CRITICS of one of the largest wind farms planned for Scotland warn it may never save more Co2 than it releases from fragile peat bogs.
Opposition is escalating against the 540 megawatt, 150-turbine Viking wind farm proposed for mainland Shetland.
Supporters argue it will provide about 20 per cent of Scotland's domestic energy needs and bring 37 million to the local economy.
However, critics warn building the wind farm could release so much Co2 from damaged peat bogs that the scheme may never save a net amount of greenhouse gas emissions.
An objection from RSPB Scotland yesterday followed another from the John Muir Trust earlier this week.
There has also been a 3,600-name petition against the plans.
RSPB Scotland highlighted that the environmental statement submitted by developers Viking Energy calculated in the worst case scenario that the "payback period" would be 48.5 years – because so much of the gas would be unleashed from peat bogs during construction.
Lloyd Austin, RSPB Scotland's head of conservation policy, said: "The lack of certainty that there would be any significant net benefits undermines the case for development. There is no point in building renewables that potentially emit more carbon, due to peatland impacts, than they save."
He also that warned nationally important populations of whimbrel, a wading bird, plus red-throated divers, golden plover and merlin could be displaced or potentially even killed by the turbines.
However, Viking Energy, a consortium of Shetland Islands Council and Scottish & Southern Energy, said the 48.5 years calculation was an error on the application document, and actually the worst case scenario was about 14 years.
A spokesman for RSPB Scotland said: "We have to respond to what has been submitted to government under due legal process."
John Hutchison, chairman of the John Muir Trust, said even with a payback of 14 years it was "hardly worth destroying such a special, wild place for the relatively small amount of carbon that may be saved".
He warned 19 per cent of mainland Shetland would be "significantly affected" by turbines.
And he added: "The scale of this proposal is truly staggering and totally disproportionate for an island like Shetland.
"Shetland's treeless landscape will be completely dominated by the development, with the turbines visible in a 15 kilometre radius around the wind farm."
However, a spokesman for Viking Energy said it was "entirely misleading" to suggest a fifth of the mainland would be affected, and insisted it was closer to 4 per cent.
He added: "We believe that the development proposed for Shetland is well planned and will contribute significantly to the UK's legally binding targets to reduce carbon emissions."
The public consultation into the plans closes on Tuesday.