The Scottish Government has no way of verifying claims by wind-farm developers on the carbon footprint of their turbines, a leading wildlife charity has revealed.
Now the John Muir Trust claims no large wind farms should be approved by planners until developers' environmental claims can be independently confirmed by government scientists.
Both the Scottish Environmental Protection Agency (SEPA) and Scottish Natural Heritage (SNH) say verifying claims of "carbon payback" by wind-farm companies is not part of their remit.
The carbon payback period - the length of time it will take for the wind farm to compensate for carbon emissions resulting from its development - is often highlighted by firms to promote their green credentials.
In their response to the proposed Viking wind farm on Shetland, SEPA said they had been requested by the Scottish Government to review the carbon balance of wind developments but that they had no funding or expertise available.
Helen McDade, head of policy for the John Muir Trust, said it was "extraordinary" that no government agency is equipped to give an independent answer on carbon payback.
She added: "For the Scottish Government to deliver on its commitment to reducing carbon emissions, it needs to give its agencies the resources to effectively review this important aspect of applications.
"Without independent auditing of carbon payback, we are basically forced to rely on the word of developers who stand to make millions of pounds if an application goes ahead.
"We need to stick to a precautionary principle and avoid siting major developments of this scale on fragile peatlands, which are an important carbon store."
SNH, which is officially consulted by the Scottish Government over the impact of wind farms, confirmed that it does not assess carbon payback claims made by developers.
Spokesman Calum Macfarlane said: "It is not part of our remit. If a carbon payback figure is mentioned by a developer, it is not something that features in our response. We look at landscape, wildlife and habitat considerations."
SEPA also confirmed it does not carry out its own audit of developers' carbon payback claims.
Viking Energy has cut the number of turbines proposed for its contentious wind farm by 23 and says the carbon payback time for the 685 million project will be less than one year.
The downward revision of the carbon payback time stems from an estimate that more than two-thirds of peat on the site is "already deteriorating and releasing stored carbon".The carbon payback of the site had been estimated at 2.3 years at best and a worst-case estimate of 14.8 years, due to disturbance to peatlands.
A Scottish Government spokesman said: "The Scottish Government commissioned a carbon calculator to assess the effects of wind farm developments on soils with peat. Developers are encouraged to use this method, and we have recommended it to SEPA.
"The carbon calculator is used to assess a wind farm's net effect on greenhouse gas emissions and also to aid in the design of wind farms to minimise the carbon costs of developments."