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Will the world resort to ‘solar radiation management’ to slow the Earth’s heating? Mark Robinson/flickr, CC BY-NC

To meet the Paris climate goals, do we need to engineer the climate?

The climate talks that convened in Paris at the end of 2015 produced a historic agreement, giving negotiators and climate activists good reason to celebrate. Now the task is to ensure that the ambition shown in Paris is matched by action.

The good news is that there are a number of viable ways to meet the Paris climate goals. It was reported a couple of weeks ago that, since 2007, the output of the U.S. economy has grown by around 10 percent, while primary energy consumption fell by 2.4 percent over the same period. It is now possible to imagine that the economy can grow, even as fossil fuel-based energy production declines. Add to this an announcement from the International Energy Agency that electricity produced worldwide from renewable sources looks to be on track to overtake coal-fired generation by 2030, and the much-needed renewable energy revolution may well be upon us.

All is not necessarily rosy, however. For one thing, international agreements don’t always translate into domestic momentum. Witness, for instance, the decision by the Supreme Court of the United States to place a stay on a key part of the Obama administration’s plan to stem carbon emissions.

A second piece of bad news, or, at least, news that will be unwelcome in many quarters, is that matching the ambition of Paris will demand consideration of options for addressing climate change that to this point have been widely deemed unpalatable.

Our read is that the Paris agreement will, through time, force closer consideration of so-called “climate engineering” or “geoengineering” schemes. In particular, we foresee increasing attention being paid to solar radiation management (SRM) or albedo modification technologies. This is a class of speculative responses that might cool the planet by reflecting some amount of solar energy back into space before it can trapped by the greenhouse gases in the atmosphere. Leading SRM proposals include depositing reflective sulfate particles into the stratosphere or increasing the reflectivity of marine clouds via the introduction of saltwater droplets.

Such ideas have to this point been confined to the fringes of the climate change conversation. That looks set to change. Here’s why.

Energy transition is imperative (but not easy)

A critical piece of the Paris agreement is a change to the agreed “threshold” level of climate warming. The prior goal, established at the 2009 international climate meeting in Copenhagen, was for the international community to work to cap global warming at no more than 2 degrees Celsius above preindustrial averages. The new agreement is more ambitious. It urges, in the preamble, “holding the increase in the global average temperature to well below 2°C above preindustrial levels and to pursue efforts to limit the temperature increase to 1.5°C.”

The new target is a welcome and important development. Less warming means less risk of catastrophic sea-level rise, runaway polar and glacial ice melt, further damaging acidification of the world’s oceans and a host of other dangers.

At the same time, as critical as it is, restricting planetary warming to 1.5°C amounts to a Herculean undertaking.

One recent study suggests that to limit warming to 2°C via energy transition alone, more than 80 percent of coal reserves, half of all natural gas, and one-third of the world’s known oil should remain buried beneath the earth. A target of no more than 1.5°C of warming means the task is that much harder. The new target rapidly accelerates the required timetable for ratcheting down greenhouse gas emissions.

The renewable energy revolution is coming, but will it come fast enough? The truth is that despite the positive intent indicated in Paris, the world to this point has shown relatively few signs that it is eager to be weaned from fossil fuels, for a few reasons.

For starters, while renewable energy availability is increasing rapidly, developed and developing countries alike are still counting on the burning of vast amounts of fossil energy to drive economic growth. Meanwhile, fossil fuel companies still play an outsized role in setting national and international priorities and policies. Breaking the hold of fossil fuels is not just a technological task, in other words. It is also an immense political and social undertaking.

Finally, it is important to note that the Paris agreement isn’t due to take hold until 2020, and even then the entirely voluntary pledges announced by countries in Paris set the world on a path to warming of 2.7°C or more. Even an optimistic reading of the kinds of follow-on actions Paris might set in motion to limit warming to 1.5°C suggests an extraordinarily tough road ahead.

Might 1.5C demand other forms of action?

So what more can be done? Another piece of the puzzle may be large-scale schemes to remove carbon dioxide and, perhaps, other greenhouse gases from the atmosphere and hold them in long-term storage or put them to productive use.

