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 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.

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.

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.

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.

The Gulf of Maine:
Warming inland, cooling offshore?

Ethan Nedeau is a science translator for the Gulf of Maine Council. He can be reached at ejnedeau@comcast.net.
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 © 2004 The Gulf of Maine Times