BRUSSELS (REUTERS) - Levels of planet-warming carbon dioxide (CO2) and methane in the atmosphere hit record highs in 2021, which was one of the world's hottest years ever and underlined the need for change, the EU's Copernicus Climate Change Service (C3S) said.

Globally, 2021 was the fifth hottest year on record, with an average temperature 1.1 deg C to 1.2 deg C above 1850-1900 levels.

The past seven years were the world's warmest on record "by a clear margin", the European Union's C3S said in a report on Monday (Jan 10).

Hours later, the US National Centres for Environmental Information released their analysis that said 2021 ranked as the fourth-warmest year on record in the United States, with December 2021 being the warmest December ever recorded.

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 past 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 48.8 deg C, 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 per cent 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.

'Heatbreaking'

In the contiguous United States, the six warmest years in 127 years of record-keeping have all occurred since 2012, NCEI said in the overview of a comprehensive climate report. 

NCEI is a division of the National Oceanic and Atmospheric Administration (NOAA). The agency will release its full annual climate report on Jan 13.

The average temperature in the contiguous United States 2021 was 54.5 Fahrenheit (12.5 deg C), 2.5 degrees above the 20th century average. The record of 55.3 Fahrenheit (12.94 deg C) was set in 2012.

"The consequences of climate change impact each and every American, especially disadvantaged communities across the nation. We must act on climate now to build a better, and more safe future for all", said Ms Eddie Johnson, chairwoman of the US House of Representatives Committee on Science, Space and Technology.

Ms Johnson said the report was "heartbreaking".

The report also found that the nation experienced 20 weather and climate disasters with losses exceeding US$1 billion (S$1.36 billion) each.

Apart from wildfires in the Western United States, those events included a cold snap in the middle of the country in February that caused power outages for nearly 10 million people, December tornadoes in Kentucky and surrounding states, among others.

It was the second-highest number of so-called billion-dollar events on record. The highest was 22 events in 2020.

Total US disaster costs topped US$145 billion for the year.

Hurricane Ida, which hit the US Gulf Coast in August, brought the most losses at US$75 billion. Fatalities related to those events reached 688 and were the highest in a decade.