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Goodbye
to the ice pond of old?
What
the thawing and freezing of lakes can tell us about climate change
By
Ethan Nedeau
In
these days of increasing societal demands on our time, we are becoming
more and more detached from Earth's natural calendar that once guided
us. Some people are still in tune with subtle seasonal changes,
but most of us are too distracted—we blink and winter turns
to summer; we blink again and the maple leaves are turning red.
While growing up on a lake, I marked time based on where and what
fish I could catch, the appearance of water lily blossoms, the congregation
of cormorants in the river, or the “rum-rum-rum” of breeding
bullfrogs. When alder leaves were the size of a mouse’s ear,
it was time to fish for brook trout. Spotted salamanders could be
found crossing our wooded paths on the first warm rainy night after
the spring snowmelt, and this meant that we could soon plant peas.
Some
of my fondest memories of growing up near a lake are of watching
the freeze and thaw of the ice. A lake does not go quietly when
it succumbs to the cold—its protests are like sharp thunderclaps
that reverberate across the skies and through the forests, or like
an oak bent to its breaking point before it finally splinters. I
used to lie in bed listening to the lake make ice, and wiggle my
toes with thoughts of skating in the morning. My grandfather used
to skate by Thanksgiving, but nowadays, my family feels blessed
if we can skate by Christmas. A few years ago, the lake was still
unfrozen in late January, and three years ago, two local fishing
derbies were cancelled in February—for the first time ever—because
of thin ice.
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People
have been recording so-called ice-out dates on lakes for well over a century,
providing insight into long-term trends in ice duration (the time between
freezing and thawing of lake ice), which can indicate climate trends.
Scientists at the U.S. Geological Survey in Maine examined 64 to 163 years
of ice-out data for 29 New England lakes. They found that average ice-out
dates are now nine days earlier in northern/mountainous regions, and 16
days earlier in southern New England. Coupled with anecdotal observations
of later freeze dates in the fall, average ice duration may have declined
by over a month in some areas in New England over the last century. The
scientists used the ice-out data to infer an average late winter and early
spring temperature increase of 1.5 ºC (2.7 ºF) since 1850. There
is similar evidence from elsewhere in North America:
- Between
1969 to 1988, average ice duration became 20 days shorter on an Ontario
lake, mostly accounted for by earlier ice-out dates.
- Average
ice-out dates became 15 days earlier from 1890-1991 on a Wisconsin lake,
and the years 1980-1991 accounted for eight of those days.
- Between
the 1950s-1990s, average ice-out became seven days earlier in six central
and western Canadian lakes.
- Between
1846-1996, in lakes and rivers in the northern hemisphere, freeze dates
became 5.8 days/100 years later and ice-out dates became 6.5 days/100
years earlier.
These
studies all suggest that springtime is arriving sooner and may mean that
some lakes are becoming warmer. Ice-out, however, is not the only sign
of spring that is arriving sooner—studies show numerous examples
of plants and animals responding to warmer springs. In the latter half
of the 20th Century, dates of the last hard frost and lilac blooming have
both become significantly earlier in New England. Scientists in Wisconsin
studied 55 springtime events—from the appearance of pussywillows
to robins to trillium blooms—and found that for all combined, these
events occurred an average of 0.12 days earlier per year over 61 years
(7.3 days). From one year to the next, 0.12 days might not seem important.
But what is important is that over the long term, the changes are consistent
and headed in one direction. The climate is changing—and plants,
animals and ecosystems are responding.
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The
Gulf of Maine:
Warming inland, cooling offshore?
Scientists
predict a doubling of atmospheric carbon dioxide over pre-Industrial
levels by 2100 caused by combustion of fossil fuels and biomass
burning. Climate change models indicate that over the next hundred
years Earth’s temperatures will increase by 1.4 to 5.8 ºC
(2.5 to 10.4 ºF) from 1990 levels.
Wintertime
temperatures in northern latitudes are expected to show the greatest
warming. Between 1895 to 1999, average temperatures for the New
England region (including northern New York) increased by 0.41
ºC (0.74 ºF), though some subregions showed higher increases
of 1.0 ºC (1.8 ºF) in New Hampshire and 1.28 ºC
(2.3 ºF) in Rhode Island. The coastal zone warmed by 0.94
ºC (1.7 ºF). Wintertime temperatures increased by an
average of 1.0 ºC (1.8 ºF) over the same period, including
a 1.94 ºC (3.5 ºF) increase in New Hampshire and 1.67
ºC (3.0 ºF) increases in Rhode Island and Vermont.
