environmental problem – and probably the biggest problem full stop – which faces humanity today. Unsustainable practices since the industrial revolution have led to huge greenhouse gas emissions and a massive increase in carbon dioxide (CO2) concentrations in the atmosphere: scientists estimate that since humans began burning fossil fuels on a large scale, we have caused the emission of almost 545,000 million, or 545 billion tonnes of carbon alone¹.
For those who don’t understand the process of global warming, excess greenhouse gases trap heat within the earth’s atmosphere and cause a warming effect – something which is becoming more and more evident every year. This warming, or average surface temperature increase, has wide-ranging effects on both the environment and on human society. These include²:
- Many coastal communities are becoming threatened by rising sea levels.
- Climate change is causing an increase in extreme weather events and natural disasters.
- Our oceans are suffering, and may cease to exist as they are today if global warming continues.
On that note, what are the effects of global warming on the ocean?
Most of us have heard about coral bleaching and the devastating effects that it is having on irreplaceable places like the Great Barrier Reef in Australia, but how many of us actually understand what is causing it? The main cause of coral bleaching – and a number of other negative effects on shellfish and corals – is increasing sea surface temperatures and rising oceanic CO2 concentrations. Corals are very sensitive species, and will usually not cope well with sudden change. Their colour comes from a symbiotic relationship with a photosynthetic alga, which provides food for the coral³.
When the coral becomes stressed – either by warmer water than they are used to, or by a decrease in the ocean’s pH (caused by an increase in oceanic CO2 concentration) – they will expel these algae and become colourless. Since the algae are the corals main source of food, they struggle to survive after bleaching³.
According to a number of experts, global warming is causing fish to migrate away from the equator and towards the poles. Since sea surface temperatures are increasing due to global warming, the fish must swim towards the pole in order to remain in water of the correct temperature. This can disrupt important fisheries, remove the food source of marine predators such as birds and seals, and can threaten some species which run out of suitable habitat⁴.
Since global warming causes the ocean to heat up, it also causes sea levels to rise – something which is becoming obvious already. Some of this sea level rise is due to melting sea ice, while the rest is caused by the thermal expansion of water as it warms. Regardless of the cause, rising sea levels are flooding low lying coastal areas around the world. This is especially evident in coastal wetlands and marshes⁵.
The rising water can inundate these wetlands, turning them into open ocean and destroying their sensitive ecosystems. Some experts say that a sea level rise of as little as 2 feet (60 centimetres) will be enough to destroy the majority of the world’s coastal wetlands⁵.
Ocean acidification is one of the major effects of global warming on the ocean. While the full mechanism is too complicated to explain here, basically dissolved CO2 causes a decrease in ocean pH. This in turn causes a decrease in the concentration of the carbonate ion, which is essential for many marine animals – including corals and shellfish – to build the skeletal structure⁶.
Therefore, global warming, and in turn ocean acidification, is affecting entire marine ecosystems. It is causing coral bleaching, affecting reef structure, and in some cases, is reducing the reproductive capabilities of many shellfish and other organisms⁶.