ePolitix.com looks at the issues behind Tuesday's publication of the Climate Change Bill, which puts into law the government's long-term ambition for cutting carbon emissions.

What will the Bill mean?

The Climate Change  Bill, which is published in draft form on Tuesday, enshrines in law a target for the UK to reduce carbon dioxide emissions by 60 per cent of 1990 levels by 2050.

The Bill will also set up an independent 'carbon committee' to monitor progress and help ministers.

It is expected to propose annual reports to parliament, with five year 'milestones' to measure progress against.

It could also propose a national carbon trading market for all sectors of industry, as now exists for certain sectors.

Is this a new target?

Cutting CO2 by 60 per cent by 2050 was already a more informal target, with an interim aim of cutting levels by 20 per cent by 2010.

This went beyond what is perhaps the best-known target, a 12.5 per cent reduction by 2008-12 required by the Kyoto protocol - a pact between many of the world's industrialised nations ratified in 2004.

The government is expected to comfortably meet the Kyoto target but miss the 2010 commitment, which was outlined by Labour before the 1997 election.

What is a draft bill?

A parliamentary innovation promoted by Robin Cook and intended to strengthen legislation, draft bills are considered by select committees and open to consultation before they become a fully-fledged bill.

Publishing the Climate Change Bill in draft form means it is unlikely to complete its parliamentary process before next year.

Green campaigners said the delay shows the government is not serious about its flagship legislation, while the government says it always planned to open the Bill for consultation.

Is there political consensus on the Bill?

There is consensus over the need to cut carbon dioxide - the most significant of the six greenhouse gases covered by the Kyoto protocol - but there is less agreement on how to go about it.

The Conservatives want the Bill to include binding annual targets, with leader David Cameron arguing the legislation "needs teeth".

The Lib Dems also back annual binding targets, and are thought to be planning to propose a tougher overall target than that of 60 per cent by 2050.

Why is it important to the government?

For Tony Blair, 2007 is his last year in office and one in which he wants to make significant progress on climate change. Last week's meeting of EU heads of state agreed the first EU-wide binding target of cutting carbon emissions by 20 per cent by 2020.

The focus of this year's G8 is also climate change, and Blair has indicated he wants to be at the meeting in June - perhaps to crown his decade in office with an international breakthrough.

The Climate Change Bill, assuming it is introduced in full towards the end of the parliamentary year, will have to be carried over to next year's session to become law.

This would require the backing of the new prime minister, expected to be chancellor Gordon Brown.

Brown has identified himself less with the issue than Blair, but has spoken frequently of the significance of climate change - saying last year the developed world had a "moral duty" to tackle global warming.

Not only has climate change become a significant electoral battlefield - although still behind 'bread and butter' issues in the polls - but it also fits with Brown's personal interest in helping the developing world, which stands to suffer most from global warming.

And why is it important to opposition parties?

Taking a tough line on the environment - tougher than the government in many respects - Cameron hopes to outmanoeuvre Brown and continue to calibrate the party's public image.

While some more traditional Tory MPs including John Redwood are still sceptical about the causes of global warming, the shadow front bench have been treating it as man-made and high profile.

The Lib Dems see climate change as a natural subject for their party, and were ahead of the Tories in last year producing plans for a series of carbon taxes on aviation as well as cars and fuel.