The ocean is warming and that is just a fact. Handling ocean warming is one of the most critical environmental challenges of our time. Estimates have the ocean absorbing more than 90% of the heat trapped by greenhouse gases emitted by humans. This in turn causes the global ocean temperature to steadily increase, and it is projected to continue to do until something is done to stop or mitigate it.
The warming of oceans has a lot of negative consequences some we can see and others we can’t. These include coral bleaching, sea level rise, ocean acidification, and changes in ocean currents, which can lead to changes in global climate patterns. We will explore and go over the causes and effects of ocean warming. We will also talk about the measures that can be taken to try and stop this ongoing issue.
Causes of Ocean Warming
While there is a lot of guessing going on about all the causes, we do know the main one. The primary cause of ocean warming is the increase in the concentration of greenhouse gases in the atmosphere, mostly carbon dioxide (CO2). Starting in the industrial revolution, humans have been kicking it up and, burning fossil fuels, cutting trees (deforestation), and land uses have changed to support more people. This has led to a significant increase in atmospheric CO2 concentrations.
When the CO2 enters the atmosphere, it traps heat from the sun. This causes the planet’s temperature to rise. Some of the excess heat is absorbed by the oceans, which has large effects on marine ecosystems.
Another cause of ocean warming is the reduction in Arctic sea ice. The Arctic has been warming at a much faster rate than the rest of the earth. This warming has led to a significant reduction in sea ice. So that means more sunlight is being absorbed by the Arctic Ocean and that increases the ocean’s temperature. This has a domino effect, the increase leads to the melting of permafrost which leads to the releasing of methane/ greenhouse gas which warms the earth.
Effects of Ocean Warming
Coral Bleaching
One of the most visible and devastating effects of ocean warming is coral bleaching. Coral reefs are key to ecosystems that provide habitats for 25% of marine life.
When the water temperature reach and exceed a certain temperature, corals release the symbiotic algae that provide them with energy. This causes them to turn white and die. Coral bleaching events have become more frequent and severe recently and many coral reefs around the world are in danger of disappearing totally as they do not grow back quickly.
Ocean Warming
As the ocean warms, the water expands (science) which leads to sea level rise. The melting of land-based ice like glaciers and ice sheets, also contributes to sea level rise.
Sea level rise can lead to flooding in low-lying coastal areas. This can and will damage infrastructure, homes, and businesses. It can also contaminate freshwater resources and increase the risk of storm surges and erosion.
Ocean Acidificaiton
As the ocean absorbs more CO2 from the atmosphere, it becomes more acidic. While plants and animals can adapt the sea creatures are more sensitive. Acidification can inhibit shellfish growth for creature like oysters and clams, and other organisms that need carbonate to build their shells and skeletons. Acidification can disrupt the food chain by altering the availability of nutrients and prey for different species.
Changes in Ocean Currents
This is one that is hard to know about if you are not a weather nerd, but you may have noticed the weather has been different the last few years for this reason. An example would be the Atlantic Meridional Overturning Circulation (AMOC) which is a system of ocean currents that brings warm water from the tropics to the North Atlantic. This water cools and sinks to the bottom of the ocean, driving the circulation of water around the globe.
If the AMOC was to slow down or just stop it could have profound effects on global climate patterns, such as altering rainfall patterns and disrupting weather patterns.
Ocean Warming Facts:
- The ocean has absorbed more than 90% of the excess heat trapped by greenhouse gases in the atmosphere, making it the largest heat sinks on Earth.
- The ocean has been warming at an average rate of 0.18°F (0.11°C) per decade since 1971.
- The rate of warming has increased in recent years, with the last decade (2012-2022) being the warmest on record.
- The top 2,300 ft. (700M) of the ocean have warmed by 0.27°F (0.2°C) since the 1960s, and the top 6,562 ft. (2000M) have warmed by 0.17°F 0.1°C since the 1950s.
- Warmer seas have resulted in sea level rise, which is primarily caused by the expansion of seawater as it warms and the melting of glaciers and ice sheets.
- The bleaching of coral reefs, from warming seas, is highly sensitive to changes in temperature.
- In 2016, the Great Barrier Reef experienced the worst coral bleaching event on record, with 93% of the reef affected.
- Sea ice in the Arctic has declined by about 12.8% per decade since 1979. The loss of sea ice in the Arctic has negative impacts on marine life, including the loss of habitat for species such as polar bears and walruses.
- Ocean warming has also led to the expansion of oxygen minimum zones these are areas in the ocean where oxygen levels are too low to support most forms of marine life.
- The melting of glaciers and ice sheets has led to an increase in freshwater input to the sea. The increase in freshwater input to the ocean disrupts ocean currents and circulation patterns, potentially leading to changes in global climate patterns.
- Ocean warming has led to changes in the distribution and abundance of marine species, some species are shifting their range towards higher latitudes to stay within in their preferred temperature.
- Subtropical zones have expanded, which are areas of the ocean that are too warm and nutrient-poor to support many forms of marine life.
- Ocean warming has led to changes in the timing of important ecological events such as the timing of migration and reproduction of marine species.
- The physical and chemical properties of seawater have changed, including changes in pH and ocean acidity due to the absorption of excess carbon dioxide from the atmosphere.
- The frequency and intensity of marine heat waves have increased, having a negative impact on marine ecosystems.
- There has been a loss of seagrasses and kelp forests, which are important habitats for a wide range of marine species.
