

Dano says:

13 July 2006 at 6:09 PM

RE 30 (Sadlov):

All plants have temps where they won‘t photosynthesize any more but continue to live

without adverse effects. Fruits, though, can be affected because metabolism shuts down,

stopping translocation of sugars and starches to the fruit. This is the 35 peak heat days‘ of

which JLoP speaks (and the SJV heat that you imply reduces quality). The PNAS paper

apparently implies that the peak heat days will increase, thus decreasing quality.

More info on temps for growing is here.

Best,

D

36. 36

Stormy says:

13 July 2006 at 7:11 PM

Gavin,

Saw you on Lou Dobbs. As Lou Dobbs said, ―Time for solutions.‖ The three of you have

to be very organized, each taking a piece of the answer.

1. What effects are we in for–how can we mitigate those

2. Is there a tipping point? How soon?

3. What precisely can we do to stop further effects.

Bring charts. Visuals will say more than words–and say it quicker.

Smile. You‘re on camera.

[Response: Yeah, I know. These things can be tricky though - we were supposed to talk

about wildfires and wine but another segment ran over and we got cut. I agree, we could

have been more focussed though. Graphics would be nice but there is never enough time

to them justice. We might get another chance soon though, so I'll try and remember to

smile... Thanks for watching! - gavin]

37. 37

Mark A. York says:

13 July 2006 at 11:42 PM

RE: #30 Here‘s the deal: sure it gets hot here in the summer, but the last few summers

have been longer and hotter. i.e. it starts in mid-May and June gloom here in inland LA is

less and less frequent in between 100+ heat waves. It‘s holding true this year. It‘s 104

today. To recap: starts earlier and lasts longer. That‘s global warming in its simplest

manifestation.

38. 38

æ½?ç??é¾? says:

14 July 2006 at 12:06 AM

I‘m a chinese student.I am very concerned about the climate problem.

I have a question:

Do you think that one day we would fly to other planets to get on because of the bad

weather on earth?

39. 39

Jaison Davis says:

14 July 2006 at 12:55 AM

I think we all need to think about our mother nature as if we don‘t do it right now then we

will not be able to do it later. It‘s our responsibility and we have to take care of it!

40. 40

Risto Linturi says:

14 July 2006 at 3:46 AM

The discussion from message 22 onwards has concentrated on the effects of deforestation

to CO2 levels and of livestock to methane. I would like to ask if there could be a more

clear link between local temperatures and deforestation through changes of humidity.

Deforestation clearly affects local humidity and that through cloud formation etc. and my

personal experience of life in Finland tells to expect 10 to 20 degrees colder nights during

winter when the air is dry. Other variations are not so obvious and I expect there have

been numerous studies about the local effects of humidity and deforestation to local

climates as this is one of the pressing problems in many areas today.

41. 41

Eric says:

14 July 2006 at 5:00 AM

Risto, here‘s a link I posted in another thread:

http://www.ccsm.ucar.edu/publications/PhD%20and%20Masters%20Theses.htm that has

some abstracts that discuss vegetation-climate interaction (e.g. 3128110).

It is an important topic in my opinion that will be resolved with much better modelling in

the next decade or two. We ought to be able to model which vegetation changes yield the

most bang for the buck, so to speak, for climate change mitigation.

42. 42

S Molnar says:

14 July 2006 at 6:48 AM

Re 38: My answer is, No, we won‘t solve the problem by going to other planets. If we

can‘t manage to put up a few windmills and solar panels, how are we going to succeed

with massive interplanetary colonization? Apparently, Stephen Hawking disagrees –

well, you can always judge a man by the quality of his opponents. (Oh, wait…)

43. 43

Barton Paul Levenson says:

14 July 2006 at 6:59 AM

Re #38 and ―Do you think that one day we would fly to other planets to get on because of

the bad weather on earth? ‖

The problem is that there are no other habitable planets in the Solar system, so you would

need some sort of cheap insterstellar travel. This is unlikely any time soon. In the

meantime, most of the people on Earth will be unable to emigrate. It would be most

efficient to fix the climate on Earth, rather than try to colonize other planets. In the very

long run, of course, we will need to move to other planets when the Earth becomes

uninhabitable (0.6-1.4 billion years from now).

