Look! Up in the sky! It's Superman, no wait, it's Spiderman, no wait, it's Underdog, no wait, it's a whole lot of dust and aerosols! Led by scientists at Columbia University's Lamont-Doherty Earth Observatory, research has shown that the amount of sunlight reaching the Earth's surface decreased by 1.3% from 1960-1990. The cause of this dimming is the ever increasing amount of made-made aerosol particles in the atmosphere. The aerosols reflect and absorb incoming solar radiation. They also alter the optical properties of clouds, making them more reflective. The cooling effect of the aerosols is counteracting the warming effect of increased greenhouse gases like carbon dioxide and methane. In other words, were it not for the aerosols the climate would be warming faster than it currently is.

In addition to their affects on global temperatures the aerosols are also changing the hydrologic cycle. When water vapor in the atmosphere condenses on the man-made aerosols the resulting cloud droplet (droplette if it is a girl) is smaller than normal. Smaller droplets lead to more clouds but less rain and the water cycle slows. The scientists estimated that water now stays an extra half-day in the atmosphere before it is rained out.

Dust and smoke can also get into the atmosphere by natural means. Dust often flows over the Atlantic from Africa to South America, and sometimes North America. NASA uses a Moderate Resolution Imaging Spectroradiometer (MODIS) on two of its satellites to track the movement of dust and smoke around the world. In the coolest movie (7MB and 22MB Quicktime movies) Gothamist has seen so far this summer, you can watch the plumes flow over the ocean. The iron and other minerals in Saharan dust help maintain the marine ecosystems of the Atlantic, while the fungal and bacterial organisms in the dust may harm coral reefs.