Don: Booking a trip to Glacier National Park. I want to go there before the glaciers disappear.

Y: What do you mean?

D: Scientists predict that within twenty years the park's remaining glaciers will melt  away.

Y: Why?

D: Whether it's because of human industry or natural cycles, temperatures are rising. And when temperatures rise, glaciers melt.

Y: Forgive me for sounding insensitive, but so what? Glaciers are nice to look at, but what difference will it make if they melt?

D: Glaciers are more than just pretty pictures. They're the main sources for many rivers that people depend on for drinking water, irrigation, and hydroelectric power.

Y: So are rivers drying up?

D: Not yet, but the amount of glacier water affects a river's flow volume. The lower the flow volume the less water there is for drinking, power, and everything else people  depend on rivers for. Also, greater water volume helps dilute a river's chemical content. The less water a river has, the higher the chemical concentration, which can      pollute a lake fed by the river.

Y: I didn't know that. But how about this...Higher temperatures mean that more water  will evaporate from the oceans, which means more precipitation, including snow. So maybe some glaciers will actually grow even though it's getting warmer.

D: Some scientists make that argument, but most don't buy it. Sure, some glaciers are growing temporarily thanks to unusual amounts of snow, but they're the exception to  the rule. Generally, glaciers grow when the amount of snow that melts in the summer is less than the amount that falls in the winter. Right now, more snow is melting than falling.

Y: I guess you should book that trip.