Climate & French fries

Author: 
November 19, 2020

Established in 1960, The Original Hot Dog Shop served generations of students and locals near the University of Pittsburgh. Named for its hot dogs, “The O,” as it was often called, was arguably better known for its fries. Cooked twice in peanut oil (first at low heat to cook the inside, again at high heat to crisp the outside), The O’s famous fries—featured in a 1999 PBS documentary—came in portions big enough to satisfy several people, even without hot dogs.

Whether at The O, a chain restaurant, an upscale eatery, or home, we Americans love our fries. According to a recent study cited by the Washington State University Potato Research Lab, the average American consumes 34 pounds of French fries each year.

Fries depend on potatoes, and like all crops, potatoes have a preferred climate. How long will America’s favorite side dish have a safe spot on our menu?

Basket of foodie fries

Fries please foodies when they involve garlic, truffles, and parsley. CC license by Flickr user L.A. Foodie.

From farm to fry basket

First cultivated in South America as much as 10,000 years ago, potato plants grow over most of Earth’s land surfaces, though most production now occurs in the Northern Hemisphere. The top U.S. producers are Idaho and Washington. The U.S. Department of Agriculture reports that in 2017, Idaho produced around 13.5 billion pounds of potatoes, and Washington produced close to 10 billion pounds. In third place was Wisconsin, with just under 3 billion pounds.

Purple potato flowers

Purple potato flowers bloom in profusion in Peru, one of the first places where this tasty tuber was cultivated. CC license by Flickr user Leonora (Ellie) Enking.

Third in volume, Wisconsin comes first in variety. According to Tamas Houlihan, executive director of the Wisconsin Potato and Vegetable Growers Association, Wisconsin grows more kinds of potatoes than any other state. About 20 percent of Wisconsin’s potatoes turn into French fries. Planting usually begins in early April and ends in late May. Tubers (the parts we like to eat) begin to form in June, and keep growing in July. Major commercial potato harvests occur in the relatively cooler months of autumn.

Top three U.S. potato-growing states, 2015-2019

The top three potato-growing states in the United States are Idaho, Washington, and Wisconsin. Although Wisconsin is a distant third, it produces the greatest variety of potatoes. Maps by NOAA Climate.gov based on data from USDA CDL.

“September and October are the primary harvesting months for the major production regions of the United States,” Houlihan says. “As those potatoes are harvested, some will go directly by truck to the factory. Once there, they are weighed and graded and sorted into different sizes. Some of those potatoes are processed immediately and turned into French fries.”

Other potatoes, Houlihan says, go into storage, able to be turned into fries later. “We now have learned how to store potatoes for almost a full year.” The most popular potato type for French fries is the Russet, especially the Russet Burbank. “I think the ideal storage temperature for a Russet Burbank is 45°F–48°F-degrees. You’ve got to be able to maintain that for up to nine months. You also need very high humidity, above 90 or 95 percent.”

Potato storage facility

“Shed” takes on a different meaning when used to store potatoes from an industrial-scale producer. Potato-storage technology has advanced to control temperature and humidity, preventing rotting and sprouting. CC license by Flickr user Washington State.

Large commercial growers, who often operate their own storage facilities, continually refine their buildings and protocols. “We’ve found if we put culverts and fresh air in storage facilities, potatoes do better and can last longer,” Houlihan says. Houlihan notes that many growers have adopted cement floors and even cement walls to nudge temperatures lower and maintain high humidity.

Sprouted tuber

Good for the next generation of tubers, bad for fry baskets, sprouting must be avoided during potato storage. Skillful storage can keep potatoes fit for frying several months after harvest. CC license by Flickr user Chris Bertram.

Multiple heat hazards

Although they can grow in a lot of places, the fungus-fouled tuber that famously failed Ireland in the mid-19th century is largely a cool-weather crop. A 2019 study in Breeding Science reported that the optimum temperature for potato vegetative growth—above-ground stems and leaves—is a relatively cool 75°F (24°C), but the maximum tuber yield occurs at an even cooler 68°F (20°C). Combine that with the need for months of cold storage, and it’s clear why the nation’s top potato states are in the northern tier of the country.

It’s also clear why global warming might pose hazards for French fries.

One hazard involves starches and sugars. Russet Burbank potatoes fry well due to their high starch content. According to Richard Novy, a research geneticist with the Agricultural Research Service at the U.S. Department of Agriculture in Aberdeen, Idaho, the key is retaining the starch as long as possible, reducing its conversion to glucose and fructose. In Russet Burbank potatoes, higher temperatures can cause an uneven starch-to-sugar conversion. “With that, when you fry it up then, you can have something called sugar ends. You have a nice, light fry except at the very end, where it’s sort of darker brown,” he says. Big producers of French fries have exacting standards that brown sugar ends don’t meet.

