Climate change: Lockdown has 'negligible' effect on temperatures

The dramatic drop in greenhouse gases and air pollutants seen during the global lockdown will have little impact on our warming planet say scientists.

Their new analysis suggests that by 2030, global temperatures will only be 0.01C lower than expected.

But the authors stress that the nature of the recovery could significantly alter the longer term outlook.

A strong green stimulus could keep the world from exceeding 1.5C of warming by the middle of this century.

Previous studies have already established that there were significant changes to greenhouse gas emissions as transport systems shut down around the world in response to the pandemic.

Global daily emissions of CO2 fell by 17% at the peak of the crisis.

The new study builds on these findings by using global mobility data from Google and Apple.

Prof Piers Forster from the University of Leeds, who led the study, worked with his daughter Harriet on the research, when her A-Level exams were cancelled.

With other researchers, they calculated how 10 different greenhouse gases and air pollutants changed between February and June 2020 in 123 countries.

They found that the drop off peaked in April, with CO2, nitrogen oxides and other emissions falling between 10-30% globally, mainly due to declines in surface transport.

But this new work shows that some of the declines in greenhouse gases actually cancelled each other out in terms of warming.

Nitrogen oxides from transport normally have a warming impact in the atmosphere.

While they went down by 30%, they were matched by a drop in sulphur dioxide, which mainly comes from the burning of coal.

Emissions of this gas help aerosols to form, which reflect sunlight back into space and cool the planet.

This balancing out, combined with the temporary nature of the pandemic restrictions, mean the impact on warming by 2030 will hardly be felt.

"Although temporary changes can help, you need to reduce CO2 permanently to make a dent in global warming," said Prof Piers Forster from the University of Leeds.

"CO2 is long lived in the atmosphere, so you effectively need to reduce emissions to zero for a long-time before you begin to cancel out the effects from decades of past emissions."

Harriet Forster, who co-authored the paper with her father, said that while the recent impacts won't last, there is a golden opportunity for governments to change course.

"Our paper shows that the actual effect of lockdown on the climate is small. The important thing to recognise is that we've been given a massive opportunity to boost the economy by investing in green industries - and this can make a huge difference to our future climate," she explained.

Right now, road traffic is still down in many countries say the authors, with the Google data showing all modes of UK transport still 25% or so down, while the official UK government data has cars still 12% down, but with buses and trains running at less than 50%.

The research team says that if transport goes back to what it was, and the world strongly invests in fossil fuels during the recovery, there is a very high probability that the world will go above the 1.5C warming threshold by 2050.

But if the recovery is strongly green, avoids fossil fuel lock-ins and bail outs, and cuts global emissions to net zero by 2050, the world would have around a 55% chance of staying under 1.5C by the middle of the century.

So what needs to be done to help that happen? Study co-author Prof Corinne Le Quéré from the University of East Anglia says there are a number of steps that should now be taken.

"In cities, it is to support cycling and walking (including electric bikes) because this has multiple benefits for climate, for reducing air pollution, and for health," she told BBC News.

"Encouraging remote working until social distancing measures are lifted releases the pressure on public transport, which can continue to be used. As soon as possible all cars will need to be electric."

"The economic stimulus post-Covid could greatly help support that change in the car manufacturing industry towards the production of electric cars alone."

Prof Forster is optimistic that the challenge can be met.

"Disasters are often historically the time of biggest change," he said.

"For once government, industry and public voices are all pretty aligned that green jobs and green investments are the way to build back better."

"We just need to do it."

The study has been published in the journal Nature Climate Change.

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