Global Dimming

Scientists these days are intent on finding the best ways to alleviate the effects of global warming. Several researches are done on how gases producing greenhouse effect can be regulated, or possibly reduced, by natural or mechanical means. But is the planet really getting hotter and hotter? Has nature itself able to address the problem as well? 

It has been observed for several years that there is a gradual reduction in the amount of direct solar irradiance that hits the Earth’s surface. This phenomenon is termed as global dimming. Global dimming is explained by the presence of aerosol particles in the atmosphere which man himself caused to happen. These particulates absorb incoming solar energy and reradiate them back into space. Moreover, they serve as nuclei for cloud droplets. Increased particulates in the atmosphere indicate more clouds consisting of greater number of smaller droplets. Consequently, these clouds become more reflective so that more incoming sunlight is reflected back into space and less enters the Earth’s atmosphere.

 It has been estimated that globally, there is a 4% reduction over the three decades from 1960-1990, though effects vary by location. During this period, there has been an overwhelming demand for petroleum and oil-based products which are produced from incomplete combustion of fossil fuels. This process releases black carbon into the air. Households, aircraft and several industries had also significantly increased the amount of particulates in the atmosphere. Major volcanic eruptions have also escalated the event, specifically that of Mount Agung (Bali, 1963), El Chichon (Mexico, 1983), Ruiz (Colombia, 1985), and Pinatubo (Philippines, 1991).

However, there has been a reversal of the trend beginning 1990, switching from a “global dimming” to “brightening”. This is attributed to the decline of global aerosol since world population acquired greater awareness and undertook certain measures. Brightening has been observed in the United States, Europe, Korea, Antarctica, and Japan. China and India experience renewed or continued dimming.

Global dimming created a cooling effect which may have partially interfered with the effect of global warming.  Though it promotes formation of clouds, global dimming has actually reduced evaporation, thereby decreasing rainfall in some areas. In reality, the apparently opposing forces of global warming and global dimming can occur at the same time so they are neither mutually exclusive nor contradictory.

Deliberate manipulation of this dimming effect is now being considered as a geoengineering technique to reduce the impact of global warming.

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