The ocean, covering 71% of our planet, is a wondrous and enigmatic ecosystem. 

However, lurking beneath the surface, the impacts of climate change on marine life are becoming increasingly alarming. 

Read on to discover some of the ways that climate change is having devastating consequences for the world’s oceans and seas, and their inhabitants. 

1. Warming oceans

As global temperatures continue to rise, the impact on marine life is becoming increasingly evident, with the warming of our oceans leading to disrupted ecosystems, changes in behavior, and even decreased reproduction among sea life. 

The severity of the issue is made even worse by more frequent and intense marine heatwaves, resulting in mass die-offs of species like coral reefs. In fact, according to WWF, over the past three decades, the world has lost half of its reefs — the result of a combination of harmful fishing practices, polluted water, development of coastal areas, shipping, and, of course, climate change causing ocean warming.

As highlighted by the UN Environment Programme, every one of the world’s coral reefs could bleach by the end of the century if the water continues to warm at current rates. 

2. Ocean acidification

Ocean acidification, which is caused by increased levels of carbon dioxide in the atmosphere, is a major threat to the world's oceans and marine life. 

The ocean absorbs around 25%-30% of the world’s annual carbon dioxide (CO2) emissions, which helps mitigate the impacts of climate change, yet at the same time causes seas and oceans to become more acidic. In the 250ish years since the Industrial Revolution began, the acidity of the ocean has seen a 30% increase.

The acidification of the ocean is already causing big problems for many species that call the world’s seas and oceans home — but particularly so for organisms that make hard shells and skeletons, like oysters, corals, and tiny sea snails called pteropods that are a vital part of the ocean food system. 

The more acidic the ocean is, the harder it is for shell-making species to build and maintain their shells — in fact, if acid levels get too high, their shells and skeletons can even start to dissolve

3. Melting ice 

The melting of sea ice at both the Arctic and Antarctic regions is a well documented result of our warming planet.

You’ve likely seen images of desperately hungry polar bears, which have become symbolic of the impacts of climate change. Polar bears are going hungry because, as sea ice melts, it means they have less area to hunt and find food

But the problem goes way beyond polar bears. 

Sea ice is also essential for the production of algae, too. Algae is a really crucial foundation to the entire Arctic food web, so less algae means an impact on lots of species — from Arctic cod to seals and whales, as well as polar bears. 

As well as food, sea ice is also a vital habitat for seals, walruses, penguins, and other animals; so as sea ice vanishes, so do these species’ homes. 

It might sound like climate change’s impacts on the Arctic and Antarctic regions are a “far away” problem — but actually, what happens in the world’s polar regions affects all our lives. You can learn more about that here

4. Increased ocean noise 

Human-caused noise pollution in the ocean is becoming a growing problem — with impacts on marine life including stress, as well as interfering with species’ communication and navigation, and disrupting predator-prey interactions. 

Climate change, you guessed it, is making this problem even worse. That’s because it’s leading to changes in both ocean temperatures and currents — which in turn, increase noise levels in the ocean. 

Meanwhile, rises in ocean temperatures and ocean acidification are both forcing marine species to adapt, including causing changes in behavior, having to find new habitats, and issues with reproduction. 

Noise pollution is making it *even* harder for these species by interrupting communication, preventing animals locating prey, and making it more difficult to find mates.

The combined effects of climate change and noise pollution are having serious consequences for marine ecosystems, including loss of biodiversity and disrupted food webs. So mitigating human-made ocean noise is essential to protect marine life in the face of climate change.

Image: Dan Stark, Unsplash

5. Changes in ocean currents 

Like a delicate web, the ocean's interconnectedness means that a small change in temperature can cause a big wave of changes in currents — disrupting marine migration and throwing off entire ecosystems. 

As the food chain shifts and species struggle to navigate, scientists are left grappling with the complex effects of these changes on our oceans. 

Changes in ocean currents can occur due to a variety of factors, including changes in temperature, changes in wind patterns, and the melting of sea ice. 

As currents change, they can disrupt the food chain, alter the distribution of plankton and other organisms, and make it harder for marine species to navigate and find their way to breeding and feeding grounds. 

But as well as affecting individual species, changes in ocean currents can also have broader impacts at an ecosystem-level. Disruptions to the food chain, for example, can lead to population decline of certain species, which can then have cascading effects on other parts of the ecosystem. 

6. Extreme weather events 

Have you ever had an outfit planned, then you wake up the next morning and it's hailing when it was supposed to be a sunny sky? Yes! That is the new norm. We’re now living in a world where weather conditions are unnaturally irregular

Climate change is causing more occurrences of intense storms, hurricanes, cyclones, and other extreme weather events that can damage habitats and life cycles. 

During a hurricane or a cyclone, rain water enters the ocean and can stress corals. According to Ocean National Service, when they move close to shore, hurricanes and cyclones can effectively shake the ocean water, leading to shifting sands and muddy shallow waters, blocking the essential sunlight on which corals and other sea creatures depend. 

Meanwhile, extreme heat events can lead to ocean heatwaves — and we’ve already covered above what warming oceans mean for sea life. 

7. Ocean Deoxygenation 

This is essentially the loss of oxygen in the ocean, and it’s driven by ocean warming — because warmer water can’t hold as much oxygen. In fact, since the 1950s, the oxygen content of the world’s oceans has fallen by around 2%. If we don’t change things, oceans are expected to lose about 3-4% by the year 2100

A lack of oxygen, unsurprisingly, is very bad news for sea life — and, because respiration uses up oxygen and puts out carbon dioxide, also often comes hand in hand with ocean acidification

There’s a lot we don’t yet know about how loss of oxygen in the ocean impacts humans; but we do know that it has severe impacts on marine biodiversity — we’re already seeing falls in fish species — as well as the healthy functioning of ocean ecosystems. 

Deoxygenation also alters the balance of marine life, especially affecting bigger fish such as tuna, marlin, swordfish, and sharks — which are hyper sensitive to low-oxygen environments. 

Ultimately, it’s painfully clear that climate change is having a dramatic and devastating impact on marine life — and urgent action is needed to protect marine ecosystems and the countless creatures that depend on them (not to mention the countless humans who do too). 

We all have a role to play — from making sustainable choices to help safeguard the ocean and our environment, to urging world and business leaders to take the urgent, widespread, and ambitious action needed to tackle climate change and protect the planet. Join Global Citizens around the world who are fighting climate change by taking action with us now

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7 Eye-Opening Ways Climate Change Is Harming Sea Life

By Cherono Keter  and  Tsholofelo Lehaha