Sugar ends

Russet potatoes are vulnerable to “sugar ends”: burnt-looking tips of French fries. Fries in the right half of this photo exhibit the problem potato producers try to avoid. Image from Zhu et al. 2015 in PLoS ONE, https://doi.org/10.1371/journal.pone.0093381.g003.

Another problem, Novy says, is second growth. “If you have high heat for extended periods, and you’re not able to put on adequate water during that period, you can get protuberances or bumps or knobs. They can result from the interaction between heat and water. The Russet Burbank tends to be a little more sensitive than other varieties to second-growth malformations.”

Changing climate also brings changing threats of potato-plant disease. Like Rich Novy, Dennis Halterman is a USDA ARS research geneticist, but he works from an office in Madison, Wisconsin. Halterman explains that most potato pathogens have favorite temperature ranges. Late blight—the culprit behind the Irish potato famine—prefers cool temperatures (65˚F–68˚F), whereas verticillium wilt—another fungal disease pestering potatoes—prefers warmer temperatures (80˚F–85˚F). As climate warms, he notes, disease risks will shift.

Halterman also recently collaborated on research showing that potatoes can lose their ability to fight disease at higher temperatures. Between temperatures of 68˚F and 75˚F, the Premier Russet resists some varieties of a pathogen called Potato Virus Y. But when temperatures rise above 82˚F, that resistance falters. “We aren’t exactly sure how this happens, but we know that it has something to do with how the potato plants respond to the virus and how they defend themselves against infection. At an elevated temperature, they aren’t able to mount an effective defense to stop the virus from spreading,” he writes in an email.

Warming climate is likely to bring yet another threat: an expansion in the range of the Colorado potato beetle, Leptinotarsa decemlineata. A 2017 study examined the relationship between the pest, its original host plant—Solanum rostratum, sometimes called spiny nightshadeand climate, concluding that climate change would expand the habitat suitable for the beetle into new parts of the Northern Hemisphere, in part because the host plant will thrive in those areas.

Potato beetle

Already a nuisance to farmers, the Colorado potato beetle, Leptinotarsa decemlineata, may menace potato plants even more in a warming climate. Image from USDA.

Past and future changes in temperature

Across most of the United States, warming is well underway. The 2018 National Climate Assessment (NCA) reported that annual temperatures from 1986–2016 increased relative to 1901–1960 over most of the contiguous United States, including Idaho, Washington, and Wisconsin. Over the past 30 years, potato-growing parts of eastern Washington and southern Idaho have experienced some of the country’s largest increases in daytime high temperatures in summer. At the peak of the summer heat in July, average daytime highs across parts of central Wisconsin have been rising by more than 1.5°F per decade. Along Idaho’s Snake River Plain, the state’s agricultural heartland, daytime highs in July have warmed by more than 2°F per decade.

Change in average daytime high temperatures in July, 1991-2020

Between 1991 and 2020, average daytime high temperatures in July rose across the top three potato-producing states: Idaho, Washington, and Wisconsin. In these maps, areas with rising temperatures appear in shades of red. Areas with falling temperatures appear in blue, and only a few isolated patches show falling temperatures. Maps by NOAA Climate.gov based on data from NCEI.

If the world follows an energy pathway that leads to high carbon dioxide emissions, these trends will continue, pushing summertime temperatures even further away from potatoes’ optimum conditions. According to the U.S. Climate Explorer, under a higher-emissions scenario, models project that by the 2050s, the number of days with extreme heat—daytime highs above 90°F—will likely more than double compared to the 1961–1990 average in many potato-growing parts of Washington, Idaho, and Wisconsin.

Animation of July daytime high temperature changes

Under a high-emissions scenario (RCP8.5), daytime high temperatures will rise substantially across the contiguous United States, affecting potato-producing regions during growth season. Images by NOAA Climate.gov based on data from PRISM and LOCA.

Water: too little or too much?

In addition to their preference for cool temperatures, most modern potato varieties—with their relatively shallow root systems that thrive in sandy, loose soils—have low tolerance for drought. According to a 2013 study in Plant Science, climate change is likely to increase drought risks to potato crops in many potato-growing regions of the world over the 21st century.

“Most of Wisconsin’s potatoes are grown in the state’s Central Sands region, which is an ideal environment for ample water supply,” says assistant Wisconsin state climatologist Edward Hopkins. He explains that some of Wisconsin’s prime potato-growing counties were once home to a glacial lake, which left behind an expanse of sandy soils.

“In Wisconsin we’re fortunate in that we get about 30 inches of precipitation a year. So, throughout the growing season, we typically get enough rain to keep the potatoes healthy. Now, 99 percent of our growers have irrigation systems just to make sure,” Houlihan says.

