Green and blue carbon: providing solutions to the climate crisis

As the climate crisis evolves, a number of definitions have emerged which outline the different variations and characteristics of organic carbon.

Professor Carlos Duarte, whose research centres on understanding the effects of global change in marine ecosystems and developing nature-based solutions to global challenges, including climate change, is well placed to describe the important next steps in ecology and biological conservation.

Duarte was recently recognised with the Frontiers of Knowledge Award in part for demonstrating how the conservation and restoration of coastal habitats is a very effective strategy for climate action, a strategy his coauthors and him named “Blue Carbon”. Duarte’s strategy also informed Extreme E’s mangrove planting efforts as part of its Legacy Programme in Senegal, as well as its upcoming focus on avoiding damages to Posidonia seagrasses in Sardinia.

As explained by Duarte, the most significant colours relating to the role of ecosystems on the climate crisis are blue and green.

“Green carbon reflects the carbon sequestered by land ecosystems and incorporates carbon in soils and within biomass such as trees in forests,” said Duarte. “Blue carbon, by contrast, describes the carbon sequestered in the ocean, the definition of which originally focused on mangroves, salt-marshes and seagrasses, but now also includes seaweed, sediments more broadly, and even carbon sequestered by whales.”

The sequestration of blue carbon, especially, has been acknowledged as a long-term solution for climate change mitigation, because carbon locked in marine soils are not vulnerable to wild forest fires, which is returning increasing spans of green carbon to the atmosphere, and because blue carbon habitats, seagrass, saltmarshes and mangroves, form the first line of defense for our shorelines, which they protect from erosion resulting from sea level rise and increased storminess.

Duarte adds: “We have also lost roughly half of the productive coastal habitats, seagrass meadows, mangroves, salt-marshes, coral and oyster reefs, that once protected our shorelines. We have lost over half of the blue natural capital that our oceans contained, along with the multiple benefits they delivered to society.”

A number of environmental scientists have determined that blue carbon has no negative impacts, contributes to adaptation by raising the seafloor and buffering waves, provides additional benefits, such as enhanced fishery resources, and can be cost-effective.

“The conservation and restoration of blue carbon habitats is a cost-effective approach to remove excess carbon dioxide and contribute to climate action,” says Duarte.

“Blue carbon projects are best delivered through partnerships between local communities, government and international investors – as we have seen as part of our Legacy Programmes in Extreme E.

The ocean is seen as a great modulator of climatic stability. It holds 16 times more carbon than the terrestrial biosphere, has absorbed almost a third of the CO2 humans released to the atmosphere and trapped approximately 93% of the excess heat in the biosphere resulting from the massive release of greenhouse gases.

Nevertheless, Duarte is surprised that it has taken so long to acknowledge the ocean as a source of climate change solutions.

Duarte explains: “Carbon is preserved in their oxygen-depleted soils, which, unlike forest soils, are free from the risk of being emitted with wild fires, as there are no fires underwater. Blue carbon habitats typically hold 50 to 100 times more carbon in their soils, and remove about 10 to 30 times more CO2 from the atmosphere per year than terrestrial forests do. They are unique and efficient carbon-capture habitats.

“However, when disturbed, the massive stocks of carbon locked in their soils could be become unstable and be emitted to the atmosphere, so the loss of about half of their extent has contributed to greenhouse emissions and, therefore, climate change.

“Ultimately, we have to repair our connections with the ocean if we are to receive a wave of ocean benefits.”

Alongside the solutions offered by blue carbon, green carbon also plays a significant role in combating the climate crisis. Green carbon is the carbon stored in the biosphere, taken up from the atmosphere by plants through the process of photosynthesis.

Green carbon ecosystems, such as those in natural forests, play a key role in impacting the levels of greenhouse gas concentrations in the atmosphere. However, forests are becoming increasingly vulnerable to forest fires, such as those that devastated forests in Sardinia and elsewhere in the Mediterranean region this year, a situation that is aggravating with climate change.

Duarte explains: “In order to help solve the climate change problem, we must also maximise the uptake of carbon in the biosphere. Protecting our natural forests is vital as part of an overarching strategy to positively impact the climate crisis.

“For every hectare of natural forest that is degraded, there is a resulting increase in atmospheric carbon dioxide which exacerbates climate change.

“In addition, maintaining the natural processes that regulate the level of carbon dioxide in the atmosphere will be crucial. If natural forests are in a position to expand then they can act as a potential buffer to the accumulation of greenhouse gasses.”

As environmental scientists continue to seek solutions, Duarte is convinced that a significant focus on blue and green carbon actions will deliver solutions which impact the climate crisis for the better.

“Marine ecosystems are so vulnerable, such as sea-ice ecosystems, including a complex food web ranging from microalgae to polar bears in the Arctic, and tropical coral reefs, which IPCC forecasts to suffer catastrophic losses under ocean warming, even if the goals of the Paris Agreement are met.

“We now know that it is possible to rebuild the abundance of marine life along the course of a human generation – by 2050 – if we start now. A greater focus on green and blue sources of carbon will be crucial in ridding vast quantities of carbon dioxide from the atmosphere. Protecting these ecosystems will be an essential part of tackling climate change.”

Further details will be revealed shortly on Extreme E’s Legacy Programme in Sardinia, which will focus on Blue and Green carbon solutions.