2020 was one of the three hottest on record, the United Nations report said, prompting the UN Secretary-General to declare that the world is "on the verge of the abyss."
A World Meteorological Organization (WMO) report says this is a "double blow" for the millions of people affected by extreme climate events.
The State of the Global Climate Report confirms its preliminary findings and is prepared for the US-led summit on April 22-23.
“We are on the verge of the abyss... We are seeing record levels in tropical storms, in the melting of ice sheets or glaciers, in relation to drought, heat waves and wildfires,” U.N. Secretary-General Antonio Guterres told Reuters.
The report shows that the global average temperature in 2020 was about 1.2 degrees Celsius above the pre-industrial period, making it one of the three hottest years alongside 2016 and 2019, despite cooling in La Niña conditions.
Indicators noted included the record low Arctic sea ice extent in two months of 2020. About 80 percent of the oceans have experienced at least one sea heatwave in the past year.
The United States has had both the largest fires in history and the largest number of hurricanes. Hurricane Laura alone, which hit Louisiana on August 27, caused $ 19 billion in damage.
Death Valley, California, recorded the highest temperature in the world in 80 years at 54.4 degrees Celsius in August, the report says.