Simonomics: A look at the global economy from a former staff columnist at The Wall Street Journal.

Enter your local supermarket and it’s hard to miss the mile-long piles of fresh produce. And when those heads of lettuce or cauliflower are in season, the prices can be low enough that feeding yourself doesn’t have to cost an arm and a leg. But that may not last much longer.

The world population continues to grow, after all, particularly in developing countries, where there’s been an increased appetite for protein. That’s put strain on the world’s grasslands, where livestock is raised for meat and milk production — and it’s worried scientists. A study recently published in the journal Nature Communications indicated that farmers would need to double their overall use of phosphorus in order to keep grasslands healthy enough to feed all that cattle. Such land hasn’t typically been fertilized directly by farmers, who do tend to add the mineral to arable land, but, with little likely relief on the horizon, that may need to change.

Could anything help the growth in production come back?

There’s also a worry that crop yields may no longer grow in the way we’ve come to expect. In the past, the use of fertilizers and genetically modified seeds boosted the amount of food that could be grown on a given piece of land. But most of the gains are behind us. The production of cereal crops, such as wheat or barley, hasn’t shown any meaningful increase per acre in the last two decades in the U.K., according to a report released in December by the Grantham Centre for Sustainable Futures at the University of Sheffield. And that contrasts markedly with steady output gains from 1960 through 1997.

Could anything help the growth in production come back? Sure, some technology has helped make minimal gains, though Shawn Hackett, who, as president of Hackett Financial Advisors, closely monitors commodity markets, warns, “I don’t see anything right now as the next big act.” In short, the land available is stretched as far as it can go.

But the situation gets worse. The sun is entering a period of reduced activity as part of its typical 11-year cycle, which is measured by how many dark spots appear on its solar surface. A lower count of sunspots has previously coincided with reduced crop yields, according to data crunched by the U.S. Department of Agriculture from 1866 through 1973. And while the relationship between the two outcomes isn’t precisely understood, NASA has pointed to steadily decreasing sunspots through 2020.

A bigger concern is whether the sun’s cycle gets stuck at the low point. “If we go to zero sunspots, it could be a disaster,” says Don Coxe, chairman of Coxe Advisors. He points to the so-called Maunder Minimum — or “prolonged sunspot minimum” — period from around 1645 through 1715, when sunspots all but vanished and temperatures plunged to a level where London’s river Thames froze over periodically. At least for some of us, that news may be chilling enough to prompt stocking up on canned soup and (frozen) veggies.