Carbon Sequestration on the Great Plains
While the concept of carbon sequestration might seem like a magic trick, researchers continue to advance its environmental and financial feasibility.
Published June 1, 2004
By Christine Van Lenten
Academy Contributor
Carbon dioxide emission dwarf in quantity all other greenhouse gases (GHGs) and exacerbate the impacts of climate change. But CO2 emissions are difficult to reduce. Chemically scrubbing them from smokestacks isn’t generally practicable, and many sources are mobile, small, and/or dispersed. Rather, achieving reductions requires adopting energy-efficient measures, converting to renewable energy sources or other sources that contain less or no carbon, or attempting to sequester the CO2 after it’s been emitted – that is, removing it from the atmosphere and storing it.
Various carbon sequestration schemes are being pursued. Exploiting soil’s capacity to store carbon is the one advocated by Dr. Patrick Zimmerman, who directs the Institute of Atmospheric Sciences at the South Dakota School of Mines and Technology. And Zimmerman has a specific carbon storehouse in mind.
While the world struggles to devise policies, practices, and technologies that can slow global warming, the Great Plains region of the United States, says Zimmerman, continues to serve as a vast “carbon sink,” silently sucking CO2 out of the atmosphere. At a March 23, 2004, event co-sponsored by The New York Academy of Sciences’ (the Academy’s) Environmental Sciences Section and the Third Annual Green Trading Summit, Zimmerman, the featured speaker, contended that croplands and rangelands can store much more carbon. And, he stated, the science needed to quantify sequestered carbon and a system for bringing credits for it to market are available right now.
Markets are Emerging
Setting the stage for Zimmerman’s talk was Peter C. Fusaro, an organizer of the Trading Summit and chairman of Global Change Associates. Fusaro said the Kyoto Protocol, the international community’s attempt to reduce GHG emissions by specifying national targets and a timetable for meeting them – yet to be endorsed by the United States – is flawed and won’t work.
But markets for trading GHG credits are emerging, he reported. They’re modeled on existing pollution-trading markets, like the successful market for sulfur dioxide run by the U.S. Environmental Protection Agency’s Acid Rain Program. SO2 emissions are capped by federal regulation; parties reducing their emissions below regulatory limits can claim credits for reductions and sell them to parties that haven’t met their targets. The overall goal of reducing emissions is served.
In the United States, CO2 emissions aren’t capped by the federal government, but various state and regional initiatives are under way, and leadership for forming GHG markets is coming from state policy makers, Fusaro observed, through bipartisan efforts that are creating the conditions necessary for markets to succeed: “simplicity, replication, and common standards.”
Why Buy Credits?
Why buy credits for reducing CO2 emissions? Anticipation of regulatory schemes is one reason; good corporate PR is another; simple good practice, yet another. And demand generates supply.
California’s Climate Action Registry for voluntary reporting of GHG emissions is the nation’s first. At the invitation of New York’s Governor Pataki, nine northeastern and mid-Atlantic states are collaborating to create a registry and formulate a model rule that states can adapt for capping and trading carbon emissions; two other states and several Canadian provinces are participating as observers. The Chicago Climate Exchange is a new, voluntary pilot market focused on North America. Some major corporations are already trading carbon credits.
Large, existing exchanges will enter the market soon, Fusaro predicted. New York City is the “environmental finance center,” and New York State will be “the template for world trade in carbon. We will have cap-and-trade markets in New York next year.”
CERCs, Cycles, and Soils
In the world of carbon trading, the unit of exchange is the carbon emission reduction credit (CERC), equivalent to one metric ton of CO2. Trading CERCs for CO2 that’s been snatched from the air and stored in the soil may sound like a magic trick. And indeed, scientists are only beginning to understand the intricate and complex feedback loops among climate, atmospheric composition, and terrestrial ecosystems that govern this form of sequestration.
Zimmerman framed the science by explaining that Earth’s carbon inventory cycles among reservoirs – the atmosphere, lithosphere, hydrosphere, and biosphere. The reservoirs vary dramatically in size; so do carbon fluxes between them. Because fluxes between terrestrial ecosystems and the atmosphere are large, over time small changes in them can produce large changes in how much carbon accumulates in the atmosphere.
Zooming in on the molecular level helps illuminate the huge potential of the carbon sequestration scheme that Zimmerman is advocating. During the growing season, green plants absorb solar energy and remove CO2 from the atmosphere, producing carbohydrates. Because these compounds contain less oxygen for each carbon atom than CO2 does, “surplus” oxygen is released; carbon is stored.
Plants also respire, taking in oxygen to metabolize carbon compounds and release energy needed for cellular processes, and producing water and CO2. When the growing season ends, photosynthesis and plant respiration cease, and organic matter, rich in carbon, decomposes, primarily because organisms in the soil feast on the carbon, metabolize it, and return CO2 to the atmosphere. When soil containing organic matter is broken up – for example, by tillage – more organic matter is exposed to this oxidizing process, accelerating release of CO2 and depletion of soil’s carbon bank.
The “Missing Sink”
If you want to prolong sequestration of carbon in soil, the crucial question becomes this: What conditions hinder decomposition of organic matter in soil, slowing down the release of CO2 back into the atmosphere?
Vegetation growing at high latitudes, Zimmerman said, fits the bill. At high latitudes, plants grow quickly in the summer, and about half the growth is underground. In winter, freezing slows the metabolic processes that oxidize carbon, trapping it within the soil in the form of organic material that’s not completely decomposed. By contrast, Zimmerman noted, “it’s really tough to store organic matter in tropical soils.”
