This micrograph shows a type of plankton called a cocolithophore. Marine organisms such as this emit sulfur compounds into the air, which become aerosols. Sulfate aerosols affect Earth's climate by changing the amount of sunlight that reaches the ground. Click on image for full size (21 Kb) Image courtesy of NASA/JPL, photograph by Stefan Gartner.

Aerosols are tiny particles or droplets that float around in the atmosphere. Aerosols play an important role in Earth's climate. Some aerosol particles help clouds form by serving as condensation nuclei. Others reflect and scatter sunlight, reducing the amount of energy that makes it to Earth's surface. The oceans are a major source of aerosols. Sea salt is lofted into the atmosphere with the spray and foam of waves, forming one type of aerosol. Microscopic plankton provide another major source of marine aerosols by emitting sulfur-based chemicals into the air.

Some species of phytoplankton emit a chemical called DMSP (Dimethylsulfoniopropionate), which is broken down by other microbes to form a second chemical named DMS (dimethylsulfide). As DMS wafts up into the atmosphere, it is oxidized to form tiny droplets of sulfuric acid and other sulfur-based acids. Chemical reactions in the atmosphere and in clouds turn these droplets into sulfate aerosols. Some droplets also stick onto other existing aerosol particles, making them larger.

Sulfate aerosols affect Earth's climate. The tiny droplets reflect and scatter sunlight, decreasing the amount of energy which reaches our planet's surface. This has a net cooling effect on Earth. Sulfate aerosols also alter droplets in clouds. This tends to make the clouds less likely to produce rain, so the clouds take longer to dissipate. More, longer-lived clouds make for a whiter, brighter planet as the clouds reflect yet more sunlight back into space. This, too, exerts a cooling influence on Earth.

At first it might seem unlikely that tiny plankton could influence Earth's global climate. However, more than 70% of our planet is covered by oceans, so there are trillions of plankton out there emitting sulfur compounds. Marine phytoplankton are by far the largest natural source of sulfate aerosols. Human activities also generate lots of sulfate aerosols, mainly as a result of burning fossil fuels. Scientists think that about 70% of all sulfate aerosols come from fossil fuel burning, while another 20% come from phytoplankton. By studying sulfate aerosol emissions from plankton, scientists get a better understanding of how similar products from fossil fuels influence Earth's climate.

This picture from an electron microscope shows a type of plankton. These plankton give off chemicals that have sulfur in them. The chemicals make tiny particles in the air. Those particles can change Earth's climate! Click on image for full size (21 Kb) Image courtesy of NASA/JPL, photograph by Stefan Gartner.

Aerosols are tiny particles or drops of liquid that float around in the atmosphere. For example, tiny flecks of smoke particles from fires or smokestacks are a type of aerosol. Some kinds of aerosols come from the ocean. Small particles of sea salt are thrown into the air by the spray from waves. Some microbes that live in the ocean give off chemicals that make aerosols, too.

Some types of plankton release chemicals that have sulfur in them. As these chemicals rise up into the air they can be turned into very small droplets of sulfuric acid! Chemical reactions in the atmosphere can turn this acid into various types of aerosol particles.

These tiny aerosol particles actually affect Earth's climate! Some particles reflect and scatter sunlight. Less sunlight makes it to the ground. That makes Earth just a little bit cooler. The aerosols also cause changes in clouds. They can cause more, smaller droplets to form, which makes it harder for the clouds to rain. Clouds that "hang onto" their water tend to last longer. Bright, white clouds also reflect sunlight away. That cools down Earth, too.

How can tiny microbes change the climate of a whole, huge planet? Remember that more than two thirds of Earth's surface is covered by oceans. That means there are trillions and trillions of microscopic plankton floating around. Plankton are by far the biggest natural source of aerosols which contain sulfur.

Humans also make lots of sulfur aerosols. The coal and other fossil fuels we burn make sulfur aerosols. Scientists think that about 70% of sulfur aerosols are made by humans. About 20% are made by microbes in the seas. Scientists who study Earth's climate want to know as much as they can about aerosols. That's why they are interested in studying all of the places aerosols come from.

This picture from an electron microscope shows a type of plankton. These plankton give off chemicals that have sulfur in them. The chemicals make tiny particles in the air. Those particles can change Earth's climate! Click on image for full size (21 Kb) Image courtesy of NASA/JPL, photograph by Stefan Gartner.

Aerosols are tiny particles that float around in the air. Some are tiny drops of liquid. Others are solid. They are all very, very small. Some aerosols come from the ocean. Small particles of sea salt are thrown into the air by the spray from waves. Some microbes that live in the ocean give off chemicals that make aerosols, too.

Some types of plankton give off chemicals that have sulfur in them. These chemicals rise up into the air. They can turn into droplets of sulfuric acid! Chemical reactions in the atmosphere change this acid into various kinds of aerosol particles.

These tiny aerosols actually affect Earth's climate! Some particles reflect and scatter sunlight. Less sunlight makes it to the ground. That makes Earth just a little bit cooler. The aerosols also cause changes in clouds. They make it harder for the clouds to rain. Clouds that "hang onto" their water tend to last longer. Bright, white clouds also reflect sunlight away. That cools down Earth, too.

How can tiny microbes change the climate of a whole, huge planet? Remember that more than two thirds of Earth is covered by oceans. That means there are trillions and trillions of microscopic plankton floating around. Plankton are by far the biggest natural source of aerosols which contain sulfur.