Bob Donaldson, Post-Gazette Chris Hoy, left, of McCandless and Matt Jinar of McCandless team up to crank their auger through the 5-inch-thick ice of North Park Lake on an ice-fishing trip in March of 2003. Paul Sabol (background) of Frazier Township sits on his cooler patiently waiting a bite. Click photo for larger image. Related articles: Fishing Notebook: Steelhead catch rate is lower than in past years Lifetime license holders need to buy Erie stamps

This won't be your great-grandfathers' ice-fishing season, say experts on climate change and global warming.

Lakes in northern states, such as Pennsylvania, are freezing later and thawing earlier than in past centuries, and an international study of 150 years of freeze-thaw dates throughout the Northern Hemisphere indicates that ice has become "a threatened and endangered resource," according to lead researcher John J. Magnuson of the University of Wisconsin at Madison.

By collating records kept by shippers, fur traders and other individuals who depended on lakes for their livelihood as well as newspaper accounts of weather, Magnuson and his team determined that lakes are frozen about half as long as they were at the dawn of the Industrial Revolution, which is often associated with the start of global warming. The change has been most rapid in recent decades.

"Ice duration has declined from four months in the 1850s to somewhere around two, two-and-a-half months in the last 10 years," he said, and the rate at which the lakes are losing ice has increased from six days less ice per century to 10 days less ice within the past two decades.

"Ice-on now comes about six days later and ice-off about four days earlier," he said.

In Wisconsin, one of the biggest ice-angling states, 2000-2001 marked one of the shortest ice durations on record, with just 22 days of ice, and it wasn't strong enough to support fishermen, said Magnuson from his office near Lake Mendota. He added that a nearby bait shop had reported a 10 percent drop in income during what had once been its busiest ice-angling week, between Christmas and New Year's Day.

Joe Hansen, who has owned Hansen's tackle shop on Presque Isle Bay in Erie for 56 years, also has seen changes.

"We used to have ice by Dec. 15," he said. "Now, the bay doesn't ice up until mid-January."

Bob Mohra of Fergie's Bait and Tackle on Lake Wilhelm sees a difference in ice quality, too. "It tends to be thinner than it used to," he said. "Too many warm-ups."

Magnuson's research, published three years ago, started with Mendota -- which is at about the same latitude as Pittsburgh -- and grew to global proportions. It took into account that weather is highly variable and marked by extremes, and that changes have occurred gradually. "If you look at short periods of time, you may not see it. But when you look at 150-year records, despite the variability, what you see is a statistically significant trend toward shorter ice durations, which is one of the strongest indicators of global warming."

Global warming results from a buildup of greenhouse gases, especially carbon dioxide, which come from burning fossil fuels such as coal, natural gas, fuel oil and wood. The burning activates carbon put into storage thousands of years ago. Released gases now blanket the earth and trap heat, causing a greenhouse effect.

"The level of carbon dioxide in the atmosphere is higher now than at any time in the past 150,000 years," Magnuson said. "And the scary part is that, at its current rate, by the end of the century, it will have doubled."

It is possible that we will see iceless winters in our lifetime, he said, predicting a future of warmer summers, warmer winters and a greater number of high-heat days along with more floods and more droughts.

While the impounded water of lakes tends to be warmer than moving water, freezing and breakup on rivers and streams also is influenced by climate changes, said Magnuson. Besides less ice, streams get high flow from rain that, in recent years, has been increasingly torrential. And it rushes directly into streams on impervious surfaces, such as concrete, associated with "suburbanization" and over-development, instead of into the ground where it can be stored and kept cool.

Muskie guide Howard Wagner of Fombell wades rivers and streams all winter. "It's been three years since I've been able to fish without so much freeze-thaw going on," he said. "It causes too much flow at the wrong time of the year. Fish are used to resting in the winter and now they have to deal with current, silt and muddy water." Any disruption to the natural order of things affects the health and longevity of any species, he surmised. "It sounds crazy, I know, but in Canada, where they still get long ice seasons, fish are bigger and live longer."

How global warming will affect fish populations remains to be seen, said Magnuson, though warm-water species such as bass and carp probably will fare better than trout and other cold-water fish.

"For every degree it gets warmer, the number of stream miles for trout in summertime will decrease," he said. Anglers can help by trying to keep trout streams cool. Removing dams is one way, since impounded water gets warmer than free-flowing water, he said. Another is to increase the amount of water infiltrating soil, by reducing run-off. Still another is to enhance forestation, which offsets carbon dioxide and provides cooling cover for trout streams. Inevitably, though, some fish will expand their range northward and others will retract, he said.

Fisheries are not the only indication of the long-term trend toward milder winters. "It's all intricately woven," said Bill Easterling of the Pennsylvania Institutes of the Environment in State College and one of a group of scientists tracking the flowering dates of lilacs, which are early bloomers and good bell weathers of climate change.

"We're indeed seeing very significant early blooming of lilacs," he said. "In the northeastern part of country, there's been a significant increase in the length of the growing season and in the frost-free time of year. We're seeing later and later killing frosts in fall and earlier planting opportunities," Easterling said of his study, which came out of the casual observations of gardeners.

Predictions for the next 100 years indicate anywhere from a 1 1/2- to a 10 1/2-degree increase in average temperatures, said Magnuson, and the Union of Concerned Scientists predicts that Northern states may begin feeling Southern: Wisconsin will seem like Iowa, and Pennsylvania like Virginia. "That's another effect of the loss of winter, which has to do with our sense of place. If I wanted to be in the tropics," said Magnuson, "I'd live there."