World leaders involved in some of the most high profile geopolitical issues are among those set to speak on the first day of the U.N. General Assembly in New York.
After opening remarks from U.N. Secretary-General Antonio Guterres, those gathered for the annual meeting will hear from a group that includes U.S. President Donald Trump, Turkish President Recep Tayyip Erdogan, Korean President Moon Jae-in and French President Emmanuel Macron.
The addresses come a day after Swedish teen activist Greta Thunberg scolded world leaders at a U.N. summit calling for climate action, saying people are suffering and dying from the effects of global warming and that all the leaders have are empty words.
WATCH: UN climate change
"We are in [the] beginning of a mass extinction and all you can talk about is money," said Thunberg, who ignited a youth movement with her Friday school strikes for climate action.
She said the science has been clear for 30 years, and still they are not doing enough.
"You are failing us! But the young people are starting to understand your betrayal," Thunberg said in a voice filled with emotion. "The eyes of all future generations are upon you. And if you choose to fail us, I say we will never forgive you."
The 16-year-old warned the more than 60 presidents and prime ministers gathered in the General Assembly hall for the summit that the youth would not let them "get away with this." She said they draw the line here and now and "change is coming," whether they like it or not.
"My generation has failed in its responsibility to protect our planet," Guterres said. "That must change."
Guterres has called for the phasing out of fossil fuels and an end to construction of new coal power plants.
"Is it common sense to build ever more coal plants that are choking our future?" the secretary-general asked. "Is it common sense to reward pollution that kills millions with dirty air and makes it dangerous for people in cities around the world to sometimes even venture out of their homes?"
He said it is time to end subsidies to the fossil fuel industry and shift taxes from salaries to carbon – taxing pollution, not people.
The U.N. chief has sought to highlight the importance of the summit and challenged leaders to "come with concrete plans" and not just "beautiful speeches," which some outlined Monday.
India, which has one of the world's highest levels of air pollution, said it would increase its renewable energy capacity to 175 gigawatts by 2022. Prime Minister Narendra Modi highlighted his country's expansion into solar energy.
German Chancellor Angela Merkel, in a rare U.N. appearance, pledged that her country would reduce its carbon emissions by 2030 by 55% compared to its 1990 emissions. She said Germany would be carbon neutral by 2050.
"In 2030 we want to get two-thirds of our energy from renewables," Merkel said. "In 2022, we will phase out the last of our nuclear power plants, and at latest, in 2038, we will phase out coal."
Trump, who announced his administration's intention to withdraw from the 2015 Paris Climate Agreement soon after taking office, was not scheduled to attend or speak at Monday's summit. Trump, however, made a brief appearance and was seen sitting at the U.S. delegation's table before attending an event on religious persecution.
The U.N. released a report ahead of the summit compiled by the World Meteorological Organization showing there has been an acceleration in carbon pollution, sea-level rise, warming global temperatures, and shrinking ice sheets.
It warns that the average global temperature for the period of 2015 through the end of 2019 is on pace to be the "warmest of any equivalent period on record" at 1.1 degrees Celsius above pre-industrial levels.
The 2015 Paris Climate Agreement, which has been ratified by 186 nations, calls for actions to prevent global temperatures from surpassing 2 degrees, and ideally remain within 1.5 degrees by cutting greenhouse gas emissions. One of the world's biggest emitters – the United States – announced under President Trump that it would leave the pact. The U.S. decision has not stopped climate action at the state, local and private sector levels.
The report warns that in order to achieve the 2-degree target, "the level of ambition needs to be tripled."