How Does Global Warming Affect the Ocean?

Global warming is undoubtedly the biggest 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.

The level of greenhouse gases in the atmosphere influences global temperatures and weather patterns because these gases absorb solar heat so efficiently.

While much of the information on climate change that we are exposed to focuses heavily on CO2 in the atmosphere, almost half of the carbon dioxide that is being produced by the burning of fossil fuels has been absorbed by the ocean

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 include:

1. Many coastal communities are becoming threatened by rising sea levels;
2. Climate change is causing an increase in extreme weather events and natural disasters;
3. Many animal and plant species are faced with extinction caused by global warming;
4. Our oceans are suffering and may cease to exist as they are today if global warming continues [1].

Due to its massive volume and the relatively large heat capacity of water, the ocean has an incredible ability to buffer the atmospheric temperatures of planet earth. It is estimated that around 90 percent of the excess heat trapped by greenhouse gas emissions is absorbed by the ocean. But for how long?

The ocean’s heat storing ability

The Intergovernmental Panel on Climate Change (IPCC) has estimated that since 1955, “over 90 percent of the excess heat trapped by greenhouse gases had been stored in the oceans.”

After reading that you may be thinking that only 10 percent of the excess heat has been used to warm the atmosphere, not so bad, right?

Wrong!

Most of these 10 percent actually go towards melting sea ice, ice caps, and glaciers, and warming continental land masses. Only a tiny fraction actually directly warms the atmosphere. This is scary because the ocean’s heat storage ability is finite – there will come a point in time where it is no longer able to keep up with the demands of humanity.

There are a number of reasons why the ocean is able to absorb so much heat. These include [1]:

• The high heat capacity of water. One liter of water is able to absorb much more heat than the same volume of air, or almost any other substance.
• The ocean is deep and contains a huge volume of water. 71 percent of the earth’s surface is covered by ocean, which has an average depth of 4 kilometers.
• Probably the main reason is that the ocean is dynamic – it is always moving due to currents, wind eddies, and other circulation methods. This allows mixing and exchange of the heat throughout the ocean, rather than concentrating on just the surface waters.

Researchers around the world are beginning to realize the importance of the ocean to world climate systems, and are therefore focusing their research like never before. Satellites orbit the globe, continually gathering data for analysis, while scientists work frantically to try and determine if and when the ocean will have absorbed as much heat as it can.

How long can this mechanism continue to work successfully for us?

While the world’s oceans are warming at an ever-increasing rate [2], this obviously can’t continue forever. There will come a point when the ocean can no longer absorb the necessary amount of heat, which will lead to a rapid rise in atmospheric temperatures.

The current rate of ocean heat accumulation is “the equivalent of five Hiroshima bombs exploding every second since 1990 [1].”

According to scientists, the ocean may begin to release some if its absorbed thermal energy in the near future, if it isn’t doing so already. Various oceanic cycles, which change with a relatively predictable time frame, will probably cause the release of some of the oceans stored heat when they change.

Some, like the Interdecadal Pacific Oscillation, are due to change at any time, while others are likely to follow in the coming years.

It is obvious therefore that we cannot continue to rely on the ocean as a climate buffer. It will stop absorbing heat as it currently is, and perhaps will even begin to release thermal energy in the near future. We must instead tackle the root of the problem – reducing greenhouse gas emissions – immediately and with full force.

How does the ocean indirectly buffer the atmospheric temperature?

Not only does the ocean absorb atmospheric heat directly, but it also helps reduce the atmospheric greenhouse gas levels.

CO2 and other greenhouse gases are easily able to dissolve in water, and therefore in the ocean. About half of the global carbon cycle is managed by photosynthetic organisms that live in the ocean such as phytoplankton, that produce oxygen and influence the levels of greenhouse gases (like carbon dioxide and methane) that are present in the ocean and in the atmosphere.

By keeping the greenhouse gas concentration lower, the effects of global warming will be slower.

Every year, human activity causes the release of around 36 billion tons of CO2, not to mention other greenhouse gases such as methane and nitrates. This has caused atmospheric CO2 concentrations to increase by around 50 percent since the industrial revolution – from 280ppm to over 400ppm [1].

