Wallace Broecker vs. Greenpeace: Climate Scientist Argues in Favor of Ocean CO2 Storage

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The Guardian has been playing host to a lively debate between Wallace Broecker, a world-renowned climate scientist at Columbia University (and originator of a scheme to deploy millions of tree-like CO2 "scrubbers"), and Bill Hare of Greenpeace. It kicked off with a lengthy piece by Broecker challenging Greenpeace's stand on ocean storage last week and has now seen the two take each other's arguments head-on. The debate: Is ocean storage a viable option or merely a "dangerous distraction"?
Broecker points to evidence gleaned from several past studies to make the point that, while not without risk, deep ocean storage should be examined further as one component of a global emissions mitigation strategy. More small-scale demonstrations will be needed to evaluate its costs and benefits, he readily acknowledges, but just shutting the door on any future research would be self-defeating. He goes on to propose several possible pilot experiments:

We know enough to say with confidence that deep ocean disposal of CO2 is certainly feasible, but unless small-scale pilot experiments are conducted, information necessary to assess the impact on the macro abyssal biota will remain obscure. The injections could be made from ships equipped for deep sea drilling, and if the CO2 were tagged with radiocarbon, its dispersal away from the sea floor clathrate pile could be sensitively monitored.

Studies of the costs associated with ocean disposal would also be conducted. The CO2 would have to be sent through pipelines from its collection point to a port, where it would be loaded on tankers that would carry it to a floating ocean station, from which it would be piped to the abyss.

Calling it a "dangerous distraction," Bill Hare responds by arguing that the solutions already exist for humanity to make the necessary deep cuts; what is required, he continues, is an overhaul of the "appropriate policy settings" -- particularly in skeptic-heavy countries like the U.S. He lays out his own evidence to refute Broecker's rationale, saying that our understanding of the deep ocean's biogeochemistry is still too narrow to effectively gauge the impact of the injection of billions of tons of CO2:

Deep water injection CO2 would cause inevitable and potentially irrevocable damage to those deep-water ecosystems directly impacted (smothering, asphyxiation, acidification), and at scale would result in far more widespread effects in the abyssal zone over time as the clathrates dissolve. Over far longer timescales it would result in changes to abyssal ecosystems which in turn feed back to the global carbon cycle.

To suggest that there is "no indication that the projected rise in upper ocean CO2 content will have adverse impacts on fish" and, on this basis, to argue that spread of CO2 through the deep sea would therefore also be benign, is misleading in the extreme. This statement ignores the growing evidence that projected rises in upper ocean CO2 and consequent acidification is likely to have profound impacts on calcification rates and calcifying organisms. It is predicted that upper ocean pH levels will drop to levels lower than those recorded at any time over tens of millions of years, and at a rate orders of magnitude greater than any previous change. There is also evidence that deep water crustacean species, sediment dwelling organisms and associated ecosystem processes could also be adversely affected, including changes to nutrient cycling thought to occur through impacts on sediment microflora.

The fact that deep water CO2 concentrations are currently lower than those of surface waters should not be taken as an indication of a vast unexploited capacity for CO2 disposal. Our knowledge of the biogeochemical processes which have contributed to the current distribution of CO2 in the deep oceans remains limited, as does our capacity therefore to predict the consequences of multi-billion tonne injections of CO2 at depth. To assume that uniformity of concentration is somehow an acceptable target, or one which will have minimal impact on marine ecosystems and the carbon cycle, is oversimplistic.

Dr Broecker argues that a series of experiments involving the release of one tonne quantities of CO2 at depths greater than 3,500m are the next logical step. One tonne release experiments to observe behaviour and determine impacts is one thing. However, one tonne experiments intended as proof of the concept for multi-gigatonne injections in the future is quite another.

An obvious critical aspect is the potential for cumulative impacts resulting from continuous injections over long periods, or a large number of injections, such as would be a necessary characteristic of any deep injection strategy for climate change mitigation. The nature and likelihood of these cumulative impacts simply could not be assessed from the results of the experiments he suggests.

In his last reply, Broecker reiterates his central argument that, given the risks posed by climate change, we need to consider all storage options -- even those that carry more risk:

My plea to allow pilot injections of CO2 into the abyssal ocean is based on the likelihood that a significant fraction of the world's coal reserves will be burned during the course of this century. Hence, we must prepare to capture and store the resulting CO2 emissions. All storage options must be explored. None is without its environmental consequences.

My proposal is to preload the deep Pacific with CO2. By preload, I mean add only that amount of CO2 that will eventually get there on its own. The capacity for storage will grow as we release ever more CO2 into the atmosphere. Were this limit to be respected, then there would be no tendency for the injected CO2 to leak back to the atmosphere. Further, the ocean-wide ecologic impact would be no different than that which would occur hundreds of years from now when the CO2 gets to the deep sea on its own.

In defense of geoengineering?
As someone who's long been a skeptic of geoengineering, I have to admit that it's become increasingly difficult for me to maintain my resolve. The planet as a whole has taken a drastic turn for the worse in recent months, and I've grown disillusioned with the prospects of an effective successor to the (failed) Kyoto Protocol (I'm not even going to broach the Bush administration's numerous failures on that front here).

While I'm still a firm believer in the ability of conventional options, like renewable energy, conservation and better energy efficiency, to get the job done, I do think we need to invest more time and research in some of these riskier schemes.

Via ::The Guardian: Deep divisions (news website)

More about geoengineering
::Andy Revkin on Geoengineering
::Giving Geo-Engineering Another Go: Dumping Limestone into the Oceans to Fight Acidification

Tags: Carbon Dioxide | Oceans

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