Other Feedback Effects

Scientists wonder about several other types of feedback effects as well. For example, as temperatures warm, frozen ground in the Arctic will thaw. Partially decayed vegetation, or peat, which has been locked in the permafrost, will start to decay and release carbon dioxide into the atmosphere. This, in turn, might exacerbate global warming. At the same time, less permafrost would mean less frozen ground, and more places for trees to grow. Trees take in carbon dioxide, so more trees might have the opposite effect, reducing the amount of CO2 in the atmosphere and slowing global warming.

Or, as another example, it is expected that global warming would cause hotter, drier weather in some areas. This change might cause an increase in forest fires. Burning wood releases

Global warming may create a feedback loop in which reduced polar ice reflects less sunlight, which leads to greater warming and more polar ice melting. DEA/C. Sappa/De Agostini/ Getty Images.

carbon dioxide into the air, which might enhance the greenhouse effect. On the other hand, greater dryness might lead to desertification in some places. As land turned into desert, more windblown dust would enter the earth's atmosphere. This dust could block sunlight, lowering temperatures and reducing the greenhouse effect.

On one hand, feedback effects demonstrate how interconnected climate and water are, and how difficult it can be to know what even small changes in temperature may do, or may not do, to climate worldwide. The danger of feedback effects has led many scientists to point to the necessity for quick action. For instance, James Hansen, director of NASA's Goddard Institute for Space Studies in New York, and a leading proponent of action on climate change has said that "strong amplifying feedbacks" may cause the earth to pass "dangerous tipping points."12

On the other hand, some kinds of feedback loops may be overestimated. For example, some scientists have suggested that an increase in global temperatures may cause soils to release more carbon dioxide into the atmosphere, resulting in a feedback loop and even more warming. Cornell professor of bio-geochemistry Johannes Lehmann studied the amount of black carbon in Australian soils. What he discovered was that black carbon actually stayed in soil much longer than researchers had originally believed. Scientists, in other words, had overestimated the feedback effect—a rise in temperature would not cause carbon to escape quickly from Australian soils, and so there would be no feedback effect. Thus, Lehmann noted that though climate change is a serious problem, "this particular aspect, black carbon's stability in soil, if incorporated in climate models, would actually decrease climate predictions" of warming.13

Because feedback effects can exert an unusually large influence on climate, understanding them is vital to predicting and dealing with climate change. Scientists believe they have made progress in identifying some of the most important areas of concern, such as the ice albedo effect and the water vapor feedback loop. Still, researchers are a long way from understanding all the ways in which water and climate may interact.

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