Why you should care
In Japan, climate change could soon be keeping sushi off menus.
The small town of Futtsu, close to the mouth of Tokyo Bay, has been farming nori — the thin sheets of seaweed used in Japanese cuisine to wrap rice balls and make sushi rolls — for centuries. Five years ago, though, the seaweed began to disappear.
What were once long and luxuriant strands come out of the water thin, straggly and sometimes discolored. “The conditions are really tough,” says Satoshi Koizumi, head of the local fishing cooperative. “People are giving up.”
In 2015, the cooperative had more than 100 members farming seaweed in the bay; last year there were only 73.
The troubles in Futtsu are part of a nationwide decline.
Last year, nori production fell to its lowest level since 1972.
That’s pushing up prices and threatening a cherished staple of the Japanese diet. The disruption offers an early hint of how environmental change will affect food production, forcing long-standing industries to adapt.
The problems are twofold: warming seas and not enough pollution. Climate change has led to a significant rise in water temperatures around Japan in recent decades. “We don’t know the causes for sure, but I think the biggest factor here is global warming,” says Koizumi.
At the same time, however, regulations to clean up Japan’s rivers have led to a decline in the runoff of agricultural wastes and fertilizers into the ocean — stripping the waters of nutrients that help the seaweed grow.
Nori is particularly sensitive to climate change because it grows in the winter, says Kyosuke Niwa, a biologist at the Tokyo University of Marine Science. The most widely cultivated species originated in the north of Japan and its growing season does not start until the water temperature drops to 73 degrees Fahrenheit.
“Recently, the sea temperature has been rising because of global warming, and there are fewer episodes when the water temperature drops,” Niwa says. “Either the timing of a drop to  degrees is later or there isn’t an episode when it drops that low. That makes it hard to cultivate nori.”
Rising temperatures delay the start of the growing season from early October to late October or even November. But even when the crop starts off well, some farmers are suffering at the other end of the season. Their maturing seaweed is often pale and brown, meaning it will be tasteless and lacking in nutrients.
“Episodes of discoloration [are} becoming more frequent and if it’s discolored, we can’t sell it,” says Hiroaki Ebisumoto of the Akashiura fishing cooperative, which grows nori in Japan’s inland sea, the waters between the islands of Honshu and Shikoku.
“It became tougher about 20 years ago. The regulations on phosphorus and nitrogen came in at pretty much the same time,” Ebisumoto says. Clean water standards have reduced blooms of algae, which used to kill fish, but unless there is winter rain to wash nutrients into the ocean, the nori loses its color.
Nori farmers are demanding a change in the rules to stabilize the level of phosphorus and nitrogen in the ocean, instead of minimizing it. Ebisumoto and his fishermen even volunteer to muck out dams and ponds in the mountains, to wash more nutrients out to sea.
Ebisumoto acknowledges that climate change is playing a role but says fishermen cannot do much about it. “We can’t change the water temperature by raising our voices. The one thing we may be able to change is how the country handles its sewerage,” he says.
Shifting production to colder, more northerly waters is not a practical option, says Niwa. For one thing, only shallow, sheltered bays are suitable for growing nori in the stormy winter months, and there are few of those north of Tokyo.
It also takes large capital investment to farm nori. The Akashiura cooperative has several multimillion-dollar drying lines, bought by small groups of members banding together, which turn the strands of seaweed into compact sheets. They stand idle for most of the year and then work frantic 24-hour days during the harvest in spring.
The best hope, says Niwa, is selective breeding. “There are different species of seaweed that are well-adapted to warmer water. Those species normally don’t grow very long but we’re working to breed them for cultivation,” he says.
For Japan’s food-obsessed public, the alternatives are unappealing. There has been a surge in imports of nori from Korea. That, for now, has helped fend off the ultimate convenience-store indignity: the noriless rice ball, wrapped only in plastic.