There are little particles in the atmosphere that are so small and light they can float in air. These particles are called aerosols. They may be small but they have the ability to change climate.

Some aerosols are a natural part of the atmosphere - coming from erupting volcanoes, sea salt, and wildfires. However, burning of fossil fuels like coal, oil, and gas has let lots more aerosols loose in the air. Aerosols are a part of air pollution. They are dangerous to human health and they also dampen the effect of global warming.

Aerosols in the atmosphere can change the amount of solar energy that is reflected away from Earth. Different types of aerosols react differently when hit with sunlight. Sea salt particles reflect sunlight back out into space. Black carbon particles from burning of wood or fossil fuels absorb most of the sunlight that hits them.

Aerosols help clouds form and clouds have an impact on climate. The millions of little droplets of water that make up a cloud each need a little particle, like an aerosol, to condense upon. More aerosols can create more clouds. Different types of clouds may have different impacts on climate and this is a topic that scientists are still exploring. But in general, clouds reflect incoming solar radiation back out to space.

Scientists think that over most of the last century the overall effect of the added aerosols was a reduced amount of global warming. Today, however, as new technologies have allowed factories, power plants, and automobiles to release less air pollution into the atmosphere, the amount of aerosols has dropped. That’s a good thing since air pollution is a problem for human health. But it has also means that the pace of global warming is likely to increase.

 Various particles viewed under a scanning electron microscope. From left to right, volcanic ash is irregularly shaped with lots of jagged edges and grooves. Pollen is generally round or oblong with small points protruding from their surface. Sea salt is cubic with square edges. Soot has small pieces clumped together in larger groups.

These scanning electron microscope images (not at the same scale) show the wide variety of aerosol shapes. From left to right: volcanic ash, pollen, sea salt, and soot. [Images: NASA, compiled from USGS, UMBC (Chere Petty), and Arizona State University (Peter Buseck)

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