Coffee climate threat

C&I Issue 4, 2023

Read time: 3 mins

Anthony King

Worldwide yields of coffee will fall due to climate change, research indicates. Bad news for many of the tens of millions of coffee farmers in developing countries, which mostly farm two species, Coffea arabica (Arabica coffee) and C. canephora (Robusta coffee).

The global land area suitable for growing coffee is widely projected to decline by around 50% according to studies. Now, new research also highlights a risk of synchronous crop failures in multiple countries due to increasing climate hazards. The analysis looked at a dozen climate hazards in the top 12 coffee producing regions. The number of climate events increased in all regions between 1980 and 2020 (PLOS Climate, doi: 10.1371/journal.pclm.0000134).

The El Nino Southern Oscillation (ENSO), which sees temperatures in the Pacific Ocean periodically change and influence rainfall, was found to ramp up climate anomalies that impact coffee production. ‘An El Nino event increases the likelihood of almost every coffee region experiencing too warm or too dry conditions,’ notes study scientist Doug Richardson at CSIRO in Tasmania, Australia.

The one exception was southern Brazil, the world’s largest producer of Arabica coffee. Arabica originates in Ethiopia and makes up around 60% of world coffee supply; Robusta makes up almost 40% of global production. Not as sweet as Arabica, Robusta has more caffeine, and is used mostly in instant coffee and espresso.

‘There is consensus that [Arabica] is a very climate-sensitive crop and therefore climate change is expected to have mainly negative impacts on it,’ says Roman Grüter, a crop scientist at Zurich University of Applied Sciences in Switzerland. In his recent study of coffee, cashew and avocado – crops with similar ecological requirements – Grüter and colleagues found that coffee was the most vulnerable to higher temperatures (PLOS One, doi: 10.1371/journal.pone.0261976). Coffee was less tolerant of high and low soil pH and choosier when it came to soil texture.

‘If you have high and sustained periods of rainfall, you may get severe outbreaks of coffee leaf rust,’ says Aaron Davis, a coffee scientist at the Royal Botanic Gardens at Kew in Surrey, UK. Conversely, during long periods of drought, insect pests may hurt coffee yields. Some coffee plant species are more susceptible.

Fortunately, there are 130 coffee species known to science that can be tapped for solutions. In 2021, Davis at Kew reported on a West African coffee species, Coffea stenophylla. This wild coffee species grows in much warmer temperatures than Arabica, and tastes similar (Nature Plants, doi: 10.1038/s41477-021-00891-4). It was commercially cultivated in the late 19th and early 20th century, but is no longer farmed and hard to find in the wild.

There are other species too. Davis and colleagues in Uganda recently reported on a coffee known as Excelsa, a type of Liberica coffee (Coffea liberica). Even though it received little attention regarding domestication, this coffee shows great promise and could be available in coffee shops within the next few years (Nature Plants, doi: 10.1038/s41477-022-01309-5). The most common type of Liberica coffee, sometimes known as Liberian coffee, is native to west and central Africa, but cultivated at small scale across the world. It comprises less than 1% of commercial coffee production, but ‘demand is on the increase,’ according to Davis.

Another native of Uganda is C. eugenioides. ‘It’s not very productive but it has got lots of useful attributes, including a delicious flavour and plenty of sweetness, and could be a great breeding partner,’ says Davis. It could be crossed with Liberica, Arabica or Robusta and has further potential as a niche coffee.

Some of the sweetness and flavour profiles recently discovered for Excelsa can resemble high-quality Robusta and even Arabica, but with its own unique character, says Davis. ‘Many coffee species have challenging flavour notes – high acidity, sausage roll, eucalyptus, lavender, some say urinal – which wouldn’t be acceptable to coffee drinkers.’

Farmers who depend on coffee crops are rightly concerned. Coffee makes up around 15% of Uganda’s annual export revenue, with 1.7m people involved in growing coffee and around 8m people working in the coffee sector. ‘We’re interested in trying to make sure that farmers aren’t left behind or forgotten,’ says Davis. New coffee species may offer a lifeline.

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