Sea Surface Temperature

The Sea Surface Temperature (SST) of the ocean is indicated by measurements taken at depths that range from 1 millimeter to 20 meters. Some measurements are made using shipboard instruments, but satellites now provide the majority of global SST data.

The primary cause of rising SST levels worldwide is climate warming due to excessive amounts of greenhouse gases being released into the atmosphere. Heat from the warming atmosphere raises the temperature of the sea surface. Downwelling currents convey some of this heat to the ocean’s deeper layers, which are also warming, though lagging far behind the rise in SST.

Water expands as it warms and the increased volume causes sea level rise. Climate warming also melts glaciers and continental ice caps, adding water to the ocean and further increasing sea level rise. The rate of global sea level rise has accelerated  over the past few decades.

According to the Intergovernmental Panel on Climate Change (IPCC), global sea surface temperatures are expected to rise by approximately 0.4 – 1.1°C by 2025.

Thermal expansion and the increased supply of meltwater from glaciers and continental ice caps could contribute a 1m-3m sea level rise by the end of this century (Dasgupta 2007).

Which Goals Does This Affect?

How Was It Measured?

This measurement does not indicate absolute temperature at a location, but instead determines the number of positive temperature deviations (anomalies) that exceed the natural range of variation for a given location, i.e. the frequency with which a location experiences unnaturally warm temperature. 

The reason for evaluating SST change is that species are adapted to their natural range of temperatures and the number of times that temperatures exceed that range provides a globally consistent proxy for likely SST impacts.

All pressures have different affects on different goals. For each goal, the affect of each pressure is weighted 'low' (1), 'medium' (2) or 'high' (3). The actual data-derived value of the pressure is then multiplied by the weight assigned to it for that goal. That process is repeated for each pressure-goal combination. The sum of those values divided by 3 (the (the maximum pressure-goal value) expresses the total affect of that pressure on the goal.

Sea surface temperature has high effect (weight = 3) on Natural Products (Coral), Coastal Protection (Coral and Sea Ice), and Biodiversity (Habitats- Corals and Sea Ice). It has medium effect (weight=2) on Carbon Storage (Seagrasses), Coastal Protection (Seagrasses), and Biodiversity (Habitats-Seagrasses). It has low effect (weight=1) on Natural Products, Livelihoods and Economies (Aquarium Trade), Sense of Place (Iconic Species), and Biodiversity (Species). 

What Are The Impacts?

Sea Surface Temperature (SST) in Relation to Air Surface Pressure and El Nino Southern Oscillation (ENSO)
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Changes in sea surface temperatures are affecting migration and distribution patterns for many marine species.

Changes in climate and SST affect ecosystems by altering species distributions, food webs,  predator/prey relationships and the reproductive timing and success of species.

A rise in SST can lead to the death of organisms unable to adapt to the change in temperature or migrate to new habitats. For example, corals that are exposed to elevated temperatures expel the symbiotic photosynthetic algae (zooxanthellae) responsible for their nutrition and coloration  in a process known as coral bleaching. Corals can recover if temperature returns to normal, but not if it remains high.

Within two or three decades, SST will cause about 50% of tropical coral reefs globally to have severe bleaching in most years.  Within four decades this will increase to 95%. Corals can recover from mild, infrequent bleaching, but projected high frequency and intensity of bleaching may cause irreversible damage (Burke et al. 2011).

Ocean acidification, also caused by rising levels of CO2, reduces corals’ ability to form and maintain their calcium carbonate skeletons.  Within two or three decades, acidification will compromise growth in half of the world’s tropical coral reefs. Within four decades, 85% of reefs may be compromised (Burke et al. 2011).

Local threats combined with SST and acidification will likely threaten more than half of all reefs within two or three decades and 90% of reefs by 2050 (Burke et al. 2011).

A rise in sea level will reduce the area of any salt marshes and or mangrove forests that cannot retreat landward, compromising their ability to store carbon, protect coastlines, enhance biodiversity and act as nursery areas for fisheries.
As SST increases, sea levels are subject to rise due to thermal expansion and the melting of glaciers and ice caps. Sea level rise will be most apparent in locations that are subsiding geologically and less apparent in locations subject to geologic uplift.

The rate of global sea level rise has increased over the past few decades. In many areas sea level rise will increase the rate of coastal erosion and flooding. Saltwater will contaminate coastal groundwater, jeopardizing water sources used for drinking and agriculture.  In some areas surface waters used for growing crops may also be contaminated with salt. 

Fluctuations in SST have caused a shift in habitat ranges for some potentially harmful marine species, driving them toward populated coastlines and forcing a reassessment of beach practices and usage (e.g. venomous jellyfish (Pelagia noctiluca) in Great Britain, Portuguese Man-of-War in the North Atlantic).

Such problems will affect some of the world's major population centers, because 17 of the world’s 30 largest cities are located in low-lying coastal regions (FitzGerald 2008).
Increased coastal erosion and flooding associated with SLR may bring enormous social and economic costs for coastal nations, cities and residents, including damage or destruction of roads, railroads, airports, subway systems and buildings, and damage to sewage and water systems.

Some low-lying island nations and coastal zones may need to be permanently evacuated, resulting in many ‘sea-level refugees' who will need to relocate.

Total global damage costs due to sea-level rise of 1 meter could amount to at least one or two trillion USD (Anthoff 2010; Sugiyama et al. 2008).

Numerous species of commercial fish have undergone range shifts as a result of changes in SST (e.g. North Sea cod).

Warming SST in the southern portion of the North Sea decreased the quality and quantity of plankton for food available to larval cod populations. This, and other temperature effects, will cause cod populations to shift northward to cooler, more productive locations (Kirby and Beugrand 2009).

A fluctuation in sea surface temperatures has a direct impact on climate conditions, because SST, in conjunction with air surface temperatures, can create of intensify extreme weather patterns (e.g. El Niño/La Niña-Southern Oscillation [ENSO]) that result in significant economic and agricultural loss.  These weather patterns are expected to become more frequent if climate change induced SST continues to increase.

On average, El Niños result in agricultural losses approaching US $2 billion, or nearly 1-2 percent of total crop output. In the 1997-98 El Niño, property losses were estimated at nearly US $2.6 billion (NOAA Magazine 2002) 

What Has Been Done?

Get More Information 

United States National Oceanic and Atmospheric Administration (NOAA)    
Keep track of regularly updated regional Sea Surface Temperature (SST) contour charts and field data.

NASA Jet Propulsion Laboratory - California Institute of Technology
Check daily, global, SST data sets through the Physical Oceanography Archive.

Intergovernmental Panel on Climate Change (IPCC) 
Endorsed by the UN and established by the United Nations Environment Program (UNEP) and the World Meteorological Organization (WMO), the IPCC provides information and ideas for policy makers on how to mitigate the effects of climate change. 

United States National Oceanic and Atmospheric Administration (NOAA)
This interactive map provides regularly updated sea level rise trends within the United States.

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PHOTO(S): © Keith A. Ellenbogen
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