Assess Proposals in the Context of Climate Risks
The risks climate change poses to human societies and ecosystems are severe. Yet pursuit of cuts in global greenhouse gas emissions has stalled for so long that it is probably too late for emissions cuts alone to limit risks to acceptable levels. This stark reality provides essential context for all discussion of the potential contributions, costs, and risks of geoengineering.
Human activities have already heated the Earth by 1ºC, bringing impacts whose severity grows clearer each year. The 2015 Paris Agreement adopted targets to limit heating to 1.5 to 2ºC, but current policies and actions are far too weak to achieve these. Absent much stronger action, the Earth is headed for 2.5 to 5ºC heating this century, bringing likely disruption to lives, livelihoods, and ecosystems at a scale human societies have never experienced.
Stopping climate change requires cutting emissions to zero. Stopping it near the Paris targets requires cutting to zero within a few decades. This means going from today’s 80 percent reliance on fossil energy to a fully decarbonized economy, plus profound changes to eliminate emissions from agriculture, forestry, and other land-use, and multiple industrial processes.
Some models say 2ºC is still technically feasible, but only with multiple favorable assumptions, including rapid emission cuts starting immediately, low global energy demand, and fortunate outcomes on major scientific uncertainties. This doesn’t mean deep emissions cuts aren’t essential, or that they can’t reduce coming climate change risks: they are, and they can. But today’s efforts are probably fighting to reduce heating of as much as 5ºC to maybe 2.5ºC, still more than the Paris goals.
If this situation is unacceptably dangerous but emissions cuts can’t do much better, what can be done? This question is the reason to discuss geoengineering. It might be able to substantially reduce climate risks. It also presents new risks and challenges, including potentially serious problems of governance. Whether these problems are manageable or severe, they must be considered in the context of the risks of climate change.
The two main geoengineering approaches have different profiles of benefits and risks. One approach removes CO2 from the atmosphere and puts it in some stable reservoir. Proposed methods range from large expansion of familiar forest or soil-conservation practices, to novel chemical methods of direct air capture. Specific methods differ in state of development, potential scale and limits, and environmental and socioeconomic impacts, but have two things in common. First, they act slowly: sucking CO2 out of the atmosphere is draining a swimming pool through a straw. Second, if done at large enough scale they can make net emissions negative and thus reduce atmospheric CO2, not just slow its increase, and so run climate change backwards.
The second approach, solar geoengineering, would reflect away a little incoming sunlight to change the Earth’s energy balance. Promising methods include spraying reflective mist in the upper atmosphere, and making low-level ocean clouds denser and whiter. Unlike carbon removal, this approach does not target the cause of climate change, but instead makes an offsetting change. It is thus an imperfect, incomplete correction for greenhouse-driven climate change, but it has the unique advantage that it can be started, controlled, or stopped over time periods of a year or less. It would also bring its own impacts and risks. Early research suggests the most obvious impacts are surprisingly moderate and potentially correctable, but this is far from a clean bill of health.
Neither approach can replace efforts to cut emissions and adapt to coming climate changes. These both remain essential. But both approaches can complement these to further reduce climate risks. Both need research to characterize how and how well they could work, what risks they would carry, and how these could be mitigated. Both also need serious consideration of how to develop needed capacity for governance, able to make competent, prudent, and legitimate decisions on whether and how they are used, to manage associated impacts and conflicts, and to integrate them into an effective overall climate strategy.
Neither approach is getting the serious investigation and critical scrutiny it needs, but in nearly opposite ways. Assumptions of enormous future carbon removals have quietly become a mainstay of climate planning, heavily relied on in nearly all 1.5 and 2ºC scenarios, with little examination of feasibility, limits, or impacts. Solar geoengineering has been marginalized in climate assessments and policy debates, based on presumptions of severe harm or impairment of climate policy that have also received inadequate research or critical scrutiny.
This has to change. To bet the future on carbon removal working at the required billion-ton scale with acceptable impacts is a reckless gamble. To exclude solar geoengineering from consideration based on untested intuitions that it would be a cure worse than the disease is equally reckless. For all their challenges, these approaches may make things less bad than they otherwise will be, for human society, for vulnerable people and communities, and for ecosystems.
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