Goodbye to the ice pond of old?
What the thawing and freezing of lakes can tell us about climate change
By Ethan Nedeau
n 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 distractedwe 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 mouses 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 coldits 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 Februaryfor the first time everbecause of thin ice.
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:
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 importantsuch as dace, chub, darters and sculpinwill 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 bluegillwill 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.
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 magnitudeexcept much fasterand 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 Canadathe 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.
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 Earths 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 Streamwhich carries warm water northward from the tropicsmight 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.
Ethan Nedeau is a science translator for the Gulf of Maine Council. He can be reached at firstname.lastname@example.org.
© 2004 The Gulf of Maine Times