Air pollution kills about 7 million people every year. Most of these pollutants are fine particles in the air that, when inhaled, cause heart and lung disease, as well as cancer.
Particles in the atmosphere also create clouds, whether it’s salt from the Southern Ocean or sulfate from industrial chimneys. Together, these particles are called aerosols.
Moisture in the air condenses into cloud droplets containing aerosols. The aerosols that burn the fuel add to the atmosphere cause the droplets to increase and the clouds to reflect the sunlight, and last longer.
All of this increases the amount of sunlight that clouds scatter back into the atmosphere instead of being absorbed by the Earth. This is why the Intergovernmental Panel on Climate Change (IPCC) stated that human-made aerosols cool the climate and mask global warming.
This may sound like good news, but there is no cause for celebration. Aerosols (and their cooling) are very short-lived. When CO2 released into the atmosphere today from cars and coal-fired power plants will still be around hundreds of years from now, the aerosols released as air pollution will cease to have an impact a month from now.
This means that once we stop emitting aerosols, their effect on climate change will cease, while the greenhouse gases in our atmosphere will continue to warm the planet.
And in a new study, we found that the effects of air pollution on cloud formation may be greater than previously estimated.
If the extent to which air pollution provokes global warming is great, the delegates who gathered in Sharm El-Sheikh for COP27, the latest UN conference on climate change, must work harder to reduce the burning of fossil fuels.
Effects of aerosols on clouds
We used ship emissions data to determine the effect of anthropogenic aerosols on climate. Emissions from ships often pollute the air far from land, making it difficult to study the effects of aerosols on their own.
Some aerosols produced by ships appear on satellite images as white streaks called ship tracks. But our data shows that less than 5 percent of this pollution is visible.
Our research used a global database of cruise lines with over 2 million cruises over a six-year period.
Combined with weather forecasting models, we compared where these gases are carried by the wind and enter the clouds, which allowed us to study how the atmosphere moves even when ships are not visible.
Using satellite data, we measured the number of droplets and the amount of water in polluted and unpolluted clouds.
We found that emissions from the ship – although not visible on satellite images – make nearby clouds more reflective. This is because the invisible air of the ships (many) increases the amount of water in the clouds.
Previous calculations showed that the amount of air that is released causes the clouds to dry out a bit, which is why scientists may not have completely ruled out the amount of air that cools the atmosphere.
The same is true of aerosols in general: Air pollution can lighten clouds more than previously thought, leading to more cooling. More research is needed before scientists can apply these results to total air pollution,
A recent study by our research team provided a glimpse into a future with less carbon dioxide.
We used computer algorithms trained to find clear navigation on satellite images ahead of regulations set in 2020 by the International Maritime Organization to reduce air pollution from ships worldwide.
We found that the reduction in ship damage reduced the amount of clear (and also, shiny) clouds in the shipping lanes by 25 percent. This shows how reducing air pollution alone can inadvertently warm the climate.
Air pollution and climate events
But controlling air pollution is not at odds with protecting the climate. In most cases, all this is achieved by eliminating the cause: burning oil.
In the transport sector, this means reducing the number of vehicles running on fuel, for example, not just putting better filters on their exhaust pipes. Similar arguments can be made for factories, power generation, and heating.
Overall, the scientific understanding of air pollution and climate change compels us to stop burning fossil fuels – for the health of people and the planet.
Peter Manshausen, PhD Candidate in Atmospheric Physics, University of Oxford; Duncan Watson-Parris, Senior Research Associate in Atmospheric Physics, University of Oxford, and Philip Stier, Professor of Atmospheric Physics, University of Oxford
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