2024 Gulf of Maine Warming Update

Reports | Feb 14, 2025

Over the past decade, our scientists have led a body of research that highlights the rapid pace of warming in the Gulf of Maine. To keep you informed, we share seasonal and annual updates about conditions in the Gulf of Maine.

2024 annual warming update feature image

The Gulf of Maine experienced its twelfth-warmest year in 2024. Sea surface temperature anomalies varied seasonally. below-average SSTs that began in 2023 gave way in 2024 to summer temperatures that rose above long-term averages. Cooler conditions returned again late in the year. The conditions seen in the Gulf of Maine were a departure from the record-setting temperatures seen elsewhere in the North Atlantic and across the world’s oceans.

Highlights from the Year

  • In 2024 the Gulf of Maine experienced its 12th warmest year on record with an annual average sea surface temperature (SST) of 51.51°F — more than 0.88°F above normal.
  • The warmest SST anomalies were concentrated in the summer and fall, with cold anomalies occurring in the winter months at the start and end of the year.

Annual Warming Trends in the Gulf of Maine

Average annual SSTs in the Gulf of Maine from 1982 – 2024 have been warming at a rate 0.84°F / Decade. This rate of warming is nearly triple that of the world’s oceans (0.3°F / Decade; Figure 1). An important aspect of the SST changes behind the rapid warming trend in the Gulf of Maine is a sudden increase in SSTs around 2010, and the extended period of high SSTs which followed.

Figure 1. A timeseries of annual average sea surface temperature anomalies for the Gulf of Maine (dotted black line) from 1982 through 2024, illustrating that 2024 was the twelfth warmest year on record. Long-term trendlines for the Gulf of Maine (orange) and the entire global ocean (blue) show how much more quickly the Gulf of Maine is warming compared to the rest of the world’s ocean surface.
Figure 1. A timeseries of annual average sea surface temperature anomalies for the Gulf of Maine (dotted black line) from 1982 through 2024, illustrating that 2024 was the twelfth warmest year on record. Long-term trendlines for the Gulf of Maine (orange) and the entire global ocean (blue) show how much more quickly the Gulf of Maine is warming compared to the rest of the world’s ocean surface.

Comparing Annual SST to Historical Conditions

The annual average Gulf of Maine SST in 2024 was 51.5°F, +0.88°F above the long-term 1991 – 2020 average. These conditions place the year at the 12th warmest year on record (Figure 2), and on the lower-end of the above-average SST years experienced since 2010.

Figure 2. The 15 warmest years in the Gulf of Maine, in order from warm to cold based on average annual SST. 2024 ranks number 12.
Figure 2. The 15 warmest years in the Gulf of Maine, in order from warm to cold based on average annual SST.

Average Monthly Conditions

Table 1 shows the average monthly conditions throughout the year, and how each month in 2024 ranks relative to the same month from all previous years (ranked from warmest to coldest). Winter months at both ends of the calendar experienced below-average temperatures in 2024. January, February, and December each experienced monthly SSTs -0.8°F or more below the long-term. SSTs in June were the second warmest on record with SSTs +3°F above the long-term average.

Table 1. Average monthly SSTs in the Gulf of Maine.
Table 1. Average monthly SSTs in the Gulf of Maine.

Daily SSTs and MHWs in the Gulf of Maine

Figure 3 shows daily SSTs and their positions relative to the long-term average and two percentile thresholds commonly used for identifying extreme events (e.g. heatwaves and cold spells). Marine heatwave events (MHW) are defined as periods of five or more consecutive days where observed SSTs are greater than the 90th percentile of the long-term average for that day. Gaps of two days or less in excess of this threshold do not constitute a break in the MHW event.

In 2024, SST anomalies ranged from as low as –1.95°F (below) and as high as +4.8°F (above) the 1991 – 2020 average, and most daily SSTs were within normal ranges (between the tenth & 90th percentiles of the 30-year reference period). SSTs at the start of 2024 were below the long-term average, but later shifted above the average for much of late spring, summer, and early fall. SSTs fell below the long-term average again as we progressed into winter.

