(Updates with reaction) By Jeremy Lovell LONDON, Dec 13 (Reuters) - Britain set out plans on Wednesday to help tackle global warming by making all new housing "zero carbon" within a decade. From 2016 new homes should generate from renewable or low carbon sources at least as much electricity as they use, local government secretary Ruth Kelly told a news conference. Homes produce some 40 million tonnes of carbon a year or about one quarter of Britain's greenhouse gases, making them the third largest emitter after business and transport. "Building the homes we need for future generations while meeting our climate change goals is one of the most complex environmental challenges facing the country," Kelly said. "We can only meet this challenge by transforming the quality of new homes, changing the way we plan new developments and galvanising the nation to play their part." Definitions of "zero carbon" range from using renewable building materials and transport fuel to sharply reducing emissions from usage -- including recycling household waste. A spokesman for Kelly's department said the definition used in the government plans included all emissions from power generation after construction but not the "embodied" carbon in building materials or transport to the site. Most scientists agree that global temperatures will rise by between two and six degrees Celsius this century due mainly to carbon emissions from burning fossil fuels for power and transport, putting millions of lives at risk from floods and famines. Former World Bank chief economist Nicholas Stern said in October that urgent action on global warming was vital, and that delay would multiply the cost 20 times. Britain, a signatory to the Kyoto Protocol on curbing carbon emissions, has pledged to go even further and cut its own greenhouse gases by 60 percent by 2050 -- a target that is proving elusive and which environmentalists say is too timid. Kelly, announcing a "green star" rating for new homes, said top rated houses would be energy efficient and use renewables like solar panels, rooftop wind turbines and mini combined heat and power stations. She also said regulations would be tightened to ensure all new buildings were environmentally friendly, and promised tax breaks to encourage home buyers to opt for green homes. Environmentalists welcomed the move, noting that although new homes now accounted for a fraction of the housing stock they would constitute about one-third of the total by mid-century. "We really like this idea. It is a big step in the right direction. Our only problem with it is the lack of urgency," a Friends of the Earth spokeswoman told Reuters. "Zero carbon homes could be built now, so why wait 10 years before insisting that builders construct them?" she added.
