How warming will affect grapes
Average minimum temperatures have risen more than maximum temperatures.
The effects of climate change on Washington State's wine grape industry are likely to be mixed, with some viticultural areas benefiting from conditions that favor new varieties, while other areas will have difficulty growing existing varieties.
For example, some growing areas in eastern Washington might approach the upper temperature limits for growing the widely planted red varieties Merlot and Syrah and exceed the limit for the white varieties Chardonnay, Riesling, and Sauvignon Blanc, predicts Dr. Greg Jones, climatologist at Southern Oregon University.
Warmer temperatures could increase the range of varieties suited to the state's cooler growing zones, such as the Puget Sound or Columbia Gorge, and these areas are likely to benefit the most from the projected warming, Jones believes.
He predicts that premium wine grape production will shift to higher elevations, towards the coast, and northward.
Dr. Mercy Olmstead, Extension viticulturist with Washington State University in Prosser, notes that the most significant changes in the climate are higher minimum temperatures.
Weather records at the Prosser station show that maximum annual temperatures have been steady over 80 years, while the minimum annual temperatures have increased.
The sweet-cherry-producing regions of southern California have been feeling the effects of this. Warmer temperatures throughout the dormant season have led to insufficient chilling hours to produce quality cherries, forcing production to creep northwards.
Olmstead wonders if this warming trend in minimum temperatures will affect when grape varieties harden off and emerge from dormancy.
Jones also observes that the global warming trend has had a greater effect on minimum temperatures than maximum temperatures. The explanation for this is that a warmer atmosphere holds more moisture, which prevents the maximum temperature from climbing as high as it would in a drier atmosphere.
Since 1930, the average daytime temperature in the Napa Valley has risen by 2.7°F, but the average nighttime temperature has risen by 5.0°F, he said.
It only takes a change of a degree or two in the average temperature to change an area's suitability for growing grapes, Jones said. For example, the Port Townsend and Port Angeles area in the north of the Olympic Peninsula is marginal for grape growing, but it has a very similar climate to the Willamette Valley in the 1970s and 1980s. The Willamette Valley has become a major growing region for Pinot Noir grapes over the past couple of decades.
"Fifty years ago, I would not have considered Port Angeles to be suitable for grape production. Today, it's right at the limits of cool-climate viticulture."
An increase of one or two degrees during the growing season would make conditions favorable for wine production.
Table grapes thrive in the warmest climates that are free of winter freezes, which is why California's Central Valley has been a major production area. Production of table grapes in Washington in the future might be limited more by a lack of marketing opportunities than by the climate, Jones said. A wine grape grower can have a viable 10-acre vineyard, but a table grape producer would need a larger acreage to market the fruit profitably.
Another crop that might be viable in Washington with average temperatures a degree or two higher is hazelnuts. Oregon grows about 99 percent of the U.S. hazelnut crop, partly because it's developed the infrastructure for the industry, but also because it has a suitable climate.
"What's to say hazelnuts don't become more suitable for the Tacoma and Olympia region?" Jones commented. "I could see that potential changing."