UCS Backgrounder: It's Cold and My Car is Buried in Snow. How Can Global Warming be Happening?

Recent
heavy snow storms and cold weather have prompted some commentators to
suggest that a cold winter proves global warming isn't really happening.

Don't let those naysayers snow you.

A
few snow storms, cold snaps or even heat waves do not prove anything
about climate change, because there is a significant difference between
weather and climate. Weather is what we experience on any given day or
even over a couple weeks. Climate describes a region's prevailing
conditions -- including such things as temperature, rainfall, wind,
humidity and atmospheric pressure -- over long periods of time. Climate
is a good indicator of what to expect. For example, in the Midwest, one would expect cold winters. Whereas, in a Mediterranean climate, one would expect a generally milder winter.

Climate
change refers to shifts in prevailing conditions observed over decades.
One such shift is a long-term rise in global average temperatures. The
current cold spells are occurring against this backdrop.

Putting
aside the difference between weather and climate, climate change
projections show that a warming planet generates more precipitation in
areas that typically experience rain or snow. Rising ocean surface
temperatures already have increased the temperature and moisture
content of the air passing over the United States, setting the stage for heavier snow and rain storms. An Intergovernmental Panel on Climate Change report
found that global warming has increased the frequency of storms that
dump heavy precipitation over most land regions that experience storms.
Most deserts, conversely, are getting drier.

"Climate
scientists aren't at all surprised that there are more drenching rain
or blizzards in certain parts of the country," said Dr. Brenda
Ekwurzel, a climate scientist with the Union of Concerned Scientists
(UCS). "That's consistent with well-documented climate change trends
over the past several decades. Unless we take some dramatic steps to
curb global warming, we likely will see a lot more regional
precipitation over the next few decades."

Precipitation in the Northeast has increased markedly over the last century, according to the Northeast Climate Impact Assessment,
a collaboration between UCS and a team of more than 50 scientists and
economists. Over the past few decades, winter precipitation in the
Northeast has increased 0.15 inch per decade.

The Northeast is not alone. According to Global Climate Change Impacts in the United States, released last year by 13 federal agencies, Great Lakes states are experiencing more precipitation because the lakes have less ice and more open water in the winter. The maximum seasonal coverage of Great Lakes
ice decreased approximately 30 percent from 1973 through 2008. That
means more lake water is likely to evaporate into the atmosphere,
resulting in heavier snowstorms.