44. 44

Risto Linturi says:

14 July 2006 at 8:43 AM

Thank‘s Eric,

this removed a contradiction from my mind as I remembered

that deforestation is also used as an explanation for

warming in certain areas. So it depends on your latitude.

I quote the abstract …

‖ Pub No: 3128110

Author: Snyder, Peter K.

Date: 2004 Pages: 205

…Using a coupled atmosphere-biosphere model (CCM3-IBIS),

the influence of vegetation on climate at the regional,

continental, and global scales is evaluated…

…..For instance, the climate response to

tropical deforestation is a surface warming due to a

large reduction in latent cooling. In contrast, boreal

deforestation causes a large surface temperature cooling

due to a higher surface albedo…

It was also shown that changes in the land surface

resulting from land cover change affect the transport of

energy throughout the three-dimensional atmosphere and

can change the climate in adjacent regions or locations

far removed from the surface forcing through modification

of deep moist convection…‖

45. 45

Jeffrey Davis says:

14 July 2006 at 10:31 AM

Re: sea level rises swamping California wine growing areas

As an adjunct to the movie we watched last night (―Eight Below‖) I got out the National

Georgraphic atlas to look at the area the movie was supposed to be about. On that map,

there‘s a small graphic which showed how much of Antarctica‘s ice sits on bedrock and

how much is on open water. I was stunned by how much of its ice rests on water. My

question: does that ice actually rest on water or is it suspended above it like the arch of a

bridge? That doesn‘t seem likely. If the weight of Antarctic ice is actually already in the

ocean then how much can its melting actually influence ocean water rises elsewhere?

46. 46

Hank Roberts says:

14 July 2006 at 11:20 AM

Most of the icecap is ‗grounded‘ — not floating because it‘s far too thick and weighs too

much. Compare the height at the surface to the depth of the bedrock and sea level.

Compare a large block of ice in a shallow tray of water.

Remember, the ocean also expands as the water warms; I think expansion due to

warming in over the past century or so has been the explanation for sea level rise, before

the ice started melting so fast in the past few years.

47. 47

tom root says:

14 July 2006 at 11:39 AM

An article and comments about micro-climates and managing micro-climates from the

very capable keepers of this site would be appreciated by myself, Risto, Doug and others.

In a world with unpredictable climate changes, the technology for finding suitable micro-

climates for any particular purpose might just be the next ‗big thing‘.

I remember the bumper sticker from 25 years ago which read: Think Global, Act Local.

In other words, think about what is good for the whole planet and work toward that end in

the local area.

48. 48

tom f says:

14 July 2006 at 12:03 PM

I‘m curious whether gavin has read _The Little Ice Age_, a recent book. Early on, the

author discusses the MWP, particularly the evidence that French kings actually sought to

block importation of English wine at this time.

My questions for gavin are, have you read the book and is the author‘s treatment of

climate change sound?

Secondly, the author specifically states that Europe during the MWP experienced

summers roughly 1 degree C warmer than in the 2Oth C (p. 17). That does not

necessarily contradict your statement that you are ―pretty agnostic with regards to the rest

of the evidence of whether northern Europe was warmer 1000 years than today‖. But, do

you disagree w/ his statement, and could you give me an idea of what counter-factuals

lead you to agnosticism on whether Europe was, across all seasons, warmer 1K years ago

than today?

49. 49

Stephan Harrison says:

14 July 2006 at 1:14 PM

Re 48. Are you talking about the book by the late Jean Grove? As far as I remember, she

discusses the MWP only in the context of Europe which doesn‘t contribute to the

argument concerning the global extent of the warming.

50. 50

tom f says:

14 July 2006 at 2:52 PM

#49. The Little Ice Age: How Climate Made History, 1300-1850 (Paperback)

by Brian M. Fagan, Basic Books, 2000