This graph shows how the average surface temperature of the world’s oceans has changed since 1880. This graph uses the 1971 to 2000 average as a baseline for depicting change. Choosing a different baseline period would not change the shape of the data over time. The shaded band shows the range of uncertainty in the data, based on the number of measurements collected and the precision of the methods used.
Data source: NOAA, 20166
Web update: August 2016
Oceans are at the brink
For decades, the ocean has been absorbing carbon dioxide dumped into the atmosphere by burning fossil fuels. It has also absorbed a lot of the extra heat produced by elevated atmospheric carbon dioxide levels.
But even the ocean has limits, and we are bumping up against them, with damaging consequences for the whole world. Even with its vast capacity to absorb heat and carbon dioxide, the physical impacts of climate change on the ocean are now very clear and dramatic. According to a 2016 report, temperatures in the shallowest waters rose by more than 0.1 degree Celsius (0.18 degree Fahrenheit) each decade between 1970 and 2010.
Here are five ways these warmer temperatures are affecting our oceans:
1. Coral bleaching
As early as 1990, coral reef expert Tom Goreau and I pointed out that mass coral bleaching events observed during the 1980’s were probably due to anomalously warm temperatures related to climate change.
Mass coral bleaching results in the starvation, shrinkage and death of the corals that support the thousands of species that live on coral reefs.
2. Fish migration
In addition, many fish species have moved toward the poles in response to ocean warming, disrupting fisheries around the world.
3. Drowning wetlands
Rising sea levels, partly the result of heat absorbed by the ocean, is also “drowning” wetlands. Wetlands normally grow vertically fast enough to keep up with sea level rise, but recently the sea has been rising too fast for wetlands to keep their blades above water.
Coral reefs and sea grass meadows are also in danger of “drowning” since they can only photosynthesize in relatively shallow water.
4. Ocean acidification
The ocean has absorbed about 30 percent of the carbon dioxide humans have sent into the atmosphere since the start of the Industrial Revolution – some 150 billion tons.
However, this great service, which has substantially slowed global warming, has been accomplished at great cost: The trend in ocean acidification is about 30 times greater than natural variation, and average surface ocean pH, the standard measure of acidity, has dropped by 0.1 unit - a highly significant increase in acidity.
This is damaging many ocean species that use calcium carbonate to form their skeletons and shells. Studies have shown that calcium carbonate formation is disrupted if water becomes too acidic.
Ocean acidification also appears to be affecting whole ecosystems, such as coral reefs, which depend on the formation of calcium carbonate to build reef structure, which in turn provides homes for reef organisms.
5. A disastrous positive feedback loop
Finally, acidification also appears to be reducing the amount of sulfur flowing out of the ocean into the atmosphere. This reduces reflection of solar radiation back into space, resulting in even more warming. This is the kind of positive feedback loop that could result in run-away climate change – and of course, even more disastrous effects on the ocean.
1. For example, see: Ostrander, G.K., K.M. Armstrong, E.T. Knobbe, D. Gerace, and E.P. Scully. 2000. Rapid transition in the structure of a coral reef community: The effects of coral bleaching and physical disturbance. P. Natl. Acad. Sci. USA. 97(10):5297–5302.
2. Pratchett, M.S., S.K. Wilson, M.L. Berumen, and M.I. McCormick. 2004. Sublethal effects of coral bleaching on an obligate coral feeding butterflyfish. Coral Reefs 23(3):352–356.
3. IPCC (Intergovernmental Panel on Climate Change). 2013. Climate change 2013: The physical science basis. Working Group I contribution to the IPCC Fifth Assessment Report. Cambridge, United Kingdom: Cambridge University Press.www.ipcc.ch/report/ar5/wg1.
4. IPCC (Intergovernmental Panel on Climate Change). 2013. Climate change 2013: The physical science basis. Working Group I contribution to the IPCC Fifth Assessment Report. Cambridge, United Kingdom: Cambridge University Press.www.ipcc.ch/report/ar5/wg1.
5. Trtanj, J., L. Jantarasami, J. Brunkard, T. Collier, J. Jacobs, E. Lipp, S. McLellan, S. Moore, H. Paerl, J. Ravenscroft, M. Sengco, and J. Thurston. 2016. Chapter 6: Climate impacts on water-related illness. The impacts of climate change on human health in the United States: A scientific assessment. U.S. Global Change Research Program. https://health2016.globalchange.gov.
6. NOAA (National Oceanic and Atmospheric Administration). 2016. Extended reconstructed sea surface temperature (ERSST.v4). National Centers for Environmental Information. Accessed March 2016. www.ncdc.noaa.gov/data-access/marineocean-data/extended-reconstructed-sea-surface-temperature-ersst.
7. IPCC (Intergovernmental Panel on Climate Change). 2013. Climate change 2013: The physical science basis. Working Group I contribution to the IPCC Fifth Assessment Report. Cambridge, United Kingdom: Cambridge University Press.www.ipcc.ch/report/ar5/wg1.
8. NOAA (National Oceanic and Atmospheric Administration). 2016. NOAA Merged Land Ocean Global Surface Temperature Analysis (NOAAGlobalTemp): Global gridded 5° x 5° data. National Centers for Environmental Information. Accessed June 2016.www.ncdc.noaa.gov/data-access/marineocean-data/noaa-global-surface-temperature-noaaglobaltemp.