Great Lakes Region Climate
There are two major factors that shape the region's climate - its location
in the middle of the North American land mass and the presence of the
Great Lakes. Being in the middle of the continent, far from the oceans,
means swings in air temperature between warm summers and cold winters.
See Section 5.2 Introduction
In the winter, bitterly cold Arctic air masses move southward into
the region, and the polar jet stream is often located near or over the
region. This causes frequent storm systems that bring cloudy, windy conditions
and rain or snow.
In the summer, a high pressure system that tends to stay in the subtropical
Atlantic Ocean forces warm, humid air into the Great Lakes region, particularly
the southern portions.
The Great Lakes themselves affect the climate. Large bodies of water
gain and lose heat more slowly than the surrounding land. The surface
water temperatures in the lakes tend to be warmer than the land during
the late fall and early winter. The reverse is true in the late spring
and summer. This moderates air temperatures near the shores of the lakes.
We see this effect especially on the downwind sides, where it helps to
create microclimates such as the wine-growing regions of southwestern
Michigan and Ontario.
Another well-known aspect of the Great Lakes influence downwind is lake-effect snow.
Cold air masses sweep across the warmer lakes, picking up heat and moisture.
This generates extreme snow storms on the lee sides of the lakes. (The
lee side is the shore across from the direction of the prevailing winds.)
The winds generally come from the north-west, so the lee side is the
south-eastern shore. (Picture a snow-fence. The snow falls on the lee
side of the fence, the side away from the wind)
Changing Climate
Natural climate variability can be quite large, with year-to-year differences
of several degrees in annual temperature, or swings from very wet years
to drought. However,the scientific evidence strongly suggests that changes
in the atmosphere caused by human activity are the primary cause of
the climate shifts now being observed worldwide. Analyses of data from
the National Climate Data Center (1895-2001) and the Midwest Climate
Center (1900-2000) reveal shifts in temperature, total precipitation,
and extreme events in recent decades.
- Temperatures over the past 30 years have ranged from near average
to somewhat warmer than average. In the past four years, however, annual
average temperatures have ranged 1 to 2 Co warmer than the long-term
average and up to 4 Co above average in winter.
- The past two decades have seen the hottest months in recorded history,
although extended heat waves have been infrequent since the 1950s.
A few episodes of extreme cold occurred in the 1990s, but most years
saw fewer cold waves.
- The last spring freeze has been occurring progressively earlier.
Current dates are approximately one week earlier than at the beginning
of the 1900s. Growing seasons have also begun to lengthen.
- Both summer and winter precipitation has generally been above average
for the past 30 years, making this the wettest period of the twentieth
century. However, water levels in the Great Lakes were higher during
the mid- to late-nineteenth century, indicating even wetter conditions
then.
- The frequency of 24-hour and 7-day intense rainfall events that result
in flooding has been fairly high over the past 50 years, relative
to the long-term average.
Water Temperatures
Water temperature records of the Great Lakes and other inland lakes
show trends in temperature change. Five of seven monitoring sites in
the eastern Great Lakes area have a lengthened period of summer stratification
which has increased by one to six days per decade.
- Increasingly over the last 80 years, warmer spring and autumn water
temperatures have been observed. Summer water temperatures have also
increased, though less dramatically.
Duration and Extent of Lake Ice
The extent of ice and how long it stays on the lakes are sensitive
indicators of climate variability. Shifts in the ice cover on lakes and
streams can provide early signs of ecosystem responses to climate change.
Researchers have found consistent historical changes in ice cover in
the inland lakes and in the bays of the Great Lakes themselves.
- The ice cover is not lasting as long. Freeze-up has been occurring
later in fall and the loss of ice cover in spring has been occurring
earlier for the past century. This change is accelerating.
The rate of change has been greater in the past 20 years than over
the preceding 80 years. Recently, the fall freeze has been moving later
by 1.5 days per decade and spring breakup earlier by two days per decade.
Records over the past 100 to 150 years consistently show increasingly
shorter periods of ice cover
- In the Great Lakes themselves, the extent of ice cover has been highly
variable from 1963 to the present with no long-term trend. In recent
years the Great Lakes have had little ice cover.
- Periods of greatly reduced or no ice cover have become more frequent,
while periods of extensive ice cover have decreased in frequency.
Shifts in ice cover have a number of impacts. Reduced ice cover allows
greater evaporation from open water in winter. This contributes to lower
water levels, loss of winter recreation on lakes, and perhaps an increase
in lake-effect snows (depending on air temperature and wind direction).
Observations from 1846 to 1995 show both the length of ice cover season
and the area of the ice cover have decreased in the Great Lakes Region.
During this time the temperature also increased 1.2 C degrees per century.
Ice break up is now an average of 6.5 days earlier and freeze up 5.8
days later. In the last 150 years the lakes and rivers in Ontario have
gained almost 2 weeks more of open water. (See Albedo Effect, Lake Snow
Effect.)
Ports and commercial shipping schedules have changed. The Hudson's Bay
ice cover has decreased one-third since 1971. Shipping grain through
Churchill, a port leading to the prairies and to the USA, is cheaper
than the ports on the St.Lawrence Seaway. Since 2002 one-third of all
grains shipped have come through Churchill in spite of the fact that
the port at Thunder Bay has an ice-free season that is twice as long.
