The "deoxygenation" of oceans is having disastrous consequences for sea life. It will "affect hundreds of millions of people," environmental experts warn.
Image: picture-alliance/Design Pics/D. Fleetham
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The oceans are losing oxygen due to climate change, with dire consequences for marine life and vulnerable communities and fisheries, a nature conservation report revealed Saturday.
This is the "ultimate wake-up call" for humanity on ever-increasing carbon emissions, according to the report, published at the UN Climate Change Conference in Madrid.
The authors say the report, "Ocean deoxygenation: Everyone's problem," is the largest ever peer-reviewed study into the causes and impacts of, and possible solutions to, the ocean's oxygen loss.
"With this report, the scale of damage climate change is wreaking upon the ocean comes into stark focus. As the warming ocean loses oxygen, the delicate balance of marine life is thrown into disarray," said Dr Grethel Aguilar, acting director general at The International Union for the Conservation of Nature (IUCN), a body composed of governmental and civil society groups.
Pointing the way: Swedish activist Greta Thunberg has been leading protests across the globe as she tries to get world leaders to "listen to the science"Image: Reuters/S. Perez
'Ultimate wake-up call'
"The potentially dire effects on fisheries and vulnerable coastal communities mean that the decisions made at the ongoing UN Climate Change Conference are even more crucial. To curb ocean oxygen loss alongside the other disastrous impacts of climate change, world leaders must commit to immediate and substantial emission cuts."
According to the report, areas of water with low oxygen concentrations are expanding, with roughly 700 ocean areas across the globe now affected by low oxygen conditions — up from only 45 in the 1960s. Over the past five decades, the areas completely depleted of oxygen have quadrupled.
"This is perhaps the ultimate wake-up call from the uncontrolled experiment humanity is unleashing on the world's ocean as carbon emissions continue to increase," said Dan Laffoley, senior adviser on marine science and conservation in IUCN's Global Marine and Polar Programme and a co-editor of the analysis. "Ocean oxygen depletion is menacing marine ecosystems already under stress from ocean warming and acidification. To stop the worrying expansion of oxygen-poor areas, we need to decisively curb greenhouse gas emissions as well as nutrient pollution from agriculture and other sources."
The Ocean: Earth's life support
The ocean covers most of our planet's surface and helps regulate the climate. It's already experiencing the effects of climate change — but most of it remains a mystery to scientists.
Our blue planet
It's not called the blue planet for nothing. The ocean covers up to 71% of the Earth's surface and 90% of the biosphere. It is integral to life and provides anywhere between 50 to 80% of the planet's oxygen, making it a vital part of the carbon cycle. The ocean's origins are still unknown, but it is thought to have formed 4.4 billion years ago, providing a catalyst for early life-forms.
Image: NASA
Mysteries of the deep
Despite its sheer size, we actually know very little about the ocean. In fact, over 80% of this underwater realm has yet to be mapped or explored. Scientists are working to unlock its mysteries, which could help us better understand environmental change and how to manage vital ocean resources in times of climate change.
Image: Colourbox/S. Dmytro
The planet's climate regulator
We do know that the ocean plays a major role in regulating the Earth's climate by absorbing solar radiation, distributing heat and driving weather patterns. But climate change is already starting to disrupt this balance, affecting the ocean's ability to perform key ecosystem tasks, such as carbon storage and oxygen generation.
Teeming with life
The ocean is home to at least 230,000 known species. Coral reefs on the sea floor provide a safe-haven for invertebrates like crabs, starfish and mollusks, as well as colorful reef fish. Plant life flourishes in the shallow depths, while bigger creatures like sharks, whales and dolphins roam the deep open waters.
Image: picture-alliance/blickwinkel
Weird and wonderful creatures
Unsurprisingly, scientists also think up to two-thirds of all ocean species may still be undiscovered. But researchers are finding new species every year — many of them unlike anything found before, such as this squidworm (pictured), discovered in the Celebes Sea in 2007. What else might be lurking down there is anyone's guess.
Image: Laurence Madin, WHOI
Warning signs
But the ocean is under pressure. One of the most obvious examples being the increase of coral bleaching events in reefs around the world. Increased temperatures and pollution stress corals, causing them to expel a special kind of algae which allows them to grow and reproduce, leaving behind a ghostly skeleton. Some corals can recover, but prolonged stressors increase the chances of reef mortality.
Image: XL Catlin Seaview Survey
No refuge
Climate change is also seriously impacting marine species, with recent research showing that local populations of fish, mollusks and crabs are disappearing at twice the rate of land species. Extreme temperatures are the main culprit, as the ocean offers fewer places to hide from the heat. Sadly, the majority of ocean species won't be able to evolve fast enough to adapt to the changing conditions.
The big melt
In the cryosphere — parts of the Earth's surface covered in solid water, including ice and snow — atmospheric warming is causing the melting of glaciers and ice. The current melting event is already contributing to global sea level rise and could also lead to higher levels of ocean acidification, thanks to methane released from seafloor permafrost in the Arctic Ocean.
Image: Getty Images/M. Tama
Losing a lifeline
Humans are inextricably linked to the ocean. For thousands of years communities have thrived along the coast, relying on it for food and livelihoods. Today, more than one billion people live in low-lying coastal regions which are likely to be impacted by rising sea levels.
Image: imago
Disappearing wilderness
But this connection has come at a cost. Just 13% of the world's oceans are completely free from human activities such as fishing, with almost no true wilderness left along coastal areas. Technological advancements mean even the farthest reaches of ocean in the Arctic are no longer untouched. Protecting the remaining wilderness will be a challenge for generations to come.
Image: picture-alliance/dpa
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Disaster for sea-life, consequences for humanity
The effects of the oceans' lack of oxygen is beginning to alter the balance of marine life, favoring low-oxygen tolerant species (e.g. microbes, jellyfish and some squid) at the expense of low-oxygen sensitive ones (many marine species, including most fish).
Tuna, marlin and sharks are particularly vulnerable to the changes. The species are starting to be driven into increasingly shallow surface layers of oxygen-rich water, making them more exposed to excessive fishing.
The report predicts that the ocean will lose 3-4% of its oxygen inventory globally by the turn of the next century. Most of the losses are anticipated to be in the upper 1000 meters (3300 feet) of the water column, which is richest in marine biodiversity.
