There is no substitute for reductions in greenhouse gas emissions to mitigate the negative consequences of climate change, the National Research Council’s Committee on Geoengineering Climate concluded in two separate reports on climate intervention techniques.
Earth. Image credit: NASA.
The reports consider the two main ways humans could attempt to steer the Earth’s system: carbon dioxide removal and albedo-modification.
These techniques have been grouped up until now under the common term geoengineering, but they vary widely with respect to environmental risks, socio-economic impacts, cost, and research needs.
Carbon dioxide removal addresses the root cause of climate change and generally have well-understood benefits and risks, but current technologies would take decades to achieve moderate results and be cost-prohibitive at scales large enough to have a sizeable impact.
By contrast, albedo-modification techniques would only temporarily mask the warming effect caused by high carbon dioxide concentrations, and present serious known and possible unknown environmental, social, and political risks, including the possibility of being deployed unilaterally.
Committee member Prof Joyce Penner from the University of Michigan said: “certain carbon dioxide-removal tactics could have a place in a broader climate change response plan. But the sunlight reflecting technologies, on the other hand, are too risky at this point.”
Prof Penner and her colleagues underscored how important it is for humans to limit the levels of carbon dioxide they put into the atmosphere in the first place, and they called for more research into all climate intervention approaches.
“I’m concerned with the continuing rise in carbon dioxide concentrations without clear efforts to reduce emissions. The widespread impacts from these increases are readily apparent, and the cost of climate change impacts is likely to be high,” Prof Penner said.
“We may need to employ some of these climate interventions techniques to avoid a catastrophe such as the loss of the Antarctic ice sheets, or even to remain below levels of climate change that are considered dangerous in the political arena.”
Techniques to remove carbon dioxide include restoring forests and adopting low-till farming – both of which trap carbon in plants and soils.
Oceans could be seeded with iron to promote growth of carbon dioxide-consuming organisms. And carbon could be sucked directly out of the air and injected underground.
“Land-management approaches such as forest restoration and low-till agriculture are mature, readily deployable technologies with well-known environmental consequences,” the scientists wrote in a report.
“Enhanced weathering processes on land and in the ocean to accelerate natural removal of carbon dioxide from the atmosphere have only been carried out on a limited scale with intermediate technological readiness. Ocean-based approaches in particular carry significant environmental and socio-political risks.”
The researchers caution against dumping iron in the oceans, as the technical and environmental risks currently outweigh the benefits.
“Ocean iron fertilization is an immature technology whose high costs and technical and environmental risks currently outweigh the benefits,” they explained.
“Approaches in which biomass is converted to heat, electricity, or liquid or gas fuels followed by carbon dioxide capture and sequestration are limited by the availability of land for biomass cultivation and the need to transport it to processing facilities.”
“Direct air capture of carbon is an immature technology with only laboratory experiments carried out to date and demonstration projects in progress. Technologies for storing the captured carbon are at an intermediate stage, but only prototypes exist and are not at the scale required for significant sequestration.”
The scientists recommended more research and development investment to improve methods of carbon dioxide removal and disposal at scales that would have a significant global climate impact.
While many albedo-modification techniques have been proposed, the committee said two strategies that could potentially have a significant impact are injection of aerosols into the stratosphere and marine cloud brightening.
Unlike carbon dioxide removal, these methods would not require major technological innovation to be implemented and are relatively inexpensive compared with the costs of transitioning to a carbon-free economy.
However, albedo modification would only temporarily mask the warming effect of greenhouse gases and would not address atmospheric concentrations of carbon dioxide or related impacts such as ocean acidification.
Many of the processes most relevant to albedo modification are among the most difficult components of the climate system to model and monitor.
“It would be irrational and irresponsible to implement sustained albedo modification without also pursuing emissions mitigation, carbon dioxide removal, or both,” the scientists said.
Albedo-modification research will have legal, ethical, social, political, and economic ramifications.
The committee recommended the initiation of a serious deliberative process to examine what international research governance structures may be needed beyond those that already exist, and what types of research would require such governance.
“The degree and nature of governance should vary by activity and the associated risks, and should involve civil society in decision-making through a transparent and open process.”
“U.S. agencies may have been reluctant to fund this area because of the sense of what we call moral hazard – that if you start down the road of doing this research you may end up relying on this or condoning this as a way of saving the planet from the cost of decreasing CO2 emissions. But we’ve stated that decreasing emissions must go hand in hand with any climate intervention efforts,” Prof Penner said.
“The recommendation is a sign of the climate problem’s urgency. We need to develop the knowledge base to allow informed decisions before these dangerous effects are upon us.”
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