Aerosols are particles that are put in the air. Some are just naturally there, while others are suspended in the air by volcano eruptions, dust storms, forest and grassland fires, living vegetation, and sea spray. Human's also put aerosols into the air by burning fossil fuels. Scientists haven't learned enough about aerosols to know whether it warms or cools the global climate, but I predict that aerosols cool down the over all climate. Most aerosols reflect sunlight, therefore, less radiation reaches earth. Although, the cooling does depend on the size and composition of the aerosols. Without aerosols, we would have no clouds. Clouds that have a lot of small droplets don't let the sun light pass through easy, reducing the amount of sunlight that reaches the surface. Even though aerosols can cause the climate to lower, there's a better chance of the climate to rise. (Aerosols and Climate Change by Mary Hardin and Ralph Kahn)