Global Dimming

Global dimming is an important concept that accompanies global warming. Little understood until recently, it is a phenomenon that plays a role in the overall environmental health of the Earth and has specific implications for global warming.

Although global dimming has existed since as long as pollution has existed, it gained particular attention during the terrorist attacks on the United States on September 11, 2001, when all commercial airline traffic was grounded for three days. During this brief time frame, scientists discovered that the atmospheric temperature rose 1.7°F (1°C) during that short interval. As they studied the possibilities, they realized it was because there were no contrails in the atmosphere left by commercial airlines.

The trails of water vapor were reflecting some of the incoming solar radiation, preventing it from reaching the Earth's surface. This discovery led climate scientists at NASA and NOAA to understand that activities that reflect insolation may act counter to global warming. In other words, particulates in the atmosphere—pollutants (sulphur dioxide, soot, ash) and water vapor—while unhealthy in themselves, causing health conditions such as respiratory illnesses, actually serve to counteract some of the ill effects of global warming by reflecting heat away from the Earth.

Although this may seem like a possible solution to counter global warming, it is not a viable option because global dimming has its own associated negative impacts. Climatologists at NASA believe it has led to

Global Dimming

Global dimming caused by airline contrails was discovered in 2001 to partially offset the effects of global warming. (Nature's Images)

decreased rainfall in the Sahel in Northern Africa, where it has caused severe drought and famine, causing heat-related deaths of more than a million people in Africa and has harmed 50 million people with hunger and starvation.

One of the harsh realities about global dimming, and one that has scientists worried, is that as cities deal with cleaning up pollution and reducing the levels of particulates in the atmosphere, it will increase the effects of global warming. Many believe that global dimming has been counteracting the negative effects of global warming. If only global dimming issues are addressed, then the negative effects of global warming will increase even more.

One worrisome aspect this has in the scientific community is that the counteracting effect of global dimming has not been adequately calculated into present-day climate models. Therefore, as the atmosphere gets cleaned up, it may trigger an even sharper rise in global warming, harming ecosystems even faster than anticipated. Experts believe this might negatively affect billions of people.

In fact, based on the Horizon documentary aired by the British Broadcasting Corporation in January 2005, scientists believe that dealing with global dimming without also dealing with the effects of global warming would cause several serious impacts with irreversible damage in only about two decades. It would increase the melting of the world's ice sheets; dry the tropical rain forests, increasing fire danger and thereby release more CO2 into the atmosphere; kill vegetation including crops and devastate the agriculture industry; degrade soil; and release enormous amounts of methane hydrate from the ocean floor, which is about eight times more powerful as a greenhouse gas than CO2. If global warming is not dealt with at the same time, it is projected that temperatures could rise 17°F (10°C) over the next 100 years—which is double what most models are predicting today.

To deal successfully with the issues of the various interactions of the Sun's radiation with the Earth and its atmosphere—the greenhouse gases, their interactions, and life cycles, as well as the interactions between global warming and global dimming—requires the joint research and attention of scientists, planners, managers, politicians, and the general public alike. An understanding of the current issues involving greenhouse gases and an applied knowledge of what will happen to the environment if they are not controlled and managed properly is half the battle facing the world population today. Once the issues are understood and accepted, moving on to the next step—informed positive action—can successfully occur.

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