Image caption Emissions data from major exporters like China can be unclear

The extent of carbon dioxide (CO2) emissions "hidden" in imported goods is growing, according to two studies.

Official data do not include emissions from making imported goods but both sets of researchers say they should.

The Proceedings of the National Academy of Sciences reports 26% of global emissions come from producing goods for trade.

The Carbon Trust found such "embedded" CO2 could negate domestic carbon cuts planned in the UK up to 2025.

'Delusion'

Researchers want all nations to publish their data on embedded emissions.

Glen Peters of research group Cicero, lead authors of the PNAS report, told BBC News: "There is a degree of delusion about emissions cuts in developed nations. They are not really cuts at all if countries are simply buying in products they used to manufacture.

"We really need all countries to be developing and publishing the full extent of their emissions, whether they are produced domestically or outsourced through traded goods."

Publishing this sort of data is the first step, the next step - what to do about it - is more difficult Glen Peters, Cicero

The issue of embedded (or outsourced) carbon emissions has been recognised for several years, and the methodology to track emissions pathways is developing.

Cicero produced a trade-linked global database for CO2 emissions covering 113 countries and 57 economic sectors from 1990 to 2008.

It found that emissions from producing exported goods increased from 4.3Gt (gigatonnes) of CO2 in 1990 (20% of global emissions) to 7.8Gt of CO2 in 2008 (26%).

Most developed countries increased their consumption-based emissions faster than their territorial emissions - particularly from goods such cars and clothes.

Border taxes

The Carbon Trust research confirms that the UK has increased emissions since 1990 rather than decreasing them, as politicians typically claim.

What may alarm ministers even more is a projection that the radical CO2 cuts planned by government into the 2020s may be offset by ever-increasing levels of CO2 in imports.

Dr Peters said: "Publishing this sort of data is the first step. The next step - what to do about it - is more difficult.

For a government which wants to be the greenest ever and is committed to data transparency it's essential that the British government publishes the best data available Guy Shrubsole, Public Interest Research Centre

"It raises questions about consumption patterns, and whether countries should consider border taxes on imports from countries with no controls on CO2 emissions… though this is controversial and will be some way down the line."

A UK think tank, the Public Interest Research Centre (Pirc), has been discovering how uncomfortable this issue is proving for rich nations.

A succession of Freedom of Information requests reveals a degree of frustration among some British civil servants that the UK insists on basing its emissions calculations solely on domestic emissions.

One piece of government correspondence reveals: "While technological efficiency has improved the CO2 impacts of our products since 1992, the rise in UK consumption has outstripped the improvements achieved.

"The government needs to be cautious about over-claiming on its achievements in decoupling economic growth from environmental degradation."

Ministers are well aware of the issue, but insist that the UK should stick to reporting domestic emissions, as these form the basis for international climate negotiations.

They also point out that emissions data from major exporters like China is notoriously opaque, and that the methodology for calculating outsourced emissions is unreliable. They say all this creates even greater pressure for the UK to persuade China to cut its own emissions.

Guy Shrubsole, from Pirc, told BBC News: "This is a cop-out. The figures aren't perfect but the problem has been recognised for several years and the calculations are getting better all the time. In the UK our emissions are up - not down.

"Of course China needs to be part of a global climate agreement. But for a government which wants to be the greenest ever and is committed to data transparency it's essential that the British government publishes the best data available right away - and then figures out what to do about it."