The steady rise in global temperatures is threatening vineyards around Bordeaux that produce some of the most esteemed and expensive wines on earth. Experts say that the region may be unsuitable for wine-growing by 2050, making the supreme wines of chateaux like Lafite, Petrus and Latour nothing but memories. Winegrowers are already switching to heat-resistant grape varieties as a precaution, Germany's Der Spiegel magazine reported this week. "The most pessimistic scenario says that the climate will no longer be suitable for Cabernet and Merlot wines by the middle of the century," said Jean-Pascal Goutouly, a wine expert at the French National Institute