Although 2050 sounds far ahead, it takes three to five years to get a first crop. And coffee planted now should be productive for much of the 2020-50 period.
The common-sense view is to say: “Big food companies will be able to get coffee from somewhere — after all, Vietnam developed a coffee industry quickly.” Or: “Even if there is a couple of degrees of warming, farmers can just grow the coffee higher up the mountains.”
But it is not as easy as that. Peter Läderach of the International Center for Tropical Agriculture, and a coauthor of the study, points out that smallholders, or farmers in major coffee producing countries such as Brazil, cannot simply move production to higher altitudes for many reasons including land tenure, terrain and to avoid further deforestation.
Indeed, most of the possible solutions — such as irrigation, extensive pest control, new or alternative crop varieties, shade systems or cultivation of new areas — are either costly or have other negative consequences. One of the few promising approaches seems to be the intercropping of bananas and coffee — with the banana plants providing an additional cash crop and shade for the coffee plants.
“This is all sobering evidence that our cups of coffee depend on the science of climate, pests and plants — and the livelihood of over 100 million people depends on this fine balance.”
The economic impact will be significant, both for exporters and smallholders. Coffee is an important export for tropical countries, even though Mark Pendergrast, author of an economic history of coffee Uncommon grounds, picks apart the ‘rural myth’ that it is second only to oil in value as a traded commodity. 
Coffee is big business, and the industry is heavily concentrated among major food firms. Tim Harford, the ‘undercover economist’, helps us understand the coffee-shop end of the equation — where a cup of coffee in the business centres of rich cities in industrialised countries will cost you at least US$3.
Let’s look at the coffee growers on the other side of the equation. In 2010, Duncan Green, blogger and Oxfam’s strategic adviser asked Ethiopian coffee farmers how much they thought a London coffee shop would charge for a cup. They guessed two per cent of the actual price — yes, 50 times lower. The girls and women sorting the beans would have to work for eight years to get what Green was earning in one day. That shows where the profit ends up — not with the small producers. An estimated 70 per cent of the world’s coffee production comes from small-scale producers in an industry with some 25 million growers.  An informative overview from global agricultural research consortium CGIAR includes a short film showing the impact on crops of even a two-degree temperature rise on disease (coffee rust) and pests (coffee borer), which would thrive in warmer conditions. It shows that Central American producers would get forced back to growing cassava (of little retail value) if their crop is decimated.
This is all sobering evidence that our cups of coffee depend on the science of climate, pests and plants — and the livelihood of over 100 million people depends on this fine balance.
Roger Williamson is an independent consultant and visiting fellow with both UNU-WIDER (UN University World Institute for Development Economics Research) and the Institute of Development Studies at the University of Sussex, United Kingdom. Previous positions include organising nearly 80 international policy conferences for the UK Foreign Office and being head of policy and campaigns at Christian Aid.
References Oriana Ovalle-Rivera and others Projected shifts in Coffea arabica suitability among major global producing regions due to climate change (PLOS One, 14 April 2015)
 Mark Pendergrast Uncommon grounds: The history of coffee and how it transformed our world (Basic Books, 2010)
 Martha Caswell and others Food security and smallholder coffee production: current issues and future directions (The University of Vermont, 2012)