1. Amazon Shrinks 50 Percent

If global warming turns more than half the Amazon rain forest (pictured) into something other than rain forest by 2200, the change "will lead to potentially dangerous climate change," according to most of the climate experts who participated in a survey about global warming "tipping points" released on March 16, 2009.

Tipping points occur when a small change in one factor, a "driver," can cause a disproportionately large response in an overall system.

In the Amazon Basin, climate shifts may lead to less rainfall, causing a large loss of species diversity--crippling the forest's ability to help maintain the region's air quality, fresh water cycle, and atmospheric circulation.

Between 2005 and 2006, 43 international climate experts volunteered to evaluate each of five tipping points, presented here--specifically, judging the likelihood that achieving a tipping point would lead to potentially dangerous global warming.

"Even though there's a lot of uncertainty and ambiguity in the results, our analysis shows these are not low-probability events," lead study author Elmar Kriegler, of Germany's Potsdam Institute for Climate Impact Research, told National Geographic News.

Experts judged the likelihood of these tipping points to strongly increase with scenarios of potentially low, medium, and high levels of future global warming, according to the study in the journal Proceedings of the National Academy of Science this week.

—Christine Dell'Amore

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