Today’s study also marks the first-ever attempt to quantify CO2 emissions on a daily basis, for the world and for 69 individual countries, in close to real time. Until now, annual CO2 emissions data has typically been published months or even years later.

A publicly available daily estimate of global or national CO2 emissions would be “incredibly useful, particularly for motivating policy action and pressure”, another researcher tells Carbon Brief.

Coronavirus crisis

The ongoing coronavirus crisis has claimed the lives of hundreds of thousands of people around the world and seen the introduction of severe restrictions on movement in many countries.

These lockdowns have included “stay at home” orders, border closures and other measures that have had direct effects on the use of energy and, consequently, on the release of CO2 emissions.

As the crisis has unfolded, so too have attempts to quantify its impact on CO2 emissions. These efforts have been challenging, however, because real-time CO2 emissions data does not exist.

The annual emissions inventories that countries submit to the UN take years to compile – and even these are estimates rather than direct measurements.

Greenhouse gas emissions are estimated using a variety of methods, often based on “activity data”. This might be the number of miles being driven, the amount of electricity generated or even – in the case of nitrous oxide, which is used as a propellant – via cream consumption.

Today’s study, published in Nature Climate Change, combines activity data for six sectors with a “confinement index” of lockdown measures in each country or region over time.

This allows for an estimate of changes in daily global CO2 emissions in January-April 2020, relative to the 100MtCO2 released on an average day in 2019.

During peak confinement in individual countries, daily CO2 emissions fell by 26% on average, the paper says. However, the size of this effect is reduced at a global level, because not all countries were under the most severe type of lockdown at the same time.

At the peak of the crisis in early April, regions responsible for 89% of daily CO2 emissions were under some form of lockdown, the paper says. Daily global CO2 emissions fell to 83MtCO2 (-17%, with a range of -11 to -25%) on 7 April, equivalent to levels last seen in 2006.