Pollution, overfishing and climate change are just some of the environmental pressures that are amplifying each other more than previously assumed, according to a new study of the world's oceans by the Stockholm Environment Institute (SEI).

"It's not just that the impacts are the sum of the parts…they can actually multiply each other," said Kevin Noone, a co-editor of "Valuing the Ocean," and director of the Swedish Secretariat for Environmental Earth System Sciences.

Other stresses that the study focuses on include acidification, due to a buildup of carbon in the oceans, and hypoxia, which happens when fertilizer runoff feeds giant algae blooms at sea that deplete oxygen and create 'dead zones.'

Overfishing weakens an ecosystem against the effects of climate change

Noone highlighted coral as an example. With their proximity to shore, they frequently bear the brunt of chemicals, acidification and human interference all at once.

"When you put all those threats together, then you can see that the resilience of corals goes down a lot more quickly than simply if you'd just added all those effects up."

Putting a price on oceans

Following in the recent footsteps of efforts to put a cost on terrestrial extinctions, the SEI's study attempts to calculate the economic burden of degrading the world's oceans this century.

It compares the costs of doing nothing on climate change with the costs of limiting warming to an extra 2.2 degrees Celsius, close to the 2-degree goal of international climate negotiations.

The cost of the "business-as-usual" scenario is projected to be $1.98 trillion (1.5 trillion euros) by 2100. Under the alternative scenario, in which the world dramatically reduces its emissions, almost $1.4 trillion of those damages are avoided.

"These figures are just part of the story," said Frank Ackerman, director of SEI's Climate Economics Group in a statement, "but they provide an indication of the price of the avoidable portion of future environmental damage…in effect the distance between our hopes and our fears."

It's difficult to put a price on things like biodiversity

The pricing part of the study took into account five categories of lost ocean value: fisheries, tourism, sea-level rise, storms and ocean's capacity to absorb carbon. But there are other crucial benefits that oceans provide that are impossible to put a price tag on.

"The oxygen in every other breath we take comes from organisms that live in the ocean. But we don't have a price on oxygen," Noone said. "Nonetheless, that's pretty darn important."

Think locally, and globally?

The environmental organization Oceana, which wasn't affiliated with the report, agrees that one of the stand-out wildcards for oceans' health is climate change.

Like the SEI, it would like policymakers to embrace a holistic approach to solving oceans' problems.

"The ecosystem-based approach starts from the idea that all these things in the environment are interlinked," said Hanna Paulomaki, a marine scientist with Oceana. "You can't take separate units from the ecosystem…you need to look at the structure as a whole."

That doesn't mean that local action is futile. Eivind Hoff, from the Bellona Foundation, an environmental protection group, points to Iceland's effective management of its fish stocks. He says that through a system of transferable quotas, Icelandic fishers have a stake in the long-term health of fish stocks and avoiding overfishing.

According to Hoff, national go-it-alone policies can have an impact on global crises like climate change, although that impact is tough to measure.

"The fact that individual nations are ready to take such actions before others, that is what gives us a chance of breaking the deadlock at the EU level to reduce emissions levels," he said.

The coral reefs can't be saved without addressing climate change, says Noone

Noone says these kinds of unilateral actions also help restore resilience at sea, which can buy time in the struggle with broader problems.

"We're not going to get around the problem of coral bleaching and perhaps even the disappearance of corals only by doing local stuff. We really have to cut down on CO2 emissions to get at those problems. But we can keep them from occurring sooner by taking care of local issues," he said.

Author: Holly Fox

Editor: Nathan Witkop