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The growing range of three economically important crops – avocados, cashews and coffee – will undergo significant shifts under even moderate warming scenarios by 2050, new research shows.
The study was published in PLOS OneThe climate, soil, and land factors that influence the suitability of each crop are examined. The researchers then map out how these optimal areas of growth could change under three different climates.
For all three crops, they find “both regions of future expansion and contraction” under shifting temperatures and rainfall patterns. But they also note that the area of land they rate “most suitable” for crop-growing in many of the major producing countries will largely shrink in the coming decades.
For example, Brazil – the world’s biggest producer of coffee – is projected to lose nearly 80% of its best growing land for the arabica bean under a moderate warming scenario. The study also warns about large reductions in prime land for avocados in Peru, the Dominican Republic, and Indonesia, as well as cashews from Benin.
According to the authors, adaptation measures such as selective breeding and different land management will be required in most of these major producing areas.
Mapping suitability
Cashew nuts, avocados, and coffee are high-value cash crops that are mainly grown in tropical countries. In addition to their high economic value, these three crops “contribute substantially to the livelihoods of smallholder farmers around the world”, Dr Roman GrüterAn environmental scientist at Zurich University of Applied SciencesTells Carbon Brief.
Grüter, who led the new work, adds that long-term planning is “especially important” for plants such as these, which are perennial crops and can take several years to reach maturity.
According to a report by The World Coffee Beans Association, the world produced approximately 7.1m tonnes worth of avocados, 3.8m tons of cashew nuts, and 10.0m tonnes unroasted coffee beans in 2019. StatisticsCompilation by the UN Food and Agriculture Organization. The 2019 harvests in 2014-16 were worth a gross production value of $1.5 billion. International dollarsI$6.6bn to I$3.7bn and I$21.0bn, respectively. (Data taken from the International Coffee Organization show that about 60% of the world’s coffee crop is coffee arabica, the species analysed in this study.)
The research focused on the four main countries that produce each crop. Brazil, Vietnam, Indonesia and Colombia together produce 64% of the world’s total coffee, although Vietnam and Indonesia predominantly produce coffee robusta, not arabica.
Taken together, Vietnam, India, Côte d’Ivoire and Benin are responsible for 73% of global cashew production. And Mexico, the Dominican Republic, Peru and Indonesia account for 58% of the world’s avocado crop.
The researchers analyzed the literature to determine climate variables and soil characteristics that lend themselves for each crop. This included average annual temperature and rainfall, lengths of dry season, soil pH, and slope of the growing soil. Each factor was classified along a four-point scale from “unsuitable” to “very suitable” for producing a particular crop.
By combining global maps of all of these variables and taking the lowest-suitability classification for each pixel, Grüter and his colleagues charted out the current suitability for growing each crop around the world, rating locations on that same four-point scale.
Below are maps showing how each of the climate variables affects the suitability to cashew-growing. The composite (in bottom right-hand corner), shows how the overall suitability.
The researchers used 14 global climate models, all from the CMIP5 suite. This helped them understand the impact of climate change on the regions where they could grow these crops. Coupled Model Intercomparison Project.
They projected future climate variables across all three scenarios. RCP2.6, RCP4.5And RCP8.5 – representing, respectively, a low-emissions scenario, a moderate-emissions scenario that roughly matches the world’s current trajectoryThis is a high-emissions situation.
The suitability maps were created using the projected future weather. This allowed them to map how the potential growing ranges would change for each scenario.
Breaking down the suitability into four classifications is “slightly more granular” than previous work, much of which has used a binary classification of suitable/not suitable, says Dr Jarrod Kath, an agroecologist at the University of Southern QueenslandThe study did not include anyone who was not involved. He says that even better would be to use crop yield to determine suitability. Carbon Brief is told by him:
“You’re taking a continuous variable like yield and you’re breaking it up into three classes. And so, as soon as you do that, you reduce the amount of information there.”
Kath states that Kath would prefer this approach for future work. But for now, he adds, the data to do so is “lacking”.
‘Expansions and contractions’
Each crop had “both expansions and contractions” in its suitable growing range, Grüter tells Carbon Brief. For all three crops, he says, “negative climate change impacts on crop suitability have to be expected in some of the main producing countries”.
The researchers discovered that coffee was the hardest-hit of the three crops.
Global area falling into the highest suitability category is expected to decline by more that half in a moderate warming scenario. This is more than 50% less than 2000 levels. The effect was even more severe in some countries that are major producers: Brazil will lose almost 80% of its most-suitable land.
Below are maps that show the changes in suitability classes for coffee-growing worldwide under the RCP4.5 scenario. Red indicates declining suitability. Green shading means that there is more suitability.
The current suitability for coffee-growing depends on many factors. Coffee-growing can be difficult if there are too many variables, such as too high average annual temperatures, too low minimum temperatures, too much rain, and soil that is too acidic.
Researchers found that future decreases in suitability could be due to rising average annual temperatures. They note that “a few” regions to the north and south of the current range “are expected to profit” from these changes.
