Scientists at Washington State University (WSU), US, are calling attention to significant threats posed by climate change to the production and quality of apples based on their analysis of over 40 years of climate conditions. 

The research indicates that key apple-producing regions in the US, including states like Washington, contribute 60% of the country’s apple production.

Food Ingredients First interviews Deepti Singh, a WSU climate scientist and the corresponding author, on how the findings can influence apple-growing strategies and which regions are most likely to lose apple-growing suitability.

“We see the largest ‘potentially harmful’ trends across the western US, including over Yakima county, which is currently the largest producer of apples, and parts of northern US.”

Other top apple-producing counties found to be most impacted include Kent in Michigan and Wayne in New York.

“That said, the risks vary across the country. Some metrics like growing degree days are increasing across the entire US with warming, while some risks such as extreme heat days are increasing in the western US and not so much across the eastern US.”

Singh explains that this is because the western part has heated up faster than the eastern half, and the cold season in the northern areas has warmed faster than the lower latitude areas.

Projecting future apple-growing conditions

Analyzing data from 1979 - 2022, the study focuses on six metrics, including chill portions, cold degree days, frost risk, growing degree days, extreme heat days and warm nights, to project future apple growing conditions.

“These metrics capture optimal and detrimental temperature conditions at different phenological stages of apples and similar tree-fruit. For instance, cold degree days represent the accumulation of cold temperatures below 0 degrees Celsius; growing degree days represent the accumulation of heat within specific temperature thresholds that are beneficial for crop growth,” Singh explains.

“Extreme heat days are days with temperatures exceeding levels that can cause heat damage like sunburn and necrosis and affect the size of the crop, while warm fall nights are days with nighttime temperatures above 18 degrees Celsius, which can inhibit color development.”

Singh notes that much of apple production in the US is irrigated, and water availability is, therefore, a key factor influenced by changing climate conditions. For now, this is beyond the scope of the WSU analysis.

Potential costs for consumers and growers

Prices of certain foods fluctuate with changing weather conditions, and experts believe climate change can worsen these conditions. Recent surges in the price of commodities like olive oil, coffee, potatoes and oranges have been strongly linked to the volatility of extreme weather events, according to ING Research.

Singh says the damages caused by increasing climate risks can affect the yield and quality of apples, with some varieties more susceptible than others. This means that the availability of different varieties might change.

“Crops that experience browning due to heat damage or sunburn or do not develop sufficient red color might not be as marketable. And yes, increasing costs to growers due to managing these risks could cascade to consumers.”

WSU scientists reveal that many apple growers have adaptation measures in place to respond to certain risks associated with rising temperatures and unpredictable rainfall patterns. However, this adaptation has nuances, including costs and capacity.

“These include evaporative cooling or protective netting that can reduce risk of sunburn damage or damage from other climate and environmental factors,” Singh reveals.

She warns that a rise in such risks can increase the costs to growers.

“Growers might also need to think about managing multiple risks that can have compounding negative effects on apples’ yields and quality (based on color and sweetness). They will likely need a diversity of tools to adapt to these risks since adaptation to early bloom and risk of frost will be different from adaptation to sunburn risk,” she concludes.