Article: Kath, J., Byrareddy, V. M., Craparo, A., Nguyen‐Huy, T., Mushtaq, S., Cao, L., & Bossolasco, L. (2020). Not so robust: Robusta coffee production is highly sensitive to temperature. Global Change Biology. https://doi.org/10.1111/gcb.15097
A tale of two beans
If you are anything like me, getting up and into the office in the morning is only possible with a nice hot cup of coffee. However, with temperatures on the rise due to climate change, that essential morning routine could be in jeopardy. While you might see a bunch of names for different types of coffee beans if you go to a fancy coffee shop, most of the world’s coffee supply comes from only two types of coffee plants: arabica and robusta. As is the case for most living things, these plants grow best under a certain temperature range. When temperatures are too high or too low, the reactions that the plant uses to make its own food and grow do not work as well. If you get even more extreme temperatures on either end, it can even damage the plant.
While we can get up and move to a cooler spot if we start to get too warm, plants are not so lucky since they are stuck in one place. As a result, you usually find that plants have temperature growth ranges that are optimal for the places that they are native to since they have adapted to those climates over a really long time. For the coffee plants, it has long been thought that robusta is better able to handle higher temperatures because it is found in warmer, lower elevation areas than compared to arabica which is found in cooler, higher elevation areas. There has been a lot of concern about how arabica probably will not be able to grow as well in a warmer future under climate change, but many have assumed that the apparently more heat tolerant robusta could help to make up the difference.
Too hot to handle?
Although there have been a number of studies of the potential climate impact on yields of arabica, not much work has been done to see if the belief that robusta will stand up better to higher temperatures is actually true. In a study led by Jarrod Kath from the University of South Queensland, a team of scientists completed the first large-scale study examining how robusta growth is impacted by temperature. To do this, the scientists gathered a lot of data on the yield (weight of coffee harvested per hectare) from farms across Vietnam and Indonesia, where more than half of the world’s robusta is grown. They also gathered climate data for those areas that recorded the temperatures the plants experienced and the rainfall they received. With all that data, the research team used a statistical model to explore the impact of temperature on yields and determine the optimal growth temperature for robusta.
Trouble is brewing for coffee production
Based on their analysis, the scientists found that the optimum temperature range for robusta was actually lower than previously thought. The optimal temperature range was previously thought to be somewhere between 22 to 30 degrees Celsius, but the model used by the research team suggested the optimal mean temperature is closer to 20 degrees Celsius. Above this temperature, they found evidence of notable decreases in the robusta yields, with a mean temperature of 24 degrees Celsius decreasing yield by more than 25% and a mean temperature of 25 degrees Celsius decreasing yields by more than 50%.
These results suggest that robusta yields will decrease under a hotter future from climate change, which does not bode well for coffee drinkers or those whose livelihoods depend on the industry. While this study increased our understanding of the potential future impacts of higher temperatures on the coffee industry, a number of a questions still remain. For instance, the impacts of climate change are not limited to just temperature, but also increases in carbon dioxide, which the plants use to make food through photosynthesis. Understanding how changes in carbon dioxide affect robusta could give us a more complete picture of what the future might hold. There is also the potential for management and farming techniques, such as adding shading, to help protect the plants, but more work is needed to see if this might help.