A closer look at the oceans’ role as powerful carbon sinks
So far, the blue part of our planet has played a massive role in slowing climate change. The oceans have absorbed a full quarter of the carbon dioxide (CO2) released since humans started burning fossil fuels during the Industrial Revolution – and they’ve also trapped around 90% of the excess heat created by climate warming gasses. Ocean-based solutions can play a huge role in limiting global warming in the critical coming years. As world leaders prepare to meet in Glasgow for the COP26 Climate Conference, we’re digging into the complex ways oceans slow climate change – and what policymakers can do to protect one of Earth’s largest carbon sinks.
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PLASTIC, CLIMATE CHANGE & THE OCEANS
Climate change, marine life, ocean ecosystems and plastic are all deeply connected, and we can’t talk about climate change policy without addressing plastic’s role. 99% of plastics are made from a compound called ethane, which comes from oil and natural gas. The U.S. Environmental Protection Agency estimate natural gas and petroleum are responsible for almost one-third of total U.S. methane emissions, one of the most potent greenhouse gases responsible for warming the planet, including the oceans.
Single use plastics are at the heart of this demand. Plastic bags, bottles and takeout containers make up a huge portion of ocean litter that harms marine life and prevents oceans from trapping CO2 – more on that below.
Countries around the world have already created policies aimed at drastically reducing the amount of single use plastic in circulation. Putting pressure on your local government to follow suit is one of the most effective ways to keep the momentum going. Read our deep-dive on plastics and climate change here.
HOW OCEANS SLOW CLIMATE CHANGE
One of the main ways oceans slow climate change is pretty simple. Water is both great at storing heat and can also absorb a lot of it before starting to heat up itself. The first few meters of the oceans’ surface trap the same amount of heat as Earth’s entire atmosphere.
The second way the oceans slow climate change is through a complex web of marine ecosystems that trap greenhouse gases like CO2, taking them out of the atmosphere where they don’t heat the planet. The world’s oceans consistently absorb about 30% of atmospheric CO2. That means that as the amount of CO2 in the air increases, so does the amount stored in the seas. Here’s how they do it:
Sources: National Oceanic and Atmospheric Administration, Intergovernmental Panel on Climate Change
Plankton
Carbon storage in the oceans (a.k.a. blue carbon) starts at the bottom of the food chain.
Phytoplankton are the basis for all marine ecosystems –– they’re also the most powerful carbon-storers in the ocean. The tiny plants capture as much CO2 as four Amazon Rainforests.
Phytoplankton need CO2 to photosynthesize. They grab excess CO2 from the ocean’s surface, where it’s pulled from Earth’s atmosphere and trapped where it can’t heat the planet. But early lab research is beginning to show that microplastic pollution is interfering with this process.
Many countries have already banned or taxed plastic bags, and a few have made moves to target other common sources of single-use plastic. In July, the EU banned the 10 most common pieces of plastic trash found on beaches. A few months earlier, Chilean lawmakers unanimously voted to pass a plastics reduction bill that will roll out over the next three years. The new legislation bans things like styrofoam takeout containers and plastic utensils, and will eliminate around 23,000 tons of single-use plastics generated by restaurants and their customers every year.
Whales
Legislation that protects whales from being hunted may not seem like the most obvious target of climate policy, but it’s crucially important. Not only is whale poop vital for plankton production, the animals themselves store an enormous amount of CO2, partly due to their position at the top of the marine food chain.
A 2019 report found that a single great whale — which includes gray, humpback, right, blue, sperm, bow- head, fin, sei, Minke, pygmy right and Bryde's whales — captures around 33 tons of CO2 during their lifetime. This carbon capture continues after they die. Unlike terrestrial beings, which release their carbon into the atmosphere as they decompose, the overwhelming majority of large marine animal carcases sink to the bottom of the ocean. Here, the carbon they absorbed throughout their lifetime is trapped deep in the sea.
Plastic plays a huge role in killing whales, but so does the seafood system. In 2019, Japan left the International Whaling Commission (IWC), which sets a moratorium on whaling in international waters. This meant Japan’s fishing fleets could once again hunt whales in the country’s national waters after a 30-year ban on the practice. Iceland and Norway, two other countries with rich whaling histories, also continue to hunt. Some say the actions of just a few countries are undermining the effectiveness of the international moratorium.
Still, deliberate whaling isn’t the only practice tied to wildlife’s role in blue carbon storage. It’s estimated 300,000 whales and dolphins die as bycatch every year, many times in areas that aren’t profitable to begin with. A study published earlier this year found that almost half of the blue carbon the fishing industry extracted from international waters came from areas that wouldn’t be profitable without government subsidies.
