Action urged on carbon emissions from ships and flights
Greenhouse gas emissions from international flights and shipping should be included in the UK's carbon budgets, the Committee of Climate Change has advised.
The government's independent advisory group says aviation and shipping were major sources of pollution.
Therefore the carbon budgets up to 2027 should be increased to allow for those emissions.
The government must decide by the end of 2012 on whether to include them.
Under the Climate Change Act, the UK is committed to cutting all its climate-changing emissions by 80%, based on 1990 levels, by 2050.
However, international flights and shipping are not included in the targets.
If the government agrees to the CCC's recommendation, it will mean tighter targets for other sectors such as motoring and electricity generation.
The committee has recommended - and the government has already adopted - a series of carbon budgets setting down the maximum scale of greenhouse gas emissions that the UK can emit over successive five-year periods.
These have been agreed up to 2027, and assume that aviation and shipping will be included.
The committee's chief executive David Kennedy said there was a "risk" the current - or future - government would not continue to make that assumption and the goals for cutting overall emissions would become less ambitious.
Mr Kennedy said: "There's a risk this government or a future government will not continue to act in the way we have done up until now.
"At the moment there's uncertainty over how aviation or shipping emissions will be treated in the future.
"There isn't any valid reason why the government should reject the advice we're giving, and if they were to do so, that would be a rolling back in terms of commitments on building a low-carbon economy."
'No draconian policies'
He also said the UK should not try to unilaterally reduce emissions from the two international sectors, which could hit its competitiveness.
"If you have draconian policies, people will take a short-haul flight to Holland, France or Germany and get on their long-haul flight.
"There wouldn't be a very well-connected economy and will you get inward investment from international companies?" he said.
The latest report from the committee also confirms that it is possible to achieve the 2050 target, including aviation and shipping, at the expected cost of 1%-2% of GDP.