In hot water: how climate change is affecting the oceans

Perhaps as a result of the nation being gripped recently by the stunning images of Blue Planet II, more and more attention is rightly being afforded to the world’s oceans – and the environmental problems which afflict them. Given the vastness of the oceans, the challenges they face are numerous. Yet one threat, climate change, appears to be particularly acute.

Our species’ centuries-long reliance on fossil fuels to produce energy, as well as trends in animal agriculture and other polluting industries, had emitted greenhouses gases into the atmosphere and changed the planet’s climate. These greenhouse gasses, like carbon dioxide and methane, trap heat close to the Earth’s surface, which have been behind the steady rise in global temperatures.

The impact on marine ecosystems

A changing climate has exhibited itself in several forms across various habitats. One serious manifestation for oceans, however, has been the problem of acidification. This refers to the steady alteration of the chemical composition of seawater, triggered largely by more and more carbon dissolving into the oceans. Since the beginning of the industrial revolution, the pH balance of surface ocean waters has fallen by 0.1. Whilst this may seem insignificant, because the pH scale is logarithmic it actually represents a 30% increase in acidity.

One of the most widely understood impacts of ever more acidic oceans is the effect it can have on organisms known as ‘calcifiers’. These are animals such as crustaceans, molluscs, and corals which use calcium and carbonate ions to build shells and exoskeletons around themselves. But acidic oceans dissolve calcium carbonate, so when the pH level drops, the ability for calcifiers to maintain themselves – let alone grow and prosper – becomes all the more difficult. In addition to this, research has found that successful fertilisation rates for some calcifiers decrease in acidic waters.

Coral reefs are some of the most biodiverse ecosystems in the world. Yet warmer waters present an existential threat to them – with experts claiming that the Paris Agreement’s commitment to 1.5℃ being the only way to save coral reefs. When the waters in which corals are found get too warm, they expel the algae which give them their renowned vibrancy, and turn white. This ‘bleaching’ does not mean the coral is dead, but without the algae corals find it more challenging to survive, and consequently often do die off as a result. Moreover, scientists have observed numbers of certain organisms which predate on corals – such as crown-of-thorns starfish – unsustainably flourishing in warmer waters, which further adds to the struggle to survive for corals.

As the climate warms, and the ice caps melt, sea levels inevitably rise. Indeed, over the past century, it is thought that the global mean sea level has risen by between four and eight inches. Even more worryingly, the rate at which it is has been rising over the past 20 years is double that of the preceding 80.

The consequences of rising sea levels for marine wildlife are multifarious, and will almost certainly result in the destruction of habitats vital for semiaquatic animals. Sea turtles, for instance, which depend on beaches to lay their eggs are one particularly vulnerable species. But one report claims that as many as 233 already endangered species will become further threatened by rising sea levels.

A lesser appreciated consequence of increased ocean temperatures is the effect it has on ocean currents. These currents influence aquatic animals’ migratory patterns, which can disturb ecosystems, as well as dispersing the nutrients vital for life below the waves. Changes in them, therefore, may starve areas of biodiversity of the nourishment necessary to sustain life.

The human cost

Whilst the impact of climate change on the globe’s seas and oceans is tragic enough in its own right, it also poses significant costs which will be borne more directly by humankind, too.

Coral reefs, for instance, are valuable sources of medicinal learning – with drugs to treat cancer, arthritis, and asthma having already been developed from resources found in corals and surrounding ecosystems. Evidence has shown that coral reefs also act as barriers to ocean waves and storms, which provides protection to millions of people the world over. Of course, pristine coral reefs also attract tourists – and are estimated to be worth over £25 billion a year globally, with that money often going into some of the most economically challenged parts of the world. Climate change, and ocean acidification, therefore, imperils all of that. Indeed, it is thought that the Great Barrier Reef is now beyond repair because of this combination of threats.

Changing ocean temperatures which alter currents can also have negative ramifications for people. Ocean currents have two significant roles in the global ecosystem. It has already been considered how they serve as a nutrient dispersal mechanism, shifting food for aquatic species up from the depths and then around the oceans. Warming waters which can decelerate these currents, therefore, could spell bad news for fishing communities who find themselves with fewer fish to catch.

Ocean currents also have an influencing role in local climates. Whilst they do not effect global temperatures per se, currents do facilitate the movement of heat – such as from the warm equator to temperate Britain, East America, and Europe. This partly explains why certain regions on the same latitude experience different temperatures. Were this process to slow down or cease, such aforementioned locations could see their localised temperatures change. 

