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NH getting warmer and wetter. Future of severe climate change clear in UNH research.

·6 min read

Heavy rains. Less snow. Up to 60 days of extreme heat, every year by the end of the century.

New Hampshire’s 2021 climate assessment, released Wednesday, paints a grim picture of the state’s future, unless greenhouse gas emissions are reduced.

The report, which was funded by the state’s Department of Environmental Services and conducted by researchers at the University of New Hampshire, shows climate change has made the state hotter and wetter. And the future heat and precipitation projected in the study could have major implications for human health, statewide infrastructure, and ecological systems, researchers said.

The study echoes the findings of the state’s last climate assessment, which came out in 2014, said Mary Stampone, New Hampshire’s state climatologist.

“What we now have a better picture of is the influence of the atmospheric greenhouse gas concentrations on exactly how much warmer, how much wetter and how much more extreme we're going to get,” she said.

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How New Hampshire has changed

Since 1901, temperatures statewide have increased by an average of 3 degrees Fahrenheit, with fall and winter warming fastest, the report says. Extremely cold temperatures have happened less frequently, and thaws have happened more often. In the last 50 years, the state has been warming up more quickly.

Heavy precipitation is more frequent. Annual precipitation has increased 12% in the past 12 decades.

A ten-foot tide in Hampton floods low-lying streets.
A ten-foot tide in Hampton floods low-lying streets.

Since 1971, the amount of water stored in New Hampshire’s snowpack decreased 59% to 91% across the central part of the state.

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Those trends are expected to continue into the future, said Stampone.

“But how bad it actually gets is still kind of up to us, and how much we want to, or are able to, mitigate greenhouse gas emissions,” she said.

What the future holds

Researchers used two different scenarios to project what changes New Hampshire could see under different climate scenarios: a higher emissions scenario, where the world continues to rely on fossil fuels and global temperatures rise 4.3 degrees Celsius, and a lower emissions scenario, where the world begins to transition to cleaner energy and global temperatures rise 2.4 degrees Celsius.

While both of those scenarios are higher than the 1.5 degree Celsius limit the Paris Agreement has targeted, the models researchers used had more simulations for those two scenarios, and the team thought they would be representative of the trajectory of the next several decades.

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“We think that brackets, sort of, the reality of where we are going to be in the future,” said Cameron Wake, a climate scientist at UNH and another author on the study.

Under the higher emissions scenario, New Hampshire could see 50 to 60 days above 90 degrees each year by the end of the century. That's reduced by half, in a lower emissions scenario.

In the lower emissions pathway explored in the assessment, there could be up to 35 more days with no snow on the ground in New Hampshire. Snowfall in the state is projected to decrease by 20% to 50% by 2099. The coldest day and night of the year could warm by 12 degrees in a lower emissions scenario – which jumps to 22 degrees with more greenhouse gasses in the atmosphere.

Under both pathways, researchers expect extreme precipitation to increase, as well as total yearly precipitation. But as summers get warmer, that extra precipitation probably won’t make up for the evaporation of water, which could lead to more short-term droughts, Stampone said.

Similar trends, more data

The 2021 assessment uses data through 2020, where the 2014 assessment included data through 2012. This updated analysis of future climate change relies on 29 climate model simulations, instead of the four that were used in the previous report.

That provides more confidence in the projections, said Cameron Wake. But, he said, researchers have known about the dangers of climate change for a long time.

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The report also looked at new signs of climate change, including something called “cooling degree days,” or measurements of how much warmer a day is than 65 degrees – a comfortable temperature for humans. Some energy companies use that measurement to figure out how much power will be needed to cool down homes or other spaces, Stampone said.

Researchers found a 74% increase in the amount of energy required for cooling in New Hampshire since 1971.

“I’ll admit it takes a lot to shock me,” Stampone said. “I knew it was going to go up, but the extent to which it went up was a lot.”

In the future, under the higher greenhouse gas concentration scenario, New Hampshire would see the energy required for cooling double, compared to a scenario where we lower emissions.

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Researchers are still looking to assess New Hampshire’s vulnerability to drought and wildfire, as well as how decreasing snowpack could impact water in the state’s lakes.

Impacts on Granite Staters

Wake said the changes outlined in the assessment – heavier rain, less snow, warmer winters, more days of extreme heat – could have wide-ranging implications for Granite Staters.

“There's big questions about infrastructure. There's big questions about…jobs and about businesses that are here, and really big questions about human health and big questions about ecosystems and outdoor recreation,” he said.

Wake is hoping decision-makers pay attention to the new assessment.

“You can interpret decision-makers as everybody who lives in the state of New Hampshire and needs to make decisions about their future, about what energy they use, about where they're going to spend their money, but where they're going to recreate,” he said.

For decision-makers responsible for other people, like those in government or business, Wake said he hopes they do two things.

“One is to develop a climate action plan that actually maps out how they can reduce their greenhouse gas emissions,” he said. “And then also begin to prepare for the inevitable changes that are going to come.”

New Hampshire’s latest climate action plan is from 2009, and lawmakers failed to move forward on legislation that would create a new plan in the past session.

These articles are being shared by partners in The Granite State News Collaborative. For more information visit collaborativenh.org.

This article originally appeared on Portsmouth Herald: NH getting warmer and wetter. How extreme will it get? Details here.