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More heat waves, rising seas, and intensifying storms will pummel the Boston area, new report finds

Cohasset High School football player Jackie Lyons examined a press box, destroyed by a storm, at Cohasset Alumni Field in October.Craig F. Walker/Globe Staff

By the end of the century, average temperatures in the Boston area could increase as much as 10 degrees above 2000 levels, while seas could rise more than 15 feet, under the worst circumstances. Over the same period, intense precipitation could increase by 30 percent and flooding from swollen rivers could surge by 70 percent.

Those are some of the findings of a new report by scientists at the University of Massachusetts Boston about the impacts of climate change on 101 municipalities in the metropolitan area.

The report by the Greater Boston Research Advisory Group, which follows a similar study it published six years ago, also found that the average annual amount of groundwater in the region is likely to decline by 18 percent by 2100, potentially resulting in less available drinking water.

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Echoing the results of other recent reports on climate change, such as those published this year by the United Nations’ Intergovernmental Panel on Climate Change and the National Oceanic Atmospheric Administration, the authors found that the impact of climate change could be much less severe if governments around the world collectively reduce their countries’ carbon emissions. This report provides a rare glimpse into how the global challenge of a warming planet will affect a specific region.

“To think we’ve caused this much change in our climate is astounding,” said Paul Kirshen, a professor of climate adaptation at UMass Boston and an author of the report. “We’ve already done a hell of a lot of damage, and this report emphasizes the need to get to net-zero emissions.”

If global emissions fall substantially over the coming decades, the region’s average annual temperatures could be held to an increase of just 3 degrees by 2100, while the number of days a year when temperatures exceed 90 degrees could be kept to an average of 20 days, up from an average of 8 to 10 days a year now, the report found.

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But if countries continue to rely on fossil fuels and spew more carbon into the atmosphere at the rates they are today — the United Nations has estimated that global carbon emissions are on track to increase 14 percent through the end of the decade — the Boston area can expect as many as 80 days a year of temperatures exceeding 90 degrees, according to the report.

Such an increase in temperatures poses a significant threat to public health, the authors noted, citing one study estimating that Boston’s heat-related deaths could triple by 2050.

“Boston’s heat-induced mortality rate will likely increase in coming decades, with marginalized populations and those living in urban heat islands facing higher risk,” the authors wrote in the report. “Air quality hazards and respiratory disease, adverse birth outcomes, and transmission of vector-borne diseases are also likely to increase due to temperature changes.”

Temperature increases also threaten the region’s signature industries, including the harvest of cranberries and maple syrup, as well as the catch of lobster and other shellfish. It also likely means an increase in the spread of invasive species, such as the emerald ash borer and Asian longhorned beetle, which have decimated forests across the country.

If carbon emissions are reduced substantially, sea levels in the region could be held to an increase of as little as 1 foot above 2000 levels by the end of the century, the authors said. Tides in Boston Harbor have already risen by about a foot over the past century.

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Sea levels are most likely to rise by about 3.4 feet by 2100, without significant reductions to emissions, though they could rise as much as 15.6 feet, depending on how much melting occurs on the ice covering Antarctica and Greenland, the report found. The group’s last report projected that the highest sea levels could reach would be 10.5 feet by 2100.

If all ice sheets on Antarctica melt, sea levels would rise as much as 190 feet. No matter how much those glaciers melt, seas will rise disproportionately higher in the Northeast than elsewhere on the planet, the authors noted.

“Melting land ice causes changes in Earth’s gravity and rotation that impact regional patterns of sea level rise,” they wrote. “When ice is lost from the West Antarctic Ice Sheet, these processes amplify the resulting sea level rise in Boston by about 25 percent, relative to the global average.”

The report also found that Boston is likely to experience a significant increase in nuisance flooding, or days when the local flood threshold is exceeded for at least an hour. By 2050, such flooding is expected during about half the days of the year, compared with about 15 days a year now.

The authors projected that even with reduced emissions, flooding that now occurs on average once every 10 years is likely to occur an average of once a year by 2050, and such deluges that occur once every century are also likely to occur every year by 2100.

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With less snow in the winter, a longer spring growing season, and more demand for water from rising temperatures in the summer, aquifers in the region are likely to have reduced supplies of drinking water. Moreover, in coastal areas, the quality of that water may be reduced, as rising seas make it more likely that they could be contaminated with encroaching saltwater, according to the report.

The authors said the projected 18 percent decline in groundwater could have a significant impact on many communities.

“This is absolutely concerning,” said Jayne Knott, a research associate at the UMass Boston School for the Environment and another author of the report. “We depend on groundwater for our drinking water.”

River flooding is likely to worsen, in part, because of greater rainfall in late winter and early spring, as precipitation is expected to become more intense at a time when there’s less plant growth to absorb the rainfall.

Again, the authors found that the amount of emissions could have a significant impact on the amount of such flooding. With sharp cuts in carbon pollution, major river flooding might only increase 15 percent over 2000 levels. Without such cuts, major river flooding could rise by 70 percent.

They also forecast that precipitation will increase between 10 percent and 20 percent by 2050 and between 20 percent and 30 percent by 2100.

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While many of the authors’ predictions don’t differ significantly from their last report, their confidence in their projections has increased.

“We don’t consider these to be conservative estimates any longer,” said Ellen Douglas, a professor of hydrology and associate dean at the UMass Boston School for the Environment and another author of the report. “These are what we now expect to see.”


David Abel can be reached at david.abel@globe.com. Follow him @davabel.