Understanding Carbon Science to Develop Effective Climate Policy

Gary Graham Hughes, Americas Program Coordinator, Biofuelwatch

The carbon cycle describes how carbon moves between the atmosphere, soils, living creatures, the ocean, and human sources. Image courtesy of the Department of Energy Office of Science.

The California Air Resources Board (CARB) is currently developing the 2022 Scoping Plan, the road map for the state’s vision for responding to climate change. Coincidentally, Humboldt County is also considering a Regional Climate Action Plan. As California residents and climate-concerned Humboldt County activists review these plans and assess how private industry, elected officials and regulatory agencies propose acting on crucial energy and environmental justice matters, it can be helpful to review some climate science fundamentals.

The majority of climate policy mechanisms in California focus on climate system flows between carbon stocks – flows are what are known as emissions and sequestration. Emissions are the flow out of a carbon stock, and sequestration is the flow into a carbon stock. Carbon stocks, or reservoirs, are where the carbon resides. Despite climate policy focus on flows – on emissions and sequestration – the climate problem is actually one of diminishing biological and geological carbon reservoirs, specifically the mobilization of carbon from stocks where carbon has resided with stability and permanence. 

The climate problem is rooted in the dilemma of how permanent carbon stocks have been and are being depleted and degraded, mobilizing carbon reservoirs so that an increasing amount of carbon is taking residence in the atmosphere and the oceans.

Carbon reservoirs can best be understood by the nature of their stock, and understanding those reservoirs illuminates the significance of sequestration and emissions, both current and legacy. Not all carbon reservoirs are the same, despite the tendencies of policy mechanisms to create a false equivalency, treating a ton as a ton as a ton. Unfortunately, such contrived carbon equivalency misrepresents the geophysical realities of our planet, undermining the effectiveness of the policy mechanisms built on that false equivalency.

Fundamentally, understanding the difference between geocarbon and biocarbon is essential for the development of effective climate policy. Carbon reservoirs in the geosphere are known as geocarbon. Primary reservoirs of geocarbon are stored in highly stable sedimentary rocks and deep ocean sediments, as well as the highly stable deposits of coal, oil, and gas that human industry extracts and mobilizes for many uses, including burning as fossil fuels. The cause of mobilization of geocarbon is almost entirely due to human activities, remaining highly stable until subject to human extraction, and requiring zero cost to maintain in place. Geocarbon has been stabilized for hundreds of millions of years, and once stabilized remains in specific deposit locations.

Carbon reservoirs in the biosphere are known as biocarbon. Primary reservoirs of biocarbon are the world’s marine and terrestrial ecosystems, and include the original old growth forests of the world, of which more than 65 percent have been lost, while in the redwood temperate rainforest ecosystem more than 95 percent of the original old growth primary reservoir of biocarbon has been depleted and degraded. 

Biocarbon is located across the entire landscape and requires extensive investment for funding ongoing ecosystem management. Permanence in storage of sequestered biocarbon can be elusive and even contrary to ecological succession processes which rely on disturbance regimes. Biocarbon stocks vary temporally and spatially and are subject to numerous natural processes that further mobilize biocarbon stocks, complicating accounting and making statistically reliable estimation difficult. 

Biocarbon stocks are not static ahistorical repositories of carbon, they must be understood in the context of past land use change. For instance, understanding the role of past deforestation in carbon sequestration by forests is crucial to having an accurate understanding of what current sequestration reveals about the depleted state of the biocarbon reservoir. It bears repeating: carbon sequestration in land-based ecosystems like forests can only be properly understood in the context of past land use change.

The hard fact is that CO2 removal by the land sector is essentially recapturing past emissions due to land use or land-use change, and therefore cannot and never will compensate for or neutralize the mobilization of geological carbon in the form of fossil fuels. In California we can imagine this by conceptualizing the liquidation of the original ancient redwood temperate rainforest ecosystem, widely recognized as one of the most carbon dense forest ecosystems on the planet, and understanding exactly how much of the original carbon stock was lost. As such, carbon sequestration in the redwoods of California is not compensating for ongoing fossil fuel use – it is simply restoring severely degraded carbon stocks resulting from the indiscriminate logging of the original ancient redwood forest.

Effective policy for mitigating the worst impacts of climate change must also recognize that the impacts of fossil fuel use are irreversible. The mobilization of geocarbon reservoirs is basically a one-way injection of carbon into the atmosphere. Essentially, it is not possible to substitute needed reductions in fossil fuel use with the highly variable and temporally fleeting carbon sequestration processes of the world’s forests and other land-based ecosystems.

Distinguishing between geocarbon and biocarbon is essential to developing climate change mitigation policies that will assist in averting the worst impacts of climate change. An increasingly substantial body of evidence shows that they are not interchangeable for climate change mitigation purposes. Our challenge is to reduce emissions from all sources, protect the stable carbon stocks that remain to us, recover those stocks that have been degraded and – most importantly – not continue with the extracting and burning of fossil fuels believing erroneously that those emissions can be made up for with sequestration in ecosystems like forests.