Gulf of Maine Warming Update: 2024

Highlights from the Year

Annual Warming Trends in the Gulf of Maine

Since the early 1980s, the rate of warming in the Gulf of Maine 0.84°F / Decade has been more than triple that of the world’s oceans (0.3°F / Decade Figure 1).

The precise causes of the pronounced jump in annual average SSTs in the region from 2009 to 2012 remains an area of active research, but the sustained warm conditions suggest a regime shift in the influence of major ocean currents (i.e., Gulf Stream vs Labrador Current) in the Gulf of Maine.

While a long-term increase in SSTs is expected as a result of human-caused climate change, we also expect each year to be influenced by large-scale patterns of natural variability, particularly on sub-global (i.e., regional) scales.

SST conditions in the Gulf of Maine for 2024 retain the region’s distinction as being one of the fastest warming ocean regions on the planet; including the 2024 data shows that the Gulf of Maine is warming faster than 97% of the world’s ocean surface.

Figure 1: A timeseries of annual average sea surface temperature anomalies for the Gulf of Maine (solid black line) from 1982 through 2024, illustrating that 2024 was the 2nd warmest year on record. Long-term trendlines for the Gulf of Maine (blue) and the entire globe (green) show how much more quickly the Gulf of Maine is warming compared to the rest of the world.

Comparing Annual SST to Historical Conditions

The annual average SST in the Gulf of Maine for 2024 (51.51°F) places it as the twelfth warmest year on record (Figure 2). This marks the third consecutive year of year-over-year declines in average temperatures, while still comfortably seated +0.88°F above the long-term average.

Figure 2: A ranking of the top 10 annual SST values and those years’ respective SST anomalies.

Average Monthly Conditions

Monthly average SSTs (Table 1.) show how variable conditions were throughout the year. For the first third of the year, monthly SSTs were among the top three warmest for those months. May, June, July, & August average SSTs ranked lower, ranging from 4th to 12th warmest. The final four months were each much cooler, ranging from 12th to 19th warmest for those months.

Table 1:
Average monthly sea surface temperatures in the Gulf of Maine
Month	Warm to Cold Ranking (1982-2024)	Observed Temperature	Climatological Average	Temperature Anomaly
Table 1. Monthly Average Sea Surface Temperatures - 2024
January	25	42.6°F (5.9°C)	43.5°F (6.4°C)	-0.9°F (-0.5°C)
February	34	39.8°F (4.3°C)	40.9°F (4.9°C)	-1.1°F (-0.6°C)
March	16	40.7°F (4.8°C)	40.1°F (4.5°C)	0.6°F (0.3°C)
April	11	42.9°F (6.0°C)	41.8°F (5.5°C)	1.0°F (0.6°C)
May	8	48.1°F (8.9°C)	46.5°F (8.1°C)	1.5°F (0.8°C)
June	2	56.6°F (13.7°C)	53.5°F (11.9°C)	3.1°F (1.7°C)
July	11	61.9°F (16.6°C)	60.5°F (15.8°C)	1.4°F (0.8°C)
August	11	64.8°F (18.2°C)	63.2°F (17.3°C)	1.6°F (0.9°C)
September	10	62.8°F (17.1°C)	61.2°F (16.2°C)	1.6°F (0.9°C)
October	7	58.6°F (14.8°C)	56.7°F (13.7°C)	1.9°F (1.1°C)
November	16	52.2°F (11.2°C)	51.7°F (11.0°C)	0.5°F (0.3°C)
December	25	46.7°F (8.2°C)	47.5°F (8.6°C)	-0.8°F (-0.5°C)
Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data.
Climatological Reference Period: 1991-2020.

Daily SSTs in the Gulf of Maine

The annual cycle of SST in the Gulf of Maine exhibits a pattern common to regions in the Northern Hemisphere, with the lowest temperatures observed in March and the highest values observed in August (Figure 3). Daily SST anomalies in 2024 never fell below +-1.95 °F compared to the long-term (1991-2020) average and reached as high as high as 4 °F above the long-term average.

