Global Warming may be a misleading factor when it comes to winters in North
America. Jet streams, Pacific-North American Oscillation (PNA), North Atlantic
Oscillation (NAO), and Arctic Oscillation (AO) can describe why winters are cold or warm
and wet or dry. Global Warming could be disrupting these natural cycles creating a chilly
future for parts of the continent. Some areas in the United States have recently been
through bone-chilling winters. There has been record snowfall and cold temperatures
recorded in the Eastern part of the United States and Canada. These records have
people questioning whether global warming is even occurring.
Global warming is in fact still happening and as long as humans continue to
pump carbon dioxide and methane into the atmosphere the earth will continue to warm
(Figure above, NOAA). The earth is all connected with natural cycles. These include
Polar vortex, PNA, AO, and NAO. A warming planet can influence these patterns. Many
places rely on the snow for business and outdoor activities, but the threat of global
warming has many people worried about rapid snow melt and shorter snow season.
Last winter had many people on the eastern continent puzzled because it was so bitterly
cold. Record snowfalls and very cold temperatures can be blamed by the PNA and AO
but scientists are starting to see more frequent cold winters since 1990.
Every year North America is under the influence of positive, neutral, or negative
phases of different oscillations. Basically the AO, NAO, and PNA can determine the type
of winter that will occur. The polar vortex also can be observed as a vault of where the
cold air for an extreme winter is held. The oscillations move this cold air and the jet
stream separates it from the warm air. These natural cycles may not be so natural with
continued burning of fossil fuels that lead to warming temperatures and changing of
temperature gradients in the Arctic.
Climate Models can predict what will happen in the future for average snow
cover in North America. The global warming trend suggests it will continue to decrease.
Cloud cover, the suns angle, and the polar vortex can play a part in the predicted
snowfall. There are some local weather events that may produce high amounts of snow
such as the mountains and the great lakes. These local events are usually due to
orographic lifting and a warm body of water supplying the moisture but still synoptic
patterns can influence lake-effect snow and mountain snow. Climate models predict
global temperatures to rise. Rising temperatures means a change in natural phases of
the atmosphere and also more frequent extreme winters.
Planet Earth has an increase of atmospheric carbon dioxide every year. The rise
of this greenhouse gas greatly increases the average global temperature. The Canadian
Climate Report by Crowe in 1985 does a study on Eastern Canada. Essentially this study
looked at how the length of the snow season changed over the course of a decade. The
snow season observed refers to the number of days a particular location has without
any melting of snow to the point where the ground is showing. This study can be
reproduced in the United States if one disregards local snow events such as lakeenhanced snow. Basically climate models were run to predict what would happen to the
length of the snow season and how much snow southwestern Canada would get over
the years. Some areas the snow season was significantly decreased while other areas to
the south the snow season became non-existent. This line snow line extent could be
estimated across the whole United States and assumed it will retreat more north every
year. On average this snow line will extend more to the north because of the rising
carbon dioxide levels increasing global temperatures.
Scientist have been using climate models to predict just how warm the earth will
get by the end of the century. Most models are saying 2 degrees Fahrenheit and even
up to 6 degrees Fahrenheit by the end of the 21st century (Figure above, NOAA). This
will mean increase in drought, hurricane intensity, sea level rise, and decrease in the
length of the snow season. Global warming is an issue for animals, as they would be
disrupted from their natural habitat as climate changes. People are in danger from
intense weather events and coastal flooding due to the melting of sea ice. For the long
term global warming will increase temperatures and continue to melt frozen surfaces
(Figure below, NOAA). The sea ice keeps the Arctic cold with its high albedo and allows
the North to stay cold. With the decreasing of sea ice, temperatures are warming at a
rapid rate disrupting natural cycles.
This past winter has brought record breaking cold to the U.S. This was the worst
meteorological winter seen in decades. Almost every city on the Eastern United States
has seen below average temperatures. Hartford, Connecticut has seen 24 days with
temperatures below 10 degrees Fahrenheit. Its coldest temperature was negative 9
degrees. Philadelphia, PA has seen 40 inches of snowfall above average. This was a 309
percent increase from last year’s snowfall of only 7 inches. This cold winter has people
wondering if global warming is still existent. The short answer to this is yes. The weather
is what happens day to day but the climate is what happens over long periods of time.
Reasons for this past cold winter was a strong Positive Pacific/North Atlantic Oscillation.
A positive PNA means that there is a trough present in eastern United States and a ridge
in the western United States. A negative PNA encompasses the opposite. The PNA is
determined by adding two differences in average height gradients in 4 locations. The
final result will be positive, negative, or neutral which directly reflects where the
troughs and ridges are present. A trough allows cold air to spill down into the deep
southern states, amplifying the Jetstream allowing lows to track in its path. The ridge
that took place in the Western states and Pacific brought warm and dry conditions for
California and Alaska. PNA can be influenced by other factors as well which originate
from global warming but can be connected to the NAO and AO.
