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Climate Intervention Is Not a Replacement for Reducing Carbon Emissions

Posted on 15 February 2015 by John Hartz

This article is a lightly edited version of a news release posted by the National Academy of Sciences (NAS) on Feb 10, 2015.

Proposed Intervention Techniques Not Ready for Wide-Scale Deployment

There is no substitute for dramatic reductions in greenhouse gas emissions to mitigate the negative consequences of climate change, a National Research Council committee concluded in a two-volume evaluation of proposed climate-intervention techniques. The two reports are:

Strategies to remove carbon dioxide from the atmosphere are limited by cost and technological immaturity, but they could contribute to a broader portfolio of climate change responses with further research and development. Albedo-modification technologies, which aim to increase the ability of Earth or clouds to reflect incoming sunlight, pose considerable risks and should not be deployed at this time.

NAS Report: Intervention - Carbon Sequestration

Carbon dioxide removal and albedo-modification 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 — high concentrations of the greenhouse gas in the atmosphere — 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 CO2 concentrations, and present serious known and possible unknown environmental, social, and political risks, including the possibility of being deployed unilaterally.

These differences led the committee to evaluate the two types of approaches separately in companion reports, a distinction it hopes carries over to future scientific and policy discussions. In addition, the committee believes that these approaches are more accurately described as “climate intervention” strategies — purposeful actions intended to curb the negative impacts of climate change — rather than engineering strategies that imply precise control over the climate.

“That scientists are even considering technological interventions should be a wake-up call that we need to do more now to reduce emissions, which is the most effective, least risky way to combat climate change,” said committee chair Marcia McNutt, editor-in-chief of Science and former director of the U.S. Geological Survey.“But the longer we wait, the more likely it will become that we will need to deploy some forms of carbon dioxide removal to avoid the worst impacts of climate change.”

NAS Report: Climate Intervention - Reflecting Sunlight

If society ultimately decides to intervene in Earth’s climate, any actions should be informed by a far more substantive body of scientific research, including ethical and social dimensions, than is presently available, the committee said. Decisions regarding deployment of carbon dioxide removal technologies will be largely based on cost and scalability, and research is needed to make current options more effective, more environmentally friendly, and less costly. Conversely, any future decision about albedo modification will be judged primarily on questions of risk, and there are many opportunities to conduct research that furthers basic understanding of the climate system and its human dimensions — without imposing the risks of large-scale deployment — that would better inform societal considerations.

“If the world cannot slow emissions or the effects of climate change are more extreme or occur sooner than expected, there may be demands to pursue additional climate-intervention technologies about which scientists need a better understanding,” said National Academy of Sciences President Ralph J. Cicerone.“Although riskier ideas to lessen the amount of energy absorbed from the sun should not be considered for deployment, they should be studied so that we can provide answers if someday these ideas begin to be considered in attempts to avert catastrophe. These reports should guide federal agencies in supporting research on climate-intervention technologies, while keeping separate any decision-making about their implementation.”

Carbon dioxide removal and sequestration

Some carbon dioxide removal strategies seek to enhance or mimic the natural processes that already remove about half of the world’s carbon emissions from the atmosphere each year. Environmental risks vary among the proposed technologies (listed below), but overall the risks are relatively low and generally understood. However, most carbon dioxide removal strategies have limited technical capacity, and absent some unforeseen technological innovation, large-scale deployment would cost as much or more than replacing fossil fuels with low carbon-emission energy sources, the committee said.

  • Land-management approaches such as forest restoration and low-till agriculture are mature, readily deployable technologies with well-known environmental consequences.
  • 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.
  • Ocean iron fertilization is an immature technology whose high costs and technical and environmental risks currently outweigh the benefits.
  • Approaches in which biomass is converted to heat, electricity, or liquid or gas fuels followed by CO2 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 carbon are at an intermediate stage, but only prototypes exist and are not at the scale required for significant sequestration.

The committee recommended federal research and development investment to improve methods of carbon dioxide removal and disposal at scales that would have a significant global climate impact. In particular, research is needed to minimize energy and materials consumption, identify and quantify risks, lower costs, and develop reliable sequestration and monitoring capabilities.

Technologies that prevent sunlight from reaching Earth’s surface could reduce average global temperatures within a few years, similar to the effects of large volcanic eruptions. 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 CO2 or related impacts such as ocean acidification. In the absence of CO2 reductions, albedo-modification activities would need to be sustained indefinitely and at increasingly large scales to offset warming, with severe negative consequences if they were to be terminated. In addition, albedo modification introduces secondary effects on the ozone layer, precipitation patterns, terrestrial and marine ecosystems, and human health, with unknown social, political, and economic outcomes.

