Having spent the last few decades piecing together the different components of the global carbon puzzle, scientists now have a good idea of how the planet’s natural carbon sinks (or reservoirs) work—primarily these sinks are plants and the oceans. But when it comes to pinpointing the locations of all the sources (areas or organisms which release carbon dioxide to the atmosphere), there remains a lot of ambiguity—mostly because climate change is constantly changing the picture of how the sources work (and it’s usually changing for the worse). Indeed, scientists are only beginning to understand how the behavior of sinks and sources will shift as atmospheric CO₂ levels continue to increase. And they do not like what they see. What many scientists are now worried about is the degree to which carbon sinks could shrink, or carbon sources could grow, in response to the rapid increase in anthropogenic CO2 emissions.

The easiest way to think of the global carbon cycle is as the sum total of different reactions—primarily those resulting in the destruction or formation of calcium carbonate or organic matter like carbohydrates—between and within the planet’s major carbon repositories: the ocean and terrestrial biosphere.^[1] The ocean is by far the larger one—estimated to hold about 38,000 petagrams (1 petagram equals one trillion grams); the land plants and soils that make up the terrestrial biosphere store only about 2,000 Pg.^[2]

Scientists are beginning to come to grips with the realization that many erstwhile sinks, primarily plants and soils, could lose their ability to draw down CO2 in a warming world.

Carbon transport between and among the reservoirs is primarily accomplished via CO₂ gas exchange. The two types of processes that affect the flow of the global carbon cycle are “long-term” fluxes—those that operate on the scale of millennia (anything having to do with weathering, or the decomposition of rocks, minerals, and soils)—and “short-term” fluxes—which are driven by natural reactions like photosynthesis and respiration (when plants absorb carbon dioxide directly from the atmosphere, for instance). These help control the concentration of CO₂ in the atmosphere.

Together, the ocean and land absorb roughly 2.1 petagrams of carbon every year; that number is the difference between the average amount of fossil fuel emissions produced, about 5.4 Pg of carbon per year, and the growth in atmospheric CO₂ concentrations, around 3.3 Pg per year. These numbers are based on measurements taken during the 1980s, one of the most recent decades for which researchers have an estimate of all sources and sinks.

So how do scientists distinguish between the contributions made by each sink? Until the mid-1990s, that question was still very much in doubt. Though researchers knew about the major sinks and sources, they were unsure as to the magnitude of the terrestrial sources—particularly the one associated with tropical deforestation (which, for a long time, they thought accounted for 10 and 50 percent of all fossil fuel emissions). Their calculations seemed to suggest that there was an additional “missing” sink somewhere, but they couldn’t put their finger on it.

In a landmark study published in 1996, Ralph F. Keeling of the Scripps Institution of Oceanography (the son of Charles D. Keeling, the man behind the famous “Keeling Curve”) and colleagues showed that it was possible to determine the difference between the two sinks by examining the partial pressures—what scientists describe as the pressure exerted by each of the constituents of a mixture of gases—of CO₂ and O₂ in the atmosphere.^[3]

Scientists already knew that an increase in atmospheric CO2 corresponded to an equivalent decrease in atmospheric O2 (because of photosynthesis and respiration). Keeling’s breakthrough was demonstrating that the ocean, though a crucial sink (and source) for CO2, did not release much O2 in response to a decrease in atmospheric O2. This meant that any change in atmospheric O2, other than that resulting from fossil fuel use, had to be attributed to a terrestrial source. Working backwards, they were able to quantify the importance of the different sources and sinks.

As most climate scientists will tell you, though, there is always a large degree of uncertainty implicit in these measurements so they could, in reality, be very different. Moreover, because the carbon balance—the difference between the amount of emissions released to the atmosphere and those taken up by sinks—is never static, year-to-year variations can be significant. These can usually be attributed to fluctuations in the response of the terrestrial biosphere to the climate—often because of increased land-use or changing water availability. The oceanic response, by comparison, is typically muted.

These sinks currently absorb around half of all the carbon dioxide emitted through fossil fuel combustion.^[4] Around 85 percent of new anthropogenic CO2 ends up in the ocean, where, after slowly dissolving into the surface waters, it gets trapped in the “conveyor belt” (also known as thermohaline circulation), the large-scale movement of currents driven by density gradients in the deep. Almost half of the total amount of anthropogenic CO2 that has been added to the atmosphere since pre-industrial times has gone into the ocean.^[5]

Indeed, as I wrote about in a recent column, scientists are beginning to come to grips with the realization that many erstwhile sinks, primarily plants and soils, could lose their ability to draw down CO2 in a warming world—with a worst-case scenario being that they would turn into sources.

