PORTLAND — Maybe it’s not global warming, but a sudden burst of winter warming made it easier for 40 or so environmental activists and their supporters to strip down and run into Casco Bay at noon today.

Both the air and water temperatures hovered in the low 40s as the third annual Polar Plunge, sponsored by the Natural Resources Council of Maine, hit the water at East End Beach.

With the wind nearly calm and sun poking through the clouds, many participants mingled shirtless on the beach, waiting for the signal to dash into the harbor. It was a New Year’s Eve gift – a period that felt warmer than some chilly afternoons that pass for a beach day during a Maine summer.

The event raises money to help the group promote energy efficiency, renewable power and other measures to fight global climate change. More than $6,000 was pledged, but the wider goal was to draw attention to environmental issues.

“We started this more to raise visibility than to raise money,” said Everett “Brownie” Carson, the council’s longtime executive director, who is retiring in 2011.

Carson later stripped to a swimsuit and ran into the water.

Maine’s first polar plunge debuted at Old Orchard Beach in 1987 and remains the state’s largest. The Lobster Dip, which raises money for Special Olympics Maine, typically attracts 400 or so people. The event takes place at noon Saturday outside The Brunswick, 39 W. Grand Ave.

Also on Saturday, a plunge to benefit Caring Unlimited takes place at Gooch’s Beach in Kennebunk at 11 a.m.

Saturday’s air temperatures are expected to be as warm or warmer than today, forecaster say.

Other cold-weather fundraisers have emerged over the years in Maine, leading some organizers to question whether newcomers are diverting interest from the more-established events. Special Oympics Maine, for instance, has been unable to boost participation above 400 in recent years, and organizers hope they can exceed that threshold Saturday. Participants are asked to raise a minimum of $100.

By comparison, today’s Natural Resources Council event was more intimate, but had plenty of color and energy.

Supporters set up tents on the beach for changing stations, as well as a shelter stocked with snacks and towels. Two women dressed in polar bear outfits held a banner reading, “NRCM polar plunge.”

Beth Dimond, public affairs coordinator with the group, stood in her bathing suit, graced with a imitation-grass skirt and Hawaiian lei. She was joined by her mother, Betty Hartley, and sister, Jennifer Dimond.

“Just think Maui,” Hartley joked, as friends snapped photos.

Scott Morse stook nearby, wearing a blue terrycloth bathrobe. He had participated at the Kennebunk plunge in the past, and remembers a day so cold that many people only dared to dip a toe.

But today’s weather emboldened dippers. Emmie Theberge wore flippers and a mask, prepared for a brief snorkel. Ben Doughty traded a swim mask for ski goggles, as well as a cape and Mardi Gras beads. He said he was a superhero.

After posing for a group photo around noon and hearing a few words of encouragement from Carson, plungers waited for a countdown. Then they turned and raced into the water. Screaming and splashing, many went in past waist level. Some wet a head, before retreating to shore and a dry towel.

Theberge took a quick swim around with her snorkel, but said the sea floor was too silty to see anything. Doughty said he felt so good, he ran in twice.

Hartley said she’d try it again next year, if she could get a day as warm as this one.

“It wasn’t as bad as I anticipated,” Hartley said, as she dried off. “The only thing that hurts is my toes.”