A deafening clap of thunder and a brilliant stroke of lightening - though sometimes fun to watch, there is something troubling about moments of nature's beauty. Rain showers may be harbingers of an unwelcome future. Extra rain and snow might be evidence that global warming is coming to the northern half of the United States. Some scientists say the extra precipitation could disrupt a balance between fresh and salt water in the Atlantic Ocean, and might abruptly cripple a massive ocean current known as the Great Conveyor. If the Great Conveyer is disrupted, it could cause catastrophic climate changes including sudden cooling in some areas and devastating droughts elsewhere.

The Secrets in Ice Cores

To figure out what may happen to our climate in the future, scientists look at what has happened in the past. To do that, some are drilling deep into polar ice sheets to learn about the climatic changes over the last 140,000 years. Sometimes they find the unexpected.

The Great Ocean Conveyor Belt

The world's oceans are in constant motion - controlled by salt, ice, and the sun. When any one of those controlling forces is disrupted, the entire system can break down - causing drastic changes in global climate. So how exactly does this system of global currents work, and how close is it to collapse?

Preventing a Climate Catastrophe

Many of the suggestions for how to reduce the human contribution to global warming, including CO2 sequestration and wind energy, seem extraordinarily difficult or expensive. But none may be as pricey as the potential consequences of doing nothing.

Read the transcript of the hour-long documentary.

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