There exists a fascinating, if admittedly niche, strand of scientific enquiry that attempts to answer the counterfactual question: what would the surface of the Earth look like if life – plants, animals, humans – did not exist? Would weathering and erosion rates be higher? Would valleys be deeper? Would rivers meander? Would tectonic features, such as mountain ranges and ocean ridges, even exist?
Such research may be of interest to the philosophically minded or, more practically, to astronomers seeking a ‘topographic signature’ of life. Its connection to efforts to combat real-world climate change is admittedly not immediately obvious, but keep reading.
Note, as well, that the reverse question is rarely asked, about the impact of geology on the biosphere. A lifeless planet seems feasible, but a rockless biosphere?
Or consider the concept of geodiversity – the range of geological, geomorphological, soil and hydrological features present in a landscape. Despite the term being first coined over 25 years ago, it’s fair to say that the concept lacks the profile of its biological counterpart, biodiversity. It’s a rare climate change mitigation or adaptation project that is asked to justify its impact, positive or negative, on geodiversity, whereas assessments of biodiversity impact are now commonplace and expected.
Or consider the fact that over 70% of the carbon atoms in anthropogenic CO2 emissions since 1750 have originated from geological reservoirs of coal, oil and natural gas. In contrast, ecosystems – mainly forest clearance and drainage of wetlands – have been responsible for ‘only’ 27% of such emissions.
Total global CO2 emissions by source. Credit: Global Carbon Project
And yet ecosystem-based solutions to climate change – reforestation, soil carbon sequestration, biochar, wetland rehabilitation, seagrasses and others – receive considerable, arguably disproportionate, attention. As recently as July, a scientific paper extolling the global carbon sequestration benefits of forest planting generated enormous publicity (admittedly negative as well as positive) in the climate change community and beyond.
There seems, in short, to be an in-built tendency to favour the biotic over the abiotic.
This is, in part at least, understandable. The distinction between ‘biological’ projects and ‘non-biological’ projects is fuzzy and, in many cases, not particularly useful: a forestry project can offer considerable watershed benefits in addition to biodiversity and livelihood impacts, just as a revegetation project can stabilise dune migration, a mangrove-planting initiative can reduce coastal erosion or no-till agriculture can improve soil health.
This is, therefore, most certainly not an argument against ‘biological’ initiatives: they are undeniably effective, they frequently offer considerable co-benefits and they are among the least-cost mitigation solutions open to us.
This is, though, a plea to pay more attention to ‘non-biological’ climate solutions: to embrace the ‘geo’ as well as the ‘bio’.
‘Geocarbon’ interventions range from the fairly mundane – capture of coal bed methane, for example; to the slightly less mundane – notably geothermal energy, a woefully neglected baseload energy source; to the verging-on-exotic – carbon capture and storage (CCS) sadly all too easily falls into this category; all the way to the truly exotic – the likes of enhanced rock weathering and ocean liming.
They span mitigation solutions, in which greenhouse gas emissions into the atmosphere are reduced, and sequestration (‘negative emission’) solutions in which already-emitted greenhouse gases are captured and removed from the atmosphere.
Geocarbon interventions tend not to be ‘charismatic’: trees are undeniably more photogenic than boreholes.
But this very lack of visibility is one of their strengths. While fears of large-scale forest plantations and biofuel production driving up agricultural prices are largely overblown, they are nonetheless real. Geocarbon solutions are, in contrast, typically underground (and potentially undersea) and offer little competition with surface land-uses, despite offering hundreds of trillions of tonnes of potential CO2 storage capacity.
Geocarbon solutions offer two other key benefits.
First, they can be highly complementary with other forms of climate mitigation. After all, biomass energy with carbon capture and storage (BECCS), the best studied negative emissions technology and the one that seems to attract the most fervent support (at least currently), owes its ‘negativity’ to the CCS part of its name. The same is true for direct air capture (DAC): the captured carbon has to be stored somewhere (unless a productive use can be found for it), and underground storage is the obvious choice.
And, second, permanence – the longevity of stored carbon – is much less of a concern in the context of geological storage than it is for biological storage.
Storage of CO2 under pressure in depleted aquifers and rock fissures – the basis of most CCS initiatives – is measured on a timescale of thousands of years. The fundamental logic of enhanced weathering is to mineralise CO2 – to transform CO2 into solid, mineral form (typically carbonates such as calcite and magnesite) – precisely in order to lock up the carbon on timescales of potentially hundreds of thousands of years. Forestry projects, by way of contrast, are considered to be doing well if they can lock up their stored carbon for 100 years (and often considerably less).
The CarbFix project in Iceland. Water-CO2 mixture is injected from the Hellisheidi geothermal power plant (left) into basaltic rock formations 1 km beneath the surface where, within 2 years, it chemically reacts to form solid carbonate minerals (right). Credit: CarbFix
Where geocarbon solutions, at least the carbon sequestration varieties, do lag behind their biocarbon counterparts is on cost.
Cost comparisons between different mitigation approaches are notoriously difficult, owing to different accounting conventions, different assumptions, different timeframes and even site-specific differences. Nonetheless, it’s undeniably true that most geocarbon solutions would struggle to be implemented under prevailing carbon prices, even if all other factors were favourable. Currently, over half of the emissions covered by carbon pricing instruments – and, remember, only20% of emissions are anyway covered by such instruments – face prices below US$ 10/tCO2e.
That said, the cost of non-geocarbon mitigation approaches – biological or otherwise – are themselves likely to increase as low-hanging fruit are depleted and difficult-to-reach sectors, such as aviation and industry, are addressed.
And, frankly, given the stark reality we face of ever-rising emissions, inadequate Nationally Determined Contributions (NDCs) and a rapidly-depleting global carbon budget, it may be time to focus on biophysical necessity rather than cost minimisation.
Geocarbon offers an attractive suite of approaches to complement ‘classical’ mitigation and sequestration solutions. In short, geocarbon rocks.