Beginning Part 2: The Oceans
David Skinner M.A. Academy For Future Science
The Earth’s oceans hold 96.5% of the planet’s water and they cover roughly 71% of the Earth’s surface. Ocean plants produce up to 85% of the oxygen we breathe and millions of people around the globe depend on them for food and jobs. Warming waters, coral reef damage, dead zones and pollution are challenging the health of our oceans and playing a role in climate change and extreme weather events.
Our oceans temper the Earth’s climate by storing heat and carbon dioxide. According to NASA, the upper three feet (1 meter) of ocean water stores more heat than our atmosphere. This “stored” heat also transfers to and from the atmosphere. Climate scientists estimate the Earth would be 20oC (32oF) warmer without this storage capacity. Ocean temperature data has been vastly improved through Argo, an international program of 30 nations providing almost 4,000 free ranging profiling floats in the world’s oceans. The floats periodically move from a depth of 2000 meters to the surface recording temperatures, salinity, currents and other data giving scientists a much clearer picture of the ocean heat content (OHC).
A paper from the Chinese Academy of Sciences’ Institute of Atmospheric Physics reported 2017 was the warmest the world’s ocean temperatures have been since reliable recordkeeping began in 1958. The records also show a clear warming trend over this same period of time.
New research appears to also confirm the slowing of the Atlantic Ocean’s Meridional Overturning Circulation (AMOC) system, which also impacts the Gulf Stream in the north Atlantic Ocean. AMOC moves warm water from the Southern Hemisphere to the northern regions and returns the colder, denser water from the Arctic Ocean southward through the deep ocean to mix with the warmer southern waters. Since the 1950’s, scientists have calculated a 15 percent decline in its strength. The AMOC is linked to the temperate climate of Western Europe and fisheries along the U.S. Atlantic coast. In recent years cod fishing has collapsed and lobster populations have moved north of their traditional habitat off the coast of Maine. Long predicted by climate models, some of the disruption is believed to be caused by the melting of Greenland’s ice sheet changing the salinity of the ocean water resulting in a shift of ocean currents.
Sometimes referred to as the rainforests of the oceans, our coral reefs are the most biodiverse environments in the oceans. They play an extremely important role in the health of our ocean fisheries, as an estimated 25% of all fish species spend part of their lifecycle in reefs – and they are struggling to survive. Global warming is generating unseen levels of coral bleaching worldwide through warming waters from rising temperatures, acidification from rising CO2 levels in the water, and plastic pollution.
Coral is an animal that exists through a symbiotic relationship with algae that lives in its tissue. Through photosynthesis algae feeds the coral. Bleaching occurs when stressed corals expel the algae and turn white as a result. Without time to recover, which can take years, the bleached corals starve to death. Scientists are seeing bleaching events occurring five times more frequently than they did in the early 1980s.
The “longest, most widespread, and possibly the most damaging” coral bleaching event occurred between June 2014 and May 2017. It impacted reefs around the world. Australia’s Great Barrier Reef, the longest (1,400 miles) Bleached Coral from Ian L.
and largest coral reef in the world, was hit the hardest with 93% of its corals being affected and 29% of its shallow water corals dying. This is the third mass bleaching event for the Great Barrier Reef, the other two occurring in 1998 and 2002. Researchers did not expect the level of destruction they have seen for another 30 years.
Researching this bleaching event on the Great Barrier Reef, Australian marine scientists discovered coral is sensitive to even small temperature changes. The El Niño event in the fall of 2015 combined with record high summer temperatures in March 2016 killed about half of all the coral in the Great Barrier Reef. “They died instantly, of heat stress,” said Terry Hughes, director of the ARC Center of Excellence for Coral Reef Studies. More warm water in 2017 triggered another bleaching event. According to Hughes, half of the two billion corals living in the Great Barrier Reef are now dead.
Plastic pollution is another significant factor impacting coral reefs around the world. A study of 159 coral reefs across the Asia Pacific region found plastic fragments choking coral of light and oxygen and providing a pathway for pathogens to infect entire reefs. With five “garbage patches” floating in our oceans, plastic waste has been described as a planetary crisis by Lisa Svensson, the UN Oceans Chief. The Great Pacific Garbage Patch is the largest, containing an estimated 1.8 trillion pieces of plastic.
