When talking about the impacts of climate change, we mostly hear about changes to land and the planet’s surface or atmosphere. However, most of the warming is going into the oceans where a lot of ecosystem changes are also occurring.
Rapidly rising greenhouse gas concentrations are driving ocean systems toward conditions not seen for millions of years, with an associated risk of fundamental and irreversible ecological transformation. Changes in biological function in the ocean caused by anthropogenic climate change go far beyond death, extinctions and habitat loss: fundamental processes are being altered, community assemblages are being reorganized and ecological surprises are likely. Although I think it has gained less mainstream media attention, the effects of increasing greenhouse emissions — in particular carbon dioxide — on the oceans may well be significant.
These are the 3 main concepts:
1. More CO2 in the atmosphere means more CO2 in the ocean;
2. Atmospheric CO2 is dissolved in the ocean, which becomes more acidic; and
3. The resulting changes in the chemistry of the oceans disrupts the ability of plants and animals in the sea to make shells and skeletons of calcium carbonate, while dissolving shells already formed.
However, I think there is one positive aspect, because oceans are able to absorb some of the excess CO2 released by human activity. We can say that this has helped keep the planet cooler than it otherwise could have been had these gases remained in the atmosphere. Nevertheless, the additional excess CO2 being absorbed is also resulting in the acidification of the oceans. Because when CO2 reacts with water it produces a weak acid called carbonic acid, changing the sea water chemistry.
As we know, millions of years ago CO2 levels were higher and I think today’s change is occurring rapidly, giving many marine organisms too little time to adapt. Some marine creatures are growing thinner shells or skeletons, for example. Some of these creatures play a crucial role in the food chain, and in ecosystem biodiversity.
As climate change warms the oceans (even just an increase of about 0.2C per decade, on average), the warmer water, which is lighter, tends to stay on top of what is then a layer of colder water. This affects tiny drifting marine organisms known as phytoplankton. Phytoplankton are a critical part of our planetary life support system, because they produce half of the oxygen we breathe, draw down surface CO2, and ultimately support all of our fisheries. And why is it so consequential? Well, phytoplankton can only live in the top 100 or 200 meters of water, but if it is getting warmer, they eventually run out of nutrients to feed on unless the cold, deeper waters mix with those near the surface. So we can affirm direct correlation between rising sea surface temperatures and the decline in phytoplankton growth around the world.
Another point is that fertilizer and sewage run-off cause huge growth of plankton. However, these then quickly die and are consumed by bacteria that deplete waters of oxygen. For example, the Gulf of Mexico has a 22,000 square kilometer dead zone every spring due to run-off from the Mississippi River. Ocean stratification, where warm water sits firmly on top of cold, nutrient-rich water, also creates dead zones and lowers the overall productivity of the oceans. Such dead zones were rare 40 years ago but now number several hundred.
We can say, that without urgent action, climate change will continue to warm oceans, increasing stratification and producing larger and more dead zones with a major impact on future fisheries. It will take a thousand years for the oceans to cool down, so it is imperative to pull the emergency brake on global warming emissions.
Another fact which is important to highlight is that coral reefs have been threatened by climate change too. Around the world, coral reefs have been dying largely due to climate change. Coral bleaching results in white, dead-looking, coral. However, healthy coral is very colorful and rich with marine life. According to scientists the future of coral life is horrific and there is no hope of reefs surviving to even mid-century in any form that we now recognize.
But I believe there is a chance to save coral life in the oceans, because coral reefs provide many ecosystem services to humans as well, for free. If, and when, they go, they will take with them about one-third of the world’s marine biodiversity. And we can see there is a domino effect, as reefs fail so will other ecosystems. This is the path of a mass extinction event, when most life, especially tropical marine life, goes extinct.