Fishing subsidies have been a topic at World Trade Organization (WTO) discussions for the past two decades. Last year, leaders failed to come to an agreement that would end fishing subsidies in offshore waters, which not only support overfishing, but also incentivize fishing in non-profitable areas. Despite the setback, countries and NGOs that oppose the subsidies are still pushing to end them.
Mangroves
Mangroves are vital coastal habitats that store massive amounts of carbon. The soil in these aquatic forests is waterlogged, which traps and compacts CO2. In some places in Belize, Grand Cayman and Panama, these carbon deposits plunge 10 meters beneath the ground. When these ecosystems are harvested for their wood or to make way for aquaculture projects, that carbon is released back into the atmosphere where it contributes to climate change.
A study published in 2018 found that in the year 2000, 6.4 billion metric tons of CO2 was stored in the soil beneath coastal mangroves, more than previously thought. But the researchers also estimated that in the first 15 years of this century, the loss of mangrove forests released as much CO2 into the atmosphere –– 122 million tons –– as Brazil produces in a year. Deforestation in just three countries, Indonesia, Malaysia and Myanmar, accounted for more than three-quarters of these emissions. Guatemala lost almost 7% of its mangrove soil carbon in those 15 years.
Habitat protection is the most effective way to keep mangrove soil carbon locked away. Since mangroves usually fall within the boundaries of multiple countries, this can be hard to do without international policy and getting communities involved in the sustainable management of mangroves.
Seagrass meadows
Seagrass meadows store twice as much carbon as terrestrial forests. And like mangroves, seagrass meadows are being destroyed by human activity.
The U.N. Environment Programme (UNEP) estimates that a patch of seagrass roughly the size of a soccer field is destroyed by human activity every half hour. This adds up to about 7% of seagrass meadows every year, according to the most recent census which was published back in 2009.
A more recent study came to another alarming conclusion: Pollution from mining and damage from fisheries has already destroyed more than 90% of seagrass meadows off the coast of Britain. The research showed that protecting seagrass meadows isn’t enough on its own. Policies that regulate mining, especially along coasts where toxic chemicals can seep into seawater, are also necessary to preserve healthy seagrass meadows.
Luckily, countries are starting to recognize the significance of seagrass meadows as carbon sinks.
The Saya de Malha, a shallow green seagrass meadow beneath the Indian Ocean, just north of Madagascar, is the largest submerged ocean bank in the world. Seychelles and Mauritius have joint jurisdiction over the Saya de Malha and this year, Seychelles began assessing its coastal seagrass carbon stock for the first time. It’s one of at least 10 countries that recognized seagrasses as part of their climate action plans.
Kelp forests
Kelp are basically the oceans’ equivalent of trees, except they’re even better at capturing planet-warming gasses. Kelp forests can store up to 20 times the amount of CO2 that land forests can. They’re also extremely resistant to heating temperatures and El Niño events –– as long as the ecosystems that surround them remain intact.
These floating forests sway along one-quarter of the planet's coastlines, but they’ve been quickly disappearing. One-third of all coastal kelp forests have vanished in the past decade. The largest diversity of kelp forests is in the northeastern Pacific, from just north of San Francisco, California, to the Aleutian Islands in Alaska. It’s also one of the patches hardest hit by decline.
It’s a paradox seen in so many ocean ecosystems: Researchers believe the warming effects of climate change are driving a mysterious parasite that’s been responsible for a mass die-off of sea stars along the West Coast of North America since 2013. The echinoderms are a vital part of kelp forests, which keep CO2 out of the atmosphere and slow Earth’s heating. Without them, kelp forests are both less resilient to extreme weather (at a time when they’re faced with unprecedented warming and ocean acidification) and more susceptible to becoming food.
Without predators to keep them in check, purple sea urchins have exploded along coastlines in the western United States and Canada. Sea urchins devour kelp’s roots faster than they can replace themselves. As a result, kelp forests off the coast of Northern California have shrunk by 95% in the past seven years. So have those off the coast of Chile and Tasmania, for the same reasons.The good news is that scientists think kelp forests can be restored. Non-profits, universities and private companies are working together to replant kelp forests and restore sea star populations in the northeastern Pacific Ocean. For these restored sea forests to thrive, humans need to drastically reduce the amount of extra heat being pumped into the atmosphere –– heat that the oceans are largely tasked with absorbing. This extra heat makes it harder for species like kelp to successfully cope with other stressors. Some scientists are also working to identify the most critical swaths of kelp forest and alert policymakers who have the power to protect them.
HOW TO TAKE ACTION
There’s strength in numbers but it starts with one. Read up, make noise, spread the word and give others the tools to do the same. This is the best way to drive world leaders to adopt policies that will slow climate change and help the oceans stay healthy so they can play their role.
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