More than half the world relies on rice as a primary food source. Yet the essential crop faces an worrisome future as global warming cranks up the Earth’s temperature and intensifies storms, droughts and heat waves.

It’s hard to overstate the danger of this development, scientists say. Rice is vulnerable to climate extremes and grows in places already experiencing many. Any disruption to that food source can cause massive problems.

Just look at recent history. In 2008, fears over rice supplies magnified a food crisis that sent prices soaring. The ensuing panic sparked riots across the globe, from Bangladesh to Egypt to Haiti.

That was 13 years ago, when there were about 1 billion fewer people on the planet. In another 13 years, the world’s population is expected to boom by another 1 billion, bringing the total to a projected 8.8 billion people. And all the while the world’s climate will keep changing.

“At a time when we’re going to add a couple more billion people to the population in the most vulnerable areas, it’s really a bit of a wake-up call,” said Louis Verchot, head of the land restoration group at the International Center for Tropical Agriculture. “We’re going to need to really rethink how we organize our food systems.”

Research underscores this concern.

The latest report from the Intergovernmental Panel on Climate Change—which brought together 234 scientists to synthesize recent climate studies—warned that human-caused global warming is happening at an unprecedented pace and is driving the deadly floods, heat and droughts we’re already witnessing (Climatewire, Aug. 9). And those events pose major risks to farming.

“Higher temperatures lead to increased evaporation, resulting in soil drying, increased plant stress and impacts on agriculture, even in regions where large changes in precipitation are not expected,” the report states.

If greenhouse gas emissions are not reduced, about a third of global land areas are projected to suffer from at least moderate drought by the end of the century, it concludes. Some changes like sea-level rise are already locked in.

Rice is especially susceptible to these changes. Rice often grows in ecosystems, such as deltas, that have low elevation and are vulnerable to rising seas. It also grows in areas that already experience extreme heat. Any additional temperature increase could push it past thresholds in which a healthy crop can develop, scientists say.

2018 study in the Archives of Agronomy and Soil Science found that an increase in the frequency and severity of hot weather could reduce rice yields by up to 40% by the end of this century.

“Most of the [world’s] rice is currently grown in regions where existing temperature is already close to the optimum range for rice production,” the study states. “Therefore, any further rise in mean temperature or short episode of high temperature during sensitive growth stages, will be catastrophic.”

While rice can grow in temperatures that reach 40 degrees Celsius (104 degrees Fahrenheit), heat stress can impair the ability of its flowers to pollinate, the study noted. Temperatures above 35 C can significantly decrease yields.

High nighttime temperatures also can impact productivity. One study found that each 1 C increase in night temperatures above 35 C leads to around a 10% decline in rice yields.

It’s not just heat. The increased potential for flooding and drought also threaten production. So will rising seas that can inundate low-lying farmland with salt water.

paper by the International Rice Research Institute said rice was expected to be “the cultivated crop most vulnerable to future changing climates.”

U.S. rice growers feel the heat

The risk to rice matters in a world where food systems are increasingly interconnected.

“One of the particularities of rice is that the market is very thin in that there isn’t a lot of excess potential supply for demand,” said Tim Benton, research director for emerging market risks at Chatham House. “So if you have a failure in any one place, it does tend to radically affect the international price.”

The United States, for example, has a small but important role in the global supply chain. U.S. farmers only produce about 2% of global rice supplies. But they ship more than 6% of global exports, according to the U.S. Department of Agriculture.

Those U.S. farmers are based almost exclusively in six states: Arkansas, California, Louisiana, Mississippi, Missouri and Texas. And they already are experiencing the impacts of extreme weather.

U.S. rice growers sent a letter to Congress last month asking for disaster assistance following a year of severe storms, floods and drought, according to USA Rice, which advocates for rice producers in the major rice-producing states.

The problem has been magnified of late in California, where rice grows mostly in the Sacramento Valley. Due to multiple years of low rainfall and snowpack, the state this year is expected to grow 100,000 fewer acres of rice, Tim Johnson, the head of the California Rice Commission, said in a report from the local CBS station.

The impacts run deep

In some drought-prone, rice-growing areas, productivity may fall even during favorable years.

That's because farmers who fear crop loss may avoid putting money into things such as fertilizer and new seeds that would help boost yields, research from the International Rice Research Institute shows.