Capturing and then sequestering the carbon released by coal-fired power plants has been discussed for years. A number of demonstration projects have been developed or are in development. The model, though, is still not considered economically viable.

Other, more exotic ideas entail pulling carbon dioxide directly from the open atmosphere. Some of the leading proposals include bio-energy with carbon capture and storage (BECCS) and “artificial trees” that could take in and trap atmospheric carbon.

Such ideas strike some as dubious propositions. In fact, though, carbon dioxide removal (CDR) schemes are already baked into the 1.5°C target. The most recent IPCC assessment report examined a wide variety of possible pathways by which atmospheric warming might be kept below 2°C. Almost all of the IPCC projections required not just decarbonization of the energy economy but also the invention and deployment of what the report called “negative emissions” technologies.

Similarly, it should be noted that the Paris agreement has language not just about greenhouse gas emissions but also about greenhouse gas “removals.” The aim expressed in the Paris document, in other words, is not necessarily full decarbonization of the energy economy, but rather “net zero” emissions. That implies greenhouse gas emissions are offset by carbon removal from the atmosphere.

Yet CDR or negative emissions technologies receive comparatively little attention. That’s a misleading way to view the climate puzzle.

If the world is to meet some portion of the new Paris obligations via speculative investments in greenhouse gas removal technologies, there should be open acknowledgment of this fact, lest the world be duped by what Oliver Geden has called, in this context, “magical thinking, questionable accounting and dubious expectations about future technology.”

We need an open conversation about climate engineering proposals

As difficult and contentious as the conversation about CDR technologies promises to be, the conversation about solar radiation management (SRM) technologies will be thornier still.

A small but respected group of scientists has been calling for consideration of SRM as a third piece of the climate change response puzzle, in addition to limiting greenhouse gas emissions and enhancing greenhouse gas sinks. The argument that they make is that SRM represents the only known option that can quickly suppress temperatures, to buy time for other forms of response to take hold.

SPICE (Stratospheric Particle Injection for Climate Engineering) was a UK government-sponsored research program to investigate the feasibility of one particular mechanism by which reflective particles could be delivered into the upper atmosphere. Hughhunt, CC BY-NC-SA

There are research programs on SRM science under way at Harvard, Stanford and elsewhere. However, to date there has been next to no public attention to SRM proposals. Nor have the nongovernmental organizations that often generate public engagement been paying SRM much attention. In fact, many groups that work on climate change policy and advocacy have been studiously avoiding consideration of SRM, for quite legitimate reasons.

A major fear is that if more attention is given to this subject by more people and groups, then momentum may build in support of the project, even should negative consequences be seen to outweigh positives. The preliminary research undertaken to date suggests clear upsides to SRM development use, but also well-documented downsides. The promise of some kind of technological “fix” for climate change may also pull support from other, more needed forms of action.

At this point, though, our contention is that there is little to be gained by willfully ignoring SRM technologies.

First, the ambition of climate response expressed in Paris is driving the world toward consideration of SRM. Remember that even with the incorporation of CDR or negative emissions technologies, the models suggest that keeping temperature increases below 2°C, let alone 1.5°C, will be immensely difficult. If the gap between what has been promised and what materializes widens, and as climate impacts become more present and urgent, then pressure on climate decision-makers to take action will increase. Even previously outlandish plans will be on the table.

Second, and related, talk of SRM is advancing, whether people wish it to or not. At this stage, the tentative conversation about SRM is taking place largely in scientific and insulated policy circles, beyond the reach of ready public scrutiny and engagement.

This must change. In our view, the concern that consideration of SRM might be a distraction from decarbonizing the global energy system is now outweighed by the need for robust, honest and open analysis that something of this magnitude deserves. This is true, if only to make it widely and abundantly known that SRM technologies are not any kind of magical climate cure-all.

What will it mean for the world to live up to the promises of Paris? The post-Paris moment calls not just for ambition, but also an honest assessment of all the potential tools available to us. Honest assessment will generate much consternation and disagreement. Better that, however, than proceeding from a position of ignorance.

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