The largest temperature anomalies were observed during November, which also turned out to be the warmest November on record (as highlighted in our Fall 2022 update). Figure 3 also illustrates that, in 2024, 41 days experienced SST anomalies that exceeded the threshold for being considered marine heatwaves, or MHW (more on MHWs below, including Figure 5)

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.

SST Anomalis & MHW Events

A marine heatwave (MHW) is defined as a period when there are five or more consecutive days when the observed SST is greater than the 90th percentile of the long-term average for that day. Gaps of 2 days or less in this threshold do not constitute a break in the MHW event. Figure 3 illustrates that the Gulf of Maine met the criteria for experiencing a MHW for 41 days in 2024 (or 11% of the year). Superimposing MHW status (black line) over the full timeseries of daily SST anomalies (blue/white/red shading) (Figure 3) reveals that the frequency, duration, and intensity of MHWs has increased in the past decade.

Figure 4: A timeseries of marine heatwave (MHW) conditions in the Gulf of Maine extending from January 1, 2024 through December 31, 2024. The black line represents the long-term (i.e., 1991 – 2020) average SST. The 10th to 90th percentile range is shaded in gray. The heavy line (red for marine heatwave or blue for a non-event) indicates the observed SST this year.

Gulf of Maine SST Heatmap

Since 2010 the Gulf of Maine has experienced a disproportionate number of anomalously hot SSTs and prolonged MHW events. Cooler than average SSTs during this period are rare, but examples of cooler periods can be found (ex. 2019).

A figure displays the temperatures for each day of year as a colored stripe, organized with a row for each day such that the day of year aligns vertically. The lower two-thirds has a roughly equal balance between colors for warm (red) and cold (blue) temperature anomalies. The top third of the image is almost completely red as temperature anomalies rarely fall below the long-term average. Black dots are overlaid onto days that meet the criteria for a heatwave, they are rare in the lower section and common in the red section. — Figure 5: 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 and duration of marine heatwave events (black lines) in the Gulf of Maine has become more pronounced in the past decade.

Quarterly SST Trends

Zooming in to sub-annual timescales reveals some interesting patterns: the observed rate of warming in the Gulf of Maine varies throughout the year. Comparisons across the four quarters of the year (Figure 6) reveal that the Gulf of Maine is warming fastest during July-September (~4x the global ocean average)—almost twice the rate seen during January-June (~3x the global ocean average).

Figure 6: 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 (blue) and the global ocean surface (green).

Annual SST Anomaly Map

In addition to the sub-annual (or temporal) variation, there can also be significant spatial variability in annually-averaged SST patterns (Figure 7).

This year the impacts of large-scale variability in major oceanic currents, such as the relative influence of the Gulf Stream versus the Labrador Current was quite apparent. With large pockets of above and below average SST anomalies present along the turbulent path of the Gulf Stream to the South of our study area.

Figure 7: Map of annual average sea surface temperature 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 SST Maps

Looking at these spatial patterns across the annual quarters of 2024 (Figure 8) shows not only the large spatial variability in SST conditions, but also the significant variation in those patterns over the course of the year.

Figure 8: Four-panel maps displaying the quarterly average SST anomalies in 2024.

North Atlantic Record SSTs

In a departure from the now-familiar pattern of regionally concentrated warming, much of the attention this year was on large areas in the eastern Atlantic experiencing a large-scale MHW event. This summer scientists sounded the alarm over record setting temperatures for much of the Eastern Atlantic impacting population centers along the European coast and contributing to sweltering temperatures on land.

By June and July, the separation between the region’s SSTs and the previous records had widened by over a degree, creating a dramatic and alarming figure that was shared widely on social media. Figure 9 captures how profoundly and consistently hot this year’s temperatures were across the North Atlantic.

