Scientists foresee a looming water crisis within the next two decades in the western United States due to human-caused global climate change.

The Rocky Mountains have warmed by 2 degrees Fahrenheit. The snowpack in the Sierras has dwindled by 20 percent and the temperatures there have heated up by 1.7 degrees Fahrenheit. All could lead to dire consequences for the water supply in the Western United States.

Led by a scientist at the Scripps Institution of Oceanography, researchers wrote in the journal Science that there has been a noticeable trend over the past half century of an intensifying decline in water which has already changed river flows, snow pack and air temperatures, accounting for 60 percent of changes.

Tim Barnett, a climate expert at Scripps Institution, part of the University of California at San Diego, told Reuters that this could cause a severe backlash for those living in the western U.S.

"It foretells of water shortages, lack of storage capability to meet seasonally changing river flow, transfers of water from agriculture to urban uses and other critical impacts,” he said.

The scientists claim that the issue has been determining whether the climate change was caused by natural variability or by human-produced greenhouse gases. Their conclusion hints that humans are to blame.

The researchers looked at water flows in three major western river systems -- Columbia, Colorado and Sacramento/San Joaquin rivers and noted that over the past half century, changes have meant less snow pack and more rain in the mountains, rivers with greatly reduced flows by summer and overall drier summers in the region.

Barnett, who worked with experts at the U.S. government's Lawrence Livermore National Laboratory, the University of Washington in Seattle and the National Institute for Environmental Studies in Japan, said that he doesn’t think that much can be done to change the trend at this time.

"We're going to have to adapt our infrastructure and some of our societal needs to fit the way the world is changing," Barnett told Reuters. "Water shortages throughout the west, hydroelectric power reductions, heat waves -- the whole litany of things that go with global warming."

The notion that historical water patterns could be relied on to continue normally has now changed due to the human-caused shifts in the Earth’s climate, Christopher Milly of the U.S. Geological Survey said.

"Our best current estimates are that water availability will increase substantially in northern Eurasia, Alaska, Canada and some tropical regions, and decrease substantially in southern Europe, the Middle East, southern Africa and southwestern North America," Milly said.

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Photo Caption: Computerized projections of western United States snowfall levels in 2050 compared to present day.

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