“The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System”

P. Falkowski et al. 2000. Science, vol. 290, pp. 291-296.
Motivated by the rapid increase in atmospheric CO2 due to human activities since the Industrial Revolution, several international scientific research programs have analyzed the role of individual components of the Earth system in the global carbon cycle. Our knowledge of the carbon cycle within the oceans, terrestrial ecosystems, and the atmosphere is sufficiently extensive to permit us to conclude that although natural processes can potentially slow the rate of increase in atmospheric CO2, there is no natural “savior” waiting to assimilate all the anthropogenically produced CO2 in the coming century. Our knowledge is insufficient to describe the interactions between the components of the Earth system and the relationship between the carbon cycle and other biogeochemical and climatological processes. Overcoming this limitation requires a systems approach.


In “Ecology in an anthropogenic biosphere” Erle Ellis (2015) posited that human transformation of the biosphere is driven primarily by sociocultural causes. Forcing of global biogeochemical cycles ranks among the top of the list of side effects of such sociocultural niche construction; this post starts with a seminal paper Ellis cites on the carbon cycle by Falkowski et al. (2000), who noted that a variety of factors are conspiring to virtually guarantee continued growth in atmospheric CO2 emissions. At the time this paper was published, over 15 years ago, atmospheric CO2 had reached (an annual average of) 369 parts per million (ppm), nearly 100 ppm over the interglacial (pre-industrial) value of ~280 ppm. The average for 2015 was nearly 400 ppm and it is on a continuing upward ascent.

This biogeochemical forcing was sociocultural—but unconsciously, unintentionally so. Our collective consciousness has slowly awakened, ultimately leading to Paris just 2 months ago, where the COP21 (Conference of the Parties to the Framework Convention on Climate Change) pledged to drastically reduce emissions. Achieving the target of limiting warming to the 1.5oC “tipping point,” however, requires zero emissions within 30 years, followed by negative emissions thereafter. And negative emissions implies—essentially requires—geoengineering. Sociocultural, yes—but this time conscious, and very much intentional.

So-called “geoengineering”—or as termed by recent National Research Council (NRC, 2015a, b) reports “climate intervention”— typically means either carbon dioxide removal (CDR), or albedo modification (AM). The former could entail, for example, direct air capture, or enhanced rock (silicate) weathering, whereas the latter involves ways to enhance planetary reflectivity (global shading), for example by marine cloud brightening (by injecting tiny droplets of seawater), or introducing sulfate aerosols directly into the stratosphere. The NRC considered CDR techniques of lower risk and greater benefit than the AM approaches.

A CDR technique that has spawned numerous climate entrepreneurs was inspired by the late John Martin, longtime director of the Moss Landing Marine Laboratories and an oceanographer famously known for research on “The Iron Hypothesis.” Huge regions of the ocean are high-nutrient, low-chlorophyll (HNLC) zones, meaning that they are virtual biological deserts with very little primary production, despite high nutrient levels. Martin hypothesized that the low iron levels of these regions might be limiting productivity, and he conducted experiments that demonstrated phytoplankton blooms in the wake of iron seeding. During a lecture at Woods Hole Oceanographic Institute shortly before his death he famously stated “Give me half a tanker of iron, and I will give you an ice age.”

Martin’s results ignited much subsequent research, and commercial ventures, on the effects of iron on ocean fertilization and consequent drawdown of atmospheric CO2, research that has only intensified as humanity’s continued hacking of the Earth’s carbon cycle continues. Geoengineering in general—an approach once dismissed as an improbable path, a frighteningly futuristic “Plan B”—is now not only discussed but implicitly presumed to be a key to limiting dangerous climate change.

Once we begin to intentionally alter planetary temperature, questions not only of unintended consequences, but morally unacceptable unintended consequences enter the argument. How will albedo management affect regional shifts in monsoonal precipitation, for example? Who controls the thermostat? Indeed, in a followup comment to Falkowski et al. (2000), Falkowski and others (Chisholm et al., 2001) called ocean fertilization to the proverbial woodshed, pointing out serious risks of such technology if applied on an industrial scale. While noting that small fertilization events may be relatively innocuous in terms of ecosystem disruption, Chisholm et al. (2001) feared a “tragedy of the commons” in the wake of entrepreneurs upscaling in the race to profit from carbon credits. The more recent (2015a, b) NRC reports echoed these concerns, calling out ocean fertilization as the CDR technique most fraught with legal and ethical issues. Nevertheless, it appears increasingly evident that the geoengineering/climate intervention bus has left the station, owing in no small part to our collectively sluggish sociocultural consciousness.

