Former US president Jimmy Carter on Tuesday urged his country andChina, two of the world's biggest fossil fuel polluters, to take the lead on haltingclimate change.If the two economic and political giants could agree on a way forward, the rest ofthe world would likely follow their lead, the statesman told AFP on the sidelines of a climate change discussion with students at the Paris Institute of Political Science."If we could put those two together as leaders of the Western world and thedeveloping world and get them to agree on almost any formula for long-term andeffective correction of the deterioration of the environment... I think the othercountries would follow their leadership," Carter said.He said he had encouraged Chinese President Xi Jinping along these lines, and has had discussions with US Secretary of State John Kerry.Carter took part in the Paris meeting on Earth Day as a representative of The Elders,a grouping of global leaders brought together by Nelson Mandela in 2007 topromote peace, justice and human rights.He told the students that climate change threatened world peace."If we don't address the global warming issue, we are going to see rapidlyincreasing conflict around the world."As people grow more desperate for food, for clean air and water, there is going tobe increasing violence within countries and between countries."The next 18 months will be crucial to determine the success of efforts to halt globalwarming "or catastrophic failure", said the Nobel Peace laureate.The UN seeks to hold warming to two degrees Celsius (3.6 degrees Fahrenheit), atwhich scientists believe we can still avoid the worst effects of climate change.UN Secretary General Ban Ki-moon will host heads of state and government in NewYork in September to "catalyse action" ahead of a meeting in Paris at the end of2015 where the world's nations are due to sign a global climate pact.The deal, which must come into operation by 2020, should outline emissions curbtargets -- a controversial issue that has been the topic of years of often belligerenttalks.Negotiators will gather again in Lima, Peru in December to come up with an outlinefor the agreement.Carter said he hoped "as many of the world's leaders as possible" will attend the September meeting with Ban."Everyone who is interested in the subject needs to marshall our efforts now tomake sure we do not fail in Paris in 2015."Carter described climate change as "the greatest challenge the human race has everfaced".The most recent scientific assessment of the UN's Intergovernmental Panel onClimate Change, released in phases over recent months, states that humankind stillhas a chance to limit warming to relatively safe levels, but warns of direconsequences if we don't.