The World Meteorological Organization (WMO), a United Nations agency, released a report on Sunday that showed the period from 2015 to 2019 is the hottest five years ever, with temperatures rising 0.2 degrees Celsius from 2011 to 2015.
The United Nations raised the alarm on the eve of a special climate summit in New York ahead of the UN General Assembly.
Among the leaders to attend the summit are German Chancellor Angela Merkel and French President Emmanuel Macron, while the list of speakers for the summit did not include US President Donald Trump and leaders of countries intending to open new coal plants, including Japan and South Korea.
UN Secretary-General Antonio Guterres called on political leaders and business leaders to take part in the summit "with plans, not speeches," and encouraged them to make pledges to abandon fossil fuels and slow global warming.
Swedish girl Greta Tonberg, who leads a global student movement to ask policymakers for concrete solutions to climate change, will participate in the "Youth Dialogue" with Guterres and other young activists.
Among the leaders scheduled to speak at the summit are British Prime Minister Boris Johnson, Indian Prime Minister Narendra Modi and Chinese Foreign Minister Wang Yi.
The report said the world's major climate challenges are exacerbated by the threat of global warming that has caused sea-level rise, a sudden drop in the Arctic, Antarctic and Greenland ice sheets, increased desertification, storms and floods.
The report warns that failure to embark on a clear plan to reduce global warming will ultimately lead to economic and humanitarian disasters.