Consumers don't have access to much information about how businesses operate, but they can ask questions and focus on one tangible item, the bottle.
The exquisite vulnerability of grapes to nuances of weather makes wine both particularly susceptible to climate change and a harbinger of what's to come for many other agricultural products.
Do wine consumers have a role in encouraging producers to take stronger steps to combat climate change? Some in the wine industry think they do, particularly by throwing their economic support to companies that are already acting decisively.
"The consumer is the key to this," Adrian Bridge, chief executive of Taylor Fladgate, the historic port producer, wrote in an email. "Changing our own behaviour matters, and asking others to change theirs as well. This does mean buying from companies that are doing a good job and avoiding companies that are not."
It's equally important for consumers to make clear to the wine industry that fighting climate change is an urgent issue. Both through their buying decisions and through old-fashioned advocacy — which might include letters and emails to producers, importers and wine publications, as well as direct conversations with wine merchants and restaurateurs — consumers must demand that the wine industry take action.
That industry is simply a microcosm of larger society. Just as politicians have little incentive to address climate change unless voters require it, many wine producers are less inclined to reduce their own carbon footprints unless consumers demonstrate that such steps are important to them.
Some producers are already actively engaged in the fight, whether by changing their agricultural practices, reducing their carbon footprints or carefully limiting their use of water. Others, whether out of a sense of fatalism or greed, have chosen either to wait it out or do nothing, seeing only the expense without the benefits.
But how can anybody distinguish the environmental heroes from the do-nothings? That requires consumers to educate themselves in ways that are not easy, particularly because reliable information is difficult to come by. Many in the wine industry are notoriously opaque about their agriculture, their cellar techniques and their ingredients.
"Consumers are most powerful, in my view, in their role as buyers of products, so they can have an impact if they are able to distinguish between products that are climate-friendly and those that are not," said Mike Veseth, a retired economics professor who writes the blog The Wine Economist. "The problem is that, unless they do a lot of research, consumers don't really know the carbon footprint of the wines they purchase and so cannot steer their dollars to those who do best."
Even knowing the agricultural and cellar practices of a winemaker will not give the full picture.
There are many reasons to prefer producers who work organically or biodynamically in the vineyard. These techniques may be healthier for vineyard workers, for the soil and for the environment in some ways, and they may yield better wine. But adopting these techniques still leaves plenty of wiggle room for dealing — or not dealing — with climate change.
Do producers plough or till the rows between the vines, which releases carbon to the atmosphere? Or do they plant and maintain a cover crop, whether grasses, legumes or something else? An organic or biodynamic grower could do either. But maintaining a cover crop creates a lower carbon footprint.
Do they mow the cover crop? Or simply roll it? Rolling it releases less carbon from the soil.
Using organic compost is good for vineyards. But do producers make it themselves? Or do they buy it and ship it, possibly from a distance?
Do they use electric or hybrid vehicles? Or standard combustion engines?
Are they practicing regenerative agriculture by minimising use of chemical sprays and acting to promote biodiversity and soil life?
Have they converted to renewable fuels? Do they practice carbon sequestration, in which carbon is captured and stored rather than released into the atmosphere?
Where does their electricity come from? How do they manage their use of water?
These are the many questions that consumers would need to address in judging a producer's carbon output, and the answers are not easy to find.
Finally, skilled farmers are empathetic and intuitive, sensing what is needed to maintain and encourage a healthy ecosystem. It's hard for consumers to determine how well vineyards and their carbon footprints are managed. An official certification for organic or biodynamic practices bears little relation to a farmer's skill or carbon management.
"I don't believe that there really exists a certifying tool that clearly identifies 'success' in carbon sequestration or environmental virtue," said Randall Grahm, proprietor of Bonny Doon Vineyard in California. "Rather like organised religion, outward piety seems to count for more than internal grace."
Bridge, the port producer, has particularly felt the urgency of the climate situation. Aside from reducing the carbon footprint and water consumption at Taylor Fladgate, conserving energy and increasing the biodiversity of its vineyards, Bridge founded the Porto Protocol, an initiative that aims to inspire companies and individuals to do more to fight climate change.
The organisation has held global conferences the past two years in Porto, Portugal, bringing politicians, scientists and wine companies together to discuss climate change and possible solutions.
Right now the Porto Protocol website primarily serves as a clearinghouse of information, offering case studies of companies that have taken steps to confront their own carbon footprints as well as the presentations that were offered at the summits.
At this year's conference, Roger Boulton, a viticulture and oenology professor at the University of California at Davis, urged wine companies to build completely sustainable, zero-carbon facilities from now on. He offered practical methods for achieving the goal, like using solar and wind to stay off the energy grid, and solutions for minimising water use, particularly important as drought conditions afflict many parts of the wine-producing world.
"Whatever you do will be insignificant, but it is very important that you do it," Boulton said, quoting Gandhi.
That applies particularly to consumers, who may feel overwhelmed both by the scale of the problem and the difficulty of getting pertinent information.
Little things do add up. Let's start with the most tangible item in wine, the glass bottle.
Over the past 20 years, wine marketers have come to believe that the public associates thick, heavy wine bottles with higher-quality wines. The heavier the bottles, the more people would be willing to pay for them: This equation seems to be accepted in marketing departments worldwide, wherever aspirations evolve into pretensions.
The association of a heavy bottle with quality is absurd, of course, just as not so long ago many people believed that deeper-coloured, darker-red wines were invariably better and worth a higher price.
In fact, the environmental cost of heavy bottles, from their production to the carbon cost of shipping them, is high. This is something wineries have the power to address. Consumers can judge for themselves.
A study by the California Sustainable Winegrowing Alliance, a nonprofit industry group, calculated that packaging, particularly the weight of glass bottles, was one of four key areas in which wineries could do the most to cut their carbon footprint, along with vineyard chemical use, energy use in the vineyard and winery, and transportation of packaged wine.
Some bottles are by necessity heavier than others, like those used for Champagne, which requires stronger glass because the contents are under high pressure. But most wines don't need the heavy bottles.
So what can consumers do? Choose the wines in lighter bottles, and complain to producers, importers, distributors and merchants about the heavier ones.
How else can you choose better packaging? Patronise bars and restaurants that serve wines-by-the-glass from kegs, which not only can be cleaned and reused but also do a better job of keeping wine fresh than half-empty bottles. Boxed wines are lighter to ship and keep better, too. I would love to see wine producers step up to put better-quality wines in those boxes.
All these measures barely scratch the surface, unfortunately. To really make informed choices, consumers need to know what wineries are doing in the vineyard. It would be great if the Porto Protocol, for example, would publish a checklist of questions that consumers could ask wine producers to help determine accurately what they are doing about climate change. And yes, they are questions that wine writers need to ask, too.
As Gandhi suggested, no step is too small. The least we can do is make climate issues more urgent in our own lives, and to pass that message on to others.
"Things change," Bridge said, "when society demands it."