Coffee farmers in Sumatra are having to find ways to cope with the increasingly unpredictable weather caused by climate change which is hitting their harvests.

Some farming groups in the Indonesian island's northern Gayo Highlands say they have seen coffee harvests fall by up to 50%, with damage to plants caused by unexpected rain or dry spells.

Rain also affects efforts to sun-dry the coffee beans, while warmer temperatures mean pests and diseases previously only seen at lower altitudes now threaten the high-quality Arabica coffee for which the highlands are known.

Co-operatives which sell their coffee as Fairtrade-certified are using money from the scheme to invest in measures to counteract the impacts of rising temperatures.

Through Fairtrade, producers receive a guaranteed minimum price for coffee and an additional "premium" which communities decide for themselves how best to spend.

In the Gayo Highlands these include schemes such as installing electricity, building libraries, cervical cancer screening and purchasing ambulances, buying pruning scissors and strimmers, and providing agricultural training.

But co-operatives are also turning their attention to preventing climate change hitting productivity, distributing new, more resilient varieties of coffee plant which have been developed.

Farmers are also encouraged to plant shade trees in the coffee gardens to protect the precious harvest, prevent erosion on sloping hillsides and provide an alternative income such as avocados, oranges or timber to reduce reliance on a single crop.

Coffee co-operatives face a number of challenges, including ageing coffee plants and young people seeking alternative jobs to farming.

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But the chairman of 2,000 member-strong Permata Gayo co-operative, Armia Ahmad, said a big issue is the changing weather.

"The climate has already changed, for example the harvest is normally starting from October to January, but now we can't predict it anymore."

The harvest had not come by December, he said, adding: "This year in December, it should be the dry season, but now rain, rain, rain."

The co-operative is providing hundreds of thousands of seedlings of the new, more resilient varieties of coffee to members, and has built a canopy for its drying areas to prevent rain damaging coffee during processing.

They are also providing avocado trees to farmers to generate income if the weather hits the coffee harvest.

At another of the region's co-operatives, KBQB, the management team also report a shift in the harvest, increases in pests and diseases being found in the region's high altitudes and a 50% drop in the harvest this year because of the weather.

Another local environmental problem is illegal logging, despite the remaining natural forest being protected, which causes flash flooding and landslides when it rains.

The co-operative is implementing environmental measures because, the team say, they have been informed by various sources that climate change is affecting Indonesia and planting trees can be climate-friendly.

Co-operative chairman Rizwan Husin said: "We distribute trees to farmers so they can plant on their farms, and we advise the farmers to grow shade trees, and on the unproductive land to grow trees for wood and avocado."

The reforestation scheme being run by the co-operative has seen a group of farmers plant 24,000 trees over 32 hectares to create sustainable agroforestry on unproductive land.

But the chairman said he was "really, really worried" about climate change.

"They say that within 50 years there may be no more coffee in Gayo, and it may be similar in Africa," he said.

"We need not just a local movement, but a world movement for the climate."