Figure 3. A timeseries of daily SSTs (January 1 through December 31, 2024) with an indication of marine heatwave (MHW) conditions in the Gulf of Maine. Black lines represent the long-term (i.e., 1991 – 2020) average SST, the 10th percentile (i.e., cold spell threshold), and 90th percentile (i.e., heatwave threshold). A solid line indicates the observed SST for each day; red and blue shading illustrates whether each day is considered part of a MHW event.
Figure 3. A timeseries of daily SSTs (January 1 through December 31, 2024) with an indication of marine heatwave (MHW) conditions in the Gulf of Maine. Black lines represent the long-term (i.e., 1991 – 2020) average SST, the 10th percentile (i.e., cold spell threshold), and 90th percentile (i.e., heatwave threshold). A solid line indicates the observed SST for each day; red and blue shading illustrates whether each day is considered part of a MHW event.

This year the Gulf of Maine experienced two distinct periods of MHW conditions lasting for a total of 41 days (or 11% of the year). The first occurred over a period of 32 days which began at the end of May, the second lasting for a period of nine days during the fall. SST anomalies were highest during this spring MHW event. Daily SSTs fell below the long-term average at both ends of the year. SSTs fell below the tenth percentile of long-term SSTs on two brief occasions, but those conditions did not persist for the five-days needed to warrant a marine cold-spell distinction.

Heatmap of Temperature Anomalies and Heatwave Events

Figure 8 shows the balance between daily SSTs that were above (red) and below (blue) average conditions for each day of the year, and how that has changed since the 1980s. Superimposing MHW status (black line) over the full timeseries of daily SST anomalies (blue/white/red shading) (Figure 4) reveals that the frequency of MHWs has increased in the past decade.

Since 2010 the Gulf of Maine has experienced a disproportionate number of anomalously hot SSTs and prolonged MHW events, often in the late summer and fall. Cooler than average SSTs during this period are rare, but examples of cooler periods can be found (e.g., fall of 2018 leading into 2019).

Figure 4. Heat map of daily SST anomalies from the beginning of 1982 through the end of 2024. Not only do more large warm anomalies (darker reds) appear more frequently in recent years, but the frequency of marine heatwave events (black lines) in the Gulf of Maine has become more pronounced since 2010.
Figure 4. Heat map of daily SST anomalies from the beginning of 1982 through the end of 2024. Not only do more large warm anomalies (darker reds) appear more frequently in recent years, but the frequency of marine heatwave events (black lines) in the Gulf of Maine has become more pronounced since 2010.

Quarterly Warming Trends

Zooming in to sub-annual timescales reveals that the observed rate of warming in the Gulf of Maine varies throughout the year. Comparisons across the four quarters of the year (Figure 5) reveal that the Gulf of Maine is warming fastest during July –September, at a rate that is nearly four times faster than that experienced globally during the same months. In the other three quarters of the year, the warming rate of SSTs in the Gulf of Maine was around three times faster than experienced across the world’s oceans.

Figure 5. Timeseries panels of the annual averages of SST for each quarter (dashed black lines) in the Gulf of Maine. Trendlines are overlaid for the Gulf of Maine (orange) and the global ocean surface (blue).
Figure 5. Timeseries panels of the annual averages of SST for each quarter (dashed black lines) in the Gulf of Maine. Trendlines are overlaid for the Gulf of Maine (orange) and the global ocean surface (blue).

Annual SST Anomaly Map

In addition to variability in SST patterns throughout the year, there was significant spatial variability in annually-averaged SST patterns. This year, persistent below-average SST anomalies were present just beyond the shelf break, in the deeper waters extending from the Mid-Atlantic through the Scotian Shelf. SST anomalies over the shallower continental shelf areas were above the long-term average (Figure 6), but were mild in comparison to previous years. Below-average SSTs near the Northeast Channel and to the east of Nantucket near Nantucket Shoals were also persistent features in 2024.

Figure 6. Map of annual average SST anomalies in 2024. The box outlined by the black dashed line denotes the region of study for the analysis presented throughout this report.
Figure 6. Map of annual average SST anomalies in 2024. The box outlined by the black dashed line denotes the region of study for the analysis presented throughout this report.