The change from Great Lakes ports to Churchill saved $10 million U.S.
in 2002.
The good news is that Canada has developed better ice-mapping
and ice detection systems. We are changing our behavior
due to reduced ice cover.
Both commercial shipping and recreation, such as ice fishing, are changing
to meet the changing climate.
The graph below highlights the Ice Cover on Lake Simcoe between 1853-1993
and reflects the changing climate.
Source: Martyn Futter, Climate, Nature and People: Indicators of Canada's
Changing Climate, Canadian Council of Ministers of the Environment, 2003 www.ccme.ca
ACTIVITY 1
- Describe the trends seen in this graph of ice cover on Lake Simcoe.
- Changes in fish populations are already happening according to the
creel census of 2004. What key characteristic will the new dominant
fish populations have?
Research: In an earlier-than-expected spring break up,
ice-fishermen were stranded on broken ice floes. Rescue by helicopter
from Lake Simcoe was extremely costly. Find an article in the newspapers
that has more details.
5.2.1c Extreme Weather Events - The '98 Ice Storm and More
There is a reason the main Canadian topic of conversation is the weather.
Many daily decisions are affected by the weather: clothing, recreation,
travel.
Weather is what we experience day-to-day. Climate is what we experience
over the longer term. Climate affects how we design the things we depend
on in our daily lives: housing, sewer systems, vehicles.
Shorter winters will likely mean lower maintenance and snow-removal
costs for our roads and railways, a shorter winter recreation season,
and a longer summer recreation season.
More frequent freezing rain events could affect energy transmission
and road and airline safety. More frequent freeze-thaw cycles could speed
up the weathering process on our buildings and roadways.
Managing extremes
We in Ontario experience a variety of natural weather hazards: drought,
heat waves, floods, rain, snow and ice storms. We can even have tornadoes
and hurricanes.
In winter, Northern Ontario can have prolonged periods of extreme cold.
Farther south, the snowbelts to the lee of Lakes Superior and Huron,
and Georgian Bay often experience heavy snowfall.
In spring, melting snow or ice jams can cause flooding of Ontario's
rivers. This is also the beginning of the tornado season in Southern
Ontario. We in Ontario have the highest frequency of tornadoes in Canada.
Summer thunderstorms can produce heavy downpours, hail, damaging
winds, and occasional tornadoes. Warm air masses from the tropics can
hover for days causing causing poor air quality, heat waves, and drought.
In autumn, an early frost can damage crops. Hurricanes much to the south
occasionally produce high winds and excessive rainfalls in Ontario.
Small changes in average climate conditions are expected to generate
significant changes in extreme events. The increased frequency of extreme
weather events are consistent with the outputs of
climate models.
Figure 1. Number of climate-related disasters per year in Ontario from
1911 to 1999
(Source: Emergency Preparedness Canada)
ACTIVITY 2
- Describe the trend indicated by the orange line. What kind of relationship
is this?
Severe winter storms
The frequency of severe winter storms in Canada has increased. Climate
models predict that we will have fewer weak winter storms, but increasing
numbers of very severe winter storms.
Figure 2. Number of Storms per Winter in Canada from 1900 to 1996. (Source
DavidSuzuki.org)
- Look at the section of the graph from the
1970s onward. What has
happened to the frequency of storms?
- What are some consequences of having fewer weak storms and more frequent
severe storms?
- Draw a line of best fit on the graph. Differentiate between the sections
before and after 1970.
The Ice Storm of 1998
This storm was not severe in normal terms. The unusual duration and
extent of the drizzle made it the most costly natural disaster in Canadian
history. It cost a total of three billion dollars. This ice storm deposited
about twice the amount of freezing rain than previous ice storms on record.
It caused
- at least 25 deaths, many from hypothermia,
- loss of power in about 100 000 Ontario households
- deployment of 14 000 troops to help with clean
up, evacuation, and security
- the destruction of millions of trees.
What Caused it?
The storm would not have been possible without the 1997-98 El Niño.
This unprecedented El Niño was probably born of climate change.
The El Niño produced an unusually strong jetstream across the
southern US. This jetstream then moved north and pulled warm, moist air
masses to eastern Canada. Meanwhile, a layer of cold air moved down from
Labrador and stalled in the St. Lawrence Valley. The warm southern air
rode up on top of the cold air mass and dropped rain into the cold air
at the surface. The rain froze on contact with the ground. The stable
jetstream maintained the situation for much longer than normal.
Figure 3. The air masses that caused the ice storm of 1998. (Source: DavidSuzuki.org)
Wildfires: Natural Causes - Pieces of Glass
Over the past several decades, the area of Canadian boreal forest affected
by fire and insects has doubled. Lightning is a natural cause of fires.
Fire can also be caused by human carelessness. Our carelessness doesn't even
have to involve a campfire. Curved pieces of broken glass can cause a
fire because they behave like a magnifying glass. The greatest increases
in fires so far have been in the regions of greatest warming. Continued
warming will produce greater seasonal contrasts. With increased dry periods
combined with an expected 44% increase in thunderstrikes, researchers
predict that the area burned will increase by 78% in the next 50 years.
- a)Find out the area of Ontario covered in boreal forest, and
how much was burned in forest fires last year.
b) If predictions are correct, in the next 50 years, what will be the
area burned?
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