And the Western states say their snow pack is melting, jeopardizing their water supply.

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For instance, the melting snow pack in the Sierras could reduce the water supply for cities and agriculture.

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"Warmer temperatures cause earlier summer droughts, less snow pack, and cause ideal breeding grounds for invasive species and pathogens, " he added.

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The sky was clear and the sun shone brightly on a heavy snow pack, but it was cold and the wind was blowing.

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Although river levels are lower this year because of a low snow pack, the Merced flows rapidly through a V-shaped canyon and chute channels, Gediman said.

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Snow-pack and glaciers provide a buffer between when the precipitation falls as snow and when it is released as water.

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Without this, a pack of snow would form underneath and the horse would slip.

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But there is no need to invest in a pack-pony or snow-shoes: by 1998 Europeans may be flying direct to Whitehorse.

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As Hansen piloted our little boat past a series of snow-crested peaks, he showed me the survival pack he had thrown on board.

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They have sub-zero temperatures to contend with, howling winds and snow, and the only source of meat on the horizon -- a pack of timber wolves -- has its own ideas about the pecking order on the food chain.

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So when things like that happen during the race, they usually get long periods where people are walking their bikes through the snow until a snowmobile goes through or a different trail-breaker go through and pack down the trails so they can ride.

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