Steven W. Running of the University of Montana at Missoula’s College of Forestry crunched the numbers in an article for Science a few months ago and was dismayed by the results.^[6] Though several of the 11 land models he ran projected that photosynthesis rates would dramatically increase under conditions of doubled atmospheric CO2 levels, he found that most did not incorporate land-use variations or episodic disturbances like wildfires and insect epidemics.

Those are crucial omissions, he says, since a recent FLUXNET synthesis determined that disturbances often caused sinks to turn into sources. (FLUXNET is a global network of micrometeorological tower sites which measure the exchanges of CO2, water vapor, and energy between the terrestrial biosphere and the atmosphere.) With droughts, wildfires and insect invasions, such as the mountain pine beetle epidemic, on the rise, Running cautions that many important terrestrial sinks could soon become sources.

The ocean, of course, faces its own litany of problems. As I’ve written about in the past, ocean acidification is a major concern—and one that has only become more acute in recent months. A study published last week in the Proceedings of the National Academy of Sciences found that increases in acidity are happening over 10 times faster than previously thought. This is a major problem, as lead author Timothy Wootton of the University of Chicago’s Department of Ecology and Evolution explains, because, as the ocean’s natural carbonate buffering system weakens—the direct result of millions of tons of CO2 lowering the pH of seawater—it will no longer be able to absorb as much atmospheric CO2. And that could spell big trouble for all of us.

One tool that promises to make scientists’ work much easier in the near future is NASA’s Orbiting Carbon Observatory, a satellite that will track the geographic distribution of atmospheric CO2—and thus help pinpoint the exact locations of all the sinks and sources. While not a solution in of itself, the OCO will help researchers refine their models, making them more useful for policymakers, which, in turn, should lead to the creation of more effective, targeted mitigation strategies.

Jeremy Jacquot is a graduate student in marine environmental biology at the University of Southern California and is a contributing writer for The Huffington Post, Discover Magazine, DeSmogBlog, and TreeHugger.

Notes

^[1] Sarmiento, J. L. & Gruber, N. (2002). Sinks for Anthropogenic Carbon. Physics Today, 30 – 36.

^[2] Emerson, S. R. & Hedges, J. I. (2008). Chemical Oceanography and the Marine Carbon Cycle. Cambridge University Press: New York, NY.

^[3] Keeling, R. F., Piper, S. C. & Heimann, M. (1996). Global and hemispheric CO₂ sinks deduced from changes in atmospheric O₂ concentration. Nature, 381, 218 – 221.

^[4] Schimel, D. S. et al. (2001). Recent patterns and mechanisms of carbon exchange by terrestrial ecosystems. Nature, 414, 169 – 172.

^[5] Emerson, S. R. & Hedges, J. I. (2008). Chemical Oceanography and the Marine Carbon Cycle. Cambridge University Press: New York, NY.

^[6] Running, S. W. (2008). Ecosystem Disturbance, Carbon and Climate. Science, 321, 652 – 653.

The Washington Post reports that phthalates are so ubiquitous today that in one study, the Food and Drug Administration found traces of the chemicals in every one of its 1,000 subjects. Despite strong lobbying from the chemical industry, especially Exxon Mobil, Congress moved to outlaw the chemicals from commercial products, pending further research. The Post indicates that a White House spokesman stated that President Bush opposes the legislation. Sarah Vogel explained the scientific maneuvering that led to this much-needed oversight earlier this year at The Pump Handle. Describing a Senate hearing on bisphenol A and phthalates oversight, she wrote: “At stake is the means by which society determines chemical risks and benefit.”

Before delving into nitrogen’s environmental impacts, however, it might help to first take a step back and ask: Why exactly should we care about the nitrogen cycle? Well, for one thing, most of the air we breathe is nitrogen gas: Fully 78 percent of the atmosphere is made up of nitrogen—by comparison, oxygen, the gas most of us associate with life, constitutes only 20.9 percent of the atmosphere [1]. While most of it is unavailable for use by organisms, nitrogen is ubiquitous in our natural environment and is vital to all life processes. The forms of the element we use in our bodies, which must be converted through a process called fixation, are collectively known as “reactive” nitrogen; examples of these abound and include ammonia, proteins, and amino acids.

Until the 20th century—and the advent of the modern industrial revolution—there existed only a limited number of microorganisms capable of fixing non-reactive gaseous nitrogen into reactive forms.

Until the 20th century—and the advent of the modern industrial revolution—there existed only a limited number of microorganisms capable of fixing non-reactive gaseous nitrogen into reactive forms. As a result, even though the amount of reactive nitrogen produced was limited—especially in light of the needs of our rapidly growing population—the global nitrogen cycle remained balanced. The invention of the Haber-Bosch process in the early part of the century, which provided an industrial-scale method to produce reactive nitrogen for agricultural purposes (mainly in the form of fertilizers), would revolutionize the pace of global development—helping sustain ever-higher population levels—and fundamentally alter the natural nitrogen cycle. The biogeochemical gears this invention set in motion would be further exacerbated by the world’s increased reliance on fossil fuels.

