Atmospheric carbon dioxide rises to highest recorded levels

The increase in atmospheric carbon dioxide, as measured by the Scripps Institution of Oceanography, UC San Diego, was recorded despite a sizable fall in global emissions last year as the Covid-19 pandemic took hold.

The average concentration for March 2021 was 417.14 parts per million (ppm), which is 50 per cent higher than the average for 1750-1800.

Daily measurements often fluctuate by a few ppm around the monthly average, due to winds bringing localised regions of air with higher or lower CO2 concentrations to the measurement sites.

Nevertheless, on April 3 2021, a daily CO2 concentration of 421.21ppm was detected at the long-running recording station at Mauna Loa Observatory, Hawaii - the first daily measurement above 420ppm, even if not representative of the average conditions.

The previous record for monthly CO2 concentrations at Mauna Loa in the Scripps dataset was 417.10ppm, recorded in May 2020.

From June to September 2020, CO2 concentrations at Mauna Loa followed the usual temporary decline due to uptake of carbon by ecosystems in the northern hemisphere growing season.

After a minimum of 411.15ppm in October 2020, CO2 concentrations increased again as ecosystems released carbon during the northern hemisphere autumn and winter. 

The annual average atmospheric CO2 concentration is increasing year-on-year and is a major driver of global warming.

The Met Office said that its ongoing monitoring of the global carbon budget confirms that the atmospheric CO2 rise is entirely caused by human activity, mainly through the burning of fossil fuels with further contributions from deforestation.

Since natural carbon sinks remove CO2 from the atmosphere much more slowly than the rate of these emissions, CO2 levels are continuously building up. Reducing emissions slows the rate of build-up, but does not stop it altogether unless the overall input of CO2 to the atmosphere reaches zero.

Commenting on the latest data, professor Martin Siegert, of the Grantham Institute, Imperial College London, said the new record high was completely expected: “Emissions may have been reduced, but we are still emitting lots of carbon dioxide and so its atmospheric concentration is bound to go up and will continue to do so until we get to somewhere near net-zero emissions.

“Our path to net zero is obvious, challenging and necessary and we must get on with the transition urgently.”

Professor Simon Lewis, from University College London, said: “It is easy to forget just how much and just how fast fossil fuel emissions are affecting our planet.

“It took over 200 years to increase the amount of carbon dioxide in the atmosphere by 25 per cent and just 30 years to reach 50 per cent above pre-industrial levels. This dramatic change is like a human meteorite hitting Earth.”