Here's the low-down. For a New York area customer, wine shipping from California produces almost 15 times more CO2 than wine coming from France, 11 times more than wine coming from Chile, and 5 times more than wine coming from Australia. Shocked? I was. The key is that trucking is vastly more wasteful than shipping by sea. According to the article, unless you live on the west coast or southwest, the calculations show that California wine is a poor choice (CO2-wise) for anyone in the US compared to other wines. I imagine the same goes for anyone buying East Coast wines, in reverse.
However, there are other factors to consider. California and other West Coast wineries are leaders in organic, pesticide free labels. And buying from them supports the American economy. In general, buying magnums also reduces packaging and the cost of shipping per ounce of wine consumed.
Of course, buying local and supporting nearby wineries is always the best choice from both a economic and environmental standpoint. You have the opportunity to meet the growers, and make new friends. Plus, many vineyards offer membership benefits for frequent buyers. One of our own local vineyards (the fabulous Hopkins Vineyard on Lake Waramaug) offers 20% case discounts to lifetime members -- all you need to do to qualify is buy 3 cases in one year at the vineyard: saving money, gas and supporting the local economy.