Action over climate change is "doable", Prime Minister David Cameron has told a UN climate conference in Paris.
Addressing the meeting, known as COP21, he said leaders should not make excuses and act to protect future generations.
Negotiators from 195 countries will try to reach a deal within two weeks aimed at reducing global carbon emissions.
Earlier, the Prince of Wales told the summit climate change was the greatest threat facing humanity and an agreement would lead to "a saner future".
Leaders from 147 nations are addressing the meeting on Monday. Their statements are limited to three minutes each.
Mr Cameron called for binding agreements to tackle climate change.
"Instead of making excuses tomorrow to our children and grandchildren, we should be taking action against climate change today," he told delegates.
"What we are looking at is not difficult - it is doable and therefore we should come together and do it."
Prince Charles also called on delegates to "to think of your grandchildren, the same as I think of mine".
"Your deliberations will decide the fate not only of those alive today but also of generations yet unborn," the prince said.
"On an increasingly crowded planet, humanity faces many threats - but none is greater than climate change. It magnifies every hazard and tension of our existence.
"It threatens our ability to feed ourselves; to remain healthy and safe from extreme weather; to manage the natural resources that support our economies, and to avert the humanitarian disaster of mass migration and increasing conflict."
UN climate conference 30 Nov - 11 Dec 2015
COP 21 - the 21st session of the Conference of the Parties - sees more than 190 nations gather in Paris to discuss a possible new global agreement on climate change, aimed at reducing greenhouse gas emissions to avoid the threat of dangerous warming due to human activities.
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Prince Charles said in damaging the climate, humans are becoming "architects of our own destruction".
"While the planet can survive the scorching of the earth and the rising of the waters, the human race cannot," he said.
Most of the discussions at the conference will revolve around a new deal that would limit global warming to 2C (3.6F).
World leaders, including US President Barack Obama, are at the first day of the talks.
President Obama said the conference could be a "turning point" in global efforts to limit future temperature rises.
Broadcaster and naturalist Sir David Attenborough, who is among those attending, told the BBC he was not confident the Paris talks would produce a deal to tackle the "hideous problem" of climate change.
He said: "The problems of a rise in temperatures are huge; it has to be avoided at all costs."