By Dr. Rob Moir, a nationally recognized and award-winning environmentalist

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. Below is the most recent chart for June 2024.

The dark blue waters were 32 to 41 degrees F.  The light blue was 54 degrees F. The green water in Massachusetts Bay was about 65 degrees, and the yellow water south of Cape Cod was 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 cool from 65 degrees by the shore to 54 degrees in the Atlantic.

Monthly Changes, Long-Term Impact

These temperatures vary by month during the year. In the next image, from NOAA, the top row shows the sea surface temperatures for April, marching back in time from 2024 to 2020. The maps of the Northeast show how much precipitation varies in the Gulf of Maine watershed. The largest river is the St. Johns, which drains the northern tip of Maine. April 2024 was the driest month, and April 2020 was the wettest. Daytime monthly average temperatures are presented. The chart at the bottom shows the 30-year average of right whale density for April. In the spring, we see slight variations in sea surface temperatures, much variation in rainfall, and little change in air temperatures. Right whales are increasing, particularly in Cape Cod Bay and Nantucket Shoals.

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

The lighter blue shown below indicates warmer surface waters (54 degrees F). The year 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 inland heat severity over the last five years below. This image shows a combination of air and land heat averages. When yearly average temperatures are above normal or approaching dangerous levels, heat is presented in bright red.

The severity of heat has increased dramatically since 2019, especially from 2022 to 2023—hot temperatures peak in the summer. As the temperature rises inland, the Gulf of Maine absorbs more heat.

By June each year, the Gulf of Maine’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.

In July, warmer surface water spread further across the Gulf of Maine. The black splotches represent a lack of data, likely due to fog and low cloud cover.  2023 was a record precipitation year, with the most rainfall since 1955. It is also the first year with orange (81 degrees F).

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

It’s in the later months of the year that the evidence of warming during summer demonstrates the long-term impact on Gulf of Maine. October 2021 saw much precipitation and warm sea surface temperatures and 2019 saw much precipitation but not as great a rise in water surface temperatures. The heat severity map shows that even though it rained a lot in 2019, water temperatures were not affected, as the heat severity was significantly lower in 2019. The temperature on the land around the Gulf was the deciding factor in surface water temperature.

The warm waters of the Gulf Stream were mapped on the lower right corner for some years and not others.  The Gulf Stream meanders to dissipate energy as it flows northwards. How close it comes to the Gulf of Maine varies monthly.

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 during the summer months. In October 2019, there was lots of rainfall and little change in surface water temperature. This was due to low land surface temperatures.

One Surprising Fix

New England’s seasons vary significantly in rainfall and heat severity. Increased air temperatures have led to high land temperatures. More rainfall, particularly on hot impervious surfaces, flows to spread more freshwater across the salty sea’s surface to warm 97% faster than the world’s oceans.

To cool the Gulf of Maine, we only need to reduce the amount of water running off the land. Slowing the flow retains more water to infiltrate into the land. Moist soils enable plants to grow and draw down more carbon. By increasing the amount of green vegetation and restoring healthy soils, the burden of carbon dioxide in the atmosphere is lessened. The Gulf of Maine will no longer be heating faster than 97% of the world’s oceans.

About the Author

Dr. Rob Moir is president and executive director of Cambridge, MA-based Ocean River Institute, a nonprofit that provides expertise, services, resources, and information unavailable on a localized level to support the efforts of environmental organizations. Please visit www.oceanriver.org for more information.