"In 100 years, we will only see a small fraction of the sea level rise we are setting in motion," says [Stefan Rahmstorf]. Unless we immediately and significantly reduce emissions, he says, "We may commit our planet to a very long-term sea level rise measured in meters."In a worst-case scenario, melting ice sheets and glaciers in the Arctic region could cause severe chilling in the United States and Europe, because the influx of fresh water into the ocean could disrupt or slow thermohaline circulation. Also known as the "ocean conveyor belt," this is the process whereby warm water from the tropics flows northward, moderating and warming the climate. When it hits the Arctic, it cools and sinks, then flows back toward the tropics. Some scientists fear extra fresh water from melting ice could prevent the water from sinking, and interrupt the cycle."The warmer you get the greater the burden from these feedbacks," says Christopher Field, an author of the IPCC assessments. "When you get a runaway greenhouse effect is when the oceans boil. We don't expect that. But it's certainly possiblet we could have a world very unattractive by the standards we live by today''