What has four stomachs and could change the world?

The average dairy cow in America produces 30 litres of milk a day; a cow in Africa, only 1.6. This 19-fold difference—call it the dairy divide—has enormous consequences.

Closing even some of it would ease poverty, help children grow up better nourished, reduce emissions of greenhouse gases and perhaps even make civil wars less likely. The good news is that cows can become more productive, thanks to the spread of technologies old and new. But unhelpful traditions—and climate change itself—make it harder.

In rich countries, cows are unfashionable. The health-conscious are shunning red meat and switching to plant-based milk. The environmentally conscious fret, correctly, is that cattle account for 7% of man-made greenhouse-gas emissions—far more than any other kind of livestock.

And techno-optimists have predicted, since the first lab-grown beef was unveiled in 2013, that cruelty-free cultured meat will replace the sort sliced from slaughtered animals as soon as it is cheap and tasty enough. Perhaps that day will come. But for now, cows are growing more important, not less so (see chart 1).

The UN’s Food and Agriculture Organisation (FAO) expects global beef consumption to increase by 11% by 2033, and milk consumption to rise by 17%, as the human population grows and more people can afford more animal protein. Farmers face two challenges. First, to meet the growing demand for bovine bounty, even as hotter, less predictable weather makes their job harder in many regio.