When the Arctic Oscillation is positive the northern hemisphere has a more zonal
pattern (Figure below, Wunderground). This means the jet stream is pretty flat lacking
troughs and ridges. Also this would mean mild winters for the U.S. and the cold air
staying well to the north. A negative AO brings a wavier pattern with trough and ridges
present throughout the northern hemisphere. This allows for cold temperatures to dip
more south and warm temperatures to move north. A negative AO brings the unusual
winters. A negative AO brought the cold temperatures and snowy conditions last winter.
The positive PNA kept the cold to the Eastern United States and Canada.
The NAO is often used to describe what type of winters Canada and The United
States will have. A negative NAO would usually mean a cold winter but in fact last winter
a positive NAO was present. A positive NAO would mean a mild winter and this did not
take place. To determine if NAO is positive or negative NOAA will find the difference
between the averages of 500-mb heights at areas in the north and south Atlantic. While
NAO was positive the Arctic Oscillation was negative for much of last winter (Figure
above, NOAA). The AO describes a very similar pattern like the NAO. The AO can be
found to be positive or negative the same as NAO except 500-mb heights are averaged
from an area in the arctic.
Arctic ice is melting and causing a weak temperature gradient in the north. Last
winter the “Polar Vortex” has made headlines everywhere and was to blame for the
cold winter. This so-called polar vortex is a counterclockwise rotation of upper level cold
air over the Arctic area. The polar vortex is always present over the North Pole. It’s just a
matter of whether or not pieces of this cold air will drift southward and brought down
to the surface. The winter of 2013-2014 some of the polar vortex air drifted southward
and stayed there for much of the winter months. When global warming warms up the
arctic this weakens the temperature gradient. The temperature gradient is the change
of temperature over time. A strong temperature gradient means that there is a big
change of temperature over a short distance. The Polar jet stream is the boundary
between warm air to the south and cold air to the north and can owe its existence to
the temperature gradient. A weak temperature gradient would also mean a weak jet
stream. If the polar jet weakens then it would be easier for the weak, cool polar vortex
air to escape southward into the United States (Figure below, NOAA).
It really has been an unusually chilly winter for a large part of eastern Canada
and United States. While this may be unusual it can be expected to happen every so
often. What is unusual is that climate scientists are seeing these extremely cold
outbreaks of cold air more frequently since 1990. This is a fairly new phenomena and
research for this mystery has already begun. While the frequency in these cold breaks
Weak Polar Vortex
Strong Polar Vortex
have people confused, cold winters can be explained by the patterns that occur. Global
warming is increasing the arctic temperature at a rapid rate. This does create for a weak
temperature gradient that weakens the polar vortex and the jet stream allowing for cold
air to escape southward. Troughs and ridges are formed creating what we know as a
negative Arctic Oscillation. A wavier pattern eventually forms lows that follow the jet
stream and bring snow, sleet, and ice to areas where cold air is present. A positive PNA
will bring cold and snow to most of eastern North America while warm and dry air will
be present on the western side of North America. A negative PNA brings the opposite
effect. So if carbon dioxide keeps increasing the frequency of cold outbreaks such as last
winter will increase.
Global warming is changing the oscillations natural cycles causing cold winters to
occur more frequently. Arctic ice is continuing to melt and the Greenhouse effect is
ongoing. Carbon Dioxide is not showing any sign of decline. Every year the amount of
Carbon Dioxide reaches a new record. High latitude and altitude regions appear to be
the most sensitive to global warming. Because snow has a high albedo, it reflects more
solar radiation than snow-free areas. If this snow is melted the temperatures in the area
will rise on average. So the lack in overall snow cover throughout the winter can greatly
affect the temperatures for that day, week and season. A key area is the arctic where it
is important to have sea ice present and maintain a strong temperature gradient.
Even though the planet is warming there are still times when there are colder
than average winters in North America. This confuses the general public as to whether
or not global warming is happening. The truth is humans are causing global warming
and as long as carbon dioxide continues to increase, the earth will continue to warm.
Warming causes many long-term cold spells such as this past winter (2013-2014).
Record low temperatures and snowfalls on the U.S. east coast had many troubled if
future winters will be the same or worse. The polar vortex air will come back but not
likely to happen every year. In the long term the earth is warming and these cold spells
can be expected to occur more frequently. The decrease of snow and arctic ice is an
important quantity that gives evidence the average global temperature is increasing.
Technology may be developed to slow down and possibly delay further global warming.
Record winters can be expected to continue with the disrupting of the planet’s
oscillation systems. PNA, polar vortex, and AO is connected so when one climate
process is disrupted, such as the temperature of the Arctic, precipitation and
temperature on land can drastically change all over the continent. With some research
people can understand what is really happening with our climate right now and learn
that a warming earth leads to unnatural cycles in the earth’s oscillation patterns.