London - Top environmental advocates on Wednesday urged the international community to increase and co-ordinate investments in research and development for renewable energy to make it cheaper than coal within 10 years."A sensible approach to tackling climate change will not only pay for itself but provide economic benefits to the nations of the world," they said in a petition, ahead of a key climate change conference in December."We urge the leading nations of the world to commit to this positive, practical initiative by the Paris climate conference," the petition said.The 27 signatories include wildlife documentary filmmaker David Attenborough and Paul Polman, chief executive of Dutch food and cosmetics giant Unilever, as well as other political and business leaders.Among the experts behind the petition were John Browne, the former chief executive of oil giant BP, as well as climate change expert Nicholas Stern."The Earth, with its spectacular variety of creatures and landscapes, is now in danger," Attenborough said in a video accompanying the release of the petition."Just one thing would be enough, however, to halt climate change. If clean energy became cheaper than coal, gas or oil, fossil fuel would simply stay in the ground," the British documentarian said.The project, launched in June, is named the "Global Apollo Program" in honour of the extraordinary achievements of the Apollo space missions of the 1960s that took humans to the Moon.The programme's demands include raising public spending on renewable energy research to an international total of at least $15bn annually for the next decade."That compares to the $100bn currently invested in defence research and development globally each year," the petition said, adding that private firms spent "relatively small sums" on renewable energy.The November 30-December 11 UN COP21 conference in the Paris suburb of Le Bourget is tasked with sealing a universal deal to roll back the threat of climate change.