High-latitude efficiencies in storing carbon also offer one answer to the mystery of the “missing sink.” Scientists calculate that quantities of CO2 produced by burning fossil fuels and resulting from deforestation and other land-use practices are greater than quantities taken up by the atmosphere and oceans. Where’s the balance? Seasonal variations in rising concentrations of atmospheric CO2 point to a slight net carbon sink that’s land-based, in the northern hemisphere, in North America, said Zimmerman. And the Great Plains, a high-latitude region, appears to be that “missing sink.” Analysis of carbon and oxygen in atmospheric CO2 samples collected from air masses as they traverse North America appears to confirm this.
Adapting Land-Use Practices
The Great Plains, he added, can store still more carbon, through alteration of land-use practices – for example, converting high-tillage cropland to low-till or no-till, or to pasture or grassland. Zimmerman, who grew up on a wheat farm, pointed out that organic matter also increases ecosystem productivity and resilience to stress.
Sequestering carbon in the Great Plains can significantly offset emissions elsewhere, he contended. For the purpose of slowing global warming, what matters is that CO2 is sequestered; not where. Thus, cropland and rangeland in the Great Plains can serve as generators of tradable CERCs and a brake on global warming.
But how can you tell how many metric tons of CO2 an acre of land is sequestering? As described by Zimmerman, the science is fiercely complex. His team of meteorologists, ecologists, plant physiologists, GIS experts, analytical chemists, computer scientists, and remote-sensing specialists virtually swarm all over the landscape – working from the molecular level, to individual leaf, to grass canopy, to atmosphere – gathering data on a host of processes and factors.
Equipment ranges from plastic bags placed over plants, to towers, tether balloons, an airplane equipped with a digital imaging system, and satellites. Measurements include variations in temperature, humidity, rainfall, snowfall, and solar radiation; quantities of water vapor, volatile organics, and CO2 emitted from vegetation, and the fluxes to vegetation; and leaf area indexes. Data on land use history, vegetation and crop dynamics, and feedback between carbon, phosphorous, nitrogen, and sulfur cycles are gathered, too.
Models Built on Data
Data are used to build numerical models of physical, chemical, and biological processes; these models are then linked, to model ecosystem carbon cycling and atmospheric chemistry, and extrapolated to landscape and regional scales. Regional modeling is essential, Zimmerman emphasized, “because that’s where the impacts are felt – where you live.” He termed the Black Hills (in South Dakota and Wyoming) “a great outdoor laboratory” that lends itself to the measurements needed to constrain regional models. His team is now establishing a network of field monitoring stations.
Determining how to link models constituted of algorithms based on physics and chemistry, across orders of magnitude that span spatial and temporal scales, is, Zimmerman observed, like trying to assemble an elephant from a box of molecules without the benefit of knowing what an elephant looks like. The work is iterative and time-consuming. And modeling rangeland to quantify incremental carbon storage poses special difficulties.
But while this science is still far from precise, it’s plenty good enough to get CERC markets going and “to make a difference,” he contends. Farmers can adapt their land use to sequester CO2 now, while we develop better technologies – and the socio-political will – to cut emissions.
And how can what Zimmerman termed “enhanced ecological carbon storage” be capitalized? For a market to be viable, he’s concluded, six conditions must be met:
(1) The business-as-usual baseline must be established.
(2) The additional CO2 each landowner sequesters must be quantified.
(3) How long CO2 will remain sequestered must be forecast.
(4) No unintended, offsetting releases can be generated; for example, converting cropland to pasture and introducing cows, which emit methane, every ton of which is equivalent to 20 tons of CO2 in its effects on global warming.
(5) Ownership of CERCs must be documented.
(6) CO2 sequestration must be verified.
Satisfying All Six Conditions
Zimmerman and his colleagues have designed a system, C-Lock (patent pending), that he said satisfies all six conditions. Internet- and GIS-based, it creates, certifies, standardizes, and verifies CERCs for specific land parcels, by integrating data on slope, climate, soil, historical land-use variables, and other factors. Farmers can access it directly online; no middlemen are required.
To create economies of scale, so benefits exceed transaction costs, C-Lock aggregates CERCs for many small landowners. Monte Carlo analysis is used to quantify uncertainty and normalize CERCs so they have universal currency. A reserve pool of CERCs with higher uncertainty values and correspondingly lower market values can be tapped to offset fluctuations in actual soil performance. The system’s transparency facilitates four levels of verification and “audits” that employ a variety of databases and scientific tools.
And because the carbon-storage capacity of tilled soil isn’t saturated, C-Lock quantifies only changes in amounts of soil carbon. Trying to quantify absolute amounts would pose daunting soil-sampling problems. Data on land-use history are key here. Quantification needn’t be precise for each individual land parcel; just reproducible and transparent. But it must be reasonably accurate in aggregate, and the uncertainty (financial risk) should be quantified to achieve maximum value.
Launching the System
C-Lock is now equipped with GIS for South Dakota, and a trade is in the works; trades in Idaho, Montana, Wyoming, and North Dakota will follow, Zimmerman predicted, adding that C-Lock can accommodate other GHG emissions and forms of sequestration, anywhere in the world.
What’s needed for it to succeed? A pilot phase, cap-and-trade policies, and policies that define soil sequestration’s role in the GHG reduction strategy, he said. But his biggest concern is that huge environmental advantages will be lost if USDA incorporates carbon sequestration into conventional farm subsidy programs. We have an obligation to make a difference, he insisted, and we can: markets can work, benefiting farmers, ranchers, and the environment.
As measures to slow global warming develop, what role is the Academy playing? Its Environmental Sciences Section is stepping up to the plate: Chair Michael Bobker says it’s creating “a dialogue around greenhouse gases and emission trading issues, as well as carbon reduction and sequestration projects” – an initiative squarely in keeping with the Academy’s historical role as a forum for exploring and debating the scientific issues that matter most, and advancing science for the public good.
