Lockdowns around the world to tackle the pandemic have not curbed record high levels of carbon dioxide in the atmosphere, experts have warned.

Shuttering factories, grounding planes and reducing energy use and traffic cut emissions of many pollutants and greenhouse gases, but had little impact on the overall amount accumulating in the atmosphere, figures show.

In 2019, the global average for carbon dioxide concentrations in the atmosphere breached the threshold of 410 parts per million (ppm) and continued to rise in 2020, the World Meteorological Organisation (WMO) said.

The last time carbon dioxide levels were that high was three to five million years ago, when temperatures were 2-3C warmer and sea level was 10-20 metres higher (33-66ft) than now, the UN’s meteorological body said.

Concentrations of other key climate pollutants, including methane and nitrous oxide, also climbed to new highs in 2019, the annual greenhouse gas bulletin from the WMO showed.

While the greenhouse gas bulletin is based on global averages for 2019, individual recording stations have shown the upward trend for levels of carbon dioxide in the atmosphere has continued in 2020.

The benchmark station of Mauna Loa, Hawaii, showed monthly average concentrations of carbon dioxide were 411.29 ppm in September, compared with 408.54ppm in the same month in 2019.

Figures for 2019 show carbon dioxide levels in the atmosphere rose faster than on average for the last 10 years, and are now at about 410.5 ppm in 2019, compared with just 278 ppm in pre-industrial times.

Preliminary estimates for 2020 indicate that as a result of the Covid-19 pandemic, global annual emissions of carbon dioxide will have fallen by between 4.2% and 7.5%.

But these kinds of reductions will not cause the amount of carbon dioxide in the atmosphere – the result of cumulative past and current emissions – to go down, the WMO warned.

Carbon dioxide levels will continue to go up, and while the rate of growth will be slightly reduced by the fall in emissions, it will have no more effect than the changes seen from year to year as a result of natural variability in the system.

Once released into the atmosphere from processes such as burning fossil fuels for power, transport and industry, as well as deforestation and agriculture, greenhouse gases trap heat.

This pushes up global temperatures and drives more extreme weather, melting ice and rising sea levels, as well as making the oceans more acidic.

Carbon dioxide, the main greenhouse gas, remains in the atmosphere for centuries, continuing to warm the planet.

WMO secretary-general Professor Petteri Taalas, warned the falls in emissions from pandemic lockdowns were “just a tiny blip” in the long term.

“We breached the global threshold of 400 parts per million in 2015. And just four years later, we crossed 410 ppm.

“Such a rate of increase has never been seen in the history of our records. The lockdown-related fall in emissions is just a tiny blip on the long-term graph. We need a sustained flattening of the curve,” he said.

He said there was no time to lose on tackling climate change.

He added: “The Covid-19 pandemic is not a solution for climate change.

“However, it does provide us with a platform for more sustained and ambitious climate action to reduce emissions to net zero through a complete transformation of our industrial, energy and transport systems.

“The needed changes are economically affordable and technically possible and would affect our everyday life only marginally,” he said.