Rebalancing the Carbon Cycle

Carbon. From the time when the first living organisms coalesced in a sea permeated with long-chained molecules, this element has been essential to life on earth. Like water and oxygen, we cannot live without it.

Carbon’s importance arises from its crucial provision of both structure and energy to living creatures. Carbon’s very long chains and rings are the backbones of most organic molecules. Break living bodies of any sort into organs, break the organs into cells, and the cells into molecules, look inside, and you will find a string of carbon atoms. If you could somehow pull all these carbon strings from the organism, little would remain of either the organism’s form or function.

But carbon also flows through organisms and, when doing so, provides the energy that allows them to laugh, play, migrate, reproduce -- to perform virtually any function that we associate with being alive. This energy comes stored in the molecular bonds that hold the carbon chains together. Think about it. If you need an energy boost, you grab a CARBO-hydrate -- a food with quickly digested and readily available carbon compounds.

Given the importance of long-chained carbon compounds, it was crucial that living creatures developed mechanisms for producing these complex molecules and assuring that they could be readily transferred from one organism to another. Hence the significance of the carbon cycle, which is diagrammed in a simplified form in Figure 1. Through this cycle, carbon (in the form of carbon dioxide, or CO₂) is pulled from the atmosphere by green plants, which engage the sun’s energy to form the long carbon chains (a process called photosynthesis). The carbon chains, and the energy they contain, are then handed from one creature to another as a series of meals -- from corn to pig to human, from grass to rabbit to decomposing fungi. Eventually, the molecules release their energy and break back down to emit CO₂ (a process called respiration).

The CO₂ released into the atmosphere plays another crucial role. CO₂, with other greenhouse gases, provides an insulating blanket that holds in the sun’s warmth and heats the earth’s surface to a temperature that is hospitable to life -- about 60°F warmer than it would be otherwise.

The problem . . .

The carbon cycle has remained roughly in balance through the eons, with carbon playing its multiple roles in a healthy and sustainable manner. But beginning about 200 years ago, the Industrial Revolution instigated a major shift in the amount of carbon stored in various forms. Society’s conversion from an agrarian to industrial state, along with its transfer of work from muscle power to machines, required cheap and abundant power sources. Complex carbon-based molecules -- stored as fossil fuels -- came to the rescue.

Ever since, oil, coal, and natural gas have powered the production and transport of goods around the globe, fueling virtually every structure and activity that we associate with modern life. Unfortunately, the obvious benefits of these fuels come coupled with unavoidable problems. One of these problems derives from the source of fossil fuels, which were formed from plant remains buried millions of years ago. These fossil fuels are, in essence, buried treasures of energy-storing carbon chains. Burning the fuels releases not only energy, but also the CO₂ that had long ago been sequestered in these buried plants.

The results of our fossil fuel consumption have been significant. Researchers analyzing the content of tiny air bubbles trapped within Antarctic ice cores have discovered that during the last 160,000 years, atmospheric CO₂ has waxed and waned, in general being lower during cold periods and higher during warm periods (see Figure 2.). However, because of the massive release of CO₂ from fossil fuels, the rate of CO₂ evolution has never been as high as it is today. In addition, the total amount of atmospheric CO₂ has not approached current levels during the past 160,000 years. In the last 200 years, atmospheric CO₂ has risen from 280 ppm to 360 ppm, with today’s growth curve skyrocketing upward. The United States releases about a quarter of the total annual CO₂ generated, thus becoming by far the earth’s major CO₂ producer.

These skyrocketing CO₂ levels have become a major concern because of their potential link to warming global temperatures. The earth’s temperatures have risen 1°F in the last 100 years. Climate models predict that a continued rise in greenhouse gases will warm the average earth temperature another 2 to 6.5°F in the coming 100 years, with the most probable estimate being 3.5°F. The warming would not be uniform; some areas would be hotter, some perhaps even cooler. Such a temperature rise would result in the flooding of coastal areas and islands, worsen droughts and rainstorms, and shift climatic and agricultural zones northward, in addition to causing other significant problems.

The world’s response . . .

What can be done about so massive a problem, a problem that strains the limits of our scientific understanding as well as our political and economic flexibility? How can one transform the energy base of the earth’s societies, steering them away from CO₂-producing fossil fuels? And how could anyone even conceive of sifting invisible, diffuse CO₂ from the earth’s atmosphere? Put another way, how can the carbon cycle be returned to a balanced state that equates with long-term sustainability?

As overwhelming as these questions may seem, they have formed the crux of recent international climate-change discussions. The United Nations Framework Convention on Climate Change grew out of the United Nations Conference on Environment and Development held in Rio de Janeiro, Brazil, in 1992. In all, 174 nations have ratified the Climate Change Convention and thus have agreed to voluntary limits to their greenhouse gas emissions.