Quarterly Average Maps

Looking at spatial patterns in SST anomalies across the quarters of 2024 (Figure 7) shows the large spatial variability in SST conditions, and how that spatial variability has changed over the course of the year. During the first quarter of 2024, a solid band of below-average SSTs extended from the Scotian Shelf down to the Mid-Atlantic. This cold-water mass also extended into the Gulf of Maine. During the second quarter, the waters over the continental shelf warmed to above the long-term average, but the adjacent off-shelf areas remained cold. Waters within the Gulf of Maine were above-average at this time. By the third quarter of the year, those below-average off-shelf areas had broken up, with pockets of cool water remaining locally off the Southern tip of Nova Scotia, East of Nantucket, and over the Mid-Atlantic continental shelf near New Jersey, Delaware, and Maryland. In the final quarter of 2024, water within the Gulf of Maine cooled, and below-average SSTs occurred over the Northeast Channel. A large mass of below-average SSTs also formed to the south and east of Georges Bank in the deeper waters off the shelf break

Figure 7. Four-panel maps displaying average SST anomalies during each quarter of 2024.
Figure 7. Four-panel maps displaying average SST anomalies during each quarter of 2024.

SSTs in the North Atlantic

In 2023, SSTs in the North Atlantic caught international attention, setting record high daily SSTs for much of the year. Similar record-setting SST conditions occurred across the North Atlantic again during 2024. North Atlantic SSTs were on average 1.6°F above the 1991 – 2020 baseline for the year, and on 194 days (53% of the year) daily SST values set record highs (Figure 8). 2024 would ultimately surpass 2023 as the hottest year on record for the North Atlantic region.

Figure 8. Average daily SSTs for the North Atlantic (0Âș - 60ÂșN, 0Âș - 80ÂșW) for the years 2023 (blue) and 2024 (orange). Record daily temperatures are highlighted by a thicker line width, all record daily temperatures for this region have occurred in this two-year period, and more than half of them during 2024.
Figure 8. Average daily SSTs for the North Atlantic (0Âș - 60ÂșN, 0Âș - 80ÂșW) for the years 2023 (blue) and 2024 (orange). Record daily temperatures are highlighted by a thicker line width, all record daily temperatures for this region have occurred in this two-year period, and more than half of them during 2024.

Gulf of Maine vs. Global SSTs in 2024

Global land and sea surface temperatures for 2024 were reported as the warmest on record (NOAA, Mercator Ocean, ECMWF), despite a transition away from El Niño conditions that are typically associated with above-average temperatures.

Figure 9 shows annual average SST & SST anomalies globally for 2024; the predominance of pinks and reds illustrates how the vast majority of the world’s ocean surface experienced above-average SSTs. Visible evidence of the transition away from the 2023 El Niño can be seen in the below-average SSTs in the eastern equatorial Pacific. In the Northern Pacific, a large region extending eastward from Japan stands out for its above-average temperatures in 2024.

Figure 9. Average annual SST anomalies globally for 2024.
Figure 9. Average annual SST anomalies globally for 2024.

Expert Insights and Perspectives

The Gulf of Maine is a dynamic environment, influenced by major ocean currents, as well as air-sea interactions. Our experts break down how these systems relate and contribute to warming or cooling in our region.

Atmospheric Conditions

The staff photo of Katie Giannakopoulos.
Katie Giannakopoulos Coastal Dynamics Research Associate

Understanding the interaction between the atmosphere and ocean is crucial for predicting climate patterns. One key example is the El Niño Southern Oscillation (ENSO), where a warming or cooling of sea surface temperatures in the tropical Pacific alters atmospheric circulation throughout the world. In New England, El Niño years (characterized by higher tropical Pacific SSTs) typically bring warmer air temperatures. However, beyond ENSO, the complexity of ocean-atmosphere interactions makes it challenging to determine cause and effect.

Clouds play a significant role in the Earth’s radiative budget. They reflect solar radiation back to space, but when cloud cover decreases, more sunlight reaches the ocean, contributing to warming. In 2024, cloud cover over the Gulf of Maine was 4 – 6% lower than the 1991 – 2020 average, likely intensifying ocean warming.