In 1970, Constant Delwiche, then a professor of soil biogeochemistry at the University of California, Davis, cautioned that, “The ingenuity that has been used to feed a growing world population will have to be matched quickly by an effort to keep the nitrogen cycle in reasonable balance” [2]. Since Delwiche’s prescient observations almost four decades ago, the world population—buoyed by the advances made under the “Green Revolution”—has increased by 78 percent. At the same time, the creation of reactive nitrogen has jumped by 120 percent. Thanks in large part to this industrial breakthrough, the most dire predictions made by Thomas Malthus and his modern adherents—predicated upon the belief that population growth would far outpace agricultural growth—never came to pass.

How do we manage to both significantly reduce the amount of nitrogen in some parts of the world while greatly increasing it in others?

While there is no denying that increased nitrogen production has been a boon for the world community—helping accommodate growing populations and alleviating poverty and hunger worldwide—it has also incurred many significant environmental costs. Air pollution, coastal eutrophication (which over-saturates waters with minerals and drives out animal life), and accelerated global warming trends, are just a few. Indeed, James Galloway, a professor of environmental sciences at the University of Virginia and the lead author on one of the articles, calls this the “cascade” effect [3]: the notion that every atom of reactive nitrogen can spur a cascading sequence of events which harms ecosystem and human health. These events can trigger terrestrial and aquatic ecosystem-wide shifts in biodiversity, facilitating the introduction of invasive species and corrupting the systems’ underlying stability. Worse still, as mentioned above reactive nitrogen can also alter the delicate balance of other greenhouse gases—including carbon dioxide and methane—and speed up ozone depletion.

Despite this growing imbalance, many areas of the world remain severely nitrogen-limited—primarily large regions in Africa and Latin America, where more cropping depletes more reactive nitrogen than fertilizers replenish. According to Galloway and his colleagues, 800 million individuals, or close to 15 percent of the world’s population, suffer from this “fertilizer deficit.” This then raises a difficult paradox: How do we manage to both significantly reduce the amount of nitrogen in some parts of the world while greatly increasing it in others? Or, as Galloway puts it, how do we, “maximize the benefits of anthropogenic Nr while minimizing its unwanted consequences”? Evidently, no single strategy will be sufficient to resolve these vexing issues.

Governments in the developed world should adopt a multifaceted, targeted approach to reducing the amount of excess reactive nitrogen by concentrating on the following objectives: reducing the amount of nitrogen oxide emissions produced during fossil fuel combustion; developing renewable energy technologies; increasing the nitrogen-uptake efficiency of crops; and improving animal management strategies. While recognizing that developing countries are primarily focused on increasing food production, the developed world should encourage them to mitigate their negative impacts while ensuring their access to fertilizers and clean energy technologies. When combined, these interventions would represent a substantial decrease in the amount of reactive nitrogen produced every year; implementing this approach would help offset some of the increases necessary to foster continued growth in agricultural production. Because these processes transcend both political and geographical boundaries, it will become necessary for governments to cooperate and to develop an integrated approach to managing nitrogen production.

Getting there won’t be easy. Put aside the sheer challenge of mounting such a global effort, and you’re still left with the equally daunting task of convincing people they should care as much about their nitrogen footprint as they do their carbon footprint. Given the right incentives, there is no question people can and will adapt—how and when they choose to do so, however, will be key.

Jeremy Jacquot is a graduate student in marine environmental biology at the University of Southern California and is the Los Angeles correspondent for TreeHugger.com.

Notes

[1] Carpenter, E.J. & Capone, D.G. (1983). Nitrogen in the Marine Environment. Academic Press: New York.

[2] Delwiche, C.C. (1970). The nitrogen cycle. Scientific American. 223, 137.

[3] Galloway, J.N. et al. (2003). The nitrogen cascade. BioScience, 53: 153 – 226.

The Nobel committee cited Ertl “for his studies of chemical processes on solid surfaces.”

AFP, AP, and Reuters hit on the implications of his work for understanding rust, fuel cells, catalytic converters, damage to the ozone layer, and the Haber-Bosch process for generating fertilizer.

The Wired Science Blog proclaims that “The surfaces of solids are one of the most important frontiers of modern science.”

Terra Sigilliata drives home the importance of understanding corrosion, which is “the term for these normally unwanted chemical reactions and is as important in industry as it is in everyday life.”

It seems hard to over-emphasize the importance of the Haber-Bosch process on modern agriculture. In The Pipeline offers technical details and Nature News quotes Andrea Sella, who declared it “the industrial process which can safely be said to have had the widest impact on mankind.” Good thing we know how it works.