RICE is in trouble as Earth heats up, threatening the food and livelihood of billions of people.

Sometimes there’s not enough rain when seedlings need water, or too much when the plants need to keep their heads above water. As the sea intrudes, salt ruins the crop. As nights warm, yields go down.

These hazards are forcing the world to find new ways to grow one of its most important crops.

Rice farmers are shifting their planting calendars. Plant breeders are working on seeds to withstand high temperatures or salty soils. Hardy heirloom varieties are being resurrected.

And where water is running low, as it is in so many parts of the world, farmers are letting their fields dry out on purpose, a strategy that also reduces methane, a potent greenhouse gas that rises from padi fields.

The climate crisis is particularly distressing for small farmers with little land, which is the case for hundreds of millions of farmers in Asia.

A farmer in Vietnam’s Mekong Delta surveying the area where salt water intrusion has increased during the dry season, and some have adapted by farming shrimp during that part of year.

“They have to adapt,” said Pham Tan Dao, irrigation chief for Soc Trang, a coastal province in Vietnam, one of the biggest rice-producing countries in the world. “Otherwise they can’t live.”

In China, a study found that extreme rainfall had reduced rice yields over the past 20 years. India limited rice exports out of concern for having enough to feed its own people. In Pakistan, heat and floods destroyed harvests, while in California, a long drought led many farmers to fallow their fields.

Worldwide, rice production is projected to shrink this year, largely because of extreme weather.

Today, Vietnam is preparing to take nearly 101171ha of land in the Mekong Delta, its rice bowl, out of production. Climate change is partly to blame, but also dams upstream on the Mekong River that choke the flow of fresh water. Some years, when the rains are paltry, rice farmers don’t even plant a third rice crop, as they had before, or they switch to shrimp, which is costly and can degrade the land further.

The challenges now are different from those 50 years ago. Then, the world needed to produce much more rice to stave off famine. High-yielding hybrid seeds, grown with chemical fertilisers, helped.

In the Mekong Delta, farmers went on to produce as many as three harvests a year, feeding millions at home and abroad.

Today, that very system of intensive production has created new problems worldwide. It has depleted aquifers, driven up fertiliser use, reduced the diversity of rice breeds that are planted, and polluted the air with the smoke of burning rice stubble.

On top of that, there’s climate change: It has upended the rhythm of sunshine and rain that rice depends on.

Perhaps most worrying, because rice is eaten every day by some of the world’s poorest, elevated carbon dioxide concentrations in the atmosphere deplete nutrients in each grain. 

Rice faces another climate problem. It accounts for an estimated 8% of global methane emissions.

That’s a fraction of the emissions from coal, oil and gas, which together account for 35% of methane emissions. But fossil fuels can be replaced by other energy sources. Rice, not so much.

Rice is the staple grain for an estimated three billion people. It is biryani and pho, jollof and jambalaya - a source of tradition, and sustenance.

“We are in a fundamentally different moment,” said Lewis Ziska, a professor of environmental health sciences at Columbia University. “It’s a question of producing more with less. How do you do that in a way that’s sustainable? How do you do that in a climate that’s changing?”

Risky balance

In 1975, facing famine after war, Vietnam resolved to grow more rice.

It succeeded spectacularly, eventually becoming the world’s third-largest rice exporter after India and Thailand. The green patchwork of the Mekong Delta became its most prized rice region.

At the same time, though, the Mekong River was reshaped by human hands.

Starting in southeastern China, the river meanders through Myanmar, Laos, Thailand and Cambodia, interrupted by many dams.

Today, by the time it reaches Vietnam, there is little fresh water left to flush out seawater seeping inland.

Rising sea levels bring in more seawater. Irrigation canals turn salty. The problem is only going to get worse as temperatures rise.

“We now accept that fast-rising salty water is normal,” said Pham, the irrigation chief. “We have to prepare to deal with it.”

Where saltwater used to intrude 30km or so during the dry season, he said, it can now reach 70km inland.

Climate change brings other risks.

You can no longer count on the monsoon season to start in May, as before. And so in dry years, farmers now rush to sow rice 10 to 30 days earlier than usual, researchers have found. In coastal areas, many rotate between rice and shrimp, which like a bit of saltwater.

But this requires reining in greed, said Dang Thanh Sang, 60, a lifelong rice farmer in Soc Trang. Shrimp bring in high profits, but also high risks. Disease sets in easily. The land becomes barren. He has seen it happen to other farmers.

So, on his 3.2ha, Dang plants rice when there’s freshwater in the canals, and shrimp when seawater seeps in. Rice cleans the water. Shrimp nourishes the soil. “It’s not a lot of money like growing only shrimp,” he said. “But it’s safer.”

Elsewhere, farmers will have to shift their calendars for rice and other staple grains, researchers concluded in a recent paper. Scientists are trying to help them. 

The cabinet of wonders in Argelia Lorence’s laboratory is filled with seeds of rice - 310 different kinds of rice.

Many are ancient, rarely grown now. But they hold genetic superpowers that Lorence, a plant biochemist at Arkansas State University, is trying to find, particularly those that enable rice plants to survive hot nights, one of the most acute hazards of climate change.

She has found two such genes so far. They can be used to breed new hybrid varieties.

“I am convinced,” she said, “that decades from now, farmers are going to need very different kinds of seeds.”

Lorence is among an army of rice breeders developing new varieties for a hotter planet.

Multinational seed companies are heavily invested. RiceTec, from which most rice growers in the southeastern United States buy seeds, backs Lorence’s research.

Critics say hybrid seeds and the chemical fertilisers they need make farmers heavily dependent on the companies’ products, and because they promise high yields, effectively wipe out heirloom varieties that can be more resilient to climate hazards.

The new frontier of rice research involves Crispr, a gene-editing technology that US scientists are using to create a seed that produces virtually no methane. (Genetically modified rice remains controversial, and only a handful of countries allow its cultivation.)

In Bangladesh, researchers have produced new varieties for the climate pressures that farmers are dealing with already. Some can grow when they’re submerged in floodwaters for a few days.

Others can grow in soils that have turned salty.

In the future, researchers say, the country will need new rice varieties that can grow with less fertiliser, which is now heavily subsidised by the state. Or that must tolerate even higher salinity levels.

 - NY Times