Greenhouse gases in the atmosphere, the main driver of climate change, hit record highs last year and have continued climbing this year, despite measures to halt the pandemic, the UN said Monday.

The World Meteorological Organization (WMO) said lockdowns, border closures, flight groundings and other measures to rein in the coronavirus crisis had indeed cut emissions of many pollutants and greenhouse gases like carbon dioxide.

But it warned the industrial slowdown due to the pandemic had not curbed record concentrations of the greenhouse gases that are trapping heat in the atmosphere, raising temperatures, causing sea levels to rise and driving more extreme weather.

"The lockdown-related fall in emissions is just a tiny blip on the long-term graph," WMO chief Petteri Taalas said in a statement.

"We need a sustained flattening of the curve."

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The WMO's main annual Greenhouse Gas Bulletin said preliminary estimates indicated that during the most intense period of the shutdowns, daily CO2 emissions may have been reduced by as much as 17 percent globally.

The annual impact was expected to be a drop of between 4.2 and 7.5 per cent, it said.

But this will not cause concentrations of CO2 in the atmosphere to go down, it said, warning the impact on concentrations was "no bigger than the normal year to year fluctuations."