None of us are strangers to the reports of the Gulf of Maine heating 97% faster than the world’s oceans. However, the actual reasons for this can be lost in the constant headlines about global warming and rising greenhouse gases. To explain this extraordinary phenomenon, let’s look closely at four factors: surface seawater temperatures, heat severity, air temperature, and rainfall, monthly for five years.

The National Oceanic and Atmospheric Administration (NOAA) produces a monthly chart of sea surface water temperatures.  Here is June 2024.  The dark blue waters are 32 to 41 degrees F.  The light blue is 54 degrees F.  The green water in Massachusetts Bay is about 65 degrees, and the yellow water south of Cape Cod is around 70 degrees F.  Note that the surface water in the Gulf of Maine does not have one temperature.  Water temperatures across the sea’s face slide from 65 degrees by the shore to 54 degrees in the Atlantic.

Here are the charts for January:

The top row are the sea surface temperatures for January marching back in time from 2024 to 2020.  The black splotches represent a lack of data. Likely due to cloud cover for much of the month. The maps of the Northeast show precipitation with January 2022 being the driest month and January 2023 the wettest. The chart at the bottom shows the thirty year average of right whale density for January with the greatest number of whale on Nantucket Shoals far off Cape Cod’s Southeast.

Moving on to February, March, and April:

In the spring, we see little variation in sea surface temperatures, much variation in rainfall, and little in air temperatures. The right whale numbers are increasing, particularly in Cape Cod Bay.   

May is where we begin to see the surface temperature start to warm. 

The lighter blue indicates warmer surface waters (54 degrees F). 2024 shows the warmest waters and the most precipitation. Some may think that rising air temperatures are warming the seas. However, I want to draw your attention to this map of heat severity over the last five years.

This shows a combination of air and land heat averages. When yearly average temperatures are above normal, approaching dangerous levels, heat is presented in bright red colors.

The severity of heat has increased dramatically since 2019, especially from 2022 to 2023. Heat severity peaks in the summer. 

Moving onto June:

In June, the GOM’s surface temperatures by the shore were warmer, reaching 65 degrees F. This aligns with the heat severity map. It’s not surprising that there is a lot of heat around Boston. Increased precipitation resulted in increased surface water temperature. 

2020 was the driest month and had the coolest surface water temperatures.

Moving onto July. The time frame has shifted a year from July 2023 to 2019.

In July, warmer surface water spread further across the Gulf of Maine. 2023 was a record precipitation year, the most rainfall since 1955.  2023 is also the first year with orange (81 degrees F). 

July sees hot air temperatures, but this does not warm surface water temperatures. 2019’s air temperature was 78 degrees F, which was cooler than in 2023, a year when the air temperature was 74 degrees F.

August

In August, warm waters between 77 and 81 degrees covered more of the Gulf of Maine. The right whales have left the Gulf of Maine and Nantucket Shoals. 

September

September had many variations. 2022 was the warmest and wettest month, while 2023 and 2020 were cooler and drier.  

Moving onto October:

October in 2021 had much precipitation and warm sea surface temperatures. 2019 had much precipitation but not as great a rise in water surface temperatures. The heat severity map shows even though it rained a lot in 2019, water temperatures were not affected, as the heat severity was significantly lower in 2019.  Land temperature was the deciding factor in surface water temperature. 

November 

In November, 2023 was the coolest and driest month.

Onto December.

For December, 2021 was the warmest and wettest month.

In July, more notable than in other months, increased precipitation resulted in warmer surface waters. Land temperatures increase with air temperatures. With increased precipitation, more water runs off the land. Heated land surfaces are a factor. In October 2019, there was lots of rainfall and little change in surface water temperature. This was due to low land surface temperatures.

New England’s seasons vary greatly in rainfall and heat severity. In the Gulf of Maine, increased air temperatures have led to high land temperatures and precipitation, which has resulted in increased surface water temperatures. To cool the Gulf of Maine, we must reduce the amount of water running off the land. 

Written by Lindsey Parziale, ORI Summer Intern.