The Gist: Putting reflective aerosols high into the atmosphere to slow climate change is too risky and not cost effective.
That’s Climate Central describing the core conclusions of the Climatic Change paper “The economics (or lack thereof) of aerosol geoengineering,” (full paper online here).
This study would seem to support the view that if you don’t do aggressive greenhouse mitigation starting now, you pretty much take aerosol geo-engineering off the table as a very limited (but still dubious) add-on strategy “” as even geo-engineering experts like climatologist Ken Caldeira have made clear.
What’s nice about this study is that it doesn’t just do an economic analysis, but also discusses intergenerational ethics. I’ll excerpt the study itself at length — after the full Climate Central summary:
Summary: Some have argued that if human society cannot sufficiently reduce its greenhouse gas emissions, than we could still avoid the worst consequences of global warming by putting highly reflective particles, known as aerosols, high into the atmosphere. These aerosols would reflect light back to space, thus counteracting warming from greenhouse gases.
The authors of this paper use an integrated assessment model to determine how costly such a method would be. The authors discuss the potential side effects of this so-called “geoengineering” strategy, since adding aerosols to the atmosphere could have unintended consequences, such as significantly altering weather patterns and damaging stratospheric ozone. Also, aerosols are short-lived, and would have to be continuously added to the atmosphere in order for this scheme to work. If society stopped injecting them, the result would be a rapid shift in the climate, something this paper argues would be highly damaging.
The authors calculate that if there is greater than a 15 percent chance that such a method will be shut down, or if the unintended consequences of aerosols are greater than half a percent of the world’s economy, then this method of geoengineering is not worth the effort.
And let’s not forget that the aerosol ‘solution’ does nothing to stop the consequences of ocean acidification, which recent studies suggest will be devastating all by itself (see Geological Society: Acidifying oceans spell marine biological meltdown “by end of century”).
Here is the conclusion to the study itself:
First, aerosol geoengineering hinges on counterbalancing the forcing effects of greenhouse gas emissions (which decay over centuries) with the forcing effects of aerosol emissions (which decay within years). Aerosol geoengineering can hence lead to abrupt climate change if the aerosol forcing is not sustained. The possibility of an intermittent aerosol geoengineering forcing as well as negative impacts of the aerosol forcing itself may cause economic damages that far exceed the benefits. Aerosol geoengineering may hence pose more than just “minimal climate risks,” contrary to the claim of Wigley (2006). Second, substituting aerosol geoengineering for CO2 abatement fails an economic cost-benefit test in our model for arguably reasonable assumptions. In contrast, (and as shown in numerous previous studies) fast and sizeable cuts in CO2 emissions (far in excess of the currently implemented measures) pass a costbenefit test. Third, aerosol geoengineering constitutes a conscious temporal risk transfer that arguably violates the ethical objectives of intergenerational justice.
Our analysis has barely scratched the surface and is silent on many important aspects. More than a decade ago, a Unites States National Academies of Science committee assessing geoengineering strategies concluded that “Engineering countermeasures need to be evaluated but should not be implemented without broad understanding of the direct effects and the potential side effects, the ethical issues, and the risks” (COSEPUP, 1992). Today, we are still lacking this broad understanding.
Caldeira made some similar points to me in a 2009 e-mail interview:
Nobody has written about this that I know of, but “¦. If we keep emitting greenhouse gases with the intent of offsetting the global warming with ever increasing loadings of particles in the stratosphere, we will be heading to a planet with extremely high greenhouse gases and a thick stratospheric haze that we would need to main[tain] more-or-less indefinitely. This seems to be a dystopic world out of a science fiction story. First, we can assume the oceans have been heavily acidified with shellfish and corals largely a thing of the past. We can assume that ecosystems will be greatly affected by the high CO2 / low sunlight conditions “” similar to what Earth experienced hundreds of millions years ago. The sunlight would likely be very diffuse “” maybe good for portrait photography, but with unknown consequences for ecosystems.
We know also that CO2 and sunlight affect Earth’s climate system in different ways. For the same amount of change in rainfall, CO2 affects temperature more than sunlight, so if we are to try to correct for changes in precipitation patterns, we will be left with some residual warming that would grow with time.
And what will this increasing loading of particles in the stratosphere do to the ozone layer and the other parts of Earth’s climate system that we depend on?
On top of all of these environmental considerations, there are socio-political considerations: We we have a cooperative world government deciding exactly how much geoengineering to deploy where? What if China were to go into decades of drought? Would they sit idly by as the Climate Intervention Bureau apparently ignores their plight? And what if political instability where to mean that for a few years, the intervention system were not maintained “¦ all of that accumulated pent-up climate change would be unleashed upon the Earth “¦ and perhaps make “The Day After” movie look less silly than it does.
Long-term risk reduction depends on greenhouse gas emissions reduction. Nevertheless, there is a chance that some of these options might be able to diminish short-term risk in the event of a climate crisis.
I would add the grave risk that that after injecting massive amounts of sulfate aerosols into the atmosphere for a decade or more, we might experience some unexpectedly bad side effect that just gets worse and worse. After all, the top climate scientists underestimated the speed and scale of greenhouse gas impacts (and the magnitude of synergistic ones, like bark beetle infestations and forest fires).
We would be in incompletely unexplored territory “” what I call an experimental chemotherapy and radiation therapy combined. There is no possible way of predicting the long-term effect of the thick stratospheric haze (which, unlike GHGs, has no recent or paleoclimate analog). If it turned out to have unexpected catastrophic impacts of its own (other than drought), we’d be totally screwed (see “the definitive killer objection to geoengineering as even a temporary fix”).
Or, rather, our children and grand-children would be totally screwed, not that our actions today suggest we care about them very much (see Is the global economy a Ponzi scheme?). The study has this to say about the intergenerational ethics issue:
While there have been careful analyses of the significance of intergenerational justice in the wider context of climate change (Gardiner, 2009; Page, 2006; Wolf, 2009), our study is the first to quantitatively examine issues of intergenerational justice raised by aerosol geoengineering for the case that aerosol geoengineering can be intermittent and the aerosol forcing can cause harm. Our analysis shows, for example, that substituting aerosol geoengineering for CO2 emissions abatement is a risk transfer from current to future generations (Figures 4 to 7). In addition, the impacts of the abrupt warming due to a discontinuation of the aerosol forcing would place a heavy burden on human communities and ecosystem integrity (Alley et al., 2002) and thus threaten the conditions required to satisfy basic welfare rights of future generations. Substituting aerosol geoengineering for CO2 emissions abatement decreases the required abatement costs in the near term but imposes sizeable risks for more distant generations (Figure 4 a, b). Since Rawlsian intergenerational distributive justice requires that current generations avoid policies that create benefits for themselves but impose costs on future generations, substituting aerosol geoengineering for CO2 abatement fails on the grounds of this particular approach to ethics.
It would appear that what science advisor John Holdren reasserted in 2009 remains true today, “The ‘geo-engineering’ approaches considered so far appear to be afflicted with some combination of high costs, low leverage, and a high likelihood of serious side effects.”
Mitigate, mitigate, mitigate — or punish countless future generations.
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