The Act makes it the duty of the Secretary of State to ensure that the net UK carbon account for all six Kyoto greenhouse gases for the year 2050 is at least 100% lower than the 1990 baseline, toward avoiding dangerous climate change.

The Act aims to enable the United Kingdom to become a low-carbon economy and gives ministers powers to introduce the measures necessary to achieve a range of greenhouse gas reduction targets.

An independent Committee on Climate Change was created under the Act to provide advice to UK Government on these targets and related policies.

On 16 October 2008 Ed Miliband, Secretary of State for Energy and Climate Change, announced that the Act would mandate an 80% cut overall in six greenhouse gases by 2050.

The original 60% figure was adopted based on the recommendation of the Royal Commission on Environmental Pollution, made in their June 2000 report Energy – The Changing Environment.

[5] The Royal Commission's figures were based on a June 1996 decision of the EU Council of Ministers to limit emissions to 550 ppm, contained in their Community Strategy on Climate Change.

The exclusion of emissions from aviation and shipping, combined with forecasts for growth in these areas, also means that the net effect of the bill would actually have only been a 35–50% total cut on 1990 levels by 2050.

Shortly after the 2005 general election, 412 of the 646 Members of Parliament signed an early day motion calling for a Climate Change Bill to be introduced, to include a requirement for 3% annual cuts in carbon emissions.

These Committees received evidence from a series of interested parties between April and July and cast votes[20] on the final wording of their reports.

[21] Among the critics giving evidence was Lord Lawson who argued that the entire concept was counter-productive because humans would easily be able to adapt to the worst predictions of a 4-degree rise in temperature by the end of the century because, with an average world economic growth of 2%, they would be "seven times as well off as we are today", therefore it was not reasonable to impose a sacrifice on the "much poorer present generation".

[30] During the debate on the Third Reading on 28 October, the government rejected an opposition amendment to allow the Secretary of State to set the maximum level of carbon dioxide that may be emitted per unit of output by any generating station.

[44] The UK Independence Party believed that the Bill was only necessary because of a failure to devise a viable plan for other sources of energy to replace fossil fuels.

[48] The other 50 or so environmental, international development and other organisations belonging to the Stop Climate Chaos coalition backed the Big Ask Campaign and shared similar views.

They also considered that the Bill should include annual 3% reduction targets, cover aviation and shipping within its scope, and ban the purchase of carbon credits from overseas, a practice which they believe exports the emissions problem elsewhere.

[50] The Confederation of British Industry, which has created its own climate change task force, welcomed the proposed Bill, stating that it combined two vital elements, long-term clarity on policy direction and flexibility in its delivery.

[52] The Committee on Climate Change, whose powers are invested by Part 2 of the Act, was formally launched in December 2008 with Lord Adair Turner as its chair.