Some say we can ‘solar-engineer’ ourselves out of the climate crisis. Don’t buy it | Ray Pierrehumbert and Michael E Mann

Some say we can ‘solar-engineer’ ourselves out of the climate crisis. Don’t buy it | Ray Pierrehumbert and Michael E Mann

As we arrive at Earth Day, there is renewed hope in the battle to avert catastrophic climate change. Under newly elected president Joe Biden, the US has reasserted global leadership in this defining challenge of our time, bringing world leaders together in Washington this week to galvanize the global effort to ramp down carbon emissions in the decade ahead.

So there is promise. But there is also great peril looming in the foreground.

Just as the world, at long last, is getting its act together, an ominous sun-dimming cloud has appeared on the horizon, threatening to derail these nascent efforts. That cloud comes in the form of technologies whose proponents call – somewhat deceptively – “solar geoengineering”.

So-called “solar geoengineering” doesn’t actually modify the sun itself. Instead, it reduces incoming sunlight by other means, such as putting chemicals in the atmosphere that reflect sunlight to space. It addresses a symptom of global heating, rather than the root cause, which is human-caused increase in the atmosphere’s burden of carbon dioxide.

While it is certainly true that reducing sunlight can cause cooling (we know that from massive but episodic volcanic eruptions such as Pinatubo in 1991), it acts on a very different part of the climate system than carbon dioxide. And efforts to offset carbon dioxide-caused warming with sunlight reduction would yield a very different climate, perhaps one unlike any seen before in Earth’s history, with massive shifts in atmospheric circulation and rainfall patterns and possible worsening of droughts.

What could possibly go wrong? Elizabeth Kolbert’s book Under a White Sky documents case after case where supposedly benign environmental interventions have had unintended consequences requiring layer after layer of escalating further technological interventions to avert disaster. When the impacts are local, as in Australia’s struggle to deal with consequences of deliberate introduction of the cane toad, the spread of catastrophe can be contained (so far, at least). But what happens when the unintended consequences afflict the entire planet?

Then there is the mismatch of time scales. The heating effect of carbon dioxide persists for 10,000 years or more, absent unproven technologies for scrubbing carbon dioxide out of the atmosphere. In contrast, the sun-dimming particles in question drop out in a year or less, meaning that if you come to rely on geoengineering for survival, you need to keep it up essentially forever. Think of it as climate methadone.

And if we are ever forced to stop, we are hit with dangerous withdrawal symptoms – a catastrophic “termination shock” wherein a century of pent-up global heating emerges within a decade. Some proponents insist we can always stop if we don’t like the result. Well yes, we can stop. Just like if you’re being kept alive by a ventilator with no hope of a cure, you can turn it off – and suffer the consequences.

Geoengineering evangelists at Harvard have pushed for expanded consideration of such technology; as panic over the climate crisis has grown, so too has support for perilous geoengineering schemes spread well beyond Cambridge, Massachusetts. And the lines between basic theoretical research (which is worthwhile – climate model experiments, for example, have revealed the potential perils) on the one hand, and field testing and implementation on the other, have increasingly been blurred.

Solar geoengineering has been cited in the Democratic Climate Action Plan. MIT’s Maria Zuber, incoming co-chair of Biden’s president’s council of advisers on science and technology (PCAST) is on record as favoring an expanded federal geoengineering research program. And now the other shoe has dropped – the US National Research Council has recently released a report going well beyond the very cautious, tentative recommendations for continued research in the 2015 NRC report one of us (Pierrehumbert) co-authored.

The new report pushes for a massive $200m five-year funding program. The growing support is based on a fundamental misconception, captured in the NRC report’s justification statement: that we likely won’t achieve the necessary decarbonization of our economy in time to avoid massive climate damages, so this technology might be needed.

Such “Plan B” framing is the worst possible justification for developing solar geoengineering technology. It is laden in moral hazard – providing, as it does, an excuse for fossil fuel interests and their advocates to continue with business as usual. Why reduce carbon pollution if there is a cheap workaround? In The New Climate War, one of us (Mann) argues that geoengineering advocacy is indeed one of the key delay tactics used by polluters.

If the world fails to achieve net zero carbon dioxide emissions, then each year’s emissions will add to the stock of atmospheric carbon dioxide, requiring ever-escalating ratcheting up any techno-fix and ever-escalating increase in the damage wrought by termination shock. And meanwhile, other dangerous effects of accumulating carbon pollution, such as ocean acidification, continue to worsen over time.

If the world decarbonizes eventually but only after pumping out so much carbon dioxide that it renders the world lethally hot, then deploying sun-dimming as a survival tactic puts the world in a precarious state, one in which current and future generations would live in perpetual fear of sudden death by termination shock. The sad fact of the matter is that there is no viable plan B for the climate crisis; rapid decarbonization is our only safe path forward.

Advocates in the scientific community, for the most part, are only recommending research, not deployment, right now. But research won’t solve any of the big unknowns. And it won’t make any of the really big known problems – millennial commitment and termination shock – go away. Research that goes beyond basic climate modeling experiments, for example that involving field tests and trial runs, will likely only serve to boost development of engineering technologies that make deployment more likely. The Harvard group, in fact, has provided a whole roadmap to deployment including working on designs of aircraft to deliberately pollute the stratosphere. That can hardly be dismissed as merely “research”.

Advocates are generally clear in stating that sunlight reduction is no substitute for decarbonization, but they are naive in their professed belief that developing the technologies can be done without risk to the push for real solutions to the climate crisis.

In his own recent book, Bill Gates insists that renewable energy is inadequate to decarbonize our economy at present. Peer-reviewed research suggests he’s wrong about that. But in being so dour about renewables he ends up advocating for the far riskier strategy of geoengineering – a strategy that will shift needed resources away from safe clean-energy solutions.

It is said that desperate times call for desperate measures. But there is still a safe path forward to addressing the climate crisis – as long as we avoid unwise detours and dead ends.

  • Ray Pierrehumbert, FRS, is the Halley professor of physics at the University of Oxford. He was an author of the 2015 NRC report on climate intervention

  • Michael E Mann is distinguished professor of atmospheric science at Pennsylvania State University. He is author of The New Climate War: The Fight to Take Back Our Planet

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