Silly numbers: The hopes and fears of climate intervention (book review)

“It would be very difficult, but it could be done” is maybe the most exuberant appraisal to derive from Wake Smith’s detailed analysis of the climate intervention landscape as it currently appears. Pandora’s Toolbox: The Hopes and Hazards of Climate Intervention explores geoengineering and carbon removal options varying across a spectrum of feasibility and cost.

Image credit: Chris Rubino /

As more detail emerges about the practicalities of addressing the problem of the warming climate, so too has come a view that climate intervention is not only indispensable, but also inextricably bound up with other priorities such as mitigation. One element of this is the fact that certain recalcitrant emissions, from sectors like aviation and agriculture, will be very expensive to eliminate – with price tags ranging up to $1,000 per tonne. And so it will actually be cheaper to deploy some of the negative emissions technologies from the climate intervention toolbox, as a 2019 report from the National Academies of Science, Engineering, and Medicine has noted.

The early parts of this book seem to grab the reader’s arm and run through a brisk course in how the Earth’s climate behaves the way it does.

Given its position in relation to the sun, our planet should have an average surface temperature of -18ºC, rather than the actual 15ºC – a boost that we have the atmosphere to thank for. And some of this greenhouse-like functionality can be attributed to GHGs.

The most common of these, water vapour, has been a harmless presence on the planet for a few billion years, and part of a self-regulating system in which – if things gets too warm – it simply falls as rain, a benefit to an agriculture-based society.

Other GHGs are more of a problem, notably CO2 (the second most abundant in the atmosphere, and “more than 80% of our climate problem”), methane and nitrous oxide.

With air pollutants, the threat they present can be assuaged by simply calling a halt to further emissions – hence some bright appraisals of the COVID lockdown era, and the sight of clear skies over LA. But it’s not so simple with emissions. Air pollutants like PM2.5 are relatively short lived in the atmosphere, enduring for a few weeks, but the GHGs of concern – notably CO2 – we can expect to endure for much longer. And the natural mechanisms that remove them from the atmosphere take bloomin’ ages (tens of thousands of years).

Circling the plughole

Smith refers to a bathtub analogy throughout – in this case it’s not enough to turn off the tap, as the drain is hopelessly clogged. But of course, turn off the tap we must which is why net zero is regarded as a non-negotiable baseline for progress.

So we have to eliminate emissions, not just reduce them, or else “the bathtub keeps filling”. But even after we reach net zero, in the current outlook, we face the prospect that climate damages will endure for a much longer time thereafter. While climate intervention has been portrayed casually as a “plan B”, in the context of ongoing problems, it has to be seen as very much a part of “plan A”, and a way to resolve the damage already done, in Wake’s anaylsis.

As he explains, it’s time to start rummaging through the geo-engineering toolbox, which in his framing has two main compartments: GHG removal, and solar radiation management.

When it comes to GHG removal, we tend to mean Carbon Dioxide Removal (CDR) – since CO2 has concentrations large enough to make them a worthy focus. Methane and nitrous oxide are much more dilute in the atmosphere, making them more effort to remove, and both can be satisfactorily assuaged by “turning off the spigot” given their relatively short residence in the air (12 years for methane). In any case, the author is aware of no feasible proposals to even attempt sucking up these gases.

An ongoing theme in the book is the unappetising nature of the various intervention solutions so far proposed, and Smith seems to frequently frown as he initially opens different compartments in the “toolbox”, and discovers how unpromising are their contents.

In the CDR section of the box, it seems, we have trees and a selection of highly speculative theories and projects. This latter compartment comprises “all kinds of crazy ideas”, he says, some of which deserve serious attention, while others are “dumb” and others “perilously specious”.

Natural CDR approaches include things like reforestation, Bioenergy with Carbon Capture and Sequestration (BECCS), soil sequestration, biochar and blue carbon, enhanced weathering, and ocean iron fertilization. Each receives a detailed treatment, with BECCS emerging as the one with the most going for it. The problem with it – and all forestation-related options – is the land area it requires, which would, over the course of a few generations, “consume most of the arable land on the planet”.

Many of these CDR approaches he discounts as offering too fragile and impermanent a storage facility for carbon that we would prefer to keep out of the atmosphere indefinitely.

There have been imaginatve but ill-considered forays into carbon-removal. Smith cites the now-discredited method of “ocean iron fertilization”, which proceeds from the concept that large portions of the ocean are iron deficient. If more of this element were added, so the theory goes, it would be a bonanza for algae growth, which would suck up large amounts of CO2, eventually ending its existence on the ocean floor where its carbon would be sequestered. US entrepreneur Russ George secured sponsorship from indigenous communities in British Columbia for such a scheme in 2012. It didn’t perform as hoped and had the result of “widely frightening the global environmental community” to whom it seemed a poorly-conceived act of marine pollution.”

Heavy metal

If nature seems ill-equipped to help us tackle the problem, there are man-made options for carbon removal, and Smith envisions a place for “massive industrial interventions that will look a lot like the fossil fuel industry that got us into this mess”.

