Climate change is going to halve the area suitable for coffee production and impact the livelihoods of more than 120 million of the world's poorest people who rely on the coffee economy, according to a new report by the Climate Institute, commissioned by Fairtrade Australia & New Zealand.
The report findings follow stark warnings by some of the world's biggest coffee producers, including Starbucks and Lavazza, who have said climate change is posing a severe risk to the industry.
Climate change is already impacting coffee crops around the world, according to the report. In Tanzania, where 2.4 million people's livelihoods rely on coffee, production has fallen by about 137kg per hectare for every 1C rise in the minimum temperature on farms. Overall there has been a 50% decline there since the 1960s.
Extreme temperatures and unusual high-altitude rains have also sparked costly waves of pests and disease through coffee farms. In 2012, coffee leaf rust affected half of the coffee across Central America - some producers in Guatemala lost up to 85% of their crop.
In 2012-13 the damage in Central America amounted to about US$500m and put 350,000 people out of work.
How climate change will impact coffee growers in coming decades will vary by region. Scientists think Nicaragua could lose the majority of its coffee-growing areas by 2050, and in Tanzania, coffee yields were projected to reach "critically low levels" by 2060.
By 2080, scientists think wild coffee, which is important for genetic diversity of farmed coffee, could be extinct.
For consumers of coffee, all of this will impact flavour, aroma and price, the report said.
Some large coffee producers have been warning the world about the impacts of climate change. In 2015, Mario Cerutti from Lavazza told a conference: "We have a cloud hovering over our head. It's dramatically serious. Climate change can have a significant adverse effect in the short term. It's no longer about the future; it's the present."
And in 2011, Jim Hanna, director of environmental affairs at Starbucks told the Guardian that climate change is a "potentially significant risk to our supply chain".
"If we sit by and wait until the impacts of climate change are so severe that is impacting our supply chain then that puts us at a greater risk," he said.
Since most coffee growers are poor smallholders, their ability to adapt to climate change on their own is limited.
To adapt, coffee farmers could move to higher ground or away from the equator. But since coffee plants take several years to become productive, that would often be impossible without assistance. Other strategies involve developing more resilient production systems and diversifying crops, which also require support.
"There are things we coffee drinkers can do to assist," said John Connor, the chief executive of the Climate Institute.
Connor said consumers should only buy brands that "provide a fair return to farmers and their communities while helping to build their capacity to adapt to climate change".
Fairtrade, which commissioned the report, said its "Fairtrade Climate Neutral Coffee" did that. And in 2010, several big coffee companies set up the "initiative for coffee and climate" which seeks to help farmers respond to climate change.