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Mangrove boardwalk

"If we were to restore just 10 percent of historic losses in tropical mangroves," said study co-author Andy Steven, "this would enhance carbon sequestration by about four to five percent." (Photo: freeaussiestock.com/cc)

Despite 'Enormous Potential' as Carbon Sink, Australia's Damaged Coastal Ecosystems Spewing Millions of Tons of CO2

"Australia is in a position to take a leading role in developing policies to offset greenhouse gas emissions which can then be implemented around the world."

Jessica Corbett

Australia's seagrass meadows, mangroves, and salt marshes absorb and lock away about 20 million tons of carbon dioxide each year, but damage to these vegetated coastal ecosystems is releasing three million tons of CO2 back into the atmosphere and limiting their potential to prevent more planetary heating, according to a new study.

"Australia is home to around 10 percent of the world's blue carbon ecosystems, so there's enormous potential for us to take a lead role in this space."
—Oscar Serrano, ECU

The "world-first research" on blue carbon—or carbon captured by the ocean and coastal ecosystems—was published Tuesday in the journal Nature Communications. The study, entitled Australian vegetated coastal ecosystems as global hotspots for climate change mitigation, makes a case for restoring these areas across the globe to help combat the human-caused climate emergency.

The research brought together dozens of scientists from 33 institutions worldwide—including lead author Oscar Serrano, a fellow at the Center for Marine Ecosystems Research at Edith Cowan University's (ECU) School of Science in Australia.

"Australia is home to around 10 percent of the world's blue carbon ecosystems, so there's enormous potential for us to take a lead role in this space," Serrano said in a statement from ECU. "Australia is in a position to take a leading role in developing policies to offset greenhouse gas emissions which can then be implemented around the world."

The researchers found that Australia's coastal zones capture about the same amount of carbon each year as the annual emissions of more than four million vehicles. However, Serrano said, "when these ecosystems are damaged by storms, heatwaves, dredging, or other human development, the carbon dioxide stored in their biomass and soils beneath them can make its way back into the environment, contributing to climate change."

Highlighting the importance of blue carbon ecosystems, the ECU statement noted:

  • Vegetated coastal ecosystems absorb carbon dioxide at rates up to 40 times faster than terrestrial forests mainly due to their enormous capacity to store carbon in soils.
  • In Australia it's estimated there is four times more carbon sequestered in soil beneath marine ecosystems over a given area than in terrestrial environments.
  • Vegetated coastal ecosystems account for 50 percent of carbon dioxide sequestered by the oceans, despite covering just 0.2 percent of its total area.

Serrano pointed out that "globally, vegetated coastal ecosystems are being lost twice as fast as tropical rainforests despite covering a fraction of the area." He added that "these ecosystems are also important as habitats and nurseries for fish and other marine life, helping prevent coastal erosion and improving water clarity."

The researchers hope the new study will help drive efforts to restore and protect such ecosystems in Australia—which, in turn, could inform similar efforts around the world.

Andy Steven is a co-author of the study as well as coasts research director at the Commonwealth Scientific and Industrial Research Organization (CSIRO), an Australian federal government agency.

"If we were to restore just 10 percent of historic losses in tropical mangroves—that is roughly an area of 1150km squared—this would enhance carbon sequestration by about four to five percent."
—Andy Steven, CSIRO

"With a carbon trading price of $12 per ton, which we report in the paper, the potential for blue carbon projects within Australia alone is worth tens of millions of dollars per year in payments from the Australian Emission Reduction Fund and voluntary carbon markets," Steven told the Australian broadcaster SBS.

"Those projects could take the form of replanting seagrass meadows, restoring mangroves by reflooding, or by preventing expected losses through environmental management," said Serrano. "These more accurate measurements of blue carbon provide more certainty on expected returns for financiers looking at investing in blue carbon projects."

As Steven explained to The Guardian, "when we started this work in 2014, we had no real numbers. We didn't know how significant it was, or even if they were worth thinking about. But we've shown demonstrably that these ecosystems are very significant."

For example, Steven told SBS, "if we were to restore just 10 percent of historic losses in tropical mangroves—that is roughly an area of 1150km squared—this would enhance carbon sequestration by about four to five percent."

Last year, according to the tracking group Ndevr Environmental, Australia's annual emissions hit a record level at 558.4 million tons of carbon dioxide equivalent.

The researchers' call for restoring coastal ecosystems to address the climate crisis aligns with the Natural Climate Solutions campaign, which proposes "drawing carbon dioxide out of the air by protecting and restoring ecosystems" to battle climate and ecological breakdown. Last month—just ahead the global climate strike and the United Nations Climate Action Summit—youth climate activist Greta Thunberg and writer George Monbiot, a leader of the campaign, released a video on the proposal.


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