Climate change is a portfolio problem. There’s no one cause, nor is there a silver bullet to fix the problem. Rather, the solution will lie in a portfolio of measures, and many of the solutions will stem from nature. To explain how natural solutions to carbon storage and sequestration can be incorporated into policy solutions, The Nature Conservancy has developed a policy brief entitled “Blue Carbon in the UNFCCC” which explains how carbon sequestration benefits from mangrove forests and other terrestrial and marine systems are engrained in the Paris Agreement and the associated Paris Rulebook.
The Nature Conservancy along with scientific partners across the world conducted a thorough peer-reviewed literature review of the best available science on ways that nature can reduce the emissions from anthropogenic climate change. What we found: Natural climate solutions (NCS) can provide 37% of cost-effective CO2 mitigation needed through 2030 for holding warming to below 2 °C. One-third of this cost-effective NCS mitigation can be delivered at or below $10 per MgCO2, and most NCS actions—if effectively implemented—also offer water filtration, flood buffering, soil health, biodiversity habitat, and enhanced climate resilience.
Into this portfolio, blue carbon is an opportunity that surpasses anything within the agriculture or grasslands opportunities. Indeed, both the restoration and conservation of coastal wetlands is even higher than natural forest management. Stuck between intertidal and shallow coastal waters, these often-understated habitats don’t appear to be a match for the vast expanses of the Amazon or the Congo, but these coastal wetlands are among the most productive ecosystems in the world. Both as carbon stores, secondly, and perhaps uniquely they are carbon scrubbers- sequester large amounts of carbon.
It’s easy enough to believe there’s a lot of carbon tied up in the shaggy splendor of giant mangrove trees, but the soil under all these ecosystems is usually a rich peat, and our best guess is 6.4 Pg carbon for the top meter of soil with a range of 86-729 Mg carbon per hectare. This carbon store out competes per hectare all other forest systems. This is because they draw in carbon as they grow, much of which is later transferred into the rich organic soils held by their roots. The carbon can remain in the soil for thousands of years, making it one of the longest-term natural solutions to climate change. Coastal wetlands are also a continuous sink as layers of carbon-rich soil naturally build up as plants die and are buried in the soil and new plants grow on top. If undisturbed, this process allows them to keep pace with moderate sea level rise.
Mangroves are an important ecosystem for sequestration – outside their massive amounts of carbon storage. Carbon is drawn in via photosynthesis, converted to complex carbon compounds and this number, 200 tonnes a minute, are permanently sequestered into woody matter, leaves and from them into the waterlogged soils where they remain trapped. Other peaty soils don’t do this – the freshwater that permeates them is conducive to other biochemical pathways that wind up releasing methane, a potent greenhouse gas. But saline wetlands release very little methane. They represent biological carbon captures on a big scale.
While there is a need for more studies on the variability of carbon capture among different types of mangroves, it estimated that per hectare mangroves store 6.4 Mg carbon equivalent per hectare.
Despite the carbon benefits and services mangroves bring, they are some of the most threatened ecosystems on Earth. Although their historic extent is difficult to determine due to dramatic losses occurring before scientists could accurately measure these habitats, it is estimated that up to 67% of historical global mangrove range has been lost. If these trends continue at current rates, a further 30–40% of tidal marshes and seagrasses and nearly all unprotected mangroves could be lost in the next 100 years .
Moving Forward: The Paris Agreement
Although the terms “coastal wetlands” or “blue carbon” are not in the decision text, mangrove forests as well as sinks, sources, and reservoirs from other terrestrial, coastal and marine ecosystems are incorporated in the Paris Rulebook. These ecosystems will not be explicitly described in the text of the Rulebook but the carbon sequestration and storage potential of these important sinks and sources are implicitly included as part of the guidance. Read more here to learn about how the management activities supporting the mitigation function of mangrove and other coastal carbon ecosystems are likely to be framed in the Paris Rulebook and what is needed to solidify their status during the upcoming COP in Poland.
Photo Credit: Jeff Yonover