Despite a long-term trend toward a warmer climate, the Gulf of
Maine region might actually experience a period of cooling in
coming decades. Scientists believe that the Gulf Stream—which
carries warm water northward from the tropics—might weaken
or shift its course due to melting of arctic sea ice, possibly
leading to a rapid cooling period with longer and harsher winters,
similar or perhaps far more severe than the 2002/2003 winter in
our region.
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Ice
duration data for North American lakes is just the tip of the iceberg
for compelling evidence of climate change. There is now an unprecedented
melting of glaciers throughout the world, particularly in polar regions.
Arctic permafrost is thawing and the Arctic growing season has gotten
significantly longer. Russian rivers are discharging much more freshwater
and threaten to upset global ocean circulation patterns. Arctic sea
ice is melting fast—both in spatial extent and depth. Some models
predict that the Northwest Passage will be ice-free in the summer
within 75 years.
Fish habitat disruptions
Why is it important that ice duration on local lakes is decreasing?
What does this mean for natural ecosystems? The main concern is not
ice duration per se, but that lakes may be getting warmer. In northeastern
lakes, climate change is expected to cause a decrease of cold-water
habitats, increase of warm-water habitats, reductions in dissolved
oxygen, reduced lake levels, changes in lake mixing regimes and altered
nutrient cycles. This will affect nearly everything about our lakes—habitats,
populations, communities and ecosystem processes. These types of effects
will also be evident in streams and rivers.
Using
climate change models, scientists predicted changes in lake fish
habitat throughout North America based on anticipated effects on
temperature and dissolved oxygen. They predicted a 45 percent loss
in cold-water habitat, with virtual disappearance of such habitats
from many shallow and medium-depth lakes. Native brook trout, blueback
trout, lake trout and salmon will lose habitat because of climate
change, as will non-native (but recreationally important) rainbow
trout and brown trout. Many non-game species that are ecologically
important—such as dace, chub, darters and sculpin—will
also lose habitat as waters warm.
Scientists
predict that warm-water habitats will increase, causing the “good
growth period” of warm-water fishes to become several weeks
longer. Warm-water fish, such as smallmouth bass, largemouth bass
and bluegill—will likely expand their habitats as previously
cool habitats become more suitable. In the Northeast, most of these
warm-water fish are also non-native predators. Their competitive
advantage over native species will increase as water temperatures
rise.
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Is warmer better?
When the woodpile is rapidly dwindling by early March, or wind-driven snow
makes for a harrowing commute home, we are all tempted to think fondly of
climate change. What are a few extra degrees? People might be more alarmed
if we were facing “global cooling.” Only 20,000 years ago, average
global temperatures were 6 to 7 ºC (10 to 12 ºF) colder than they
are now, and most of our region was covered with glaciers up to two miles
thick. Native plants and animals were forced into refugia far out on the
continental shelf or to the south. We are now facing the prospect of a warming
period of nearly the same magnitude—except much faster—and the
effects will be equally dramatic. The ten hottest years of the last millennium
have all occurred since 1983. If Boston's average annual temperature were
to increase by 5.6 ºC (10 ºF), its climate would be similar to
that of Atlanta, Georgia. In Nova Scotia, if Halifax's average annual temperature
were to increase by the same amount, its climate would be similar to that
of Philadelphia.
Perhaps in 100 years April will no longer signify wood frogs and spotted
salamanders, June may no longer signify brook trout rising for caddisflies,
July may no longer signify fireflies and painted turtles and January may
no longer signify ice skating and snow angels. Climate change threatens
everything about the nature of New England and eastern Canada—the seasons
that shape our lives, the woods and waters that have sustained us for centuries,
and our cultural and economic prosperity. Whether we bicycle to work, or
encourage our political leaders to support regional and global initiatives,
it is important that we do all we can to address this global problem.
Ethan Nedeau is a science translator for the Gulf of Maine Council. He
can be reached at ejnedeau@comcast.net.
. ©
2004 The Gulf of Maine Times |