Also affecting the health of our oceans is an increasing number of “dead zones” where marine life struggles to survive in oxygen depleted waters. Rising nutrient loads, primarily from agricultural run-off loaded with excess fertilizers and warming waters are changing ocean chemistry. Without enough oxygen in the water, the nitrogen cycle changes allowing nitrous oxide to be released into the atmosphere. Additionally, feeding off the added nitrogen in the water, algae blooms toxic to marine life appear and deplete oxygen levels in the water. Running along coast lines, these areas have increased worldwide from 50 to 500 locations since the 1950s. During this same time, open-ocean “oxygen minimum zones” have increased to about the size of the European Union (as seen in the blue areas of the above map.) Areas of the ocean completely devoid of oxygen have quadrupled. New research just published in Geophysical Research Letter in April 2018, reports an oxygen minimum zone (OMZ) larger than Scotland covering most of the Gulf of Oman. 
Rising Sea Levels
Rising sea levels have two primary sources: meltwater from the Greenland and Antarctica ice sheets and the thermal expansion of ocean waters as they warm. Scientists have calculated 55% of global sea level rise is due to warmer waters. In another finding, the warmer water, which weighs more than cold water, has caused the ocean floor to sink 2.1 mm from 1993-2014 except for the Arctic region which is rising due to the loss of ice.
A 2016 study in Nature Climate Change reported the burning of fossil fuels was responsible for the majority of the 17 cm (6.69 inches) global average sea level rise from 1990 to 2005. Based on 25 years of NASA and European satellite data, the rate of sea level rise has been accelerating. Scientists are projecting a conservative sea level rise of 65 cm (26 inches) by 2100 from this data. The IPCC 2013 estimate of sea level rise was one meter (3.3 feet) by 2100, noting the number was dependent upon carbon emissions. The report had a high degree of confidence that 95% of ocean area will rise and 70% of all coastlines will impacted.
Image via NASA
Sea level rise is not uniform across the globe. Low-lying coastal areas in the United States, China, India, Vietnam, Germany and the UK, are already feeling the effects of “sunny day” flooding from King tides, and storm surge. In the United States, Miami, FL, Charleston, NC and Norfolk, VA are experiencing tidal flooding that is producing one or two feet of standing salt water. It is enough to block roads, contaminate fresh water supplies, kill trees and lawns and clog storm drains. The frequency is increasing as sea levels rise. Studies over the past two years are projecting 153 to 500 million people will be driven to higher ground due to rising sea levels by the end of the 21st century.
So, it is not just the land but also the oceans which are being affected by climate change. However, the oceans are not separate from us as we have a direct connection with them because they constitute more than 70% of the planet and are all around us. The world’s oceans are truly a planetary mirror of our way of life.
End of Part 2
- Johnson G.C., J. M. Lyman, T. Boyer, C. M. Domingues, M. Ishii, R. Killick, D. Monselesan, and S. E. Wijffels, 2016: [Global Oceans] Ocean Heat Content [in “State of the Climate in 2015”]. Bulletin of the American Meteorological Society (BAMS), 97 (8), S66-S70. https://www.climate.gov/news-features/featured-images/2015-state-climate-ocean-heat-storage ↑
- https://earth.esa.int/web/eoportal/satellite-missions/a/argo ↑
- Cheng, L., and J. Zhu, 2018: 2017 was the warmest year on record for the global ocean. Adv. Atmos. Sci., 35(3), doi: 10.1007/s00376-018-8011-z. https://link.springer.com/article/10.1007/s00376-018-8011-z ↑
- Global warming transforms coral reef assemblages, Terry P. Hughes, et al. Nature volume 556, (2018) ↑
- Hughes, Terry P. (2018) “Global warming transforms coral reef assemblages” Letters Nature, Vol. 556, 26 April 2018, p. 492. ↑
- Evidence that the Great Pacific Garbage Patch is rapidly accumulating plasticL. Lebreton, et al. Nature Scientific Reports volume 8, Article number: 4666 (2018) ↑
- Queste, Bastien Y., et. al. (2018) “Physical Controls on Oxygen Distribution and Denitrification Potential in the North West Arabian Sea.” Geophysical Research Letters Research Letter Open Access, 27 April 2018. https://doi.org/10.1029/2017GL076666 ↑
- Frederikse, Thomas, Et. Al. (2017) “Ocean Bottom Deformation Due To Present‐Day Mass Redistribution and Its Impact on Sea Level Observations.” Geophysical Research Letters, Vol. 44, Issue 24. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017GL075419↑
- Consequences of twenty-first-century policy for multi-millennial climate and sea-level changePeter U. Clark et al. Nature Climate Change volume 6 (2016) ↑