But there is no question that in recent years, British winemaking has benefited from warmer, if more erratic, weather. Britain's climate is warming faster than the global average, according to the Intergovernmental Panel on Climate Change, an international group. In Sussex, in southeast England, the average temperature in 2013 is 1.8 degrees Fahrenheit (1 degree Celsius) warmer than it was for most of the second part of the last century.

According to scientific projections, Britain can expect wetter winters, drier summers and less snow and frost. In this way Britain is joining a list of prospective new wine countries that include China, Russia and even the Scandinavian states.

"Global warming is definitely benefiting the U.K. wine industry," said Chris Foss, who oversees the wine department at Plumpton College. "My family is from Bordeaux, but I've been living in England for 45 years now. The change over time is just amazing. The industry has potential to expand at least five times, if not 10."

On the other hand, climate change could have a negative impact on traditional wine regions in France, Italy and the United States. According to forecasts this year in the journal Proceedings of the National Academy of Sciences, by the middle of the century, if the warming trend continues, wine production in the Bordeaux region of France and the Tuscany region of Italy could decrease as much as 85 percent, while that in California and Australia would decline 70 percent.

Such projections fuel the imagination of people like Richard C. Selley, professor emeritus of geology at Imperial College London, who has studied the potential effect on winemaking.

"I can imagine that there will be vineyards on the shore of the Loch Ness in Scotland — it has the same geology as parts of South Africa," Mr. Selley said. Convinced that viticulture in Britain is moving farther north because of climate change, he pointed to a map in his book "The Winelands of Britain: Past, Present and Prospective" that shows the projected suitability for various types of grapes in Britain by 2080.

"The scary thing is that the newest predictions indicate that by 2080, in some of the southern areas of the U.K., it will be too hot for winemaking," Mr. Selley said. "The London- and Hampshire-based vineyards will be great for raisins."

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Whether Mr. Selley's forecast will be borne out is anyone's educated guess. But other consequences of climate change, including erratic and unpredictable weather patterns, rapid hailstorms and sudden cold snaps, might yet have adverse effects on the British wine industry.

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Last year for instance, chilly and damp conditions forced some vineyards to scrap entire grape harvests. The overall annual production fell to just over a million bottles, from about three million the previous year.

"Though we can see the trend going up with global warming, it isn't always good news," said Christopher White, general manager of the Denbies vineyard. "You can't really plan for the short term."

That is why Mr. White is taking the long view. Denbies continues to develop the vineyard, planting 30,000 vines this year alone, raising the total to more than 300,000. Mr. White is also planning to expand international distribution to include Abu Dhabi, Japan, the United Arab Emirates and the United States.

And with the weather warming, Denbies is also trying new grape varieties in England that might have seemed far-fetched only a couple of decades ago. "Twenty years ago we were told not to really worry too much about pinot noir," Mr. White, the vineyard manager, said. "But we did plant a lot of it, and now it's our best grape."

The pinot noir grape is mainly associated with the Burgundy region in central France, where it is typically sunny, dry and warm but not hot. Now, though, pinot noir is the second-most-planted grape variety in Britain, after chardonnay. And Denbies is about to release Britain's first sauvignon blanc, made from grapes the vineyard added in 2010.

All this must be kept in perspective. While the growth of British wine production has been phenomenal, it has risen from a relatively low level