At least 530 billion tons of CO2 has been dissolved in the ocean since the industrial revolution, which is a massive number [3]. If the ocean wasn’t able to dissolve this gas, it would remain in the atmosphere, pushing CO2 concentrations towards 500, 600, or even 700ppm.

This would translate to huge rises in global temperature, which would destroy the world as we know it. We need to protect the oceans, not only for their beauty and incredible biodiversity, but also for the indispensable role they play in regulating the earth’s climates.

The ocean influences regional climate

In addition to affecting climate on a global scale, the ocean also influences the climate of various regions around the world. The difference in temperature between the land in the middle of a continent and the surrounding ocean drives the development of monsoons.

In the winter, the much colder air over a continent flows outward toward the ocean, and in the summer, the much hotter air over a continent draws moist air inland, bringing forth summer rains.

Cities located along coastlines also benefit from ocean breezes, a result of the difference in temperature between land and sea, where the land is cooler at night and warmer during the day.

What are some of the effects of global warming on the ocean?

As global warming and climate change become a bigger and bigger issue throughout the world, it’s current and future effects are becoming better understood. One of the most talked about and publicized issues is that of rising sea levels. Although this has a number of effects, none are greater than the impacts on coastlines and coastal communities around the world.

#1 Rising sea levels

The general consensus is that we can expect a sea level rise of between 0.8 and 2 meters (approximately 3 to 6 feet) by 2100, which would be enough to flood a number of cities around the world.

Direr models predict the loss of the entire Greenland ice sheet, which would increase sea levels by a huge 7 meters (23 feet) – this would submerge much of London [6].

If sea levels rise as little as one meter, island nations such as the Maldives will disappear from the map.

We have already seen two of the islands of Kiribati disappear, while others have been contaminated by salt water from high tides and storm surges.

There are two main ways that global warming induces sea-level rise – the melting of ice caps and glaciers, and the thermal expansion of water.

Melting ice caps

As global air temperatures increase, the polar ice-caps are melting – as would be expected. Since most of the ice caps are above sea level, when they melt, it adds extra water to the ocean.

Together, the Greenland and Antarctic ice sheets contain 75 percent of the world’s fresh water. If they both melted, then sea levels would rise by around 75 meters (246 feet).

The temperatures in Antarctica are low enough to keep the Antarctic ice sheet relatively safe in the near future. An increase in temperature should not have such a profound effect to melt the whole ice sheet, as it should still be cold enough to prevent melting [7].

However, atmospheric temperatures near the Greenland ice sheet are a worry. Currently, temperatures are low enough to prevent widespread melting – just. However, with a small temperature increase in the future, there is the potential for widespread surface melting. This could cause huge problems, including sea-level rise of a number of meters, and could potentially begin an irreversible warming process. Scientists have been already observing large-scale melting events in the last couple years with 2019 being the 7th highest since 1978 [8].

The second, albeit smaller, problem related to melting icecaps is the breaking up of ice-sheets and the quicker movement of glaciers. As it gets warmer, icebergs begin to break off the edge of the ice-sheets more and more rapidly. Although this currently isn’t a major issue, it has the potential to become a much bigger problem in the future.

Thermal expansion of sea water

One of the major laws of the physics, which holds true in almost every case, is that things expand when they heat up. This expansion may be hugely noticeable, or negligible, but regardless, it is there.

Over the past century, the average ocean temperature has risen by around 0.6 degrees Celsius. Most of this warming has been in the surface waters. Thermal expansion contributes to a large proportion of sea level rise – up to 75 percent.

#2 Disappearing wetlands

Since global warming causes the ocean to heat up and sea levels to rise – something which is becoming obvious already.

Rising sea levels are flooding low lying coastal areas around the world. This is especially evident in coastal wetlands and marshes.

The rising water can inundate wetlands, turning them into open ocean and destroying their sensitive ecosystems.

#3 Coral bleaching

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 color comes from a symbiotic relationship with a photosynthetic algae, which provides food for the coral [4].

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 colorless. Since the algae are the corals main source of food, they struggle to survive after bleaching [4].

#4 Fish migration

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 habitat.

#5 Ocean acidification

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 structure.

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 organisms.

We need to reduce greenhouse gas emissions and do what we can in order to try and mitigate the effects of climate change, or else huge numbers of people throughout the world are going to suffer for years to come.