The drop in global carbon-dioxide emissions following the coronavirus pandemic could be large enough to noticeably slow the build-up of CO₂ in the atmosphere this year, a team of scientists at the Met Office and Scripps Institution for Oceanography have predicted.

But this will not be enough to slow the rise in global temperatures.

The Met Office has a successful track record of predicting the rise in CO₂ concentrations each year, as measured at the Mauna Loa Observatory in Hawaii by the Scripps Institution and NOAA. The CO₂ rise speeds up and slows down as natural carbon sinks – parts of the environment which can absorb carbon-dioxide – become temporarily weaker or stronger due to swings in the climate.  2020 was initially predicted to see a relatively fast rise due to weaker carbon sinks linked to the weather conditions in recent months, such as in the Australian bushfires. But the impact of weaker sinks now looks likely to be offset by reduced emissions from fossil burning this year.

The International Energy Agency (IEA) projects global fossil fuel emissions to decrease by 8% in 2020 due to the economic impact of the coronavirus pandemic. As a result, the Met Office and Scripps team predict the CO₂ rise measured at Mauna Loa to be 2.48 ± 0.57 parts per million (ppm), smaller than the 2.8 ppm rise predicted without the coronavirus impacts.

“Although emissions are reducing this year, this does not mean the build-up of CO₂ in the atmosphere will reverse – it will just be slightly slower” said Professor Richard Betts MBE, who leads the CO₂ forecast production for the Met Office. “An analogy is filling a bath from a tap – it’s like we are turning down the tap, but because we are not turning off the tap completely, the water level is still rising”.

If you think of the atmospheric concentration of carbon-dioxide like a bath, you can think of the flow of emissions like water flowing through a bath tap, which can be turned up or down.

The team predict the average CO₂ in May to be 417.1 ± 0.6 ppm, 0.4 ppm lower than it would have been without the pandemic, but still be the highest CO₂ concentration for at least two million years.

From June onwards, CO₂ concentrations will fall – not because of reduced emissions, but due to uptake of carbon by plants in the northern hemisphere growing season. “Plants don’t grow equally all year” explains Professor Ralph Keeling, leader of the Scripps programme for monitoring CO₂ at Mauna Loa and whose father David Keeling discovered the seasonal cycle in atmospheric CO₂.  “The CO₂ goes down in the summer months and then back up”, says Ralph.

After a minimum in September, now predicted to be 0.5 ppm lower than without the coronavirus impacts, the CO₂ will rise until the end of the year and onwards until next year’s peak.

Crucially, the reduction in the CO₂ rise this year will not be enough to slow the ongoing rise in global temperatures. To halt the CO₂ rise and prevent further warming, CO₂ emissions would initially need to halve, and reduce by even more in the long term.

A more in-depth feature on this topic is being hosted by Carbon Brief.