A world without chocolate. It is a possibility.

"I think that in 20 years chocolate will be like caviar," says John Mason, executive director and founder of the Ghana-based Nature Conservation Research Council (NCRC).

"It will become so rare and so expensive that the average Joe just won't be able to afford it."

The prospect of a future without a ready supply of chocolate is not a pleasant thought for anyone with a sweet tooth, but it's an even more terrifying prospect for producer countries that depend on cocoa beans for a huge portion of their GDP.

Yields are declining all across the cocoa plantations of West Africa, where two thirds of the world's supply is grown, as soils are degraded and the area able to support the crop retreats, according to Mason.

"The way we farm is just not sustainable," he says. "I'm afraid by the time we wake up to that fact it will be too late. I've worked in Ghana for 25 years and I can show you huge areas that can no longer support a crop."

The problem is that cocoa is naturally a rainforest plant that grows in shady conditions surrounded by a high biodiversity, but recently hybrid varieties have been grown on cleared land as mono-cultures and in full sun.

While this will give higher short term yields, the soil quickly becomes degraded and the lifespan of plants can be cut from 75 or 100 years, to 30 or less. When the trees die and the land is exhausted the farmers must move on and clear more rainforest to plant cocoa.

But the looming decline of West African cocoa is not only a problem for farmers and chocolate producers - Cadbury sources 100 percent of the beans they use for UK chocolate production from Ghana - environmentalists are increasingly concerned about the destruction of the rainforest for short-term gain.