7 million people are killed annually by air pollutants. Many of the pollution is suspended in the air and can cause diseases such as heart and lung diseases when breathed in.

Sea salt from the Southern Ocean or sulfate from industrial chimneys are some of the small particles that make up the atmosphere. Aerosols are particles that are aerosol.

Clouds can only hold mist from the atmosphere. Fossil fuel burning adds aerosols to the atmosphere that make these droplets more numerous and reflect sunlight.

Clouds scatter the sun's light back to space instead of being absorbed by the Earth. The Intergovernmental Panel on Climate Change has concluded that human-made aerosols cool the climate.

There is no reason to celebrate this good news. Aerosols are not long-lived. The aerosols that come from air pollution will no longer have an effect on the atmosphere in a month.

The buffering effect on climate change will disappear as soon as we stop emitting aerosols.

The effect of air pollution on the reflectivity of clouds may be larger than previously thought.

If the extent to which air pollution masks the greenhouse effect is bigger, delegates must work harder to reduce fossil fuel burning.

The effect of aerosols on clouds

The effect of human-emitted aerosols on the climate was quantified using data on ship emissions. It's easy to study the effects of aerosols in isolation because of the clear air pollution caused by ship emissions.

Satellite images show some of the aerosols that ships emit. Our data shows that less than 5% of the pollution is visible.

We used a global database of ship routes to conduct our study.

With the help of weather forecasting models, we were able to study the aerosol effect even when no ships were visible.

We used satellite data to measure the amount of water in polluted clouds.

Satellite images don't show ship emissions, but they make nearby clouds more reflective. The amount of water in the clouds is increased due to invisible ship emissions.

Scientists may have underestimated how much air pollution cools the atmosphere because previous estimates suggested that ship emissions had a small drying effect on clouds.

The same may be true for aerosols, as air pollution may cause clouds to be brighter. Scientists need more research before they can apply the results to all air pollution.

A recent study showed a future with less air pollution.

Before and after regulations were introduced in 2020 to lower air pollution from global shipping, we used computer programs to find ship tracks in satellite images.

The reduction in ship pollution reduced the number of bright clouds in the ship tracks by 25%. Reducing air pollution might unintentionally warm the climate.

Air pollution and climate action

Air pollution is regulated to protect the climate. Both are possible if fossil fuels are eliminated.

Reducing the number of cars that run on fossil fuels is one way to do that in the transport sector. There are similar arguments for industry, electricity generation, and heating.

Climate change and air pollution are both caused by the burning of fossil fuels.

The University of Oxford has a PhD candidate in Atmospheric Physics, a senior research associate in Atmospheric Physics, and a professor of Atmospheric Physics.

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