Enlarge /. There was a significant decrease in aerosol pollution in India in April.
Given the radical changes people have been making to limit the spread of COVID-19 (Hello, sixth month of quarantine excluding food), many have naturally wondered what impact this has had on pollution, including greenhouse gases and Climate change. Some short-lived pollutants decreased noticeably during the heavy lockdown in April as shops closed and travel expenses reduced. However, due to such short-term events, the CO2 values do not fluctuate. Hence, the long-term impacts on climate change were expected to be trivially small – assuming economies recovered relatively quickly.
A new study conducted by Piers Forster (and his daughter Harriet) of the University of Leeds uses the phone's location data to re-examine the first six months of the year and capture more than just CO2. While they ultimately find that the impact was small, their results also show that the way economies choose to recover could have a much larger effect in the long run.
The work is based on mobility data published by Google and Apple in 114 countries. Together with energy and emission datasets, the researchers converted behavioral changes into pollution changes. The changes in transport usage of the phone record are quite good, although alleged changes in activity between residential, commercial, and industrial environments are more difficult to relate to energy. The researchers compared the changes they saw in their phone data to a May study that estimated April emissions using data such as supply data. They found that their telephone estimate of home energy use likely overestimated the actual change.
Why could this be the case? For example, data from smart meters in the UK shows that energy use increased 20 percent when people started in houses that were previously empty during the day, but only four percent for houses that were previously occupied. The phone data would not capture these differences. The researchers also find that changes are likely to be exaggerated in countries like India, where the subset of the population with smartphones may have been more likely to have jobs that allowed them to work from home. The pollution reductions estimated from this data are therefore probably plausible at the upper end.
It's also worth noting that no data was available for China, so figures from this May study were used to fill this in.
In the end, they estimate a significant decrease in emissions for a number of pollutants – the biggest change in April with a gradual recovery through June. The biggest changes for the climate are sulfur dioxide and nitrogen oxides.
Emissions of many pollutants were significantly reduced – at least for a while – during the lockdown.
The sulfur dioxide pollution creates aerosol particles in the atmosphere, which scatter sunlight back into space and cool the planet. The reduced emissions of this pollutant were mainly due to the slowdown in industrial activity. The changes were also quick, as aerosols were washed out of the atmosphere fairly quickly. In contrast, nitrogen oxide emissions were mainly reduced by reduced transport activity. These gases react to form ozone in the lower atmosphere. Since this is a greenhouse gas, it leads to a warming effect.
When estimating the impact on average temperatures from 2020 to 2025, these two changes roughly cancel each other out. The decrease in nitrogen oxide emissions in the first half of the year would result in a cool of about 0.01 ° C (0.018 ° F if "tiny" isn't enough for you), while the decrease in sulfur aerosols would cause a little more warming than that.
Factor in the brief drop in CO2 emissions, and the overall effect of the lockdowns would be around 0.01 ° C cooler in temperatures by 2030. It's not impressive.
The bigger question is whether anything will change after the pandemic ends. To investigate this question, the researchers are simulating several scenarios through 2050. There is the "two-year blip" scenario in which the lockdown reduction continues to a lesser extent through 2021 and then recovers to match the emissions curve that we would get if countries met their requirements current pledges from the 2015 Paris Agreement. They are also running a "fossil fuel" scenario in which national stimulus packages favor fossil fuels and two "green stimulus packages" where plans encourage greater investments in efficiency and renewable energy.
Different emission scenarios for post-pandemic economic recovery will make a big difference in the long run.
The high and low scenarios will differ by around 0.3 ° C by 2050, with the low scenario actually representing a peak warming of only 1.5 ° C above the pre-industrial value.
The researchers write: “Our work shows that the global temperature signal is likely to be low due to the short-term dynamics of the pandemic. These results show that even without massive, system-wide decarbonization of economies, even massive behavioral changes will only lead to a small reduction in the rate of warming. However, economic investment decisions for the recovery will have a large impact on the warming curve by mid-century. Seeking a rebound in the green momentum from the post-COVID-19 economic crisis may put the world on the right track to keep an eye on the long-term temperature target of the Paris Agreement. "
Climate change in nature, 2020. DOI: 10.1038 / s41558-020-0883-0 (About DOIs).