Avocados and cashews
Avocado plantations are more complicated. While there is a global reduction of high-suitability land of about 20% under the moderate warming scenario, not all of today’s high-producing countries will be negatively impacted.
Below are maps showing where the RCP4.5 scenario will change avocado-growing ability by 2050.
Mexico will for instance increase its highly-suitable growing land by more that 70%. However, the other major growing nations examined in the study – the Dominican Republic, Peru and Indonesia – will all lose between 55% and 70% of their prime avocado-growing area.
Current avocado production is limited by average minimum temperatures and annual rainfall – the crop “has a narrow precipitation optimum”, the authors write, so both too-wet and too-dry climates are incompatible with avocado growth.
As minimum temperatures rise, the model shows an expansion in growing areas at both the northern- and southern borders of the current range. Avocado-growing in some parts of the globe, such as sub-Saharan Africa may also be benefited by an increase in rainfall. Negative impacts on avocado suitability are mainly explained by changes in rainfall – either increased and decreased, depending on the location.
The study shows that the optimal growing area for cashews worldwide will increase by 19% under RCP4.5. This scenario would lead to a significant increase in the high-suitability land area in Vietnam, which would see a 33% increase in its total area. The other major growers of cashew would not fare so well – a 16% reduction for Côte d’Ivoire, a 29% reduction for India and a 78% reduction for Benin.
Below are maps that show how global growing suitability for cashews will change in 2050 under moderate warming.
The length of the dry season, low temperatures, and the difficulty in cashew-growing are the main limitations. The rising minimum temperatures are responsible for much of the expansion in suitable land, but regions such as Australia and east Africa also benefit from an increase in the average temperature.
These same rising average temperatures are responsible for the negative effects on central and southern America, west Africa, and south and southeast Asia. The cashew crop may also be affected by an increase in the average annual rainfall.
Adaptation & mitigation
The study was “well-written and well done”, Dr Christian Bunn, an agricultural economist at Alliance of Bioversity International & International Center for Tropical AgricultureCarbon Brief is told by, At the same time, Bunn – who was not involved in the study – adds, “I struggle to see new insights for coffee”.
Bunn notes – as does the paper – that the study’s results are largely in line with what he and his colleagues found in a 2015 study published in Climatic ChangeThe researchers looked at both Arabica and Robusta coffees. He calls it a “bit of an odd choice” for the researchers to have left robusta out of the analysis.
Kath agrees with Kath that the results for the coffee section of the paper are not surprising. Carbon Brief is informed by him:
“You could argue it’s not super novel from the perspective of coffee…It’s pretty well known that coffee is, amongst the important plant species we grow, exceptionally sensitive to changes in climatic conditions.”
Kath says that the literature on avocado- and cashew-growing is less extensive. “That’s probably where the novelty in the paper is”, he says.
That said, the paper’s findings on avocados are largely in line with Previous workAlso, Dr Joaquín Ramírez Gil, an agricultural scientist at The National University of Colombia. Ramírez Gil was a reviewer of the new paper but was not involved in the study itself.
Ramírez Gil’s work on avocados used “different approaches [but] found similar results”, he tells Carbon Brief – both in terms of projected future areas of expansion and the limiting factors for future avocado-growing. His research has been limited to avocado suitability in the Americas. The new study, however, is global.
Grüter tells Carbon Brief that the choice of crops – from a well-studied system like coffee to a less-studied crop like cashews – was designed so the team could evaluate and compare their modelling approach.
This type of study is “very, very important”, says Ramírez Gil. He says that this kind of information is “necessary” for governments and producers alike to be able to make sound decisions about growing in the future. Carbon Brief is told by him:
“In my country, every day the avocado crop is increased – the area planted with avocado crops is increasing, increasing, increasing. And many of these crops are planted in an area where the conditions are not suitable and the climate and environmental conditions are no good.”
Ramírez Gil stresses that policies need to be designed with this kind of work in mind, and that scientists need to better communicate their results to governments and other parties.
These results and others show that adaptation in the coffee sector is an urgent matter – and one that will take a “massive effort”, Bunn says. Carbon Brief hears from Bunn:
“Changing varieties or changing species is really hard to do, because you have this long lead time…If you want to grow for 2050, you need to plant a shade tree right now so that it is there in 10 or 20 years. You can’t plant it in 10 years, you need to plant it now.”
Bunn warns that coffee farmers could be forced from their land if they don’t take adaptation measures. These areas would likely then be planted with “field crops”, which have much less carbon storage potential than coffee does. The coffee production would be moved to new areas, which would likely lead to deforestation. Carbon Brief is told by him:
“In coffee production, adaptation goes a great deal towards emissions mitigation, because coffee farms are high carbon-stock systems…In the coffee sector, adaptation is the ethical thing to do, it’s the climate action, the mitigation thing to do. And at the same time, there needs to be investments so that we don’t go down the alternative scenario.”
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