* New objective casts Britain as relative climate leader
* Success would imply sweeping change across the economy
* Campaigners says target still does not go far enough
LONDON, June 12 (Reuters) - Britain has announced it will enshrine a new commitment to reach net zero greenhouse gas emissions by 2050 into law, marking a first among G7 nations facing increasingly severe impacts from the climate crisis.
With global carbon emissions at record highs despite decades of talks aimed at bringing them within safe limits, outgoing Prime Minister Theresa May said the goal was ambitious but essential for protecting Earth's future.
"Now is the time to go further and faster to safeguard the environment for our children," she said in a statement.
"Reaching net zero by 2050 is an ambitious target, but it is crucial that we achieve it to ensure we protect our planet for future generations."
Britain's existing target is to cut greenhouse gas emissions by 80 percent from 1990 levels by 2050. However, campaigners say this does not go far enough to meet pledges made under the 2015 Paris climate agreement to try to limit a rise in global warming to 1.5 degrees Celsius.
Temperatures have already risen about one degree Celsius since pre-industrial times. Scientists warn further increases risk triggering tipping points that could render swathes of the globe uninhabitable, devastate farming and drown coastal cities.
May, who is due to step down this summer after her political career became a casualty of the turmoil over Brexit, said legislation would be put before parliament on Wednesday to incorporate the new target into an existing climate change act.
Although May had staked her legacy on delivering an orderly exit from the European Union to respect the result of a 2016 referendum, the new target earned her praise from climate specialists heartened by any sign of greater ambition from a major economy.
"It's momentous," said David Reay, professor of carbon management at the University of Edinburgh. "Achieving net zero by 2050 will change all our lives. It will transform the ways we travel, the homes we live in and the food we eat."
Britain's independent climate advisers, the Committee on Climate Change, recommended last month that the country move to the new target, which implies sweeping changes in energy, transport and agriculture.
For example, new petrol and diesel cars might need to be phased out by at least 2035, the committee said. Households would also need to be weaned off natural gas heating and switch to low-carbon alternatives.
Although the new target has cast Britain as a relative climate leader, the government's decisions to back projects such as a third runway at London's Heathrow airport and fracking have raised questions about the depth of its commitment.
Extinction Rebellion, a climate movement that paralysed parts of London with a civil disobedience campaign in April, said Britain was still not acting quickly enough.
"Were we to put our minds to it and do what is required to mobilise society to address the threat with the seriousness it deserves, the UK could embrace transformative change and decarbonise in years, not decades," the group said.
Nevertheless, many businesses see big opportunities in any low-carbon transition, hoping progress at home will help innovative British companies grow rapidly in emerging markets hungry for climate-friendly goods and services.
Carolyn Fairbairn, director general of the Confederation of British Industry (CBI), welcomed the new target and emphasised the need for coordination to deliver the necessary changes.
"Some sectors will need clear pathways to enable investment in low-carbon technologies, and it is vital that there is cross-government coordination on the policies and regulation needed to deliver a clean future," she said.
Britain hopes its decision will encourage other governments to adopt more ambitious climate targets and said that a further assessment would take place within five years to discern the extent to which other countries are taking similar action.
The government also said it would continue to use international carbon credits to help meet the target - a move some see as a loophole to allow polluters to stay in business.
"Fiddling the figures would put a huge dent in our ability to avoid catastrophic climate change," environmental group Friends of the Earth said in a statement. (Reporting by Susanna Twidale Editing by Mark Heinrich)
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