GLOBAL DIMMING - SHOULD WE BE CONCERNED?
Global Dimming is the concept of the Earths atmosphere not receiving as much irradiance as in previous years. In other words, there is less light reaching the planets surface. This is evident from lower evaporation rates recorded from evaporation pans on farms. Evaporation occurs when photons of light hit the surface of the water, increasing its energy and causing the water molecule to rise into the air. Light is the key driver, and outweighs temperature, humidity and other factors that influence evaporation.
So if less light is penetrating the Earths atmosphere, it means that less energy is reaching the Earths surface. It could be the result of greenhouse gasses and other aerosols reflecting the light fro the sun, or change in cloud chemistry due to air pollution.
A concern is whether this reduction in light affects the planet. At present, Carbon Dioxide is a major contributor to global warming. Its source being anthropogenic. With global dimming, less energy is reaching the planet, so less energy in the form of heat is contributing to global temperature. It is therefore considered to balance out global warming. So is global temperature change really such a major issue.
Change in light intensity however could be of major concern. Records of light intensity have only been dated by man, which means the records are fairly recent. This makes it difficult to create models and therefore uncertainty of what future events it may lead to.
Light is the source of all life on the Earth. Primary producers use it to produce simple sugars, which put them at the base of all food chains. With lower or no light energy, the process of photosynthesis would occur at such a slow rate, primary consumers would not be able to survive. So as one link in the food chain is broken, an entire ecosystem is destroyed.
With humans already exploiting resources at current rates, it would only be a matter of time till an issue like global dimming will be fully recognized as a worldwide crisis.
Reviewed by Eugene M Marinus
Biodiversity & Conservation Biology Department
University of the Western Cape