Le Bourget - Soaring rhetoric from US President Barack Obama and other leaders about their deep commitment to fighting climate change should be taken with a hefty pinch of salt, Greenpeace chief Kumi Naidoo said on Tuesday.At a landmark UN summit in Paris on Monday, Obama led a chorus of pledges about the urgent need to contain global warming and prevent its most catastrophic impacts.The summit of more than 150 leaders, the biggest-ever gathering of heads of state and government, sought to inject energy into the start of the conference, which is seeking an unprecedented post-2020 climate pact.But Naidoo, executive director of the influential environment activist group, cautioned against believing the messages of "hope" and "urgent action" promoted by Obama and others."We heard political language from many leaders that we had not heard before. We welcome that. The tone of urgency was there, which has been lacking for quite some time," Naidoo told AFP on the sidelines of the Paris conference."However people watching this have to be very, very careful about judging whether this is simply hot air from our politicians, or is backed up by real intentions in the coming years."Naidoo contrasted Obama's rhetoric about mankind being in grave danger from global warming with US policies to continue subsidising the burning of fossil fuels that are the main climate change culprit."We know that the United States, for example, is the best democracy money can buy. And if you unpack what money buys that influence, it is disproportionately oil, coal, gas and other polluting industries," he said."So the question for the political leadership of these countries is whether they will finally put the interests of ordinary people and their citizens ahead the interests of the powerful fossil-fuel lobbies in their countries."1.5 to stay aliveNaidoo also cautioned against believing that the goal of keeping global warming to two degrees Celsius above pre-Industrial Revolution - a target backed by the United States, China and other big polluters - would keep vulnerable countries safe.Leaders of low-lying island nations and poor African countries are pushing for a Paris accord to enshrine a target of 1.5°C, which would require high-emitting countries to cut down on fossil fuels much more quickly."The debate between 1.5 versus 2 degrees: Now this may just sound like a number. But to put it in a context, the people in the Pacific [islands] are chanting a slogan these days: '1.5 to stay alive'," Naidoo said."Because basically if we go above 1.5, we are talking about dangerous climate change."The UN conference, involving 195 nations, is aiming to end on December 11 with a global climate change pact.But divisions between rich and poor nations, as well as entrenched dependence on coal, gas and oil in many countries, mean a pact is far from assured.