1. Great Pacific Garbage Patch

What is it?
What’s known as the Great Pacific Garbage Patch (or the Pacific Trash Vortex) — a massive accumulation of plastic waste in the ocean — is actually two separate entities: the Western (between Japan and Hawaii) and the Eastern (between Hawaii and California) Pacific Garbage Patches. Connected by a thin current called the Subtropical Convergence Zone, the combined area of the two patches is estimated to be around 1.5 times the size of the US.src It’s considered the biggest landfill on the planet.

What’s causing it?
Whether intentional (ocean dumping) or unintentional (carelessly discarded trash), a lot of human-made waste ends up in the ocean, around 90% of it being plastic.src Through wind and ocean currents the garbage accumulates in large areas where there is significantly less current.

Why you should care
Sea creatures and birds — most famously the albatross — often mistake the flotsam for food; the plastic disrupts the digestive systems of these animals and they die. Humans end up consuming this plastic too — the material breaks down into smaller and smaller particles and is eaten by very small creatures, which are then eaten by their predators, and so on up the food chain until it gets to our tables.

Besides being harmful to living beings, the presence of this vast amount of garbage is changing the ecosystem. Algae and plankton populations — which create their own food from oxygen, carbon, and sunlight — can be affected by less sunlight due to accumulating surface debris. This in turn affects animals that feed on them and, again, up the food chain, altering nature’s balance. Besides all that, much of the trash also washes up on islands in the Pacific, burying beaches in layers of our waste.

What’s being done about it?
Since 80% of sea garbage comes from land, there is considerable effort in the developed world — where a large proportion of plastic is consumed and tossed — to stem the use of plastic (e.g., banning plastic bags in grocery stores, using bio-degradable containers, etc.). Education and awareness raising will also go a long way in decreasing the amount of waste we generate. Of course, while lowering our consumption is the most effective way to avoid compounding the problem, there still remains this massive landfill in the middle of the ocean, and no one yet has come up with any clear idea of how to clean it up (one potential solution is Boyan Slat’s Ocean Cleanup Array). To me it really comes down to two words: Consume less.

2. Warming sea water

What’s the issue?
Compared to the last 50 years, the overall temperature of the world’s oceans today is at its highest; surface temperatures, where this increase is most evident, have been increasing rapidly since the late 1800s.src

What’s causing it?
Despite increasing greenhouse gas emissions, the Earth’s average surface temperatures haven’t risen over the past 15 years. According to a November, 2013 study published in Science, the expected heat increase is likely being absorbed by the oceans.src In the study, researchers found that in part of the Pacific Ocean, middle-depth temperatures increased at 15 times the rate over the past 60 years than they did the previous 10,000 years. This amounts to about a 0.32-degree Fahrenheit rise in the past six decades.

Why you should care
In our frame of reference, this heat increase sounds very small, but even tiny changes in ocean temperature can have significant impact on life:

Coral bleaching – The algae that live in coral provide it with nutrition and also all the colours that we see in images from, say, the Great Barrier Reef in Australia. But coral is very sensitive to temperature increases, and once the water gets too warm it expels the algae and turns white. If the coral can’t reabsorb the algae it dies. While coral only constitutes about 1% of the planet’s undersea ecosystems, they are home to around a quarter of all marine species, help to protect shorelines, and support fishing and tourism industries.src

Rising sea levels – As temperatures increase, the oceans expand. With the help of melting sea ice, absolute sea levels are currently rising at a rate of about 0.13 inches per year.src This causes a host of major problems, like: the drowning of shallow-water sea life (coral reefs, sea grass meadows), loss of coastal habitat for animals (in many cases, animals are unable to migrate further inland because of man-made barriers like seawalls and other developments), and loss of habitat for humans. Around 10% of the human population stand to be directly affected by rising sea levels.src

Migration of aquatic life toward the poles – A study published in August, 2013 found that species of sea life, “from plankton and ocean plants to predators such as seals, seabirds and big fish,” are migrating at a pace of 7km per year toward the poles to chase appropriate survival and breeding conditions. Compare this to land species, who are moving at around 1km per year.src Species unable to migrate — like barnacles and shellfish, which rely on coastal ecosystems — are put at greater risk.

What’s being done about it?
Since human-caused greenhouse gas emissions are largely to blame, efforts to lower these are of the utmost importance. World leaders and policymakers have been slow to react and implement any meaningful regulations. In the meantime, it’s up to each individual to do their best to lower their carbon footprint.

3. Over-fishing

What is it?
Put simply, humans are taking fish out of the ocean at rates faster than they can reproduce.

What’s causing it?
The problem began in the mid-1900s when governments around the world made significant efforts to increase catches. By providing subsidies, loans, and industry-favoured policies, they fuelled commercial fishing in extracting ever-increasing numbers of fish to provide a wide variety to the public at low prices.