In Idaho and Washington, meanwhile, irrigation isn’t a backup, it’s a necessity. Potato production in Idaho is concentrated in the southern and eastern portions of the state; production in Washington is concentrated in the eastern half of that state. Both places are much drier than famously rainy Seattle or Portland.

Potato irrigation

Although it’s mostly a backup in Wisconsin, irrigation is a necessity for potato growers in Idaho and Washington. CC license by Flickr user Washington State.

Reliance on irrigation has an upside, says the USDA’s Novy. In the northwestern United States, annual precipitation in potato-production regions can be less than 12 inches per year, and heavy rainfall events are rare, especially during the potato-growing season. “But as long as you have enough water to irrigate, you generally have very high-quality potato crop just from the standpoint that you are the one controlling the water that goes onto that crop. You don’t have Mother Nature throwing a monkey wrench into that production,” he says. But reliance on irrigation has a downside, too. Population growth in the western half of the United States places increasing demands on scarce water resources. “If water becomes more limited, that creates issues for future production.”

Though drought is less likely in Wisconsin than in western states, Houlihan says, it still happens. But for all the damage drought can cause, Houlihan worries more about another issue: too much water. “We had a disaster in 2018,” he says. That year, waterlogged potato fields prohibited growers from harvesting for weeks. Harvesters that collect potatoes on an industrial scale weigh tons. In soil that’s too moist, they simply sink. “By the time they got into their fields, it was October and we had an early frost. It just devastated the crop.”

Potato harvester

A potato harvester works a field in Colorado. Industrial-scale potato harvesters weigh thousands of pounds and can sink in waterlogged terrain. CC license by Flickr user Colorado Farm Bureau.

Past and future changes in precipitation

According to the National Climate Assessment, between 1986–2015, annual precipitation declined over much of the western half United States and increased over much of the eastern half relative to the period from 1901–1960. But conditions vary substantially from place to place and season to season.

In the past three decades, spring precipitation has risen slightly across parts of Washington and Idaho where potatoes are widely grown, while summer precipitation has declined. For the most part, however, these changes are small compared to the range of natural variability.

Calculating precipitation trends for Central Wisconsin since 1961, climatologist Hopkins has found a 23-percent increase in spring precipitation, and a 24-percent increase in summer precipitation. Most years, potatoes fare just fine, but like all plants, they can get too much of a good thing. “In sandy soil, water can saturate up, and where does it go? It comes out of the ground. And potatoes don’t want to get their feet wet.”

According to projections of future precipitation in the National Climate Assessment, wet feet will be a bigger concern in some seasons than others. If the world follows a pathway with high greenhouse gas emissions, Washington and southern Idaho are likely to see a 5–10-percent increase in spring precipitation by the end of the century, a relatively small change compared to the area’s natural year-to-year variability. But in potato-growing parts of Wisconsin, spring precipitation may increase by a more significant 15–20 percent. Falls may get a tiny bit wetter, too, though again, the projected changes are small relative to natural variability. In summer, the pattern diverges, with small declines projected for Wisconsin and southern Idaho, and more serious declines (up to 15–20 percent) in parts of Washington.

Predicted precipitation changes

These maps show predicted changes in precipitation for spring and summer in the late 21st century under a high-emissions scenario (RCP8.5). Increased precipitation appears in shades of blue-green. Reduced precipitation appears in shades of brown. Red stipples indicate strong confidence in changes. Hatch marks indicate small anticipated changes relative to natural variability. Adapted from U.S. National Climate Assessment, 2018.

But as Dan McEvoy of the Western Regional Climate Center points out, crop stress may increase considerably in summer even without significant declines in rainfall. McEvoy coauthored a study on irrigation demands and water stress across the American West. The study found that, in the Columbia River Basin, the growing season is likely to lengthen for potatoes, but the potential for evaporation will also increase. These factors will likely combine to increase evapotranspiration—evaporation from soil and transpiration from plants. "So, the longer growing season could actually benefit agriculture in places like Washington and Idaho, but there will also be more stress on the crops and higher water demand during peak growing season due to increased temperatures and evaporative demand," he writes in an email.

Finally, there’s the issue of snow. In Idaho and Washington, irrigation is key to potato cultivation, and irrigation relies on snowpack. A 2018 study in Climate and Atmospheric Science found that, since the mid-20th century, April 1 snow water equivalent had fallen across the western United States by about 15–30 percent. A 2020 study in Nature Climate Change examined projected changes in snowpack runoff assuming warming of 4°F (2°C) and 7°F (4°C). The study predicted shifts in runoff timing to earlier in the spring, affecting potatoes and other irrigated crops in the western United States. Although not expected to fare the worst among western U.S. river basins, the Columbia River was projected to experience significant snowmelt deficits.

