Scientists have seen dramatic shifts in when and where snow falls, and the change could mean trouble for hundreds of millions of people.
According to a NASA report, in the Northern Hemisphere, snow cover has shrunk by a million square miles since 1967.
Snow is vital for water security in some parts of the world. The report says more than 1.2 billion people rely on meltwater from seasonal snowpack and glaciers.
In the western U.S., NASA says melting snow makes up at least 70 percent of water resources, so changes in snowfall change the water supply.
Timing of the snowfall also makes a difference. For example, earlier spring runoff tends to prolong droughts. That's bad news for states like California, which has suffered a multiyear drought.
Other parts of the world could see similar effects. A recent study found warmer global temperatures may cause the Alps to experience a shorter winter season and lose as much as 70 percent of its snow cover by the end of the century.
While it is still too early to determine this year's average global snow accumulation, scientists are already seeing changes in snowfall patterns. Many of the recent winter storms arrived earlier than average.
But scientists are tracking these changes on Earth and from space. NASA recently launched its SnowEx campaign, which measures not only how much snow is on the ground at any given time, but also how much water is in that snow. The campaign expects its first results in the next couple of years.