Everything changed though in terms of fishing…with the addition of steam power to the fishing fleet, and this changed all the rules. We were now cut loose from the bonds of wind and tide that had held us for so long. We were able to travel much farther offshore, we could get fish back to market in a fresh state from much greater distances. You could go deeper down, you could drag bigger nets, you could fish round-the-clock…it was an incredible alteration in the amount of fishing power being expended.
– Professor Callum Roberts, Marine Conservation Biologist, University of Yorksrc

Why you should care
By 1989 the fishing industry had caught 90 million metric tons of fish — since then yields have declined or stayed flat. Large ocean fish populations (e.g., blue fin tuna) have decreased to about 10% of pre-industry levels according to a scientific report from 2003. This reduction in yields has spurred the industry to move to the deep waters, which is “triggering a chain reaction that is upsetting the ancient and delicate balance of the sea’s biologic system.” It was predicted in a study published in Science that if the pace of fishing continues, all fisheries will collapse by 2048.src

According to the UN, over 200 million people around the world rely heavily on fishing for their livelihoods and food security, while 20% of the Earth’s population look to fish as their main source of protein.src

What’s being done about it?
The problem of overfishing is reversible. We just need to give species a chance to recover.

The World Wildlife Fund (WWF) helped found the Marine Stewardship Council (MSC), a certification body that works with fisheries around the world to help them become sustainable. Today, over $3 billion in annual sales (of over 15,000 seafood products) carries the MSC mark. You can locate dealers that carry MSC-certified products here.

Co-management of reef systems — in which local communities, conservation groups, and governments work together — is also appearing to have positive results in regards to sustainable fishing practices. A study by the Wildlife Conservation Society, carried out by 17 scientists from eight countries, concluded that this arrangement can support communities’ livelihoods while protecting fish stocks.src

“Catch shares” is a fisheries management system in which allowable fishing limits — determined by scientists — are distributed among fishermen as a quota. Around 65% of fish caught in US waters is done so under this management system, which has proven to increase fish stocks, decrease wasted fish (bycatch), and increase revenue for fishing fleets.src

4. Ocean acidification

What is it?
Over the past 300 million years, sea water has had an average pH of 8.2 (pH is measured on a scale from 0 – 14, 7 being neutral, below that being acidic, and above being basic, or alkaline). This has dropped (meaning the ocean is becoming more acidic) by 0.1 pH units to 8.1. This amount of change — because the scale is logarithmic and not linear — represents a 25% increase in acidity.src

What’s causing it?
Since the beginning of the industrial revolution, humans have released billions of tons of carbon dioxide (CO2), half of which has been absorbed by the ocean. When CO2 is absorbed by the ocean it forms carbonic acid, thus making the water more acidic, especially near the surface. While the seas have helped to mitigate the negative effects of these emissions in our atmosphere (i.e., slow down climate change), we’re now starting to understand how it’s affecting the oceans.

Why you should care
Based on our current levels of CO2 emissions, it’s been projected that ocean pH levels may drop by a further 0.5 units. Acidity has a detrimental effect on the ability of certain marine life to build shells (corals, oysters, lobster, etc.) because of the decreased amount of calcium carbonate, a mineral that is the building block of these shells. Acidification is also suspected to cause reproductive problems for some fish. On the other hand, certain plant life like algae and seagrasses may benefit as they require CO2 to survive. In the end, though, the result is an ecosystem out of balance.

In addition to a changing ecosystem, the capacity for our oceans to store CO2 is limited, meaning more and more of the emissions we produce will remain in the atmosphere, accelerating global warming.

What’s being done about it?
Because acidification is directly related to the amount of CO2 in the atmosphere — which, currently, is by far the most in the past 1 million years — the logical and most practical course of action is to reduce any actions that result in excess CO2, namely burning fossil fuels and deforestation.

5. Mercury contamination

What is it?
Mercury is a toxic metal. It is found naturally in air, water, and soil, but due to human activity oceanic levels are rising, which is contaminating marine life.

What’s causing it?
The biggest contributors to mercury pollution are coal-fired power plants and other coal-burning equipment like boilers and heaters.src Coal contains mercury, and when it’s incinerated that mercury enters the atmosphere.

Source: NRDC

Small-scale gold mining operations and artisans are the world’s largest users of mercury, who employ it to extract gold from ore (the mercury binds to the gold and is then burned off, leaving the gold behind and releasing mercury into the air). Metal smelting and refining are also significant contributors to mercury pollution. Atmospheric mercury falls back to earth via precipitation and enters the ocean through rivers and groundwater systems.src Electronics and other consumer goods are also major sources of mercury.

In the past century, mercury levels in the top layer of the ocean have doubled, according to the UN Environment Program.src

Why you should care
Methylmercury, which often results from mercury entering the ocean, is the main concern when it comes to human health. It is consumed by us through fish and other seafood and can impair neurological development in fetuses, newborns, and children. It is so widespread in our environment that almost everyone has at least trace amounts in their tissues.src If you love eating canned tuna, here is a table that describes safe consumption. You can also read this to find out which fish are the least and most contaminated.

What’s being done about it?
In the US, the Environmental Protection Agency has set clean air safeguards (Clean Air Act) that apply to power plants and other atmospheric-polluting operations.

The Minamata Convention on Mercury is an international treaty that was signed by 94 nations in late 2013; its goal is to protect human health and the environment from the effects of mercury pollution. From the website:

The major highlights of the Minamata Convention on Mercury include a ban on new mercury mines, the phase-out of existing ones, control measures on air emissions, and the international regulation of the informal sector for artisanal and small-scale gold mining.

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