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Despite its prominence in the conversation about climate change, carbon dioxide is only one of the ways that human activity has disrupted the atmospheric balance. This change can cause global warming to double between 2010 and 2050 - compared to the previous four decades. The newest report from the Intergovernmental Panel on Climate Change, was one of the few positive stories with a catch. For the past two centuries, human activity has allowed global warming to advance at a slower rate—by as much as 0.8 degrees Celsius. The negative part is that emissions of aerosols, which are tiny carbon, sulphur, and nitrogen compound particles, have been the major contributors in driving that cooling. They are tiny particles hanging in the air, like spray aerosols, although very few of them originate from aerosol cans. The majority are created by the same methods of burning carbon-rich fuel that result in greenhouse gas emissions. The floating particles influence cloud formation, reflect solar radiation back into space, and float in the atmosphere. It balances out the warming effects of other gases, such as methane and carbon dioxide. Hence, rising aerosol emissions cool the atmosphere whereas falling aerosol emissions warm it.

In some regions, the effects of this have already been quantified. Temperature increases of approx. 0.3 degrees Celsius may have resulted from the Covid-19 lockdowns in early 2020, with warming from reduced aerosol emissions outpacing cooling from reduced greenhouse gas emissions. A team of Chinese researchers discovered last month that during the height of China’s lockdowns, solar radiation at ground level in Wuhan nearly doubled due to reductions in aerosols. According to another study in the year 2022, declining nitrogen oxide levels may have altered the balance of chemical reactions in the atmosphere and increased amounts of methane, a particularly potent greenhouse gas. Reducing aerosol emissions should be a key priority for global health. There were about 4.23 million excess deaths in 2015 caused by exposure to such chemicals.

The worst effects were caused by inhaling smoke from wood and dung fires in poor countries, and transport fuels and road dust in rich ones. The environmentalists are making progress on this. Since the 1980s, when concerns about acid rain prompted power plants to install scrubbers to remove Sulphur compounds from smokestacks, Sulphur dioxide, or SO2, concentrations in Europe and the US have been falling. Similar laws have significantly reduced aerosol emissions from power plants in China and even India, where a campaign by the government to use LPG burners has also reduced smoke from domestic cooking. Yet, the advancement in health implies that the cooling impact that aerosols have offered since the beginning of the industrial age is no longer present, which is a setback for the climate. As a result, even a reduction in carbon emissions might not be enough to stop the earth from warming.

The concept of geoengineering, which involves spraying SO2 into the sky to slow global warming and make the sun appear less bright, is typically dismissed as science fiction. The ensuing decades will be exceptionally difficult as a result. While CO2 can linger in the atmosphere for up to 1,000 years, aerosols normally evaporate within a few weeks. As a result, when smokestack emissions are cleaned up, the negative effects last longer than the positive ones. Despite its prominence in the conversation about climate change, carbon dioxide is only one of the ways that human activity has disrupted the atmospheric balance that humans have enjoyed since the birth of civilisation.