Environmentalists from around the world are meeting in Montreal, Canada, to discuss global warming and slowing the effects of greenhouse gas emissions.  The conference attendees are also discussing what to do after the Kyoto Protocol, an international agreement setting future greenhouse emissions targets for countries that agree to its terms.  The United States refuses to join the Protocol for economic reasons.  Scientists are saying one aspect of global warming could be a water shortage. 

Scientists at the Scripps Institution of Oceanography predict there will be a water shortage due to global warming in as little as 20 years in the United States.  Their study shows water supplies from glaciers and snow reserves will dwindle as more of the polar icecap melts. 

Dr. Tim Barnett is with the Scripps Institution. "In a warmer world, there is less snowfall, right?  Because it's warmer.  And in a warmer world, the snow melts earlier.  That -- that's the bottom line.  That's all that is behind it."

Scientists say the timeline for loss of water in other parts of the world will vary, but it will not happen overnight. 

"For other places in the world like Peru, probably sooner, and yet other places like China, maybe a little bit later,” said Dr. Barnett.  “So it's not something you're going to wake up to in the morning and say, ‘Oh my God, we're out of water,’ it's not going to happen like that, it will just be slow."

Greenhouse gases -- gases that trap heat and contribute to global warming -- play a significant role in accelerating the melting process in ice- and snow-dependent regions.  This, in turn, affects our fresh water supply.

"It's like having a credit card and spending wildly, and not thinking about how you're going to pay it off."

Dr. Barnett recommends water conservation, such as using recycled water, and desalinization plants.

But even salt water may be scarcer.  Over the years, even the Dead Sea, a body of salt-water that is replenished by fresh water from the Jordan River, has shrunk significantly.

The U.S.-based Pew Center on Global Climate Change also released a report on global warming.  The report recommends a flexible international framework allowing countries to take on different types of climate commitments. 

To accomplish this goal, the report urges a closer political dialogue among major economies to find post Kyoto Protocol strategies -- much like the conference going on in Montreal now.

The Kyoto Protocol expires in 2012.