Many of the processes most relevant to albedo modification — such as those that control the formation of clouds and aerosols — are among the most difficult components of the climate system to model and monitor. Present-day observational capabilities lack sufficient capacity to monitor the environmental effects of an albedo-modification deployment. Improvements in the capacity to monitor direct and indirect changes on weather, climate, or larger Earth systems and to detect unilateral or uncoordinated deployment could help further understanding of albedo modification and climate science generally.

The committee said it would be “irrational and irresponsible” to implement sustained albedo modification without also purse emissions mitigation, carbon dioxide removal, or both. It opposed deployment of albedo-modification techniques, but recommended further research, particularly “multiple-benefit” research that simultaneously advances basic understanding of the climate system and quantifies the technologies’ potential costs, intended and unintended consequences, and risks.

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.

The study was sponsored by the National Academy of Sciences, U.S. intelligence community, National Aeronautics and Space Administration, National Oceanic and Atmospheric Administration, and U.S. Department of Energy.  The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council are private, independent nonprofit institutions that provide science, technology, and health policy advice under a congressional charter granted to NAS in 1863. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. For more information, vsit

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Comments 1 to 3:

  1. "Climate Intervention" should not be deployed at any time.

    Even at some future date it will be abused to excuse a lack of rapidly reducing the impacts of burning fossil fuels, particularly to excuse further delays by the most fortunate who refuse to give up any of the clearly illigitmate unsustainable and damaging ways of living they are addicted to getting away with.

    "Attitude Intervention" to force the most callous pursuers of personal benefit to behave decently, or fail quickly and repeatedly, is the required intervention and adaptation.

    The future of humanity is clearly at stake here. The threat is clear. And the interests of people who pose the greatest threat are also clear. Wasteful damaging unsustainable mass-consumerism must be curtailed, particularly by the most fortunate, if there is to be any chance of 'sustainable economic growth' and a future for humanity and advancing any of its civilizations.

    People who are wealthy and powerful have no excuse. They canot calim to not be aware of this. All that is left is for such a person to admit they care and will change, including forcing change on the undeserving unwilling trouble-makers. And that is where the curret socio-economic-political system fails clearly fails. Many fully aware leaders deliberately mislead and can be popular because of their deliberate damaging deceptions.

    That may seem harsh, but the irrational damaging global trade systems created in the past few decades are clearly causing a major part of the problem. In the current world of trade national sovereingty is limited by laws when 'free trade is impacted'. Yet the same people who will abuse those laws to their advantage will demand that national sovereignty must be respected when it comes to 'reluctance to act responsibly to reduce global human impacts'. Those unacceptable people will try to profit from 'climate intervention'. And there is little doubt that what they will push for will be as unsustainable and damaging as the global trade actions they try to profit from. They are clearly in need of "Attitude Intervention".

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  2. There is no substitute for dramatic reductions in greenhouse gas emissions to mitigate the negative consequences of climate change

    I hope you guys are all leading by example ? I know I have been keeping my emisons as low as I can: no flying for holidays, no driving, cut back on eating meat, no meat eating pets, use only renewable energy and only voting for politicans with effetive mitigation strategies ie The Greens... the low hanging fruit on the the emissions reduction tree.  I do more than that but that's the minimum everyone needs to do to ensure we start mitigating effectively.

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    Moderator Response:

    [Rob P] - Not being a hypocrite is important but, apart from a feeling of superiority or smugness, your own personal measures aren't even remotely enough to stem the problem. Unless there is a worldwide mobilization to rapidly decarbonize the global economy all you're achieving is shuffling deck chairs on the Titanic. Having some perspective is important too.

  3. Pursuit of "Climate Intervention" is a misdirection of human intelligence and ingenuity. Investigating and reporting the consequences of such pursuits is a necessary activity, but is also a 'misdirection of effort' from the sustainable advancement of humanity, or any of its societies and civilizations.

    The current social-economic-political systems places 'pursuit of profit and popularity' well above the 'meaningful advancement of understanding toward the development of a sustainable better future for all'. That misplaced prioritization is a fundamental fatal flaw. It can easily lead to 'profitable and popular' damaging and unsustainable actions by a sub-set of a given generation of humanity on this amazing planet, to the detriment of all others.

    Humanity could have a 'brilliant sustainable constantly improving future for all life on this amazing planet'. It just needs the chance to effectively focus efforts on the pursuit of that type of development, without anyone getting away with hindering the progress. That will require diligent monitoring and actions to thwart the many unacceptable attempts at personal gain to the detriment of others that will be made by people who only care about themselves.

    The solution to that challenge deserves significant attention. Until that issue is effectively dealt with any developed better understandings of what is going, and efforts to try to better understand what is going on, will be less effective than they need to be.

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