Last December, at a follow-up meeting held in Japan, the signatory nations agreed to the Kyoto Protocol, which stipulates specific limits to greenhouse gas emissions from developed nations. This Protocol is significant as the very first agreement among the world’s nations to binding (rather than voluntary) limitations on their greenhouse gas emissions.

Agreeing to such limitations is one thing. Implementing the limitations is quite another, and here comes the rub. The Kyoto Protocol addresses net greenhouse gas emissions: it allows nations to remain within their CO₂ limits either through decreasing emissions or through sequestering carbon -- pulling carbon from the atmosphere and storing it in terrestrial ecosystems. However terrestrial ecosystems are active biological systems with complex cycles that are not easily deciphered. The soil, for example, holds about twice as much carbon as above-ground organisms, and the oceans of the world store many times more carbon. How can the sequestering and release of carbon from its multiple sinks be accurately monitored and pinned to political boundaries? The world’s nations will be meeting regularly for the indefinite future to discuss this difficult bookkeeping task, with the first such meeting scheduled for November 1998 in Buenos Aires, Argentina.

CGRER’s involvement . . .

Scientific research today is perhaps most beneficial when directed toward topics where the need is great, the science is inexact, and questions far outnumber answers. Understanding the intricacies of the flow of carbon is one such topic. CGRER’s researchers have for years been involved in projects directed toward better comprehending the carbon cycle and returning it to a balanced, sustainable state. Current projects are described below.

Sequestering carbon . . .

One CGRER project deals with increasing the size of the "Photosynthesis" arrow in Figure 1. Newly planted buffer strips along roads and streams, and native tree plots, can be used to pull CO₂ from the atmosphere and sequester the carbon within the soil and living tissues of plants. But exactly how much carbon could such plantings sequester?

To answer this question, CGRER has been conducting the Iowa Carbon Storage GIS Mapping Project. This project, which grew out of CGRER’s 1996 preparation of the Iowa Greenhouse Gas Action Plan, will produce Iowa’s first comprehensive quantification of carbon storage from various forms of land use. The data collected will provide baseline information for measuring future carbon-storage gains and losses, and also will permit reliable estimates of potential carbon sequestration from plantings made in the future. Data will be presented through maps such as that shown in Figure 3. -- one of the first project outcomes.

This form of carbon sequestering admittedly is a short-term solution to the problem. Any carbon tied up in rapidly growing plants will, when the plants die and decay, be returned to the atmosphere. However, young rapidly-growing forests pulling carbon from the atmosphere constitute a powerful mechanism for tying up carbon for a few decades, while we search for longer term solutions such as alternatives to fossil fuels. Also, to the extent that trees can be harvested and used as feedstocks and as biofuels to replace fossil fuel combustion, there is a net benefit to the carbon balance.

Analyzing Deregulation . . .

The second CGRER project is concerned with decreasing the size of the "Burning of Fossil Fuels" arrow in Figure 1. -- that is, decreasing the release of CO₂ through fossil fuel combustion. CGRER, through a grant administered by the Iowa Utilities Board, is analyzing the change in greenhouse gas emissions (including CO₂) that would accompany a deregulation of the electric power industry. First, the emissions of every power plant in Iowa had to be calculated -- an analysis that revealed that Iowa utilities as a whole emitted over 27 million tons of CO₂ in 1996. Now CGRER is predicting the effects that deregulating the energy industry will have on greenhouse gas emissions, according to Iowa Utilities Board market estimates. In a deregulated market, customers will be able to choose their power company. Thus, because power is relatively inexpensive in Iowa, deregulation will increase the demand for Iowa’s power. Preliminary results indicate that deregulation of the electric utilities market will provide Iowa utilities with an incentive to increase production. Because Iowa’s utilities will use relatively efficient large coal-fired units (rather than smaller, less efficient units) to meet this demand, efficiency (as measured by the pounds of CO₂ emitted per million BTUs generated) will improve. Nevertheless, total emissions of CO₂ in Iowa are expected to increase because of the increased power being produced.

Growing Green Power . . .

A third CGRER project, the Biomass Power for Rural Development Program, is attempting to create an entire new loop for the production of energy, a closed loop that provides for the trapping as well as release of CO₂. This trial program, funded primarily by the U.S. Department of Energy, proposes to tie up CO₂ in "biofuels," fast-growing plants that can be used as fuel sources. Since any CO₂ released by the combustion of these plants would have been drawn from the atmosphere quite recently, the resulting energy would be produced without any net CO₂ emissions. Actually, biofuels do better than breaking even on CO₂ emissions. Because of the relatively small amount of energy needed to process biofuels, and the ability of their roots to store carbon in the soil, the use of biofuels leads to a net reduction of atmospheric CO₂ relative to fossil fuel combustion. Chariton Valley Resource Conservation and Development, Inc. plans to establish switchgrass on 40,000 acres of marginal, Conservation Reserve Program-enrolled cropland as an energy crop. This switchgrass is slated to be burned with coal in an existing power plant, with the expectation of its generating 35MW of power. CGRER’s role will be to develop the estimates of net emissions of CO₂ (as well as other gases) from the switchgrass growth, harvest, and combustion, and to compare these data to emissions data relating to coal mining, processing, and combustion.

