Shipping is responsible for ferrying more than 90 per cent of global trade and produces about three per cent of mankind's carbon emissions, or more than the CO2 produced by the German economy.

Yet reducing these emissions means tackling idiosyncratic maritime laws, the vested interests of countries such as China that rely on shipping to fuel rapid economic growth, and convincing conservative ship owners to embrace green technology.

Convincing shipping companies to buy costly green technologies is easier said than done as the industry recovers from the economic slowdown and faces volatile fuel prices that make it difficult to calculate returns on investment.

A carbon emissions scheme, in which ships would be penalised for inefficient fuel use and rewarded for conserving fuel, would spur green investments in a conservative industry that has been slow to embrace new technologies.

Developing a carbon scheme for shipping is politically charged and highly complex as the vast majority of vessels sail under flags of convenience of other countries to avoid tighter regulations and higher taxes and labour costs.

Ships from countries such as Denmark, Britain and Germany are largely registered in developing countries such as Panama, Liberia and even land-locked Mongolia, which, under the UN's Kyoto Protocol, have no duty to cut carbon emissions.

The International Maritime Organisation (IMO) has estimated that greenhouse gas emissions from shipping could grow between 150 and 250 per cent by 2050. Meanwhile, the split over responsibility for emissions has proved just as divisive in the IMO.

The UN body responsible for shipping usually deals with technical issues to reduce pollution and improve safety. For example, world nations have agreed to steps to progressively cut the sulphur content of shipping fuels and the nitrous oxide emissions from engines. But mandating cuts to CO2 emissions is another matter.

Due to the difficulties of obtaining a global maritime agreement which may end in failure if China and others fail to compromise, Roche believes regional schemes may be set up first.

The EU would likely take the lead followed by other regional blocs until a patchwork quilt of schemes are formed. Over time, they may eventually merge into one scheme to reduce CO2 emissions from shipping. However, this would be a painful route for the industry as ship owners and others would have to deal with multiple schemes rather than one global scheme administered by the IMO.

According to experts it is unrealistic of the global community to expect the IMO to reach a global agreement on emissions, when, at a wider level, the international community cannot agree a way forward, as illustrated at Copenhagen. If emissions are attributed to the country where the ship is flagged then what would happen with ships flagged in developing countries which, under the Kyoto Protocol, are exempt from making carbon emissions cuts following the "common but differentiated responsibility" principle. This runs completely counter to the cornerstone IMO principle of "no more favourable treatment" for any ship or any flag.

At Copenhagen, negotiators discussed, but did not agree, to a bunker levy on shipping and aviation fuels to drive efficiency and to raise funds for poorer nations to green their economies.

For example, the European Union is pushing for shipping to cut emissions to 20 per cent below 2005 levels over the next decade, and for aviation to cut by 10 per cent. It also wants a levy on the two sectors' emissions to go to poor countries.

The IMO has just established an expert group, which has to conclude its work in August and report back in October to put all market-based measures on the table. More advanced is a plan to launch a ship energy efficiency management plan, which should be on board every vessel and would allow port inspectors to see what a vessel is doing in terms of reducing its emissions, whether it has implemented any specific measures and what targets have been set.