NH gets hotter, wetter

Heavy rain. Less snow. Up to 60 days of oppressive heat, each 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 Department of Environmental Services and conducted by researchers at the University of New Hampshire, shows that 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, the researchers said.

The study echoes findings from the state’s latest climate assessment, released in 2014, said New Hampshire state climatologist Mary Stampone.

“What we now have a better idea of ​​is the influence of atmospheric concentrations of greenhouse gases on exactly how much warming, wetness and extreme extremes we’re going to get,” he said. she stated.

How New Hampshire Changed

Since 1901, temperatures across the state have risen an average of 3 degrees Fahrenheit, with fall and winter warming the fastest, the report said. Extreme cold temperatures occurred less frequently and thaws occurred more often. Over the past 50 years, the state has warmed up faster.

Heavy rainfall is more frequent. Annual precipitation has increased by 12% over the past 12 decades.

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

These trends are expected to continue in the future, Stampone said.

“But how bad the situation is still depends on us, and how much we want or are able to mitigate greenhouse gas emissions,” she said.

What the future holds

The researchers used two different scenarios to project the 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 by 4.3 degrees Celsius , and a lower emissions scenario, where the world begins transitioning to cleaner energy and global temperatures rise by 2.4 degrees Celsius.

Although both of these scenarios are above the 1.5 degree Celsius limit targeted by the Paris Agreement, the models used by the researchers had more simulations for these two scenarios, and the team believed they would be representative of the trajectory of the coming decades.

“We think that kind of brackets the reality of where we’re going to be in the future,” said Cameron Wake, a UNH climatologist and another author of 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 halved, in a lower emissions scenario.

In the lower emissions pathway explored in the assessment, there could be up to 35 more days without snow on the ground in New Hampshire. Snowfall in the state is expected to decline 20% to 50% by 2099. The coldest day and night of the year could warm by 12 degrees in a lower emissions scenario – which is climbing at 22 degrees with more greenhouse gases in the atmosphere.

In both pathways, the researchers expect an increase in extreme precipitation, as well as total annual precipitation. But as summers get warmer, that extra precipitation likely won’t make up for water evaporation, which could lead to more near-term droughts, Stampone said.

Similar trends, more data

The 2021 assessment uses data up to 2020, while the 2014 assessment included data up to 2012. This updated analysis of future climate change is based on 29 climate model simulations, instead of the four used in the previous report.

This gives more confidence in the projections, said Cameron Wake. But, he said, researchers have long known about the dangers of climate change.

The report also looked at new signs of climate change, including so-called “cooling degree days”, or measurements of a day’s temperature above 65 degrees – a comfortable temperature for humans. Some energy companies use this measurement to determine how much energy is needed to cool homes or other spaces, Stampone said.

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

“I 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.”

Going forward, under the higher greenhouse gas concentration scenario, New Hampshire would see the energy needed for cooling double, compared to a scenario where we reduced emissions.

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

Impacts on granite staters

Wake said the changes described in the assessment — more rain, less snow, warmer winters, more days of extreme heat — could have far-reaching implications for Granite Staters.

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

Wake hopes policymakers will pay attention to the new assessment.

“You can interpret decision makers as everyone who lives in the state of New Hampshire and has to make decisions about their future, what energy they use, 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 will do two things.

“One is to develop a climate action plan that outlines how they can reduce their greenhouse gas emissions,” he said. “And then also start preparing for the inevitable changes that are coming.”

New Hampshire’s last climate action plan dates back to 2009, and lawmakers failed to advance legislation that would create a new plan during the last session.

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

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