The impact of clouds on climate depends on their height. Low clouds are thicker, reflect more sunlight, and have a net cooling effect. High clouds, in contrast, are thinner and allow more sunlight to reach the surface. Additionally, high clouds trap outgoing longwave radiation, further amplifying warming.

Emerging research suggests that as the climate warms, high clouds may become more prevalent, intensifying ocean and atmospheric warming. It remains to be seen how these trends will shape the Gulf of Maine in the coming years, but continued monitoring will be essential for understanding these changes.

Figure 10. Cloud area fraction (the portion of each grid box that is covered by clouds) anomaly (x100; shading) from the European Centre for Medium-Range Weather Forecasts Fifth Reanalysis. The climatology is based on the 1991 – 2020 mean.
Figure 10. Cloud area fraction (the portion of each grid box that is covered by clouds) anomaly (x100; shading) from the European Centre for Medium-Range Weather Forecasts Fifth Reanalysis. The climatology is based on the 1991 – 2020 mean.

Ocean Currents

Adam Kemberling Quantitative Research Associate

The behavior of major ocean currents also plays a role in ocean warming. Two major currents influence the region’s ocean temperatures: the warm Gulf Stream and the cold Labrador Current. Scientists studying the warming of the Gulf of Maine and the surrounding region believe that changes in the positions and interactions between these two currents may help explain the rapid pace of warming here.

Around 2008 – 2010, warm water eddies associated with the Gulf Stream began obstructing the flow of the cold Labrador current near the Grand Banks, an undersea plateau off the coast of Newfoundland. A shift in the Gulf Stream position is thought to have contributed to this at-sea traffic jam. These changes reduced the supply of cold water flowing westward towards the Gulf of Maine, accelerating regional warming at paces beyond those experienced in other parts of the world’s oceans.

Scientists are now looking to bottom temperatures as a potential early-warning system for detecting changes in water mass composition. Unlike SSTs, bottom temperatures are less affected by short-term weather patterns and may provide clearer insights into the interplay between warm and cold water masses entering the Gulf.

Ocean observation buoys play a vital role in tracking these changes. Buoy M, deployed in Jordan Basin in 2003, has sensors extending to 250m depth, offering one of the best records of deep-water conditions. Data from this buoy show a clear warming trend beginning in 2010, mirroring surface temperatures. Recent preliminary data suggest bottom temperatures may be cooling again, possibly signaling a shift in ocean currents. Scientists continue to track these developments to better understand their implications for the Gulf of Maine ecosystem.

This is a still image depicting two major currents with arrows, the Gulf Stream which heads north, and the Labrador Current which heads south. The Gulf stream current is warmer water, and the Labrador current is colder, depicted by orange and blue hues, respectively.
Figure 11. Temperatures in the Gulf of Maine are shaped by the Gulf Stream, which brings warm water northward from the equator (depicted in orange), and the Labrador Current, which brings cool water from the north (depicted in blue). We are keeping a close eye on the interaction of these two major ocean currents and how they influence the Gulf of Maine.

A Note on Data Sources

The figures in this report are created using remotely-sensed satellite data as part of publicly funded research efforts. Satellite SST data was obtained from NOAA’s National Center for Environmental Information (NCEI), with all maps and figures displaying NOAA’s Optimum Interpolation Sea Surface Temperature Data.

Recommended Citation

Gulf of Maine Research Institute, 2025. 2024 Gulf of Maine Warming Update. https://gmri.org/stories/warming-24

The Gulf of Maine Region

For analyses like these, it is important to be clear about the spatial extent that “defines” the Gulf of Maine (Figure 12), as different borders could produce different results. The spatial domain we use as the “Gulf of Maine” is displayed below. This area is consistent with previous reports and publications GMRI has produced.

Figure 12. Spatial domain used for Gulf of Maine SST analyses. Depth contours colored at 100m intervals with all depths greater than 600m shown in dark blue.
Figure 12. Spatial domain used for Gulf of Maine SST analyses. Depth contours colored at 100m intervals with all depths greater than 600m shown in dark blue.

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