Note: I ran a quickie version of this story in the blog/newsletter on May 31. This expanded version ran in the Monitor on June 10:

Mention the concept of “ice in” and “ice out” to a New Hampshirite and chances are we’ll think of Lake Winnipesaukee.

Our biggest lake gets all the publicity for the annual pronouncements when it’s sort-of-officially covered with ice, and when the ice sort-of-officially goes away. But every lake and pond has an ice-in and ice-out event noted by locals who can’t wait to go ice fishing or play pond hockey.

That includes Mirror Lake in Hubbard Brook Valley. Except that last winter Mirror Lake didn’t have an ice-in and ice-out event – it had four of them.

“I was really surprised. It’s distressing, just because it has never happened before,” said Tammy Wooster, who as a research technician for Hubbad Brook Experimental Forest has been recording data on Mirror Lake since 2000.

On Dec. 5, 2023, Wooster said the ice had arrived based on her daily observations but on Dec. 18, following heavy rains that led to flooding, she saw that the ice had broken up. The lake refroze Dec. 22 then re-unfroze Dec. 29. The ice was back Jan. 2, 2024, but gone again March 15. Back on March 24, gone by March 27.

Even during the longest iced-in stretch, the weather was too erratic to be trusted. “Ice fishermen go every year but this past winter there were no bob-houses. I’ve never seen that before,” Wooster said.

She’ll be seeing it more often, alas.

“This is a pattern that we are increasingly seeing in lakes around the world – shorter periods of ice and changing ice-on-ice-off dynamic. Lake ecologists think a lot about it,” said Chris Solomon, senior scientist at the Carey Institute in New York, which has a long-term research connection to Hubbard Brook.

“The timing of ice-on and ice-off can play a pretty big role in setting up the way the lake works for the year. It dictates the temperature of the column for the rest of the year … (which) controls all the other aspects of the way a lake works, from where there’s oxygen, where organisms can live, a big role in controlling the timing of when seasonal events happen,” said Solomon. Erratic and shorter periods of freezing can lead to more algae, weeds and other biomass, to waters that are less clear. Even the way a lake processes carbon and emits greenhouse gases are affected by patterns of ice cover.

The Mirror Lake measurements were begun in the early 1960s by Gene Likens, who co-founded the Hubbard Brook Ecosystem Study, as a way to quantify effects of human-caused climate change. Consider it New Hampshire’s answer to the Keeling Curve, the measurement of atmospheric CO2 made from a Hawaii mountaintop since 1958 that acts like a thermometer to measure how much we’re screwing up the only planet we have.

“I established a protocol so that I could determine in the same way every year when the ice was fully formed on the lake and when it melted from the lake,” said Likens, who at age 89 is still active. “I knew the period of ice cover, the length of ice cover, is a very important variable and a relatively easy one to study if you do it properly, to give you insights about climate change.”

This is a reminder that scientists have known for more than half a century that our energy patterns are altering the global climate. That’s why they get so exasperated with head-in-the-sand climate deniers.

Mirror Lake’s winter weirdness is a reflection of how the change that we’ve ignored for so long is scrambling the weather patterns we’ve built our civilization around.

“It’s indicative of what others are seeing in a variety of areas and conditions. … Things that have been trending for a long time become much more variable. That’s a feature that we’re seeing in many aspects of climate change,” said Likens.

Solomon agrees that things are not what they were: “Established patterns of weather and seasons are changing, changing rapidly, and becoming more variable.” But he says we shouldn’t give up hope of being able to predict and plan for the climate future even though there’s hardly any normal weather anymore.

“These are outside of our experience but I think they’re not totally unknowable. Climate modelers use data and math to understand and predict what things will look like in the future,” he said.