This is the final installment of a four-part series on wine and climate change.

ST. HELENA, Calif. — Every wine region has had to deal with some manifestation of climate change, but few have had to deal with as many devastating consequences as Napa Valley.

On Labor Day 2017, as the weekslong harvest was getting underway, the temperature reached 110 degrees here in the heart of cabernet sauvignon country. But extreme summer heat has not been the only issue.

An abnormally warm January and February in 2015 set the growing season in motion early. But a cold snap in May caused many growers to lose 40 to 50 percent of their crop.

Wildfires, sparked by high winds and extremely dry conditions, are threatening Northern California wine country. In October 2017, fires in Napa and Sonoma destroyed precious housing, blackening fields and threatening the quality of grapes that had not yet been harvested . The 2017 fires followed five years of extreme drought in California.