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How is climate change affecting the ocean and its marine life?

As the atmosphere has warmed due to human-driven climate change, it has been estimated that the ocean has absorbed a third of the carbon and 90% of the excess heat that has been created. The ocean is now warmer than at any time since records began being kept in the 1880s. From pole to pole and from sea surface to the depths of the ocean, the climate change effect on marine life is widespread. The warmer waters pose a serious threat to life in our seas. Below we explore four key ways that a warmer ocean is impacting our marine life.

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1) Sea levels are rising, displacing marine life

Coastal habitats are particularly impacted by the rising sea levels. For instance, beaches that marine species rely on for important life functions, like nesting, are decreasing as high watermarks on land continue to rise. Also, mangrove forests that line the coasts globally, and cover over 53,000 miles of the Earth’s surface, are essentially drowning due to the rising sea levels. These forests that are made up of trees, plants and palms, act as fertile nurseries for numerous marine species and are famously resilient to change. However, now the forests as well as the marine life that relies on them are in jeopardy due to rising waters.

Sea level rise is undeniable. For the past 25 years the seas have not only been rising, but also the rate of that rise has been increasing. In fact, by 2100, the seas could rise anywhere between five inches and 10 feet. National Geographic reports that there are two primary factors contributing to the rise. Thermal expansion, or the expansion of water as it warms, is credited with nearly half of the sea-level rise over the last 25 years. The second main contributor is increased velocity of the melting of glaciers and ice sheets at our poles. With less snowfall, and increased temperatures, there is an imbalance between runoff and ocean evaporation.

2) Ocean warming is driving species extinction

Warm water coral reefs host a wide variety of marine life and are very important for tropical fisheries and other marine and human systems. These living reefs are particularly vulnerable to the warmer water temperatures and are increasingly experiencing coral bleaching. Coral bleaching is a phenomenon where corals will expel the algae (zooxanthellae) living in their tissues when water becomes too warm. This causes them to turn completely white. Corals can survive a bleaching event, but they are under more stress and are subject to increased risk of mortality. After mass coral mortalities occur due to bleaching, reef recovery typically takes at least 10–15 years. 

The Washington Post shares, “Warming waters are cooking creatures in their own habitats. Populations that have managed to survive overfishing, pollution and habitat loss are struggling to survive amid accelerating climate change.” The article further explains that Princeton University earth scientists Justin Penn and Curtis Deutsch used climate models to run a study that predicted the behavior of species based on simulated organism types. They found that animals can’t lose much more than 50 percent of their habitat. Beyond that amount the species will face irreversible decline. 

3) Marine oxygen levels are decreasing as ocean temperatures increase

Cooler water is able to hold more oxygen than warmer water. As the ocean temperatures increase, by default there is less oxygen available. Additionally, the warmer ocean temperatures impact the ability of the of ocean water to mix, so that the oxygen absorbed on the top layer doesn’t properly get down into the deeper ocean layers. Further compounding the issue is the fact that the oxygen that is available to marine life gets used up more quickly because there is simply less of it.

Scientists have documented expanding “shadow zones” where oxygen levels are so low that most life can’t survive. Ultimately, the deoxygenation of our oceans poses one of the greatest climate threats to marine life.

    4) Marine species are on the move due to increased ocean temperatures and are impacting fisheries

    With the warming ocean, many marine species are found to be moving to the earth’s poles seeking cooler water temperatures. Fish, being a mobile species, seem to operate similarly to Goldilocks – they don’t want their water too hot, or too cold, it needs to be just right. As such, fish have increasingly been seen moving from their original habitats to waters of a preferred temperature and oxygen level. This movement will ultimately damage some fisheries and benefit others. Unfortunately, the losers outweigh the winners and some regions particularly around the equator have been hit hard. 

    Species such as lobsters, jumbo squid and plankton have also been found to be moving north and driving the reshaping of marine communities in the ocean and on land. The movement of species is impacting those animals that migrate, such as grey whales, and there have been increased incidents of malnutrition and death among these populations. 

    Fisheries and climate change are intrinsically intertwined. According to Mongabay, a U.S. based conservation and environmental science news platform, an international study found that “By 2030 climate change will force 23% of shared fish stocks to move from their historical habitats and migration routes, if nothing is done to halt greenhouse gas emissions. By the end of the century, that number could rise to 45%.”

    Solutions to climate change in the ocean

    Climate change impacts on marine ecosystems is certainly alarming. Some scientists have even indicated the climate change effects on marine organisms and ecosystems could be compared to canaries in a coal mine, alerting humanity to invisible forces that will affect all of mankind such as oxygen depletion and increased carbon dioxide accumulation. 

    As an individual and a society, each one of us can work to combat the effects of climate change. Minimizing greenhouse gas emissions, following sustainability practices, supporting businesses that make sustainability a priority are all actions that can be taken that will be impactful. 

    We only have this one wild planet, and even small steps that we choose to make each day have the potential to slow the effects of climate change on our ocean and the marine ecosystems they contain. 


    1. https://www.epa.gov/climate-indicators/oceans
    2. https://www.shapeoflife.org/climate
    3. https://earthobservatory.nasa.gov/images/47427/mapping-mangroves-by-satellite#:~:text=They%20are%20most%20often%20found,11%20percent%20in%20South%20America.
    4. https://www.nationalgeographic.com/environment/article/sea-level-rise-1#:~:text=When%20sea%20levels%20rise%20as,fish%2C%20birds%2C%20and%20plants
    5. https://www.washingtonpost.com/climate-environment/2022/04/28/mass-marine-extinction-event-science/
    6. https://www.ipcc.ch/srocc/about/faq/final-faq-chapter-5/
    7. https://www.conservation.org/blog/5-ways-that-climate-change-affects-the-ocean
    8. https://oceanservice.noaa.gov/facts/coral_bleach.html
    9. https://news.mongabay.com/2019/05/climate-change-is-causing-marine-species-to-disappear-from-their-habitat-twice-as-fast-as-land-animals/
    10. https://oceanconservancy.org/blog/2019/05/24/marine-animals-face-heat-climate-change/?ea.tracking.id=22HPXGJAXX&gclid=Cj0KCQjw94WZBhDtARIsAKxWG-92kZEygWUzhGHEcJagq6_cOlZ-EhFjHCEDQh6jhGCZNvfdlOk0JVsaAkPMEALw_wcB
    11. https://www.nytimes.com/2019/12/07/climate/ocean-acidification-climate-change.html
    12. https://www.weforum.org/agenda/2021/05/climate-change-ocean-damage-action/
    13. https://theconversation.com/ocean-warming-has-fisheries-on-the-move-helping-some-but-hurting-more-116248
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