For many good reasons, some of the most populous cities can be found next to the sea – Shanghai, Miami, and Rio de Janeiro to name but a few. Yet, faced with rising sea levels, their coastal locations could be their very downfall. One estimate places the figure at risk from rising sea levels, and the increased flooding and intensified storms associated with global warming, just shy of two billion individuals.


Seas and oceans cover almost three-quarters of the Earth’s surface. Though often thought to be harsh and uncompromising environments, they contain fragile ecosystems, and have intimately felt the effect of anthropogenic climate change. The future consequences of this are hard to predict, however signs are already beginning to show the costs – for humans and wildlife – of climate change for our oceans.

Eamonn Ives is a researcher at Bright Blue

Drowning in plastic waste

We have now had over a year of the plastic bag charge. Since October 2015, shoppers in England have had to pay 5p for plastic bags at retailers with over 250 employees. Many people can now be seen juggling grocery items on their way home from the shops in a desperate attempt to avoid the levy. But have these super-human feats of contortion been worth the effort? Have they together had an impact on the environment?

We now have the data to answer this question, and the answer is a firm yes. The Marine Conservation Society has already reported a 40% drop between 2015 and 2016 in the number of plastic bags they collected from UK beaches. Official figures suggest a total of six billion single-use plastic bags were avoided in the first six months of the charge. Ministers also announced the charge had already raised £29 million for good causes, with many chains opting to support environmental charities.

The harm of plastic pollution

Plastic bags are, however, just a subset of plastic pollution, which is a major environmental challenge, particularly in marine ecosystems. Bigger pieces of plastic can entrap fish, causing injuries, suffocation, or strangulation. Smaller plastics can be ingested. This harms the creature themselves. Scientists have found evidence of plastic making fish larvae less active, more likely to be eaten by predators, and less likely to thrive. This also has implications further down the food chain: For instance, by eating six oysters you are likely to ingest around 50 microplastic particles.

The scale of the problem is immense: Eight billion tons of plastic waste ends up in the oceans every year. A Greenpeace report for the United Nations Environment Programme (UNEP) found evidence of 267 different marine species affected by plastic pollution. Another study has estimated that around half of marine mammals has either been entangled by or ingested plastic. There is growing evidence that plastic pollution affects freshwater rivers too. Researchers found 8,490 pieces of plastic in the River Thames during a three-month-long observation.

The process of plastic manufacturing contributes to climate change. The Committee on Climate Change reports that the industrial sector in general produces 32% of the UK’s greenhouse gas emissions (including both direct emissions and its share of electricity emissions). The plastics industry makes up 2% of this total. Plastics provide another market for oil, and so help to support global fossil fuel supply chains. Incineration of plastic waste releases carbon dioxide into the atmosphere.

Policies to cut down plastic pollution

In the spirit of Edmund Burke’s “little platoons”, litter-picking groups which collect plastic debris from beaches and coastline can ameliorate the problem. The Marine Conservation Society frequently runs such events. While the impact on the total mass of plastic in the ocean is minimal, the activity gives people a tangible connection to their local environment. This can also help raise awareness of plastic pollution, and in turn change behaviour to encourage people to use less disposable plastic.

Increased recycling rates could also help clean up plastic pollution. Single-use plastic bags have been dramatically reduced. But single-use plastic bottles, for instance, remain a major challenge: The average household recycles just 44% of the 480 plastic bottles it uses each year. Fiscal nudges like landfill taxes can encourage recycling, by ensuring businesses to pay for the effects of plastic waste. Improved and more frequent council recycling services could also cut down on such waste.  

Plastic pollution has become a major focus of circular economy studies, which seek to increase resource productivity. As well as harming the environment, single-use plastic is an inefficient use of resources. The Ellen MacArthur Foundation has found that 95% of the economic value of plastic is lost after its first use. This is worth between $80 and $120 billion annually. They call for a rapid scaling up of the global supply chain for reused and recycled plastics, with improved infrastructure for collection, sorting and reprocessing to expand the current market.

Microbeads used in cosmetic products are another area where the Government has acted to cut plastic pollution. Next year, a consultation will be launched on how to ban these entirely. This could have a significant impact: A single shower can release up to 100,000 tiny particles of plastic into the sea, according to the Environmental Audit Committee. Up to 4.1% of all microplastics in the ocean are estimated to derive from microbeads in cosmetics. Some are calling for the ban to be extended to other products containing microbeads, such as washing detergents.

Many of these different levers may be needed if the tide is to be turned on plastic pollution. Scientists found earlier this year that since the Second World War we have manufactured enough plastic to cover the entire earth in cling film. The oceans are some of our most precious environments, which host most of our diverse species and flora. We cannot afford to keep damaging them.

Sam Hall is a researcher at Bright Blue