Globally, 2021 was the fifth hottest year on record, with an average temperature 1.1-1.2C above 1850-1900 levels. The last seven years were the world's warmest on record "by a clear margin", the European Union's C3S said in a report on Monday.
As greenhouse gas emissions change the planet's climate, the long-term warming trend continued and record-shattering extreme weather swept the world last year, from floods in Europe, China and South Sudan, to wildfires in Siberia and the United States.
"These events are a stark reminder of the need to change our ways, take decisive and effective steps toward a sustainable society and work towards reducing net carbon emissions," C3S director Carlo Buontempo said.
Global levels of CO2 and methane, the main greenhouse gases, continued to climb, and both hit record highs in 2021.
Levels of CO2 in the atmosphere reached 414.3 parts per million in 2021, up by around 2.4ppm from 2020, C3S said.
C3S said levels of methane, a particularly potent greenhouse gas, have jumped in the last two years, but the reasons why are not fully understood. Emissions of methane range from oil and gas production and farming to natural sources like wetlands.
Europe experienced its hottest summer on record in 2021, after a warm March and unusually cold April had decimated fruit crops in countries including France and Hungary.
In July and August, a Mediterranean heatwave stoked intense wildfires in countries including Turkey and Greece. Sicily set a new European temperature high of 48.8C, a record awaiting official confirmation.
In July, more than 200 people died when torrential rain triggered deadly flooding in western Europe. Scientists concluded that climate change had made the floods at least 20% more likely.
Also that month, floods in China's Henan province killed more than 300 people. In California, a record-smashing heatwave was followed by the second-biggest wildfire in the state's history, decimating land and churning out air pollution.