US President Barack Obama has asserted that the UN climate conference in Paris could be a “turning point” in global climate efforts to reduce future temperature rises.
Negotiators from 195 countries will try to reach a deal within two weeks aimed at reducing global carbon emissions and limiting global warming to 2C (3.6F).
Leaders from 147 nations are addressing the meeting, known as COP21.
President Obama urged negotiators to deliver a meaningful deal, because the “next generation is watching”.
COP21: Latest updates from Paris
He told delegates: “Climate change could define the contours of this century more than any other (challenge).
“I came here personally to say the United States not only recognises the problem but is committed to do something about it.”
He added that recent years had shown that the global economy had grown while emissions had remained flat, breaking the old arguments for inaction “that economic growth and environmental protection were in conflict”.
During negotiations for the preceding Kyoto Protocol, Russia was the last industrialised nation to ratify the global agreement, allowing the landmark deal to come into force in 2001.
Echoing President Obama, Mr Putin said: “We have demonstrated we can ensure economic development and take care of our environment at the same time.”