An airline introducing a “sustainable coffee” to protect forests has been told by environmentalists that it would have to plant a forest “twice the size of Wales” to make up for carbon emission damage caused by its aircraft.

KLM this week announced that 30 per cent of all coffee provided on its flights would come from sustainable farms in a partnership with a group called Rainforest Alliance, which works to protect forests. KLM serves 25 million cups of coffee a year. But environmentalists are sceptical that the move is “greenwashing”, designed to shift focus from the damage that emissions cause to the environment.

Pete Lockley, in charge of policy development at the Aviation Environment Federation, said: “While this is not a directly hypocritical move and it’s great that sustainable coffee is being used, it does not make KLM an ethical company.”

He said that the airline would have to plant 40,000 sq km (15,500 sq m) of forest to offset the carbon emissions caused by the airline over the next 20 years. Wales is 20,000 sq km in size. This was a “rough estimate” but illustrated the scale of emissions and the difference “sustainable coffee” would make.

A spokeswoman for KLM would not comment on “sustainable coffee” but said: “(KLM) is considered a leading performer in the airline industry in terms of sustainable developments and the airline supports the introduction of emission trading at a European level, provided that the effects on our global competitive position are taken into account.”

KLM estimates that 80 per cent of aircraft carbon dioxide emissions are produced on trips longer than 1,500km. The spokeswoman said: “The dilemma facing the industry is that there is still no real alternative to air transport over long distances.”

Details: Rainforest Alliance (www.rainforest-alliance.org).

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