Much attention has been paid to the disappearance of ice and snow in the Polar Regions and mid-latitudes in the Northern hemisphere in recent years attributed to global greenhouse gas warming.
Of course in the summer, the snow and ice cover retreats to the highest latitudes. Satellite (NOAA CPC) data suggest that the summer levels of polar ice have been at unusually low levels in recent years, perhaps the lowest since the 1930s and 1940s (Polyakov, 2004).
Regardless of the changes in the summer season, the snow and ice have come roaring back each year in the early fall, and winter levels of ice and snow across many parts of the hemisphere are higher than they have been in many years and in some places in over a century.
Memorable snow years in parts of the US
Here in the U.S., it all started in March of 1993, when the "Storm of the Century" brought heavy snowfall (up to 4 feet) from Alabama to New York and New England with losses that totaled $7.6 billion and approximately 270 deaths. Then the "Blizzard of '96" in January deposited 1 to 4 feet of snow over the Appalachians, Mid-Atlantic, and Northeast; followed by severe flooding in parts of same area due to rain and snowmelt inflicting approximately $3.5 billion damage and 187 deaths.
That winter, the snows started early and never stopped coming. All-time seasonal snowfall records were set in dozens of cities in the east and central states including Boston (107.6" or 286% of normal), New York City (75.6 inches of 276% of normal), Philadelphia (63.1 inches or 303% or normal) and Baltimore, MD (63.5 inches or 303% of normal)
In the last few years, all time single storm records were shattered in the northeast cities. Just this last winter, on February 11-12th 2006 a blizzard set new all-time snowstorm record for Central Park in New York City with 26.9 inches. On February 17-18, 2003 a snowstorm set new all-time snowfall record for Boston with 27.5 inches. Another blizzard on January 24-25 2005 brought 22.5" at Boston's Logan Airport, along with high winds, 6 foot drifts and bitterly cold temperatures. Many measurements near Logan were 27-28" and the storm was compared by many to the blizzard of '78.
Boston since 1992/93 had had 5 years that rank among the top 10% snowiest winters in over 130 years of record, including numbers 1, 3, 5, and 7. If you do a 12-year running mean of average snowfall, the period from 1993/94 through 2004/05 for Boston, the average is the highest in the entire record dating back to the 1880s.
New York City (with annual snowfall data back to 1869), for the first time ever, had four successive years with over 40 inches of snow the last four winters. Its four-year running mean is the highest its entire 137 year record.
A few years ago you might recall, the Mt. Baker Ski Area in northwestern Washington State reported 1,140 inches of snowfall for the 1998-'99 snowfall season ending June 30, 1999. This was a new world record for seasonal snowfall.
Not just a local phenomenon
When you look at the Northern Hemispheric winter snow data (recorded back to 1967) you see a recent similar heavy snowfall trend. The average snowfall during the October to March period of 2002/03 exceeded the previous records set in the infamous cold and snowy period of the late 1970s.
The 5 year average snow across the hemisphere has increased each year for the last 7 years. Eurasia especially has experienced large snowfall increases. In fact this past January and the five year January average snowfall were both the greatest on record (since 1967).
What's behind the winter snow-blitz?
Snowfall here in the Northeast and across much of the Hemisphere relate to decadal scale cycles in the Atlantic and Arctic. Two atmospheric oscillations which generally operate in tandem -- the North Atlantic and Arctic Oscillations -- have significant control over the weather pattern including storm tracks and temperatures in both Europe and the eastern United States.
Since the middle 1990s, these oscillations have tended to be often in the phase that favored cold and snow (the negative or 'cold' phases) in both Europe and the eastern United States. The NAO and AO tend to be predominantly in one mode or the other for decades at a time. This relates to ocean temperatures in the Atlantic which exhibit decadal behavior.
Over the last decade the behavior of the NAO/AO has been similar to the 1930s and 1940s (Taylor, 2005) when the NAO moved from a positive to increasingly negative state. Interestingly, that was the last time the Polar Regions were this warm and the summer polar ice this thin and reduced in coverage (Polyakov et al, 2004). Unlike Antarctica where the ice sits on land, in the arctic it is floating on water and the water from one ocean (the Atlantic) can readily flow beneath the ice and if unusually warm, melt more of the ice from beneath.
As George Taylor summarized on this site in his story "Arctic Sea Ice -- Is It Disappearing?"
"A number of researchers have suggested that inflows of Atlantic water into the Arctic profoundly affect temperatures and sea ice trends in the latter ocean. Polyakov, et al (2004) are among these. The first sentence of their paper states 'Exchanges between the Arctic and North Atlantic Ocean have a profound influence on the circulation and thermodynamics of each basin.' The authors attributed most of the variability to multidecadal variations on time scales of 50-80 years, with warm periods in the 1930s-40s and in recent decades, and cool periods in the 1960s-70s and early in the twentieth century. These are associated with changes in ice extent and thickness (as well as air and sea temperature and ocean salinity). The most likely causative factor involves changes in atmospheric circulation, including but not limited to the Arctic Oscillation"
By the way, this latest mode of the North Atlantic Oscillation is the one that Dr .William Gray talks about that favored the sudden increase in Atlantic hurricane activity since the middle 1990s. Last year, Atlantic temperatures were the warmest on record, helping contribute to the record 28 named storms.
Snowfall has been on the increase in parts of the United States and the world to record proportions in recent years even as summer snow and ice levels reach multi-decadal lows. The changes relate to natural cyclical changes in the Atlantic Ocean and atmosphere that favor both more tropical activity in summer and more snowfall in winters.
Climatologists believe the current phase of the Atlantic cycle may last another decade or two. If this outlook is correct, we might expect both more big snows and hurricanes for years to come.
REFERENCES
Gray, William, "Global Warming and Hurricanes", Presentation to Florida Governor's Hurricane Conference, May 12, 2006 and podcast on TCS Daily.
Polyakov, I., Alekseev, G.V., Timokhov, L.A., Bhatt, U.S., Colony, R.L., Simmons, H.L., Walsh, D., Walsh, J.E. and Zakharov, V.F., 2004. Variability of the Intermediate Atlantic Water of the Arctic Ocean over the Last 100 Years. Journal of Climate 17: 4485-4497.
Taylor, George, "Arctic Sea Ice, Is It Disappearing?", TCS Daily March 2005,
Taylor, George, "Hurricanes and Global Warming. Is There a Link?", TCS Daily September 2004
Global Snow Cover Data: http://climate.rutgers.edu/snowcover/ and http://www.cpc.ncep.noaa.gov/data/snow/.