The Effects of Climate Change Already Visible in Our Oceans

For decades, scientists have warned of the effects that climate change will have on our planet but for many of us, these changes to our environment feel far off in the future. Unfortunately, this is no longer the case as researchers believe many of the shifts occurring on Earth may be attributed to climate change. Let’s take a look at some of the effects that are occurring in the ocean as we speak.

2023 has already delivered an unheard of marine heatwave across many areas of the world, with the global sea surface temperature reaching an all-time high since records began in 1850 in April this year. The UK has not escaped this bout of unusually hot weather and parts of the North Sea have been placed into a category 4 marine heatwave. This is considered an extreme classification, with some areas of the coast sitting at 5°C hotter than their usual temperature for this time of year. This is believed to be in part due to El Nino, a naturally occurring climate phenomenon which sees certain areas of the world’s oceans increase in temperature. Yet it is also thought that we may have entered a more erratic climate phase, fuelled by our high emissions of greenhouse gases. So far this year in the UK, almost every month seems to have set a new record, whether that be the driest, hottest or wettest as our weather turns more extreme, a classic effect of climate change.

This extreme weather has posed a challenge to marine wildlife, many of which become stressed under hot conditions. Already, high numbers of fish, such as sea trout, have been found dead in the UK, a sight not usually seen until late summer. This is due to low water levels and low oxygen levels. In addition to this, dried pollutants, both chemical and plastic, accumulate on the land and are then swept into waterways in high quantities when flash floods and storms occur, making our wildlife ill. The effects of this heatwave have already been seen on kelp, seagrass, fish and oysters, all essential creatures which have important roles to play within the marine habitat, whether that be filtering and cleaning water, absorbing carbon dioxide or providing food for those higher up the food chain.

The hotter sea surface temperatures are also fuelling more tropical storms which form in areas where the sea temperature is 27°C or warmer. Already, storms have been seen forming in the Atlantic Ocean earlier in the year than normal due to all the extra heat energy which is stored in the ocean, a consequence of both El Nino and greenhouse gases trapping heat within the Earth’s atmosphere. These storms have the potential to wreak havoc on land with flooding, strong winds and destructive rain dumps later in the year.

Of course, the most well known sufferer of warm oceans are our icy environments. This year, global sea ice has dropped to more than one million square kilometres below the previous low. This change is not happening at a uniform rate however, with the Arctic seeing slightly more sea ice than usual for the time of year whilst parts of the Antarctic are rapidly melting away. This increase in melting ice is actually causing a very important shift in a global ocean current, one that could affect the weather across the globe.

The Southern Ocean Overturning Circulation is a global ocean current which carries water, oxygen, carbon, nutrients and heat around the world and from deep areas of the ocean to the surface. This current begins in the cold, dense waters off the coastline of Antarctica where cold, oxygen-rich water sinks to the deep ocean, delivering oxygen to the creatures living there. From here, the water moves north into other oceans where the water warms and rises to the surface, taking with it nutrients which are essential in the food chain. As the ice on Antarctica’s continental shelf melts and flows into the ocean, the seawater becomes less salty, less dense and less cold. This means that the cold, deep, nutrient-rich water no longer mixes with the warm surface water as effectively, slowing down the whole circulation process. Whilst there have always been variations in the speed of this current, these changes have previously occurred over thousands of years, not mere decades. Since the 1990s, the current is believed to have slowed by 30% due to melting ice sheets, with the effects of this already seen in the Antarctic-Australia ocean basin. A slowdown in the current would cause the surface water to increase in temperature which would further fuel the melting of ice which in turn would lead to an even greater slowdown of the overturning circulation in a negative downwards spiral. It also means that fewer nutrients reach the surface of the ocean where phytoplankton live, an essential food source for many of our most famous marine animals. The effects on the climate would also be far reaching as, for example, the Atlantic Meridional Overturning Circulation could slow down too. This includes the Gulf Steam which carries warm wind and water from the Caribbean to Europe and, if this shuts down in a worst case scenario, Europe could see a drop in temperature of 5-10°C.

The little-known twilight zone is just one area of the ocean which is being affected by this shift in ocean temperatures. This zone represents the water which lies 200 – 1000 metres deep and is home to creatures which survive with very little light. They do however, rely on the nutrients which float down from the surface. Studying preserved shells, scientists believe that in previous warmer temperatures, the amount of life in the twilight zone decreased as bacteria enjoying the warm surface waters were eating the nutrients before they could float down the water column. In cooler times, the ocean acts more like a fridge, preserving the nutrients for longer and providing a larger food source. Scientists believe we are already losing some of the species which live in this area, many of which store carbon and actually help us combat climate change. Here also lies what is believed to be the world’s largest and least exploited fish stock which could provide an important source of food to fuel our growing human population.

With the temperatures of the world’s oceans fluctuating so rapidly over the last few decades, it is no surprise that its inhabitants are on the move. This mass migration towards the cooler poles allows creatures to stay in the conditions they are adapted to live in and consequently, marine species are moving their home ranges on average 45 miles every decade. This is an enormous shift in comparison to their terrestrial counterparts which are moving a much slower four miles per decade. Not only does this affect which creatures we might spot from our coastlines but it massively impacts the fishing industry that may no longer be able to catch the species they have hauled in for decades. In places such as West Africa and Indonesia, this is a serious problem as species are fleeing the increasingly hot Equator and heading to the poles, with no new species moving in behind them. In Australia, Moorish Idol fish were a common sight in the North but have now moved all the way down the coast to the cooler New South Wales. Even corals have been seen migrating south where they are providing a home for the creatures moving with them.

Other species are being forced to move too and are struggling to find new homes in a much smaller marine area. Coastal squeeze is a term being used to describe what is happening to our shorelines and refers to the steadily rising sea levels which are meeting the increasing number of new human developments which are popping up on the edge of the coast. This means that intertidal species, such as crabs, seaweed and barnacles, have less and less space to live in between the tideline and our man-made seawalls. In a bid to solve this issue, scientists are creating artificial vertical rockpool-like structures to attach to human-made infrastructure, such as seawalls and groynes, which give these species somewhere to live, the equivalent of us building skyscrapers to accommodate more people in one small area.

Soon it seems the human population may be facing a similar fate as melting ice is leading to sea level rise which is already being seen in low lying coastal areas around the world, from America to Bangladesh. One example is the town of Ban Khun Samut Chin which lies just 10 kilometres from the outskirts of Bangkok. Much of the town has already been swallowed by the sea, with old electricity poles now mere wooden sticks poking above the water. The school has been forced to retreat inland twice as just over one kilometre of land has disappeared since the 1950s. With many locals leaving the area, the school now has just four pupils. Many small island nations are facing a similar fate with some Pacific islands questioning what happens when their whole country is under water. Do they still exist as a nation? The current definition of a state means that you need physical land and so places such as Tuvalu, Vanuatu and Saint Kitts could be at risk of losing their status as a state. This is why many of these islands are pushing for a change in the law which would allow their nations to keep their identity, even when their land has vanished. They are also pushing for international guarantees which will allow them to still access the resources which lie within their maritime zones, such as fish stocks. All of these actions are hoping to secure a future for their citizens whilst also preserving their culture and history before it is washed away.

Whilst sometimes it may feel a little futile doing your bit for climate change when the problem is so great, we really are now in a race against the clock to halt these disastrous effects on our environment before it is too late. The only way we can really make a difference is by everyone playing their own part and committing to make a change in their way of life before we lose the places and creatures we treasure the most.

By Neve McCracken-Heywood