So far carbon capture and storage (CCS) has made little dent in the climate challenge, although we need to put the foot down and build more plants.

It dates back to 1978, when a chemicals plant near Los Angeles first deployed the approach as a means of sourcing carbon for chemicals manufacturing, rather than for climate remediation. It collected the CO2 directly from the flue pipe of a coal boiler, and employed the amine process that still dominates the sector today.

Once carbon is captured, the problem becomes what to do with it. The most feasible destination at this point seems geological sequestration, although recent years have seen much-touted efforts to “reuse” it for things like chemicals manufacturing, the production of urea for fertilizers (the largest market at present), carbonated drinks (a “tiny demand”) and enhanced recovery for the oil and gas industry, or EOR.

Estimates cited here envisage a use for about 1% of the CO2 that is anthropogenically produced, about 90% of this for fertilizers and EOR. The demand “could triple” with the emergence of markets such as new building materials, but this hasn’t happened yet, and even if it did – it seems unlikely to move the dial on climate change. Not all the storage methods are permanent either, as when a “Pepsi drinker belches”.

One possibility is to combine CO2 with hydrogen to get “synthetic fuel”, a low-carbon alternative to fossil fuels. This wouldn’t allow us to lower the water level in the bathtub but would slow the rate at which it’s being filled – we would be endlessly recycling the carbon already in the atmosphere, “a huge step forward from where we are today”.

Despite promising demonstration projects, synthetic fuel is still at best twice the cost of oil, so there is little incentive for its use.

To get to net zero, it’s accepted that there will have to be a greater capability for “negative emissions”, or removing CO2 from the climate system. And this will offset some of the pressure of the difficult-to-decarbonize sectors. In Smith’s framing, we reduce the flow from the tap by 80-90% and then “bore a new anthropogenic drain pipe that can evacuate the last 10-20%”.

Direct air carbon capture and sequestration (DACCS) would seem to provide one such pipe, and is being developed by three notable start-ups. Drawing on a similar infrastructure to CCS at the back end, the approach is also not so novel at the front end, and seems focused on finding ways to propel large amounts of air past materials impregnated with chemicals that can remove CO2. The choice of chemical seems split between hydroxide- and amine-based approaches. It “remains to be seen” which approach will come out on top.

DACCS has attracted high-profile investors, and Bill Gates is a backer of one firm, Carbon Engineering, but it seems enormously energy intensive, and the amount of air it would have to scrub to make a dent is gargantuan – not so much “cubic miles” as “fractions of the entire atmosphere”.

One chapter (“The path forward for climate removal”) cites a “landmark report” from 2019, “Negative Emissions Technologies and Reliable Sequestration: A Research Agenda”, which appears to write-off direct air capture as “unaffordable” having assessed it as costing $100 – $600 per tonne.

Still, techniques for removing GHGs from the atmosphere and burying them underground seem guaranteed a place in Smith’s toolbox (“I can’t see foresee a world in which we WON’T need to do that, and in a big way, and for a long time”). But only as part of a larger system of levers to be pulled.

Carbon removal is a way of “thinning the blanket” of GHGs that is surrounding the planet, and which would otherwise continue to make it difficult for the energy received from the sun to escape. But we can also address the other side of that equation, an area explored in chapters on Solar Radiation Management (SRM) and Stratospheric Aerosol Injection (SAI).

SRM includes potentially simple approaches such as marine cloud brightening. Clouds already reflect about 20% of the sun’s rays – if we could just nudge that up by 1-2% then it would make a difference. This might be as simple as spraying salt water in the air (the aerosol droplets seeding a thickening of cloud cover). If it could be applied across large portions of the oceans, the resulting cloud cover could increase the reflectivity of the Earth in a manner sufficient to cool the planet by 1ºC, in the estimates of UK physicist Stephen Salter – a “vanishingly inexpensive” solution that could be accomplished via a fleet of several hundred boats (about the size of small ferries). Question marks remain around its viability and scalability.

Controversial but promising

From the idea of launching aerosols into the sky to help plump up cloud cover, it seems not too great a leap to that of launching aerosols into the sky that might themselves help to reflect sunlight. However, the method of SAI is “probably the most” controversial in the book, says Smith, and while no one relishes the prospect of “a gigantic global experiment with the only planet we have”, SAI is also potentially the most promising method of them all, and the other options on the table are sufficiently unappealing as to make its inclusion a necessity. The choice of aerosols so far seems to favour sulphate materials, such as SO2 or sulphuric acid, as they are native to the atmosphe, with better-understood risks, although sulphuric acid is a threat to atmospheric ozone.

The launch mechanism requires the development of a new kind of aircraft – “a leaping aerial dump truck” – which is described in detail, a project in which former Boeing executive Smith has formerly advised.

If such a project got underway by 2035 (“it won’t be that soon”, he says) and reached completion by 2100, the aggregate cost could be around $2.5 trillion – or around an $18 billion annual cost for each degree C we want to remediate. All the same, says Smith, this program is “big but not unmanageable”.