Cameron is at a turning point on climate change David Davies, the MP for Monmouth, and his other backbench colleagues will call during a debate in Westminster Hall for the Government to review the Climate Change Act, which commits the UK to cut its emissions by at least 80 per cent by 2050 compared with 1990. The Act, which was passed in the House of Commons by an overwhelming majority in 2008 when only 5 MPs voted against it, is regarded around the world as a model of evidence-based climate change policy. It is intended to ensure that the UK plays its part in international efforts to avoid global average temperature increasing more than 2°C above the level it was at before the Industrial Revolution, when widespread burning of fossil fuels started to dump large volumes of carbon dioxide into the atmosphere. The last time global average temperature were more than 2°C above the pre-industrial level was 3 million years ago, during the Pliocene Epoch, when the polar ice caps were much smaller and global sea level was about 20 metres higher than today. But Mr Davies, who voted for the Act five years ago, now questions the need for the emissions target and disputes scientists" explanations of the causes of climate change. Mr Davies is just one of a handful of Conservative backbenchers, including Peter Lilley, the MP for Hitchin and Harpenden and part-time vice-chairman of Tethys Petroleum, who have justified their opposition to the Climate Change Act by rejecting the science. But Mr Cameron will find it extremely difficult to appease these rebels because the Intergovernmental Panel on Climate Change is preparing to publish at the end of the month a comprehensive scientific assessment that provides the clearest warning yet of the risks posed by global warming. Not only is the report likely to confirm that climate change is already having a growing impact on the climate around the world, increasing the risks of extreme weather events in many regions, it is also expected to set out for the first time a budget for greenhouse gas emissions which cannot be exceeded over the rest of this century if global warming of more than 2°C is to be avoided. So Mr Cameron will have to choose between pandering to "sceptics" in his own party by weakening the commitment to the evidence-based target in the Climate Change Act, or instead side with the world's scientific community. It may not be an easy choice for the Prime Minister. Many of his backbench MPs are worried about the challenge of UKIP, which has embraced climate change denial as a central plank of its eccentric energy policy. And most of the editors of Britain's right-wing newspapers have been coaxed by Lord Lawson into carrying out a concerted campaign of misinformation about the causes and consequences of climate change. Mr Cameron has already responded to the rising tide of ideological opposition to climate science by appointing Owen Paterson as Environment Secretary. Mr Paterson is supposed to be responsible for developing a national adaptation programme to make the country resistant to those impacts of climate change that cannot now be avoided, but he has chosen instead to focus his efforts on disputing the science and criticising wind farms. In June, Mr Paterson's department published proposals for a new scheme to provide insurance for those households most at risk of flooding, but omitted any consideration of climate change, even though the Met Office has warned that annual rainfall is increasing and heavy downpours are becoming more intensive. So Mr Cameron now faces the task of either confronting the climate change "sceptics" within his own ranks or finding himself marginalised as world leaders negotiate a new international treaty to reduce emissions ahead of a summit in Paris in December 2015. President Obama and President Xi JinPing of China made tackling greenhouse gas emissions one of the key issues at their first meeting in June, and even leaders at the G20 summit in St Petersburg last week were able to agree a declaration that warned of the increasing economic costs of delaying action on climate change. Yet Mr Cameron has still not delivered a major speech about climate change since he declared that the Coalition would be the "greenest Government ever." And with his backbench colleagues now openly calling for an abandonment of the UK's emissions reduction target, private companies are losing confidence in the Government's policies which are supposed to be encouraging billions of pounds in investment in creating a modern, low-carbon power sector that is clean, efficient and secure. If the Prime Minister does allow the UK's climate change policies to be based on ideology instead of science, he will damage his credibility on the world stage, undermine low-carbon investment in the UK, and expose millions of households and businesses to increasing risks. Bob Ward is policy and communications director at the Grantham Research Institute on Climate Change and the Environment at London School of Economics and Political Science