Guest essay by Eric Worrall
h/t Telegraph – the “end of coffee” climate scare story which has been circulating recently has just been exposed as nonsense by a new study from Exeter University.
No evidence climate change boosts coffee plant disease
Fears that climate change is promoting a fungal disease which can devastate coffee crops may be unfounded, research by the University of Exeter suggests.
Media reports have linked coffee leaf rust – also known as CLR or roya – with climate change, but the new research finds “no evidence” for this.
Researchers tested the hypothesis that “the weather was responsible for a recent outbreak of CLR in Colombia and that climate change increased the probability of weather conditions favourable to CLR”.
The paper, published in Royal Society journal Philosophical Transactions B, concluded: “We find no evidence for an overall trend in disease risk in coffee-growing regions of Colombia from 1990 to 2015, therefore, while weather conditions were more conducive to disease outbreaks from 2008 to 2011, we reject the climate change hypothesis.”
Colombian coffee production fell by about 40% from 2008-11, and this decline has been linked to a severe CLR outbreak across Colombia and neighbouring countries.
Dr Dan Bebber, lead author of the University of Exeter study, said there was a “perfect storm” of factors favourable for CLR at that time, including weather conditions and a decrease in fertiliser use due to price rises during the 2008 financial crisis.
“Farmers weren’t treating coffee bushes as they normally would, and this was probably one of the factors that led to the rise in CLR,” he said.
“The climate at the time was conducive to CLR but there had been earlier periods of similar conditions when there wasn’t an outbreak.”
Dr Bebber and co-authors Sarah Gurr and Angela Delgado Castillo (a student on Exeter’s MSc in Food Security at the time of the research) found that Colombian coffee yields had been highly variable over time due to varying weather, the effects of disease, management and socio-economic factors.
Dr Bebber said more research was needed to fully understand the causes of the 2008-11 CLR outbreak, which caused hundreds of thousands of people to lose their jobs in coffee farms in Central America.
Temperature and leaf wetness are the most important determinants of infection risk for fungal plant diseases including CLR, which does not usually kill coffee bushes but can dramatically reduce the crop they produce.
The study was supported by University of Exeter alumnus Gerry Brown and his wife Clemencia Brown.
Date: 24 October 2016
The abstract of the study;
Many fungal plant diseases are strongly controlled by weather, and global climate change is thus likely to have affected fungal pathogen distributions and impacts. Modelling the response of plant diseases to climate change is hampered by the difficulty of estimating pathogen-relevant microclimatic variables from standard meteorological data. The availability of increasingly sophisticated high-resolution climate reanalyses may help overcome this challenge. We illustrate the use of climate reanalyses by testing the hypothesis that climate change increased the likelihood of the 2008–2011 outbreak of Coffee Leaf Rust (CLR, Hemileia vastatrix) in Colombia. We develop a model of germination and infection risk, and drive this model using estimates of leaf wetness duration and canopy temperature from the Japanese 55-Year Reanalysis (JRA-55). We model germination and infection as Weibull functions with different temperature optima, based upon existing experimental data. We find no evidence for an overall trend in disease risk in coffee-growing regions of Colombia from 1990 to 2015, therefore, we reject the climate change hypothesis. There was a significant elevation in predicted CLR infection risk from 2008 to 2011 compared with other years. JRA-55 data suggest a decrease in canopy surface water after 2008, which may have helped terminate the outbreak. The spatial resolution and accuracy of climate reanalyses are continually improving, increasing their utility for biological modelling. Confronting disease models with data requires not only accurate climate data, but also disease observations at high spatio-temporal resolution. Investment in monitoring, storage and accessibility of plant disease observation data are needed to match the quality of the climate data now available.
In my opinion this debunking of a climate myth which was promoted by the likes of the Fairtrade Charity undermines all claims about anthropogenic CO2 aggravating pest or fungus damage to food crops. Not only does it demonstrate how eager climate advocates are to pin any problem on their favourite bogeyman, it also demonstrates that current generation fungicides and pesticides are more than adequate for the job – providing they are correctly applied.
As to the future, we are currently in the midst of a biotech revolution – unprecedented control of plant and animal genetics, and next generation pest and fungus management technologies, are on the verge of commercial realisation. If current generation pesticides and fungicides ever loose their effectiveness, for any reason, there are plenty of better products and technologies in the pipeline.
EDIT (EW): Fixed the link to the Fairtrade story.