Climate change as a result of global warming attributed to excessive greenhouse emissions in the atmosphere is a serious threat to the societies across the world. In response, the stakeholders are working towards reduction of carbon emissions in the atmosphere which is thought to be the key to the prevention of climate change. The recent lockdown measures aimed at containing spread of SARS CoV-2 virus responsible for COVID-19 pandemic temporarily reduced human economic activities leading to reduced emissions in the atmosphere. This provided a potential future scenario of changed atmospheric composition due to reduction in emission. A recent study reveals that improved air quality due to lockdowns did not slow down atmospheric growth rates of greenhouse gases as expected. This was because of increased lifetime of methane (an important greenhouse gas) and partly due to reduced oceanic uptake of CO2. This suggests that threats of climate change and air pollution are not two separate but interlinked problems.Hence, efforts to reduce greenhouse gas emissions and improve air quality should be considered together.
COVID-19 disease following its outbreak in Wuhan in China was declared an outbreak of international concern on 30 January 2020. Soon it took the an extremely serious form and spread worldwide and declared a pandemic on 11 March 2020. Since then, the pandemic has caused unprecedented human suffering and tremendous economic damages.
Efforts to contain and mitigate COVID-19 warranted imposition of severe restrictions on human activities by way of lockdowns which led to sharp decrease in industrial and economic activities, transport and air travels spanning over several months. This resulted in sharp reduction in emissions in atmosphere. Carbon dioxide (CO2) emissions fell by 5.4% in 2020. Air quality improved during lockdown. Clearly observable changes were seen in the composition of the atmosphere.
One would have expected the rate of growth of greenhouse gases in the atmosphere to slow down due to lockdown however it did not happen. Despite sharp decline in industrial and vehicular/transport emissions, atmospheric growth rates of greenhouse gases did not slow down. Instead, amount of CO2 in the atmosphere continued to grow at about the same rate as in preceding years.
This unexpected finding was partly because of reduced uptake of CO2 by the ocean flora. The key factor however was atmospheric methane. In normal time, nitrogen oxides, one of the air pollutants (the six air pollutants are carbon monoxide, lead, nitrogen oxides, ground-level ozone, particulate matter, and sulphur oxides) play key role in maintaining level of methane and ozone in the atmosphere. It forms short-lived hydroxyl radicals which help breaking down long-lived gases like methane in the atmosphere. Lockdown related decline in emission of nitrogen oxides meant reduced ability of the atmosphere to cleanse itself of methane. As a result, the lifetime of methane (a greenhouse gas that is far more effective in trapping heat in the atmosphere than CO2) in atmosphere increased and the concentration of methane in the atmosphere did not decrease with the lockdown related decline in emission. On the contrary, methane in atmosphere grew at faster rate of 0.3% last year which is higher than any time in the last decade.
Reducing concentrations of greenhouse gases in the atmosphere is an imperative and phased reduction of carbon emissions is the key to climate change action plans however, as the study suggests, overall response of atmospheric composition to emissions changes is heavily influenced by factors such as carbon-cycle feedbacks to CH4 and CO2, background pollutant levels, the timing and location of emissions changes, and climate feedbacks on air quality, such as wildfires and the ozone climate penalty. Therefore, threats of climate change and air pollution are not two separate but interlinked problems. Hence, efforts to reduce greenhouse gas emissions and improve air quality should be considered together.
Laughner J., et al 2021. Societal shifts due to COVID-19 reveal large-scale complexities and feedbacks between atmospheric chemistry and climate change. PNAS November 16, 2021 118 (46) e2109481118; DOI: https://doi.org/10.1073/pnas.21094811188