And if yields drop and income is lost, farming families may relocate or send some members to find work elsewhere, said Amanda Carrico, a professor in the environmental studies program at the University of Colorado, Boulder.

That's one of several problems that loom for countries that rely on rice. Population booms compounded by climate change impacts and land conversion—particularly in rice-growing regions of Asia—could add challenges for countries to remain self-sufficient in food production.

“It’s a whole livelihood, it’s a cultural crop, you have religion involved, you have beliefs, stories. Life in Asia, and Southeast Asia in particular, has evolved around rice,” said Bjoern Ole Sander, a senior scientist and climate change lead at the International Rice Research Institute, which is based in the Philippines.

A recent study led by researchers at Cornell University found that global agricultural productivity has slowed about 21% in the last 60 years due to climate change, with the effects more pronounced in warmer, tropical areas. Part of that, the study discovered, was because agriculture wasn’t adjusting to new climate extremes, which made them worse over time.

“You don’t have to be a rocket scientist to know that the projections are for higher temperatures,” said Ariel Ortiz-Bobea, an associate professor at Cornell’s school of applied economics and management. “So it’s pointing to an increasing slowdown of productivity growth, and that has a whole range of implications.”

His team at Cornell is planning to study how much investment in research and development is needed to either maintain or counteract the effects of climate change. One goal is to develop a strategy that doesn’t depend solely on using more fertilizer or expanding the land area in production.

“If we don’t grow productivity, then you’ll make up the production deficit through more inputs, and that has irreversible consequences on the environment,” said Ortiz-Bobea.

Plant early, reduce water, develop new seeds

Rice production has increased greatly since the Green Revolution of the 1960s transformed global agriculture and brought higher-yielding varieties, new methods of cultivation and mechanization.

Global rice production is forecast to hit a record 506 million tons for 2021-2022, according to the Agriculture Department’s latest rice outlook. It forecasts global consumption at a record 514 million tons.

Climate change could roll back some of those gains, especially if it leads to more deforestation or loss of wetlands, a buffer against sea-level rise and a natural sink for carbon dioxide.

“There’s this whole transformation in landscapes that’s going to really put the whole human-economic enterprise at risk. It’s going to roll back gains that we’ve made in the past 40 years in many places, and it’s going to increase the vulnerability of the poorest,” said Verchot from the International Center for Tropical Agriculture.

To avoid these problems, researchers are working to make food systems more resilient. That includes decarbonizing irrigation systems and developing stress-tolerant rice varieties that can withstand high temperatures or flooding.

The International Rice Research Institute has around 150,000 rice varieties in its seed bank, Sander said. But most are not being grown or reaching production scale. Countries also have their own rice research programs and are constantly breeding new varieties, he added.

One goal is to develop seed varieties that have a higher tolerance to drought or heat or can survive submergence in areas that are expected to see even more precipitation. There is also growing recognition of more traditional varieties, which have a strong resistance to salt water and lack of water.

Better farm management can help, too. Rice uses a lot of fresh water, but scientists have found it can grow with half the typical amount. That means farmers can apply water-saving techniques in areas where drought is projected to increase.

Methane an issue for rice growers

Improved farming techniques also can cut emissions of methane, a potent planet-warming gas.

Rice is the second-largest source of methane from agriculture after livestock. In Vietnam, a major rice producer, it accounts for 15% of the country’s total emissions.

Studies have found that alternate wetting and drying of rice paddies can halve emissions and save up to 30% of the water needed for irrigation.

Planting at different times also helps. That’s what the International Rice Research Institute worked with farmers to do in the Mekong Delta following the 2016 drought. That year, several hundred thousand hectares of rice saw reduced yields in part because of salt water pushing into freshwater supplies used for irrigation, Sander said.

In its aftermath, the International Rice Research Institute promoted a new approach: plant rice a few weeks earlier so it wouldn’t be at its most vulnerable stage of growth when salt water started to inundate the fields.

Not every solution will be as easy. Extreme and compound events—such as successive flooding and drought or drought exacerbated by heat stress—will be harder to overcome.

As those disasters become more frequent, scientists expect to see more yield declines more often. It's one of many reasons scientists say the world needs to focus on rice as the Earth heats up.

“Rice has such a high carbon footprint, but the investments are still relatively low,” Sander said. “It is definitely a crop that deserves more attention.”

Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2021. E&E News provides essential news for energy and environment professionals.