Can Scientists Save Your Morning Cup of Coffee?

Global warming is posing a significant threat to the world’s coffee supply, as temperatures are rising and rainfall patterns are shifting across South America, central Africa, and Southeast Asia. By the end of the century, between 35% and 75% of the coffee-growing land in Brazil could be unusable, according to a recent paper published in Science of the Total Environment by Cássia Gabriele Dias, an agricultural engineer at the Federal University of Itajubá, in Brazil. Another paper concluded that by 2050, between 43% and 58% of the world’s coffee-growing land would be rendered unsuitable, depending on how high greenhouse gas levels rise.

Coffee is a fussy plant, and Coffea arabica, the beans of which account for 70% of the world’s production, is especially so. Its best yields come when temperatures remain between 18°C and 23°C throughout the year. Many of the places in which it is grown are already near the top of that range. It is susceptible to diseases such as coffee rust (a fungal infection) and the depredations of berry-borer beetles, which lay eggs inside growing beans. Both are expected to spread more readily in a warmer world.

Farmers growing Robusta (Coffea canephora), Arabica’s tough, bitter cousin, have a bit less to worry about. Robusta beans fetch a lower price than Arabica ones, and are mostly used in instant coffee. For coffee-lovers, therefore, the solution is not to shift to Robusta but to save Arabica.

One option is simply to move uphill. Other options include moving uphill, which has significant areas of land 150 to 200 meters above sea level where Arabica is currently grown that ought to work well for coffee-farming as temperatures rise. However, higher altitude usually means steeper slopes and shallower soils, which increase the rate at which nutrients are washed out by rain. Replacing them with artificial fertiliser is expensive, and higher slopes are often covered in dense, species-rich forests. Cutting them down to make room for coffee plants might not be compatible with a country’s climate pledges.

Another option is to change the way in which existing plantations are managed. Coffee plants are relatively short and evolved to live in the shade beneath a forest canopy. As demand grew in the 20th century, farmers removed the taller trees in order to fit more coffee plants on their land. Nicholas Girkin, an environmental scientist at the University of Nottingham, published a paper that reviewed these historic “agroforestry” techniques. Dr. Girkin and his colleagues note that the shade provided by taller trees helps prevent coffee plants from getting scorched in hot weather. Trees also provide homes for useful predators and pollinators, which can help feed on pests like the berry-borer beetle.

However, the balance of costs and benefits shakes out, and agroforestry can only go so far. In many parts of the world, climate models suggest that temperatures will eventually get too hot for the sensitive Arabica to cope, meaning that if coffee cultivation is to continue, the bean itself will have to change.

Around 130 known coffee species, including Arabica and Robusta, have been ignored or forgotten due to unpalatable flavors, poor yields, or small beans. Aaron Davis, a botanist at the Royal Botanic Gardens in Kew, has been learning about these lost species to address the danger faced by mainstream coffee crops. Historical records show that many have flourished in environments warmer or drier than those in which Arabica and Robusta grow now. In 1834, George Don, a Scottish botanist, described a coffee species called Coffea stenophylla growing wild in Sierra Leone, which he found growing wild in Sierra Leone. Dr. Davis and his colleagues discovered the species still growing in Sierra Leone and another lost coffee species, Coffea affinis, in 1925 for its pleasant flavor. Both species come from Sierra Leone’s hot and seasonally dry lowland hills, hinting that they can cope with warmer climes than either Arabica or Robusta.

In 2021, Dr. Davis published a paper revealing that C. stenophylla was fruitier, had a better acidity, and had a more complex flavour profile than Ethiopian Arabica. In a blind taste test, judges given C. stenophylla thought they were drinking Arabica 81% of the time. Dr. Davis also noted that C. affinis has demonstrated similar flavours.

Coffea dewevrei, also known as Excelsa, is easy to grow, high-yielding, and has a good flavor. Its biggest advantage might be its resistance to the coffee-rust fungus. However, in 1933, a new disease called coffee wilt emerged, devastating crops and leaving farmers destitute. Now, with climate change making rust a more serious issue, researchers like Dr. Davis are giving Excelsa another look. While the limits of its heat resistance are not yet known, it seems to be more drought-tolerant than Robusta.

No single species has been found that could serve as a drop-in replacement for Arabica. Instead, the hope is that a mix of genetic engineering and old-fashioned cross-breeding could allow traits from these rediscovered species to be transferred into Arabica or help transplant Arabica’s traits into a new species. Dr. Davis is undertaking two research projects to achieve this goal.

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