"The consequences of global warming are already being felt. Harvests are already coming 10 days earlier than before in almost all wine-growing regions," said Bernard Seguin, the head of climate studies at France's INRA agricultural research institute.
He was speaking at the opening of the Second International Congress on Wine and Climate Change.
More than 350 experts from 36 countries, including France, Spain, the United States, New Zealand and Australia, are taking part in the two-day conference in Barcelona.
It concludes Saturday with an address by former US vice president and climate campaigner Al Gore.
"Wine and wine-producing will change in a way that will depend on how we confront" global warming, said Seguin.
"If the temperature rises two or three degrees (centigrade), we could manage to see Bordeaux remain as Bordeaux, Rioja as Rioja, Burgundy as Burgundy. But if it goes up five or six degrees, we must face up to huge problems, and the changes will be hard," he said.
Grapes are damaged if they ripen too quickly, due to higher temperatures and a lack of rain.
"When a grape matures more quickly, you get higher concentrations of sugar, lower acidity and a higher PH level," said Fernando Zamora of the oenology faculty at the University of Tarragona in Spain.
The result is coarser wine, with a higher alcohol level and lower acidity which can destroy the delicate flavour of good quality wines, he said.
It would also lead to higher prices in countries which tax wine according to its alcohol level.
"The types of wines will change in almost all regions," said Vicente Sotes, a professor at the Polytechnic University.
And some regions which still produce good wine would no longer benefit from the ideal climatic conditions that are responsible for their world renown.
"The French will have problems," especially in the Bordeaux region, said Pancho Campos, the president of the Wine Academy of Spain, who organised the Barcelona conference.
"There are (French) Champagne producers who have bought land in Sussex and Kent," in southern England, he told the newspaper El Periodico.
German producers on the banks of the Rhine will be the least at risk, he said.
The French "Grand Crus" could be further threatened by the "New World" wines of Australia, California, Chile, Argentina, South Africa and New Zealand, who would have the best climatic conditions.
"The countries in the southern hemisphere are next to a greater mass of water, and it is sea currents which maintain the temperature at its level," said Campos.
Friday evening, experts are to deliver their verdicts on wines affected by climate change at a tasting session.