- Changes in the behavior of marine predators like sharks, with some species moving to deeper and cooler waters to escape warming temperatures
- Marine plankton behaviors have changed as well with some species adapting to warmer temperatures by changing their metabolism and physiology.
- Harmful algal blooms can have negative impacts on human health and the environment.
- Changes in the global carbon cycle, with the ocean absorbing less carbon dioxide as it warms.
- There has been an increase in the frequency and intensity of tropical cyclones, hurricanes, and typhoons, which can cause significant damage to coastal communities and marine ecosystems.
- The structure and functioning of marine food webs has shifted some species becoming more dominant and others becoming less abundant.
- Ocean warming has led to an increase in the acidification of seawater, which can have negative impacts on the shells and skeletons of marine organisms such as corals, oysters, and mollusks.
- Migration patterns of marine animals have changed such as whales, dolphins, and sea turtles can impact their survival and reproductive success.
- The distribution and abundance of commercially important fish stocks has changed, some stocks shifting their range towards higher latitudes and/ or deeper waters.
- There has been a distribution of the abundance of phytoplankton, which is key to the marine food web and plays a key role in the global carbon cycle.
- An increase in the number and severity of coral bleaching events can cause the death of entire coral reefs.
- Ocean warming has led to changes in marine ecosystems’ nutrient cycling and biogeochemical processes, which can have cascading effects on the entire food web.
- The warming of the ocean has led to changes in the oxygen levels of seawater, with some areas experiencing decreased oxygen levels that can lead to the formation of “dead zones” where marine life cannot survive.
- The intensity and distribution of ocean currents, which can impact global climate patterns have gone up because of warmer seas.
- The behavior and physiology of marine animals, with some species showing alterations in their feeding, reproduction, and migration patterns have also shifted.
- The frequency and intensity of ocean waves can impact coastal erosion and flooding due to warming oceans.
- The intensity of ocean upwelling has gone up and can impact marine productivity and biodiversity.
- There have been shifts in the frequency/ intensity of ocean heat waves, which can impact marine ecosystems and fisheries.
- Ocean warming has led to changes in the distribution and abundance of zooplankton which are a keystone species in the seas.
- The warming of the ocean has led to changes in the dynamics and distribution of sea ice, which can impact Arctic and Antarctic ecosystems and the global climate system.
- Marine mammals’ migration patterns and behavior have been changing, with some species showing alterations in their feeding, reproduction, and communication patterns.
- Ocean storms and extreme weather events have increased, which impact coastal communities and marine ecosystems are happening due to global warming.
- Increased ocean acidification, harms marine organisms that rely on calcium carbonate to build their shells or skeletons.
- The timing and extent of seasonal sea ice cover impacts polar ecosystems and the global climate system.
- Ocean warming has led to changes in the geographic range and distribution of marine species, which can impact marine ecosystems and fisheries.
Sources:
- Anderson, D.M., et al. (2012). Harmful algal blooms and eutrophication: Nutrient sources, composition, and consequences. Estuaries and Coasts, 35(2), 393-408.
- AMAP (2017). Snow, Water, Ice, and Permafrost in the Arctic. Chapter 7, Page 292.
- Behrenfeld, M.J., et al. (2006). Climate-driven trends in contemporary ocean productivity. Nature, 444, 752-755.
- Cheung, W.W.L., et al. (2013). The shrinking of fishes exacerbates the impacts of global ocean changes on marine ecosystems. Nature Climate Change, 3, 254-258.
- Deutsch, C., et al. (2011). Impacts of climate warming on terrestrial and marine organisms. Science, 341(6145), 492-495.
- Doney, S.C., et al. (2009). Ocean Acidification: The Other CO2 Problem. Annual Review of Marine Science, 1, 169-192.
- Hughes, T.P., et al. (2018). Spatial and temporal patterns of mass bleaching of corals in the Anthropocene. Science, 359(6371), 80-83.
- IPCC (2019). Special Report on the Ocean and Cryosphere in a Changing Climate. Chapter 4, Page 258.
- Jorgensen, S.J., et al. (2007). Temperature influence on swordfish (Xiphias gladius) vertical distribution in the eastern Pacific Ocean. Marine Ecology Progress Series, 348, 257-267.
- Litchman, E., et al. (2015). Global climate change and the oceanic plankton: What can we expect? Annual Review of Marine Science, 7, 81-104.
- Lusseau, D., et al. (2003). The bottlenose dolphin community of Doubtful Sound features a large proportion of long-lasting associations. Behavioral Ecology and Sociobiology, 54, 396-405.
- Oliver, E.C.J., et al. (2018). Longer and more frequent marine heatwaves over the past century. Nature Communications, 9(1), 1324.
- Poloczanska, E.S., et al. (2013). Global imprint of climate change on marine life. Nature Climate Change, 3, 919-925.
- Rahmstorf, S. (2006). Thermohaline Ocean Circulation.
- Stramma, L., et al. (2008). Expansion of oxygen minimum zones may reduce available habitat for tropical pelagic fishes. Nature Climate Change, 2, 33-37.
- Smale, D.A., et al. (2019). Marine heatwaves threaten global biodiversity and the provision of ecosystem services. Nature Climate Change, 9, 306-312.
- Walther, G.-R., et al. (2002). Ecological responses to recent climate change. Nature, 416, 389-395.
