Weather

The past three weeks have been the warmest ever recorded in Boston

Boston Weather
Pat Greenhouse/Globe Staff

Monday marked the seventh day of a major heat wave, the second of the summer across southern New England. The unrelenting heat and humidity have taken their toll on our collective mood as this is not normal summer weather in our part of the country.

The past three weeks have seen the warmest 21 days ever recorded in 151 years of records in Boston, similar to temperatures in Missouri or North Carolina where this type of heat and humidity is expected. Coupled with growing drought, damage to plants has spread from wilting flower boxes to struggling trees and shrubs. Drought is actually not increasing in New England but in a warmer climate, the impact of even semi-regular droughts can be greater when accompanied by hotter air.

The past three weeks have brought the warmest average temperatures, both day and night, ever recorded during that timespan in Boston. – NOAA

These types of hot and dry weather events are ripe for all sorts of hyperbole. On one end of the spectrum, you’ll find people saying we’ve had hot and dry weather before and this is more of the same. Other people will claim the past three weeks is yet more evidence of climate change in action.

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After tomorrow the heat will break and eventually the humidity will as well. I expect we’ll also have numerous showers although the drought could linger well into the fall.

When summer is over, we will have another opportunity to fully analyze the statistics, but already a few things are true. In addition to the extreme temperatures, we are experiencing the longest stretch of 80 degree or above weather on record —Tuesday will be the 26th day in a row of temperatures that are 80 degrees or higher.

What is also true is that the changing climate means these types of hot weather events become more likely to occur, and when they do, the upper limits of temperature, along with the length of time the heat lasts, are increasing. Warm records far outpace cooler ones and the gap is growing. This is clear from the two graphs below.

This graph shows the percentage of the land area of the contiguous 48 states with unusually hot daily high and low temperatures during the months of June, July, and August. The thin lines represent individual years, while the thick lines show a nine-year weighted average. Red lines represent daily highs, while orange lines represent daily lows. The term “unusual” in this case is based on the long-term average conditions at each location. – NOAA
This graph shows the percentage of the land area of the contiguous 48 states with unusually cold daily high and low temperatures during the months of December, January, and February. The thin lines represent individual years, while the thick lines show a nine-year weighted average. Blue lines represent daily highs, while purple lines represent daily lows. The term “unusual” in this case is based on the long-term average conditions at each location. – NOAA

I see people point out how there are still older, warmer records in the books. This is a flawed way of looking at our unambiguous warming trend. As an example, no one would say that life expectancy hasn’t increased over the past 25 years just because Jean Calment’s record of living to 122 hasn’t been broken yet.

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With the current accelerating warming, all the high-temperature records across the globe will likely be broken in the coming decades as well Calment’s. Outliers are interesting and make for good headlines, but they don’t tell us anything about a trend as long as they’re outliers.

Maximum summer temperatures show a clear trend that is accelerating over time. – NOAA

The heat will abate later this week, but these past three weeks of unprecedented warmth should be a wakeup call to what lies ahead. The number of hot days will continue to go up, and everything that goes along with this type of heat will continue to be amplified.

Daily Local Weather Forecast

  • Today September 25
    Partly sunny with showers
    Partly sunny with showers
    70° 61°
  • Mon September 26
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    74° 58°
  • Tue September 27
    Intermittent clouds
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  • Wed September 28
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  • Thu September 29
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  • Fri September 30
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    60° 47°
  • Sat October 01
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    63° 51°

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