Thanh Nguyen for The New York Times
Rice is in trouble as the 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 paddy 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. “They have to adapt,” said Pham Tan Dao, the 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.
在中国,研究发现极端降雨在过去20年里导致了大米产量的下降。印度因为担心粮食不足以喂饱自己的人民,对大米出口进行了限制。在巴基斯坦,酷热和洪水造成庄稼歉收,而在加利福尼亚,长时间的干旱导致许多田地休耕。对于越南的小农庄主来说,这是辛苦的劳动。对于越南的小农庄主来说,这是辛苦的劳动。 宰湄公河三角洲晾干农作物。宰湄公河三角洲晾干农作物。
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 fertilizers, 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 fertilizer 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 from each grain.
Rice faces another climate problem. It accounts for an estimated 8 percent of all global methane emissions from human activity. That’s a fraction of the emissions from coal, oil and gas, which together account for 35 percent 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 H. 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?”
A risky balance: Rice, or shrimp?
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 freshwater 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 Mr. Pham, the irrigation chief. “We have to prepare to deal with it.” Where saltwater used to intrude 30 kilometers or so (about 19 miles) during the dry season, he said, it can now reach 70 kilometers inland.
“我们现在承认,海水快速上涨是正常的,”灌溉主管范先生说。“我们必须做好应对的准备。”他说,过去在旱季,海水侵入内陆30公里左右的地方,现在可以到达内陆70公里。越南的大米出口帮助养活了世界。越南的大米出口帮助养活了世界。 一个农民检查他的田地。他说,他有时种水稻,有时养虾。一个农民检查他的田地。他说,他有时种水稻,有时养虾。 Thanh Nguyen for The New York Times
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 seven acres, Mr. 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 already trying to help them.

Secrets of ancient rice
The cabinet of wonders in Argelia Lorence’s laboratory is filled with seeds of rice — 310 different kinds of rice.
在阿格利亚·劳伦斯的实验室里,陈列柜里装满了水稻的种子——310种不同的水稻。在劳伦斯的实验室里,有数百种不同的水稻。在劳伦斯的实验室里,有数百种不同的水稻。 她专注于研究隐藏在许多品种中的有价值的遗传特征。她专注于研究隐藏在许多品种中的有价值的遗传特征。
Many are ancient, rarely grown now. But they hold genetic superpowers that Dr. 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.”
Less watery rice paddies?
Rice is central to the story of the United States. It enriched the coastal states of the American South, all with the labor of enslaved Africans who brought with them generations of rice-growing knowledge.
Today, the country’s dominant rice-growing area is spread across the hard clay soil near where the Mississippi River meets one of its tributaries, the Arkansas River. It looks nothing like the Mekong Delta. The fields here are laser-leveled flat as pancakes. Work is done by machine. Farms are vast, sometimes more than 20,000 acres.
What they share are the hazards of climate change. Nights are hotter. Rains are erratic. And there’s the problem created by the very success of so much intensive rice farming: Groundwater is running dangerously low.
Enter Benjamin Runkle, an engineering professor from the University of Arkansas at Fayetteville. Instead of keeping rice fields flooded at all times, as growers have always done, Dr. Runkle suggested that Arkansas farmers let the fields dry out a bit, then let in the water again, then repeat. Oh, and would they let him measure the methane coming off their fields?
Mark Isbell, a second-generation rice farmer, signed up.
第二代稻农马克·伊斯贝尔报名参加。新的灌溉理念可以节约用水,减少甲烷排放。新的灌溉理念可以节约用水,减少甲烷排放。 朗克尔博士:“就像对土地进行酒精测试。”朗克尔博士:“就像对土地进行酒精测试。”
On the edge of Mr. Isbell’s field, Dr. Runkle erected a tall white contraption that an egret might mistake for a cousin. The device measured the gases produced by bacteria stewing in the flooded fields. “It’s like taking a breathalyzer test of the land,” Dr. Runkle said.
His experiment, carried out over seven years, concluded that by not flooding the fields continuously, farmers can reduce rice methane emissions by more than 60 percent.
“We kind of look over the hill and see what’s coming for the future, and learn now,” said his father, Chris Isbell.

Somini Sengupta自阿肯色州和孟加拉国、Tran Le Thuy自越南报道。Thanh Nguyen自越南、Rory Doyle自阿肯色州进行了图片拍摄。