A lobster boat heads out to sea at sunrise off shore from Portland, Maine in this Sept. 13, 2017 file photo. Data collected last month by scientists at Gulf of Maine Research Institute show that the gulf had its hottest average daily temperature ever recorded on Aug. 14, 2020. Temperature data show that in the past 10 years heatwaves have become the norm in the Gulf of Maine, which is one of the fastest warming parts of the oceans in the world. Credit: Robert F. Bukaty | AP

Join the BDN for the second event in its Climate Conversations series on Thursday at 4 p.m., when the topic of discussion is “A Warming Gulf of Maine and our Marine Economy.”

In the latest sign that climate change is already affecting the ocean along the Maine coast, scientists last month recorded the hottest single day in the waters of the Gulf of Maine.

The average of surface temperatures taken throughout the day on Aug.14 in the Gulf of Maine, one of the fastest-warming marine bodies of water on Earth, was measured at 69.85 degrees Fahrenheit, according to the Gulf of Maine Research Institute. Because it takes a few weeks for scientists to analyze the data after the numbers come in, researchers at GMRI only realized this week that it marked a new record.

The prior record, less than a degree lower than the record set last month, was 68.99 degrees Fahrenheit on Aug. 23, 2012. The records date back to 1982, when scientists began collecting satellite data on the gulf’s surface temperature.

In addition to recording the highest single-day average temperature in the gulf, the data show that a four-day period from Aug. 13 through 16 — which includes the new single-day record — is the warmest four-day period ever recorded in the gulf.

To determine the gulf’s average temperature, scientists use readings taken by various methods, at multiple locations, and at different times of day. Most of the surface temperature readings are obtained via satellites, but relative heat measurements also are obtained via buoys, aquatic gliders, and ships, and other means, according to Kathy Mills, a research scientist at GMRI.

The data reflect a trend that shows temperatures in the gulf have been increasing sharply overall for the past decade. From mid-January through early March of this year, average daily temperatures in the gulf were higher than 90 percent of the averages from each corresponding calendar date from 1982 through 2011, a metric that defines it as a “heatwave day.”

The effects of climate change in Maine have already been seen through shorter periods of winter ice covering the state’s lakes, larger lobster hauls moving east toward cooler waters, and the virtual disappearance of northern shrimp from the gulf, to name a few examples.

Average temperatures fell back toward normal in the spring, but from June through at least mid-August, the gulf has seen another heatwave, according to GMRI scientists. As of Aug. 13, 102 of the first 226 days of 2020 were considered heatwave days, Andrew Pershing, GMRI’s chief scientific officer, wrote in a blog post.

The hottest year on record in the gulf was 2012, when all but eight days that year were heatwave days, and high temperatures caused catches in Maine’s spring baby eel fishery to soar. In the past 10 years, 2019 has been the coolest year in the gulf, with 2017 the next coolest.

Overall, in recent decades the Gulf of Maine has been warming faster than 99.9 percent of the world’s oceans, according to previous scientific reports. In a paper published last year, scientists said water deep in the Gulf of Maine has been warming twice as fast as the surface over the past 15 years.

“Since 2010, the temperature in the Gulf of Maine has been above average 92 percent of the time,” Pershing wrote in a blog post about last month’s heat data. “It’s been at heatwave levels for 55 percent of the time. Whether it’s the temperatures alone, or some of the species that come with them (e.g. recent reports of black sea bass and bonito), observations that would have surprised us a decade ago now feel expected.”

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Bill Trotter

Bill Trotter

A news reporter in coastal Maine for more than 20 years, Bill Trotter writes about how the Atlantic Ocean and the state's iconic coastline help to shape the lives of coastal Maine residents and visitors....