Detrimental Impacts of Rising Sea Temperatures Build Up
November 19, 2020
Living in Rhode Island, we are aware how the ocean rules our weather. What is less well known is that climate change is fundamentally altering the waters off our coast.
The image above shows how the January temperature of the ocean off the coast of southern New England has changed since 1980. For example, vast areas of dark blue — representing temperatures around 41-43 degrees Fahrenheit — have shrunk and are now a lighter blue, representing temperatures around 43-45 degrees.
The effects of a temperature rise in the ocean are significantly different from a temperature rise over land. We experience this difference when we walk across a sandy beach on a hot day. Exposed to the same sunlight, the sand burns our feet while the ocean warms gradually to the perfect temperature for a summer swim.
Rhode Island’s climate is moderated because the ocean takes longer than the land to heat up over the summer and longer to cool down during the fall.
The global impact of this effect is shown in the image below, which shows that, over recent decades, the continents have warmed much more rapidly than the oceans. The Earth’s land areas were 1.4 degrees Celsius (2.5 degrees Fahrenheit) warmer than the 20th-century average, while the oceans were 0.8 degrees Celsius (1.4 degrees Fahrenheit) warmer.
Unfortunately, the ocean’s smaller temperature rise isn’t good news, because the oceans can store more than four times as much heat as the land.
Even though ocean temperatures havve risen less than the land’s, it’s becoming clear that the impacts of climate change depend on a complex interaction between dry land and the warming ocean.
Ships and buoys have been recording sea surface temperatures for more than a century. International cooperation and sharing of data between nations has created a global database of sea surface temperatures going back to the middle of the 19th century.
In addition, modern satellites remotely measure many ocean characteristics over the entire extent of the Earth’s oceans. The data are now so accurate that it’s possible to detect the small temperature rise from ships’ propellers as they traverse the oceans.
The warming of both the land and the oceans is caused by rising levels of atmospheric carbon dioxide. When CO2 dissolves in the ocean, it forms carbonic acid, which in turn, breaks into hydrogen and bicarbonate ions. Clams, mussels, crabs, corals, and other sea life rely on those carbonate ions to grow their shells.
In 2015, Mark Gibson, deputy chief of marine fisheries at the Rhode Island Department of Environmental Management, noted that ocean acidification is a “significant threat” to local fisheries.
In fact, a study published in 2015 found that the Ocean State’s shellfish populations are among the most vulnerable in the United States to the impacts of acidification.
In polar regions like Alaska, the ocean water is relatively cold and can take up more CO2 than warmer tropical waters. As a result, polar waters are generally acidifying faster than those in other latitudes.
The water in warmer regions can’t hold as much CO2 and are releasing it into the atmosphere. Therefore, the acidification from carbon dioxide is damaging the oceans in both polar and equatorial regions.
Warming oceans are also changing the winds that whip up the ocean, resulting in upwells from deep waters that are nutrient-rich but also more acidic.
Normally, this infusion of nutrient-rich, cool, and acidic waters into the upper layers is beneficial to coastal ecosystems. But in regions with acidifying waters, the infusion of cooler deep waters amplifies the existing acidification.
In the tropics, rising temperatures are slowing down winds and reducing the exchange of carbon between deep waters and surface waters. As a result, tropical waters are becoming increasingly stratified and more saturated with carbon dioxide. Lower layers then have less oxygen, a process known as deoxygenation.
Warming ocean temperatures have also caused a rapid increase of toxic algal blooms. Toxic algae produce domoic acid, a dangerous neurotoxin, that builds up in the bodies of shellfish and poses a risk to human health.
In coastal areas, like Rhode Island, temperature changes can favor one organism over another, causing populations of one species of bacteria, algae, or fish to thrive and others to decline.
The sum of all these impacts is damaging to the Rhode Island economy. The state’s shellfish populations are already among the most vulnerable in the United States to the impacts of a warmer ocean.
Roger Warburton, Ph.D., is a Newport resident. He can be reached at email@example.com.
Figure 1 was generated using data from the Copernicus Climate Change and Atmosphere Monitoring Services (2020). The ERA5 dataset is produced by the European Space Agency SST Climate Change Initiative based on global daily sea surface temperature data from the Group for High Resolution Sea Surface Temperature and made available by the Copernicus Climate Data Store.
Figure 2 was generated using data from NOAA’s National Centers for Environmental information, Climate at a Glance: Global Time Series.