Premium winemaking in Napa Valley could be impossible in 30 years according to a study into climate change.

Scientists at Stanford University in California looked at four wine-growing counties in the western United Sates — Santa Barbara County and the Napa Valley in California, Yamhill County in Oregon’s Willamette Valley and Walla Walla County in Washington state’s Columbia Valley.

The scientists said that by 2040 there could be 50% less land suitable for cultivating premium wine grapes in high-value areas of Northern California.

However, some cooler parts of Oregon and Washington state would become correspondingly better for growing grapes.

The study examined climate change over the next 30 years, Noah Diffenbaugh (pictured), of the Woods Institute for the Environment at Stanford University said.

This is ‘a timeframe over which people are actually considering the costs and benefits of making decisions on the ground,’ he said.

These results follow the researchers’ 2006 climate study, which projected that as much as 81% of premium wine grape acreage in the country could become unsuitable for some varietals by the end of the century.

For the present study the team assumed a 23% increase in greenhouse gases by 2040, which would amount to a 1C increase in global temperature.

Researchers used a climate model incorporating local, regional and global conditions and including factors such as wind conditions and coastal variations. The model was tested against actual data between 1960 and 2010.

They predicted that by 2040 all four wine regions are likely to experience higher average temperatures during the growing season and an increase in the number of ‘very hot days’ when the temperature reaches 35C.

In Napa the average temperature could increase by 1.1C, with 10 more very hot days.

As a result the amount of land suitable for growing Cabernet Sauvignon, Pinot Noir and Chardonnay would shrink by half. In Santa Barbara, the corresponding loss of suitable land would be 20%.

In Oregon’s Willamette Valley there would be slight increase in suitable land, but in Columbia Valley in Washington there would be a 30% reduction.

Diffenbaugh stressed that there while there is ‘a lot more than temperature that goes into making wine’, temperature is a consistent factor that can be measured across decades.

Growers have two options, the report’s authors warn. They can either find grape varieties that can withstand up to 45 very hot days, or they can move their growing operations and employ a range of strategies, such as new trellising methods and irrigation, to keep vines cool.

Written by Adam Lechmere