The $3 (£1.90) surcharge was introduced by several US airlines in January including United – formerly Continental – and US Airways, which fly from Scotland.
However, Edinburgh-based Ecometrica said passengers should only be charged $1.54 (97p) to cover the cost of the European Union’s emissions trading system (ETS) to cut carbon dioxide emissions.
The firm also calculated that no-frills airline Ryanair’s 0.25 (30p) ETS surcharge mirrored its 0.24 (29p) cost.
David Jarrett, of Ecometrica, whose software helps firms cut emissions, said: “The response from the American airlines, to impose a surcharge of $3 on transatlantic flights, is effectively the passing on of double the cost of the scheme.
“Ryanair’s response appears to be far more generous as their surcharge of 0.25 only covers slightly more than 100 per cent of the extra ETS costs at the current carbon price.”
Laurie Price, director of aviation strategy at consultancy Mott MacDonald, said that ETS charges would be an extra tax on passengers because the British government had not made an expected cut in air passenger duty to compensate.
He added: “The fear has to be that once a tax has been introduced, it will be unlikely to be rescinded.”
Aviation analyst John Strickland, of JLS Consulting, said: “The difficulty airlines face is they have to collect the tax many months before having to pay it, so there’s a degree of estimation.”
A spokesman for United, which flies between Edinburgh, Glasgow and New York, said: “United does not discuss this type of market pricing information. More broadly, United does account for regional increased taxes and regulatory costs in our cost and revenue models, including regulatory costs such as the EU ETS.”