Benefits to Iowans . . .

All three of these projects will help Iowans improve the health of their environment, and also will involve Iowans in actions that address the risks of global warming to future generations.

CGRER’s projects also pose economic advantages for Iowans. The Biomass Power Program, if successful, may transform switchgrass and other grasses into cash energy crops that could generate about $200 per acre. In the existing project alone, up to 500 local farmers will have a chance to sell this new cash crop to the cooperating power plant.

In addition, in the future, Iowa’s economy on multiple fronts may be boosted by the creation of emission credits for CO₂. As governmental bodies and industries work through the details of implementing the Kyoto Protocol, energy-producing nations and industries with higher-than-expected releases of CO₂ may be required to purchase credits -- permissions to release CO₂ -- from producers (or nations) with lower-than-expected release rates. Such emission credits are already sold on the open market for SO₂, and are now being established for NO_x. Many consider it only a matter of time before CO₂ credits enter the marketplace. Thus energy efficiency itself will become an economic commodity, with efficient power plants gaining the profits.

Credits in the future also may be purchased from individuals involved in large-scale CO₂ sequestering efforts. Iowa farmers would be likely to gain here, through entering set-aside programs focused on a new crop: tree plantings or permanent grasslands that pull in and sequester atmospheric carbon. Thus, the import and storage of carbon may, in the future, join the export of grains as one of Iowa’s chief agricultural commodities. Tying economic incentives to the production of pollutants is an important first step toward internalizing the total environmental cost of various forms of consumption.

Expansion into Policy and International Affairs . . .

If efforts to rebalance the carbon cycle are to be meaningful, they must be integrated into governmental policy and applied around the globe. Greg Carmichael (UI Dept of Chemical and Biochemical Engineering and co-director of CGRER) has been working toward that end. His research focuses on developing and applying computer models that address the long-range transport and fate of air pollutants and trace gases such as CO₂. For the past several years, he has concentrated on the magnification of such pollutants by economic development in Asia.

Because of Asia’s size, vibrant economies, and large population growth, CO₂ and pollutants from energy consumption are high. Total energy-related carbon emissions in East Asia, for example, grew by 4.5% a year compared to a world average of 0.6% a year. These emissions are expected to continue to soar. Because of their magnitude and consequent effects outside the region of origin, Asia’s CO₂ and air pollutants have become an issue of worldwide political consideration.

One recent expression of the concern over this "globalization of pollution" was Carmichael’s invitation to be one of two speakers at a seminar hosted by the federal government’s U.S. Global Change Program. He spoke on Capitol Hill in June to about a hundred legislators, embassy officials, congressional staffers, administrators of environmental groups, and other such policy makers. His talk, "Development of Asian Megacities: Environmental, Economic, Social, and Health Implications," educated about a hundred Washington decision makers and, by doing so, will feed his insights into the framing of future discussions and policies. Talks such as this raise the consciousness of policy makers to the need for regional and international cooperation in guiding the rapid development of a continent whose environmental health and future will generate worldwide repercussions.

A Sustainable Carbon Cycle . . .

All complex carbon compounds are tiny storage vaults for the sun’s energy. We know now that those vaults can be opened to fuel a forest or our own bodies, our cars, our hospitals, and our factories. The trick is not how to do so -- it’s how to do so in a sustainable manner. It’s how to maintain the cycles so that carbon can continue to provide balanced services -- as a global temperature regulator as well as an energy source and structural building block for life on earth. CGRER’s research is directed toward further deciphering and better tending the intricacies of the carbon cycle so that the earth’s thin film of carbon-dependent life can continue to flourish.

Figure 2. Data from tiny air bubbles trapped in an Antarctic ice core show that atmospheric CO₂ concentrations and temperatures from 160,000 years ago to pre-industrial times are closely correlated. CO₂ concentrations in the last 100 years have shot skyward and show no sign of slowing; the temperature during this period has raised 1°F. At present, CO₂ concentrations are increasing 0.5% per year, or 1.5 ppm, reflecting an average of 3.4 gigatons (Gt) of net CO₂ accumulation in the atmosphere each year. The majority is a product of the approximately 6 Gt released annually from fossil fuels and industrial activity, although some of this (1.6 Gt) reflects continued destruction of the globe’s forests.

(graph source: Climate Change, State of Knowledge. 10/97. Executive Office of the President, Office of Science and Technology Policy, Washington D.C.

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Figure 3. CGRER is helping to develop a workable mechanism for pulling carbon from the atmosphere and storing it within living plant tissues and the soil. The first step is to determine how much carbon is already stored in Iowa. The CGRER project will generate GIS maps such as this one, which shows that the amount of carbon presently stored in Iowa’s soil varies from nearly none, up to over 100 tons per acre in the rich flatlands of the Des Moines Lobe.

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