Boston Could Have Three Months Of 90 Degree Weather By 2100: Report

BOSTON — Greater Boston typically has between 8 and 10 days per year with temperatures over 90 degrees, but a new report from a group at the University of Massachusetts Boston says that number could rise to as many as 90 days per year within the century.

The report by the Greater Boston Research Advisory Group (GBRAG), was published Wednesday as a five-year update to previous climate research. It details projected changes to temperature, precipitation, sea-level and more over the next 100 years.

"We are proud to deliver these updated projections ... and are empowered by the opportunity to continue these critical updates every five years as we near targets and decisions on climate actions become more high-stakes," Paul Kirshen, a UMass Boston professor and co-lead for the report said.

GBRAG aims to give the 101 cities and towns that make up Greater Boston highly localized, relevant information about how our changing climate will affect their communities. Local changes in sea level, for example, can differ up to 30 percent from the global mean sea level, making relative sea level a much more effective measure when looking at the effect of sea level rise on a single city.

Temperatures aren't the only measures on the rise, according to the report. The relative sea level along the Massachusetts shoreline is rising faster than the global average. By 2100, the sea level around Boston will likely be about 3.4 feet higher than it was in 2000, but it could rise as much as 15.6 feet under the worst circumstances, the report found.

Each year, Boston will likely have more nuisance flooding days — or days in which the local flood threshold is exceeded for at least an hour — if greenhouse gas emissions keep rising. More significant floods, which now happen about once every 10 years, could happen annually by 2050, even with lowered emissions, the researchers said.

Changes to groundwater in coastal areas of Massachusetts could affect the quality and availability of drinking water, according to GBRAG. Over the next 50 years, groundwater will likely fluctuate with the seasons each year, but decrease overall by the end of the century. The change could mean less available drinking water.

The report's findings underscore the importance of reaching net-zero emissions by 2050, both in Boston and globally, to prevent catastrophic levels of warming and sea-level rise.

"We know that the window of time to act on climate change is closing quickly and it is critical to align our policies and programs with the latest science," Mayor Michelle Wu said in a statement. "The GBRAG report analyzes Boston's climate risk projections so we can make the most informed decisions on how to protect our communities."