Gulf of Maine Warming Update
2021 is the hottest year on record.
Oceans are warming across the globe. Since water covers more than 70% of the Earth’s surface and can absorb heat easily, oceans have stored most of the excess heat caused by climate change. In fact, more than 90% of the heat from global warming has been absorbed by oceans.
Closer to home, The Gulf of Maine is a section of the Atlantic Ocean that stretches from the tip of Cape Cod to Nova Scotia. Historically known for its cold waters, the Gulf of Maine features high biodiversity and a rich history of productive fishing grounds. The watershed of the Gulf of Maine — the streams that and rivers that flow into it — includes the entire state of Maine and parts of New Hampshire and Massachusetts in the United States and Quebec, New Brunswick, and Nova Scotia in Canada. Many places far from the coast are connected to this body of water.
Climate change is having a particular impact on the Gulf of Maine as it is warming faster than most of the world’s oceans. In March 2022, the Gulf of Maine Research Institute announced their findings that 2021 was the warmest year on record in the Gulf of Maine.
The data visualizations below explain how 2021 was uniquely warm in the Gulf of Maine. Additionally, they explain how the year was also part of a warming trend in the region over the past 40 years and how that stacks up to warming in other waters around the globe.
The annual average sea surface temperature (SST) in the Gulf of Maine for 2021 was 54.1 °F. It was 4.17 °F above the long-term average from 1982 to 2011; this is known as the temperature anomaly.
This time series of annual average SST anomalies for the Gulf of Maine (solid black line) from 1982 through 2021.
Long-term trend lines 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.
Sea surface temperatures and temperature anomalies vary by location. This map shows the variation in SST anomalies across the Gulf of Maine. The box outlined by the black dashed line denotes the region of study for the analysis presented throughout this report.
The region southeast of Georges Bank, shown in dark red in the corner of the boxed area, experienced the highest SST anomalies in 2021. This area is particularly sensitive to variability in ocean currents as it lies close to both the Gulf Stream and the Labrador Current.
Comparing the record 2021 sea surface temperature to the next warmest years (top panel), the difference between the warmest five years may not seem so large.
Yet, when we compare the annual SST anomaly (bottom panel), it becomes clear just how unusually warm the Gulf of Maine was this past year.
The Gulf of Maine wasn't the only place that experienced exceptional warmth in 2021.
According to the National Oceanic and Atmospheric Administration (NOAA), 2021 was the 4th warmest year on record for the contiguous United States and the 6th warmest year globally .
This map shows annual average SST anomalies for oceans all over the world in 2021. While some areas, like the Southern Ocean parts of the Pacific Ocean, were cooler than usual, most of the world’s oceans experienced unusually warm temperatures in 2021.
This was particularly true for James Bay in Canada, the Labrador Sea, the Baltic Sea, and a swath from ~35 °N to ~45 °N across ocean basins — a region that includes the Gulf of Maine.
There is also much to learn by looking at SST more closely throughout the year.
The annual cycle of SST in the Gulf of Maine exhibits a familiar pattern with low temperatures in March and high temperatures in August.
This graph shows the record high daily SST in the Gulf of Maine for every day of the year. Record-breaking temperatures that were observed in 2021 are denoted with red dots; when a record-breaking temperature for a given day was observed in any other year, that daily record is in gray.
In total, there were 169 record high temperature days in the Gulf of Maine in 2021; a record high daily temperature was set on 46% of the days that year!
This bar plot displays all the record high daily SST in another way. It shows the percentage of days during each month in 2021 when a record-high temperature was observed in the Gulf of Maine.
Most of the record-setting high daily sea surface temperatures happened during cooler months. 100% (every day!) of October 2021 experienced a record high SST.
A marine heatwave (MHW) is defined as a period when there are 5 or more consecutive days when the observed SST is greater than the 90th percentile of the long-term average for that day.
In this graph, the long-term average is illustrated with the gray dashed line and the threshold for being a MHW day is illustrated by the dashed red line. The solid red line in the figure shows the observed SST for that day.
The Gulf of Maine met the above criteria for MHW status for 360 days in 2021. Additionally, successive heatwaves separated by a gap of two days or fewer are considered part of the same MHW. Because all of the stretches falling below this threshold lasted no longer than two days, the Gulf of Maine experienced a marine heatwave event that lasted the entirety of 2021 — a first for the region.
This heat map shows the trends in daily sea surface temperature anomalies in the Gulf of Maine since 1982.
Large warm anomalies (darker reds) appear more frequently in recent years. Additionally, the frequency and duration of marine heatwave events (black lines) in the Gulf of Maine has become more pronounced in the past decade.
Under historical levels of natural variability in the region, hot and cold SST anomalies tend to balance out within a year or over several years. What is being observed in the Gulf of Maine, however, is a loss of that balance: larger fractions of recent years are experiencing above average temperatures and cold spells are becoming vanishingly rare.
These maps illustrate how fast different areas of the Gulf of Maine (left) and the world’s oceans (right) are warming from 1982 through 2021.
Yellow areas indicate regions that are warming faster than 97.5% of the world’s oceans. Areas in black show regions where the warming rate over that time period is at or below the 80th percentile of warming rates across the globe.
GMRI research was the first to reveal that the Gulf of Maine has been warming faster than the vast majority of the world’s ocean. As of the end of 2021, the Gulf of Maine is warming faster than ~98% of the world’s oceans.
The reason why this is so important is because the rate of change can have profound consequences for the biology of individual species and for entire food webs.