Two wrongs to make it right? How much more sociocultural niche construction can the Earth System take? In last week’s post, Kiza pointed out some of the problems that might follow from Ellis’ (2015) suggestion that “To sustain nonhuman nature, it will be necessary to assist species and ecosystems in changing, for example, by translocating species” (p. 319). If anything, geoengineering goes even further, hacking not just ecosystems, but the very globe—although we must remember the interconnectedness of all systems. Each hack begets further hacking—a fact that Ellis memorializes as the “First Law of the Anthropocene”—that humans (have always, and always will) shape planetary ecology. We ARE part of nature, so let’s hope that “the better angels of our nature” prevail as we move forward in evolving cultural traits for beneficial Earth System engineering.

Chisholm, S.W., Falkowski, P.G., and Cullen, J.J. 2001. Dis-crediting ocean fertilization: Science, v. 294, p. 309-310. The authors warn that iron fertilization would be extremely difficult to validate and would significantly alter oceanic food webs and biogeochemical cycles.warn that iron fertilization would be extremely difficult to validate and would significantly alter oceanic food webs and biogeochemical cycles.
National Research Council, Committee on Geoengineering Climate. 2015a. Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration. Washington, D.C.: National Academies Press.  http://doi.org/10.17226/18805. Considers how to actively remove carbon dioxide from the atmosphere to make a bigger difference more quickly.
National Research Council, Committee on Geoengineering Climate. 2015b. Climate Intervention: Reflecting Sunlight to Cool Earth. National Academies Press, Washington, DC. http://doi.org/10.17226/18988. Discusses albedo modification—changing the fraction of incoming solar radiation that reaches the surface. This approach would deliberately modify the energy budget of Earth to produce a cooling designed to compensate for some of the effects of warming associated with greenhouse gas increases. 

3 thoughts on ““The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System”

  1. Thanks for your post, Lynn. Let me alert readers to another one you did a while back that touches on some related themes.

    Two things occurred to me as I thought about your current post.

    First, you point to some moral issues associated with hacking the climate system—substantive concerns about harmful consequences, and procedural concerns about who will make the decisions (raising the question, by what authority?). There is an additional concern that has been raised—the problem of “moral hazard:” the idea that, just as having insurance might tempt people into riskier behavior than otherwise, having the Plan B of geoengineering might undercut support for lessening emissions of CO2. Here is a piece from Slate on this point.

    But second, here’s a question: do you think that geoengineering is just an extension of the kind of sociocultural niche construction Ellis talks about in his paper? Is it just one more way our species has of altering its surroundings to make them better meet our needs for survival? Or is it something qualitatively different—perhaps because of its deliberate, self-conscious quality? At the very end of your post you seem to accept Ellis’ general picture of the inevitability of pervasive human influence over the biosphere. Do you think his theory can explain (let alone encourage) the kind of self-imposed restraint on human niche construction that the “better angels” you refer to would support?

  2. You’re absolutely right, Zev, that the “promise” of geoengineering our way out of our climate conundrum raises the specter of delaying real action on the carbon problem. This has been raised by many, and it’s especially alarming in the case of albedo modification, because AM simply masks the effects of continued carbon-induced warming, and if AM is halted, emissions-induced warming would be even more intense than before.

    Regarding your second comment— is geoengineering an extension of our ongoing sociocultural niche construction or qualitatively different— in the final analysis, it is probably an extension, but it SEEMS qualitatively different owing to the intentionality. It is this intentionality that causes many to categorically disparage (or at least label as “scary”) any geoengineering scheme, when what we should probably be doing is assessing the possible merits and unintended consequences of such schemes in order to make progress in mitigating our (current) unintentional Earth System experiment. This is what I hope we can do in drawing upon the “better angels of our nature,” because doing nothing IS perhaps scarier.

  3. I’d agree with Lynn that climate geoengineering is just a HUGE extension of sociocultural niche construction- noting that so is unintentional anthropogenic global climate change (niche construction can be detrimental and beneficial). I am still somewhat hopeful that societies can move toward reducing anthropogenic global climate change- both intentional and unintentional. However, the past record shows a tendency for societies to fix one problem with an even greater problem….

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