When Larry Marsicano first came to the area in the late 1970s, he was able to walk across Candlewood Lake, which borders several Danbury-area towns, in the winter with no problem.

A thick sheet of ice would have covered the lake by the end of December.

“That’s not a given anymore,” said Marsicano, who was the Candlewood Lake Authority executive director and now serves as a consultant. “I don’t think the middle of Candlewood froze this year, or if it did, it wasn’t for long.”

Connecticut is one of many areas in the Northern Hemisphere already seeing intermittent ice coverage, a trend that is expected to continue due to climate change, according to a study published this winter in Nature Climate Change.

Titled “Widespread loss of lake ice around the Northern Hemisphere in a warming world,” the study offers the first large-scale look at ice loss and the impact it will have on lake ecosystems and the cultural heritage frozen lakes offer to these areas.

“Lake ice is one of the world’s resources most threatened by climate change,” the study states.

But aside from jeopardizing the future of ice skating and ice fishing on Connecticut’s lakes and ponds, less ice coverage could also affect the ecosystems there and might cause more blue-green algae blooms in the summer.

What Connecticut is experiencing now could also serve as a model for what the lakes farther north will experience in the coming years.

A change in ice

Those who ice fish around the state are already seeing less ice coverage firsthand.

The state Department of Energy and Environmental Protection has had to cancel ice fishing classes and tournaments because the ice is unsafe, said Mike Beauchene, the supervising fisheries biologist with the department.

The availability of safe ice is what limits ice fishing the most in Connecticut, where thick ice is considered 10 to 12 inches, he said. The state advises people to only go on the ice if it’s at least four inches thick.

Lake ice used to be considered safe in January and now it’s in February or March, much closer to the start of trout season on the second Saturday in April. There’s also more fluctuation within the winter with temperatures going from single digits to the 40s.

“You can’t rely on what you’re used to,” said Jennifer Klug, a biology professor at Fairfield University. “If it was safe on Jan. 1, it might not be safe on Jan. 1 anymore.”

In January, one man died and another was hospitalized after the pair fell through the ice while skating on a pond at Rogers Park in Old Lyme. A man and his dog were rescued the following month when they fell through the ice on a pond in Milford.

Less ice might benefit some fish species though and earlier melting could free up any that are trapped in the ice, Marsicano said.

The warming is a trend that’s been gradually happening over the past few decades. “It’s not something that’s changing overnight,” Beauchene said.

The changes also vary depending on the type of lake. The ice levels seen at Candlewood, a man-made lake is different than those seen on lakes like Lillinonah and Zoar.

The amount of ice coverage on the latter lakes, which are essentially widened sections of the Housatonic River, depends on the river’s flow and so those lakes already tend to get less ice than others in the state.

Summer side effects

When there is less ice coverage on a lake, there is more time for the waters to absorb sunlight and get warm.

“More warming leads to less ice, which leads to more warming,” said Mitch Wagener, a biology professor at Western Connecticut State University in Danbury studying climate change.

More exposure to sunlight could also translate to lower water levels through evaporation and more plant or algae growth. “The lakes are freezing later if they freeze at all and the ice is coming off earlier so the plants are getting more light,” Marsicano said.

No ice also means the upper levels of the water can be blown around, which mixes the lake at the surface, Wagener said. Stagnant water generally allows cyanobacteria to thrive, while movement and mixing in lakes leads to the opposite.

Also, the faster ice melts, the quicker a lake stratifies — or creates layers of water with different temperatures — and generally, the longer it stays that way. This means there’s also a greater chance for toxic blue-green algae blooms to form because the cyanobacteria is able to regulate its buoyancy through the different densities. It could also lead to more algal blooms.

Longer and stronger stratification could also result in hypoxia buildup, or places where there’s no oxygen. This could happen when the algae blooms die and decompose at the bottom of the lake, eating up oxygen, Klug said.

“Anything that would need oxygen to live would have to move out of that area,” she added, noting this is a threat for fish.

Example for the north

The recent lake study’s authors estimate that about 14,800 lakes in the Northern Hemisphere already experience intermittent winter ice cover. Connecticut is at the southern end of this group.

The number of lakes with intermittent winter ice is expected to increase to 35,300 and 230,400 at 2 and 8 degrees Celsius, respectively. These increases can impact up to 394 and 656 million people, according to the study.

Right now there are big differences in how people further north interact with the lake compared to Connecticut. For example, indigenous communities in northern Canada use ice roads on lakes in the winter to get food, supplies and visit each other, which is not the case here.

“What we are now, they may become,” Wagener said.

Marsicano suspects some of the northern lakes already are experiencing this, just maybe not to the extent Connecticut is. But in the same way northern lakes could look to this state for what’s in store for future climate changes, Connecticut could look to the mid-Atlantic for a preview of what’s to come.

“When we’re looking at climate change, geography is a good model for what we’d expect to see,” Klug said.

kkoerting@newstimes.com; 203-731-3345