Because the atmosphere is such an immense part of the natural world, people have always assumed that we could not alter it on a large scale – until about the 20th century, when scientific findings led to the international agreements at Montreal, Kyoto, and Paris; each addressing GHGs. It is still a common sentiment that the natural world’s vast cycles of renewal are far beyond human technology in terms of sheer capacity. Thus, if we simply modify our atmosphere-disturbing behavior – avoiding emissions, achieving net-zero; the natural balance could spontaneously be restored. CDR opponents often hold this viewpoint to some extent. And it is true that the natural carbonate-silicate cycle can, in a geological age, bring carbon dioxide back to pre-industrial levels; though the excursion of high CO2 will rewrite the biosphere – erasing much of what is familiar in the short term, then giving rise to new forms in the coming millions of years. But that timeline is inimical to our modern world order – the familiar creatures and the humans alive now deserve our concern. We want to preserve this biosphere and this civilization, and to do that, we need to start cleaning up our mess now.
So if the natural balance is not restored as fast as we’d like to wait, maybe we can help nature – apply some nature-based solutions to the problem! What kinds of natural processes can we augment? Certainly we can look to the world’s forests for help. We can change agricultural practices to increase soil carbon. We can grow and manage biomass – burying it, burning it for fuel and then capturing the CO2 emissions (BECCS), partially burning it to make biochar, or increasing the ways we use biomass for long-term construction with engineered materials.
In coastal regions, we know that estuaries are extremely productive ecosystems. In many places, we have degraded these ecosystems for the sake of community development. But because the sediments of these ecosystems can store a vast amount of carbon and because we are facing significant sea level rise, we have opportunities to plan expansion of coastal ecosystems in various ways, referred to as Coastal Blue Carbon, with potential for carbon sequestration and a range of add-on benefits.
The world’s oceans contain far more dissolved inorganic carbon than the atmosphere and yet could contain even more. If we could find a way to not acidify the oceans with carbon dioxide – by increasing alkalinity, then we could devise various ways to use the ocean capacity to remove and store carbon.
The difficulty we face with all these nature-based solutions is that natural systems – while cycling vast amounts of carbon every year, are exquisitely balanced. If we speed up one part of the cycle, we can throw the entire system (on which all life depends) out of balance. Maybe instead we should use our technology to invent whole new ways of carbon dioxide removal, and leave the natural cycles alone. Most of the technology-based ideas for CDR are associated with direct air capture (DAC). But there is also plenty of technology required to mine and crush mafic rock for enhanced rock weathering (ERW). In lieu of burning fossil fuels for energy, perhaps we could burn biomass for energy, capturing the CO2 emissions for sequestration – this is BECCS again and we already thought of it in the context of naturally growing the biomass. The same applies with many paths to engineered materials, and biochar. So all these technological solutions: rock weathering, processes that use biomass, even many aspects of CDR involving DAC; they involve the acceleration of natural processes. The distinction between technological and natural solutions for CDR is somewhat arbitrary – the natural solutions we identify are ones that we must accelerate with technology, and the technological solutions we identify are technological enhancements to processes that already exist in nature.