Shocking report on the consequences of climate change in the U.S. 0:54

(CNN) -- Snowfall is declining globally as temperatures rise due to human-caused climate change, according to a new analysis and maps from a climate scientist at the U.S. Oceanic and Atmospheric Administration.

But less snow falling from the sky isn't as harmless as having to shovel less often; It threatens to reinforce warming and disrupt food and water for billions of people.

Climate scientists say the future of snowfall is pretty clear: A warmer world driven by human pollution means precipitation is more likely to fall as rain than snow, all things being equal.

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It's possible that in the short term climate change will lead to more extreme winter storms and some years of increased snowfall (as the data for the northeastern United States shows), but as global temperatures rise, there will be fewer of those years, and, eventually, we could see snow amounts decline.

"Over time, the laws of thermodynamics mean that as you keep warming, more and more snow will turn to rain," said Brian Brettschneider, a climate scientist with the National Weather Service in Alaska and the brains behind the data analysis in this paper. "You can get away with it for a while and hide some trends, but in general the laws of thermodynamics will prevail," he said.

Less snow falls around the world

Snowfall has decreased by 2.7% globally since 1973. The decline is particularly notable in the mid-latitudes of the Northern Hemisphere, where much of the world's population resides.

Snow also won't decrease linearly, or at a 1-to-1 rate with rising temperatures, according to Justin Mankin, a climate scientist and associate professor of geography at Dartmouth College. Instead, there will be a tipping point, which would mean that once a certain temperature threshold is reached, "we should expect losses to accelerate," he explained.

"This means that we can expect that a lot of the places that haven't shown massive snowfall decreases will maybe start to show them with just a little bit more warming," Mankin told CNN.

There has already been a 2.7% decline in annual global snowfall since 1973, according to Brettschneider's analysis of data from the European Union's Copernicus Climate Change Service. The downward trend is particularly noticeable in the mid-latitudes of the Northern Hemisphere — the mid-area north of the tropics and south of the Arctic — where much of the population of the United States and the rest of the world resides.

The Sun is more direct there compared to higher latitudes, especially during spring and autumn when it still snows. The white of the snow acts like a car's sunshade, deflecting sunlight and its heat back into space. Without it, the soil absorbs more sunlight, warming the atmosphere.

Less snow falling from the sky also means less snow accumulated in the deep, persistent snowpacks that accumulate during the winter and are crucial to the water supply because they act as a natural reservoir, storing it as snow during wet times and then releasing it as melting when water is harder to come by. Jessica Lundquist, a professor of environmental engineering at the University of Washington, told CNN.

The threat to water supplies from declining snow is most pronounced in climates subject to more extreme precipitation cycles, such as the Mediterranean climate found in California and other parts of the western United States, Lundquist said.

"California is the model: It doesn't rain in the summer, so runoff from snowmelt, snow that waits and runs off later in the season, is absolutely essential for every ecosystem, every agriculture, every city or anyone who wants water during the dry season," Lundquist said.

These deep snowpacks provide water to more than 50% of the supply in the arid regions of the West, according to a 2017 study. The same study predicted that the levels of these snowpacks in the western region would continue to decline by more than a third by 2100, in a scenario of high increase in global warming pollution.

More precipitation falls in the form of rain in the 48 continental states

Much of the U.S. is seeing less snow as a proportion of its total winter precipitation, especially in the Midwest and parts of the South. Elsewhere, precipitation is falling more in the form of snow, a trend that scientists say will likely cease as temperatures continue to rise.

As the map shows, the decline in snowfall over the past 50 years has been particularly pronounced in parts of the western United States. This trend is in line with other studies that have shown a decrease in deep snowpack in more than 90% of the western sites where it is measured.

The increase in snowfall in the Northeast seen on the maps illustrates the complicated nature of changes in precipitation patterns with climate change, the scientists told CNN.

"While the overall snowfall trend was positive, the trend of days per year with snowfall is negative," Brettschneider told CNN. This means that more snow was falling on fewer days, which could be a sign of more extreme snowfall predicted along with climate change.

"The likelihood of extreme snowfall actually increases with global warming and that's because as we warm our atmosphere, the ability of the atmosphere to be a reservoir of moisture increases," Mankin told CNN. "So you get this compensatory response where extreme snowfall can actually increase with global warming," he added.

The increase in snow in the Northeast is also partly due to the period these maps analyze, Brettschneider told CNN. Data on snowfall is much less reliable before 1970, but starting to use the data in that decade also meant that the analysis included some exceptionally snowy years in that part of the United States. If the analysis had started earlier, it could also show a decline, he said.

Manage water with less snow

Understanding the implications of less snowfall on the world's water supply is much more complicated than simply saying less snow means less water available, Mankin said. It depends largely on location and a variety of other snow dynamic factors.

The important thing to track to determine water availability is not the amount of snow, but the amount of water in the snow, Mankin said, which can vary greatly. A light, fluffy snow will have a low water content, which will be high in dense, heavy snow.

What's more, the same extreme precipitation events that generate more snow can also mean more rain, which "could offset those snow losses," Mankin explained.

But the extent of the problem of lack of snow remains enormous.

A 2015 study by Mankin found that 2 billion people who rely on melting snow for water are at risk of a decline in snow reduction of up to 000%. This includes parts of South Asia, which depend on the melting of the Himalayas; the Mediterranean, including Spain, Italy and Greece; and parts of North Africa such as Morocco, which depend on melting ice in the Atlas Mountains.

But Mankin said the study didn't capture hyperlocal water management, including potential strategies that could mitigate or even replace water lost to missing snow.

"Snow loss becomes a huge management challenge," Mankin said. "This isn't necessarily an insurmountable challenge everywhere, but it's a considerable management challenge, particularly in places like the western U.S. that rely heavily on melting runoff."

Mankin and Lundquist said more research is underway to better understand the nuanced relationship between snow and water supply, especially at a hyperlocal scale, which will help water managers better plan for a more volatile relationship with snow.

"There is no silver bullet here: it will be a constellation of solutions and money at various scales that can only be conceived after the scope of the problem is understood and identified," Mankin said.

"To the extent that any one of these places is managing water for the status quo, global warming is eliminating that status quo ... To the extent that our infrastructure and our management practices are rigidly coded for a historical climate, that's irrelevant to the climate that's unfolding," he added.

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