Methane, which remains in the atmosphere for only about 10 years, but has a much more powerful warming impact than CO2, had its biggest year-on-year jump in 2021 since systematic measurements began nearly 40 years ago.
The annual increases in 2020 and 2021 -- 15 and 18 parts per billion (ppb)respectively -- are the largest since systematic records began in 1983, the agency said.
Atmospheric methane is the second largest contributor to climate change. Since 2007, globally-averaged atmospheric methane concentrations have been increasing at an accelerating rate, the WMO said.
The WMO said the "reason for this exceptional increase is not clear, but seems to be a result of both biological and human-induced processes."
The figures, released in the UN weather agency's Greenhouse Gas Bulletin, underlined "the enormous challenge -- and the vital necessity -- of urgent action to cut greenhouse gas emissions and prevent global temperatures rising even further in the future", said WMO chief Petteri Taalas.
"The continuing rise in concentrations of the main heat-trapping gases, including the record acceleration in methane levels, shows that we are heading in the wrong direction," he added.
The bulletin comes shortly ahead of COP27, the UN climate change conference, being held in the Egyptian resort of Sharm el-Sheikh from November 7-18.
In a report released just over a week before those high-stakes climate negotiations, the United Nation's climate change organization said combined commitments from nearly 200 nations put Earth on track to warm around 2.5C compared to pre-industrial levels by the century's end.
With the planet already battered by weather extremes after 1.2C of warming, experts say the world is failing to act with sufficient urgency to curb greenhouse gas emissions.
"We are still nowhere near the scale and pace of emission reductions required to put us on track toward a 1.5 degrees Celsius world," said UN Climate Change chief Simon Stiell.