Figure 9: Timeseries for each of the three years that hold record daily SSTs for the North Atlantic (2020 = light green, 2022 = blue, 2024 = orange), record setting SSTs shown in bold. The 1991-2020 average daily SST (black) and 10th - 90th percentile range is shown in gray.

Changes in a Global Context

It was not just the Gulf of Maine that experienced exceptional warmth in 2024. Globally, 2024 was the warmest year for both sea surface temperatures and combined land & ocean temperatures.

Figure 11 shows annual average SST anomalies for oceans all over the world in 2024. From this view we can see how much of the Southern Ocean and expanses of the southeastern Pacific were anomalously warm (a general feature of El Niño conditions). Closer to home here in the United States, we see both unusually high and unusually low SSTs along the Gulf Stream’s path as it extends East away from Cape Hatteras.

Global SST

Figure 10: Map of annual average sea surface temperature for the world’s oceans in 2024.

Global SST Anomalies

Figure 11: Map of annual average sea surface temperature anomalies for the world’s oceans in 2024.

Percentile Warming Ranks

Expert Insights and Emerging Questions

Oceanic conditions in the Gulf of Maine are known to be influenced by shifts in the position and flow of major ocean currents systems. Elevated sea surface temperatures of the past decade are believed to be in-part a product of an increased influence from the Gulf Stream, the major warm-water current flowing North-West off the east coast of the US.

Northward shifts in this current influences Gulf of Maine conditions by increasing warm-water inflow into the region directly and by obstructing the flow of cold water flowing South from Nova Scotia and the Labrador Current.

The push-and-pull between the two water masses, and ultimately the relative inflow from each source, can produce large swings in temperature, salinity, nutrient/mineral concentrations, and stratification patterns for the region.

Gulf of Maine Bottom Temperatures

Scientists following bottom temperature changes in the region have raised the notion that changes to bottom temperature may be a useful early-warning system for changes in the relative influence of major ocean currents.

Bottom temperatures are less directly impacted by local weather systems and can in some applications provide a more clear view interactions between different water masses.

Bottom Temperatures from Buoys

Bottom Temperature Reanalysis

Bottom temperatures are not as easily observed or directly measurable, and for tracking broad-scale changes researches rely on modeled data known as ocean reanalyses.

Regional Bottom Temperature Maps

From an overhead perspective, sea bottom temperatures shifted to cooler temperatures during the Fall of 2023. Bottom temperature anomalies reveal that below average temperatures were concentrated along the shelf break and the Northeast Channel, and extended as far south as off the coast of Maryland.

Sea bottom temperature anomalies during 2024 reveal that the below-average temperatures became more widespread, with above average sea bottom temperatures concentrated along more near-shore areas.

The difference in bottom temperatures between these two years shows us that sea bottom temperatures fell broadly, and for many areas this difference was several degrees (C).

Gulf Stream Positioning

The Importance of the Gulf of Maine Region

For analyses like these that characterize environmental conditions for a particular area—in this case, the Gulf of Maine—it is important to be clear about the spatial extent that defines the region of study; different domain boundaries could produce different results. The spatial area we use to define the “Gulf of Maine” is displayed in Figure 13, and has remained consistent throughout our seasonal and annual warming updates.

An overhead view of the Gulf of Maine region. Landmasses and political boundaries for the United States and Canada are displayed. A blue dotted line outlining a box with a transparent blue fill is shown to demark where satellite data for the analysis has been used. — Figure 13: Spatial domain used for Gulf of Maine SST analyses. Dashed line denotes the region of study for this analysis. Depth contours are colored at 100m intervals to a maximum of 600m, deeper blues indicate deeper water depths.

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.

NOAA High Resolution SST data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html.

Recommended Citation:

Gulf of Maine Research Institute. 2024. Gulf of Maine Warming Update: 2024. https://gmri.org/stories/warming-22

A work by Adam A. Kemberling

Akemberling@gmri.org