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Boston reaches 13th day of temperatures 90 degrees or above this year

A person cooled off by the waterfront in East Boston during the June heat wave.
A person cooled off by the waterfront in East Boston during the June heat wave.David L. Ryan/Globe Staff

Wednesday marked the 13th day this season of temperatures reaching 90 degrees or above in Boston, according to data collected by the National Weather Service.

The milestone comes relatively early in the year following multiple heat waves that have hit the Boston area.

On June 30, Boston hit 100 degrees for the first time in 10 years, smashing a previous record for the day, and the month as a whole was the hottest June ever recorded. The National Weather Service began recording local temperatures in 1871.

Though it’s only early July, Boston looks set to easily pass last year’s tally of 15 days of 90 degree temperatures or above. 1983 still holds first place for the most 90-degree days in Boston at 30.

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According to the Climate Projection Consensus, developed by the City of Boston and a team of the region’s top climate scientists, these hotter temperatures will increase in frequency as the effects of human-induced climate change become more apparent.

Temperatures in the northeastern United States have already increased by almost two degrees Fahrenheit between 1895 and 2011. According to the consensus, there may be as many as 40 days over 90 degrees by 2030 and 90 days by 2070 — nearly the entire summer.

In addition, heat waves will become more common, last longer, and be more intense. The City of Boston defines heat waves as “periods of three or more days above 90 degrees.” Heat waves are currently a leading cause of weather-related mortality in the United States.

Compared to the period from 1971 to 2000, when an average of 11
days per year were over 90 degrees, there may be as many as 40 days over 90 degrees by 2030 and 90 days by 2070 — nearly the entire summer.
Compared to the period from 1971 to 2000, when an average of 11 days per year were over 90 degrees, there may be as many as 40 days over 90 degrees by 2030 and 90 days by 2070 — nearly the entire summer.Boston Research Advisory Group (BRAG)

Maria Elena Little Endara can be reached at mariaelena.littleendara@globe.com.