Growing spuds in a warmer climate

In 2014, the USDA ARS examined the effect of the primary driver of global warming—carbon dioxide—on potato production. Carried out in soil-plant-atmosphere research chambers, the study indicated that elevated carbon dioxide levels could actually increase tuber yield, provided the plants were properly irrigated. A 2016 study compiling research on carbon dioxide, temperature, and water availability found that potato plants might use water more efficiently and even slightly increase yields—provided temperatures don’t climb too much.

In the face of risk and uncertainty, one strategy for growers in a changing climate is to partner with climate experts to identify opportunities for increasing their resilience. Where should growers be thinking about adding refrigerated storage in the next decade? Should a given farm be more concerned with improving drainage to combat heavier spring downpours or improving irrigation to cope with longer spans of hot summer days without rain?

Climate information isn’t just about planning for the distant future, though. It can also mitigate today’s threats. Houlihan, with the Wisconsin growers association, has worked with NOAA on such a project funded by the Sectoral Applications Research Program (SARP) in NOAA’s Climate Program Office. The group helps decision makers better prepare for climate impacts such as extreme floods and droughts.

Collaborating on a SARP-funded project for growers of specialty crops in the Midwest, Houlihan assembled a focus group of growers and advisors to help develop a decision-support calendar for potato production in the event of drought. Released in August 2020, the calendar addresses management decisions for potato crops year-round—from aquifer recharging in the winter months through harvesting the following autumn. Each month, the calendar offers advice on what problems to watch for, and how to deal with them.

Decision calendar snippet

NOAA’s Sectoral Applications Research Program (SARP) collaborated with potato growers and the University of Nebraska’s Drought Mitigation Center to produce decision calendars for Midwestern specialty crop growers. Houlihan pulled together a focus group to address drought risks affecting Midwestern potatoes, vegetables, apples, and cranberries.

To help potato producers deal with those threats, NOAA’s Climate Program Office has partnered with other agencies and institutions to offer season-specific guidance through the National Drought Mitigation Center at the University of Nebraska. Each season, potato farmers can turn to NOAA-sponsored data products to better spot and mitigate drought-related issues at that time of year. Among the products are the drought monitor of current and past conditions, soil-moisture maps for different layers of the soil, soil-temperature maps, and seasonal outlooks.

Alongside crop-specific climate information like the Wisconsin potato calendar, part of the solution to the climate challenges facing French fries might come from the potato itself. Also a part of the USDA ARS, John Bamberg is the project leader for the U.S. Potato Genebank in Sturgeon Bay, Wisconsin. He and his team search the genomes of wild potato species for traits that will prove useful in domesticated varieties.

In one wild species, Solanum microdontum, Bamberg found genes conferring resistance to potato greening, a trait Novy is working to incorporate into a domestic cultivar. He’s also found a useful wild potato relative in the Four Corners region of the American Southwest. The species, Solanum jamesii, may be instrumental in warding off problems ranging from drought to nematodes to freezing. In collaboration with University of Wisconsin-Madison professor Jiwan Palta, Bamberg is also finding promising heat and drought resistance another wild species, Solanum kurtzianum.

Mesa Verde

For over 700 years, from 600 to 1300 CE, Ancestral Pueblo people resided at Mesa Verde in southwestern Colorado. The desirable qualities of Solanum jamesii, a wild potato from the Four Corners region, prompts Bamberg to wonder whether human selection centuries ago drove the characteristics of some of today’s wild potato species. CC license by Flickr users Jerry and Pat Donaho.

Though it might be tempting to assume that some cool-weather potato threats will retreat in a warming climate, Bamberg expresses caution, saying, “I think it’s safe to say if climate is changing, it could make anything be worse—any disease, pest, or stress.”

Even with a wealth of wild genes at their disposal, potato breeders must consider multiple priorities, Bamberg explains. “Decades ago, when late blight was really a bad problem in this country, I went to a big convention and one colleague stood up and said, ’The problem is not resistance to late blight. We have plenty of resistance to late blight, but we don’t have it in the kind of potatoes that meet the super-high-quality standards of the American consumer.’ When you’re talking about French fries, it isn’t so simple as to find some kind of potato that will stand up to heat and drought. It has to be incredibly high quality and high yield.”

Focused on fries

In April 2020, during the COVID-19 pandemic, The Original Hot Dog Shop closed. The Pittsburgh Post-Gazette reported that the restaurant donated seven tons of potatoes to charity. WQED|PBS documentary maker Rick Sebak lamented the closure, saying the O’s fries were without comparison.

For fans of The O, it was the end of an era. Still, fries won’t disappear anytime soon, even with climate uncertainty. Farmers, breeders, and climatologists are keeping their eyes on the future of our favorite spuds.

Houlihan reflects, “I think what you might see is that the demand maybe outweighs the supply sometimes. So, you pay a little more. The price might go up. But I don’t think it will get to the point where we’re not going to be able to order fries anymore.”

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