However, the analysis also shows that putting the huge sums of post-COVID-19 government funding into a green recovery and shunning fossil fuels would give the world a good chance of keeping the rise in global temperatures below 1.5°C.
The scientists said we are now at a “make or break” moment in keeping under the limit, as compared with pre-industrial levels, agreed by the world’s governments to avoid the worst effects of global heating.
The analysis, published in the journal Nature Climate Change, used mobility data from Google and Apple that tracks the location of individuals.
This was used to assess changes in levels of transport and office and factory working, and then the emissions of 10 different greenhouse gases and air pollutants.
These estimates matched the measurements available for some gases, such as nitrogen oxides, pollutants mostly emitted by diesel vehicles.
The team assumed that significant restrictions on activity caused by COVID-19 remained in place until the end of 2021.
However, using computer models, the team showed this would only produce a tiny reduction in long-term global heating.
The data covered 123 countries that together are responsible for 99per cent of fossil fuel emissions.
The researchers found that global carbon dioxide (CO2) emissions dropped by more than 25 per cent in April 2020, and nitrogen oxides (NOx) by 30 per cent.
These falls show that rapid changes in people’s behaviour can make big differences to emissions in the short term, but the scientists said such lockdowns are impossible to maintain.
Therefore, economy-wide changes are needed for a transformation to a zero-emissions economy, such as greening transport, buildings and industry with renewable energy, hydrogen or by capturing and burying CO2.
“The direct effect of the pandemic-driven lockdown will be negligible,” said the researchers, whose analysis was led by Professor Piers Forster at the University of Leeds.
“In contrast, with an economic recovery tilted towards green stimulus and reductions in fossil fuel investments, it is possible to avoid future warming of 0.3°C by 2050.”
The global average temperature in 2019 was 1.1°C above the long-term average and even with current emissions-cutting pledges a further rise of 0.6C is expected by 2050.
“It is now make or break for the 1.5°C target,” said Professor Forster.
“This is a once-in-a-generation opportunity to really change the direction of society. We do not have to go back to where we were, because times of crisis are also the time to change.”
Professor Keith Shine, at the University of Reading and not part of the study team, said: “It is deeply impressive to get such a near-real-time analysis of the climate impact of the lockdowns.”
Professor Shine said a green recovery from the pandemic is essential to meet the United Nations sponsored Paris Agreement target: “The study shows that, because CO2 is so persistent in the atmosphere, short-term emission reductions resulting directly from the pandemic lockdowns lead to undetectable reductions in warming.
“It is only via sustained and radical changes in the way we use fossil fuels that we can hope to meet the Paris Agreement target.”
The scientists also examined recovery scenarios.
If the recovery mirrors the investments made after the 2008 financial crisis, which included major support for fossil fuels, the global temperature will rise by more than 1.5°C by 2050, which scientists say will cause widespread damage across the world.
However, a strong green recovery that invests 1.2 per cent of global GDP in low-carbon technologies, more than US$1trillion, and does not support bailouts for fossil fuel companies is likely to cut warming by 0.3°C, the scientists found.
Professor Forster said the recovery investments being made today were backing both green technologies and fossil fuels.