The Phenomenon Called Global Dimming

Global dimming is a fairly new concept, one introduced largely to the general public at the beginning of the 21st century, although it had already existed in the scientific community. It was first documented by Gerry Stanhill, an English scientist. While in Israel, he was comparing sunlight records from the 1950s with current ones. He discovered that today there is a noticeable drop in solar radiation—up to 22 percent. And the effect is global; it is not related to just one geographic location.

Stanhill named the phenomenon "global dimming" and wrote his findings in 2001. He received skeptical responses from other scientists. Recently, however, Australian scientists used a completely different method to estimate the incoming solar radiation, and their results confirmed Stanhill's findings. After this, other scientists worldwide began taking the global dimming concept seriously.

Dimming is a result of air pollution. The burning offossilfuels (coal, oil, and gas) and wood produces not only carbon dioxide but tiny airborne particles of soot, ash, sulfur compounds, and other pollutants. The visible air pollution reflects sunlight back into space, preventing it from reaching the surface. The idea is that through the introduction into the atmosphere of pollution particulates and aerosols that incoming solar radiation is either absorbed or reflected back into space. Through global dimming, the amount of sunlight reaching Earth is reduced, lower temperatures are reached, and the warming effects of greenhouse gases are masked.

Renowned climate scientist James E. Hansen, from NASA's GISS, estimates that global dimming has cooled Earth by more than 1.8°F (1°C) over the last 100 years. He is concerned that as global pollution levels are lowered, that global warming may increase to the point of no return. According to Hansen, scientists had long known that pollution particles reflected some sunlight, but they are only now realizing the magnitude of the effect. "It's occurred over a long time period," Hansen explains, "so it's not something that perhaps, jumps out at you as a person in the street. But it's a large effect."

Although improving the quality of the air is a desirable goal, part of what pollution is providing, ironically, is a counterbalance for increasing global warming. Its negative effects are masking, or offsetting, global warming's negative effects. This has created a serious problem. While pollution issues cannot be ignored—for the health of all life on the planet, it needs to be reduced—at the same time, humans need to increase their efforts at fighting global warming. Many people think global warming is really a problem for future generations to face, but this is simply not true. Because of pollution, global warming is actually already more serious than the public thinks, and the effects will escalate as pollution levels drop in the future. As scientists continue to study past ice ages and look at today's climate phenomena, however, it enables them to apply the principles they learn to better plan for the future.

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