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That climate change report? Let’s look at the facts


Instead of reading second- and third-hand accounts of that notorious National Academy of Sciences report on the impact of climate change on the world’s grape growing areas, let’s do something radical: look at the actual report itself, to see what it does–and doesn’t–say.

I don’t know about you, but after reading different articles about it in newspapers and magazines, and hearing about it on the tube, it seems to me that all the reporters are fastening onto the sexy prediction that coastal California will be too hot for premium winegrowing by 2050. (In reporting lingo, that’s known as a Wow! headline.)

So onto the report. Its most attention-grabbing sentence is “the impacts of climate change on viticultural suitability are substantial,” but this is, of course, a sweeping statement, and the devil is, as usual, in the details. If we grant that “25% to 73%” of suitable areas in “major wine producing regions” are in jeopardy (a big assumption), we have to ask if coastal California is among them. We have also to look at the water situation; the NAS study suggests that warmer climates may increase the need for water use (such as to combat heat stress), although it does not state categorically that climate change will bring decreased precipitation. It “may,” in “some regions,” says the report; but again, that’s pretty abstract, and can mean whatever the reader wants it to mean (which if often true of these long-range predictions).

The report does flat out say that the suitability of “the Bordeaux and Rhone valley regions [and] Tuscany” is “projected to decline.” It also predicts that “more northern regions in America” should have increased suitability (hence all those silly headlines about “Chateau Yukon Cabernet”). As for California, the part of the study that has gotten the most attention in the media here is the map, on page 2, that seems to suggest a swathe of prime coastal land, from Santa Barbara up well north of the Golden Gate and including Napa and Sonoma, will experience “decreases [in suitability] by mid-century.” But look closely at the map: I did, zooming in to 200%. From the coast to what looks like about 50 miles inland, there are alternating stripes of (from west to east), blue [indicating “novel” or increased suitability for premium grape growing], dark green and light green [both indicating “current suitability that is retained”],  then red [“current suitability that decreases by mid-century”]. So you can appreciate that defining precisely where the boundaries are between colors is important. But this is nowhere explained in the text. The map, then, with its generalized colors, is the only guide we have, and an imprecise one at that.

So what are we to make of it? The blues along the immediate coast seem to indicate that the narrow coastal strip where, say, the Russians found viticulture impossible at Fort Ross, in 1812-1813, might by 2050 be warm enough to grow Chardonnay. The greens, where suitability is retained, look like they include most of the tenderloin growing areas from the Santa Ynez Valley, up through the Central Coast and into Napa-Sonoma. The reds seem to this observer to lie from about 35 miles inland to the borders of the Great Central Valley–if you’re familiar with the Bay Area, the red zone would start on the east side of the East Bay Hills, in what is now Livermore Valley. Other red regions include the far eastern parts of San Luis Obispo and Santa Barbara counties  and, perhaps, Lake County (although Clear Lake would have a cooling effect, wouldn’t it?).

But interpreting specific conditions from a colored map is dangerous. It’s like trying to figure out if your house will fall down from a USGS earthquake shaking map. There is, in fact, no mention at all in the report of individual coastal California counties, American Viticultural Areas or general winegrowing regions. There is a single reference to Napa, but it is to housing development and its impact on wildlife preservation–an issue that is not pertinent to Napa’s suitability as a winegrowing region. And that is that: the study is remarkable for its silence about the California coast.

The authors seem to understand that much of their report is obscure. “Uncertainties in our estimates of viticulture suitability,” they write, change[,] and its conservation consequences arise from climate models, concentration pathways, wine suitability models, and estimates of water stress and habitat condition.” I’m not one of these ridiculous anti-science people, and I deplore the know-nothingness of certain parts of the American political spectrum that deny, for example, evolution, or age models of the physical universe. But I also think that research scientists get grants to conduct research, in a kind of publish-or-perish model; and the media, being what it is, is in the position of a heroin addict who knows he shouldn’t be looking for another fix, but just can’t help himself. A report, such as the one from the NAS, is hedged by all sorts of provisos and fine print warnings that it should not be considered as the gospel truth, and next thing you know, the media is reporting it as the gospel truth, lazy reporters are predicting that Napa vineyards are going to have to be relocated in Montana, and wine company executives start shopping around for land in Tasmania. No wonder that distrust of the media in America has hit an all-time high.




  1. Carlos T says:

    Steve, so much for your suggestion regarding Tasmania (though it was witty and humorous). They make terrific wines; pinots, sauvignon blancs, chardonnays and sparkling alike. Awesome wines.

    Not sure these wines make to the USA, but if someone has a chance, get them.

    Disclaimer: I have nothing to do with that industry or country.

    PS: god will bless america, the global warming will hit only the infidels.

  2. Steve,

    Well done. Well done.

    Imagine someone critically reading the report and responding in such a manner.

    You had many of the same questions and comments I had after seeing it earlier this week.

    Nice to see it finally happening…

    Rex Stults
    Napa Valley Vintners

  3. Thanks for taking the time to discuss this Steve. I started writing a response, but it got obscenely long so I decided to write on this subject in SVB on Wine this weekend instead. In short though …. thank you for reading the report and not reporting on the reports.

  4. As you seem to like Dr. Lewin’s work, well on Cabs at least, read his comments on what has happened in Bordeaux over the last 25-30 years and his predictions of lowering water table and warming in the years to come found in “What Price Bordeaux?”.

    Shifts in temps will affect California as well as the rest of the world. Time to buy land in Central British Columbia for your grand children’s vineyards 😉

  5. Unfortunately you can’t get any grant money unless you sing the company tune which is “Global Warming is Real”.
    The fact is that temp’s have not risen for 10 years & it was warmer in Roman times when they drank a lot of wine. The climate models are junk science designed by chicken little.

  6. Graham Fisher says:

    We had a chuckle here in England that it would take until 2050 for our climate to be suitable for vine growing. God only knows what we have been doing for the last 25+ years!

  7. Why wait until 2050? I want to plant vines on endangered panda habitats now!

  8. The problem with this articles, is that we honestly don’t know how global warming will actually alter patterns of change, both in terms of heat and water consumption, which is what this article is mostly interested in, but water consumption is difficult to predict because it is a secondary outcome that is due to climate, dynamic human populations and usage and obviously politics. In addition, we’re guessin’ ’cause it’s never been this hot ever! Models are tough to predict accurately when you don’t have an established pattern.

    No question that sites on the extremes of viticulture of in terms of heat and drought will likely be worsened and probably will go off a cliff. So yeah, the hotter sites (livermore anyone?) probably aren’t the site to plant your next pinot vineyard. But these estimates are so wide, 25-75% decrease? So you’re saying you have no idea. Well, neither dose anyone else.

  9. Blake Chambers says:

    Liking what you are saying and nice on going to the source. With all this “getting warmer” talk, pretty wild we just came off two cooler vintages in Napa.

    What would you say about the “global warming” issue, having attending Premiere Napa Valley this year?

  10. Blake, I believe that climate change is real and much of the cause is man-made emissions. I generally steer away from the term “global warming.”

  11. Joel Weiss says:

    Seems to me that we should invite the National Academy of Sciences article author to a panel discussion comprised of CA viticulturists, UC Davis professors of enology and viticulture, and other climate specialists (i. e. NOT Al Gore) and dive into the details of the report. Then have them suggest practical options (if there are any) to maintain and enhance our grape growing regions with clear and sound strategies.

  12. Joel Weiss: I”m afraid regardless of who was on that panel, there would still be no consensus. We’re in a culture in which entire segments of the population reject scientific expertise.


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