With rising global temperatures already presenting risks to coffee farmers across the tropics, the findings of two studies published recently should serve as a warning to growers and drinkers everywhere, said Aaron P. Davis, a senior research leader at England's Royal Botanic Gardens and an author of the studies.

"We should be concerned about the loss of any species for lots of reasons," Davis said, "but for coffee specifically, I think we should remember that the cup in front of us originally came from a wild source."

Davis' studies, published this week in the journals Science Advances and Global Change Biology, assessed the risks to wild coffee. One examined 124 wild coffee species and found that at least 60 percent of them are already at risk of extinction, even before considering the effects of a warming world.

The other study applied climate projections to the wild Arabica from which most cultivated coffee is derived, and the picture darkened: The plant moved from being considered a species of "least concern" to "endangered." Data constraints prevented the researchers from applying climate models to all coffee species, but Davis said it would almost certainly worsen the outlook.

"We think our 'at least 60 percent' is conservative, unfortunately," he said, noting that the other chief threats—deforestation and limits on distribution—can be worsened by climate change. "All those things are very tightly interconnected."

The Value of Wild Coffee

Most brewed coffee comes from varieties that have been chosen or bred for taste and other important attributes, like resilience to disease. But they all originated from wild plants. When cultivated coffee crops have become threatened, growers have been able to turn to wild coffee plants to keep their businesses going.

A century and a half ago, for example, nearly all the world's coffee farms grew Arabica, until a fungus called coffee leaf rust devastated crops, one of the papers explains.

"All of a sudden, this disease came along and pretty much wiped out coffee production in Asia in a really short space of time, 20 or 30 years," Davis said. Farmers found the solution in a wild species, Robusta, which is resistant to leaf rust and today makes up about 40 percent of the global coffee trade. (Robusta has a stronger flavor and higher caffeine content than Arabica and is used for instant coffee and in espresso blends.) "So here we have a plant that, in terms of domestication, is extremely recent. I mean 120 years is nothing."

Today, Climate Change Threatens Coffee Farms

Climate change is now threatening cultivated coffee crops with more severe outbreaks of disease and pests and with more frequent and lasting droughts. Any hope of developing more resistant varieties is likely to come from the wild.

The most likely source may be wild Arabica, which grows in the forests of Ethiopia and South Sudan. But the new study show those wild plants are endangered by climate change. Researchers found the region has warmed about 0.5 degrees Fahrenheit per decade since the 1960s, while its wet season has contracted. The number of wild plants is likely to fall at least by half over the next 70 years, the researchers found, and perhaps by as much as 80 percent.

That could present problems for the world's coffee growers.

In addition to jolting hundreds of millions of bleary-eyed drinkers, coffee supports the livelihoods of 100 million farmers globally. While new areas of suitable habitat will open up for the crop, higher up mountains, that land may already be owned and used for other purposes, and the people who farm coffee now are unlikely to be able to move with it. Davis said a better solution will be to develop strains more resilient to drought and pests, and that doing so will rely on a healthy population of wild Arabica.

"What we're saying is, if we lose species, if we have extinctions or populations contract, we will very, very quickly lose options for developing the crop in the future," Davis said.

By Nicholas Kusnetz