The United Nations is holding a climate action summit ahead of the meeting of its General Assembly, stating that in order to confront the climate crisis, the world needs to increase its efforts between three and fivefold.
You can watch live footage in the video player, above.
UN Secretary-General Antonio Guterres opened the Climate Summit. The opening panel included Greta Thunberg, a Swedish youth activist whose protest has sparked rallies around the world.
She criticised adults for looking to children for inspiration. "This is all wrong. I shouldn't be up here. I should be back in school on the other side of the ocean. Yet you all come to us young people for hope. How dare you."
"For more than 30 years the science has been crystal clear, how dare you continue to look away and come here saying that you are doing enough when the politics and solutions needed are still nowhere in sight," Greta Thunberg tearfully told the summit audience on Monday, adding that world leaders had "stolen" her dreams and her childhood with their "empty words".
In a statement, Guterres said: “The best science, according to the Intergovernmental Panel on Climate Change, tells us that any temperature rise above 1.5 degrees will lead to major and irreversible damage to the ecosystems that support us,”
“Science tells us that on our current path, we face at least 3-degrees Celsius of global heating by the end of the century.”
Speaking at the summit, Guterres also said he would not be an "accomplice" in destroying his granddaughters' home.
"I will not be a silent witness to the crime of dooming our present and destroying their right to a sustainable future," he said. He asked people to heed the call of young activists.
"Let us lace up our running shoes and win the climate race for us all."
World leaders address the summit
The US President Donald Trump, who withdrew from the 2015 Paris climate accord, was not scheduled to attend the summit but made a brief appearance with Vice President Mike Pence.
He listened to remarks from the German Chancellor Angela Merkel and Indian Prime Minister Narendra Modi, Reuters reported.
During their remarks, German Chancellor Angela Merkel pledged to increase funding for climate protection to €4 billion, and French President Emmanuel Macron said that Russia had ratified the Paris agreement which he called tremendous news.
Chinese State Councilor Wang Yi spoke about honouring commitments under the Paris Agreement.
"The withdrawal of certain parties will not shake the collective will of the international community nor will it possibly reverse the historical trend of international cooperation," Yi said in reference to the U.S. withdrawal from the accord.
Indian Prime Minister Narendra Modi pledged to increase renewable energy capacity by 2022.
New Zealand Prime Minister Jacinda Ardern said it was "within our grasp, not just to prevent the worst, but to build the best possible world, for the generations to come."
Iceland's Prime Minister Katrin Jakobsdottir spoke about the emergency but also mentioned solutions.
She said Iceland was reversing the loss of woodlands and that they were transforming carbon dioxide into solid minerals.
"The solutions are at hand to reach carbon neutrality and Iceland has declared its goal of becoming carbon neutral by 2040," Jakobsdottir said.
Prime Minister Mia Mottley from Barbados spoke on behalf of small island states who are suffering from natural disasters.
"The Alliance of Small Island States needs to keep temperature increases in this global community to less than 1.5 degrees to stay alive, not to thrive but to stay alive. In other words, 2 degrees needs to be taken off the table once and for all," she said.
The summit comes after a UN youth climate summit on Saturday in which Guterres credited young activists in highlighting the challenge.
Last week, millions of people around the world joined Thunberg's Friday school strikes for climate, marching to encourage politicians to reduce carbon emissions and find solutions to the climate crisis.