Negative Emissions Technology: Winner 2020

Did you know that stopping the increase of carbon dioxide in the atmosphere is not enough to avoid global warming of two degrees Celsius? Emissions cannot be cut fast enough to keep the stock of greenhouse gases below this dangerous threshold level – unless carbon is actually taken out of the air.

The Intergovernmental Panel on Climate Change (IPCC) publishes scenarios that describe how greenhouse gases emissions could evolve between 2000 and 2100, depending on various hypothesis. A shocking fact is that over 100 of the 116 scenarios involve carbon removal schemes to remain below two degrees Celsius of global warming. The median scenario assumes that a total of 810 billion tons of carbon dioxide are extracted from the atmosphere before 2100. That is the equivalent of extracting around twenty years of global emissions at our current levels.

What do these “negative emissions technologies” look like that we depend on to extract these vast quantities of carbon from the air, and which one is the best?

Since Earth is really an ocean planet, one geo-engineering idea involves increasing the capacity of the oceans to absorb more atmospheric carbon by “fertilising” the oceans with tons of iron or other nutrients to stimulate plankton blooms. These organisms pull carbon out of the atmosphere and become deposited in the deep ocean when they die. Researchers worldwide have conducted thirteen major iron-fertilisation experiments in the open ocean since 1990, until the U.N. Convention on Biological Diversity put in place a moratorium in response to the adverse effects of these experiments. Aside from the immediate toxicity of massive algal blooms, the unintended impacts of ocean fertilisation may be so far removed in distance and time from the initial sites where these interventions take place that it is extremely challenging to quantify the amount of carbon removed with any acceptable accuracy.

Another big idea is “solar radiation management” that would have us inject sulphide gases into the atmosphere to block sunlight and cool down the atmosphere, rather than suck up any carbon emissions from the air. Deluded in its intention to regulate global temperature directly, ironically we would pump even more substances into the environment.

The plan is straightforward: spray a mist of sulphuric acid into the lower stratosphere from planes flying above typical cruising altitudes; the sulphate aerosols formed are swept upwards by natural wind patterns and dispersed over the globe including the poles; once spread across the stratosphere, these aerosols will reflect about one percent of the sunlight back into space and offset some of the warming effects of our carbon emissions below. According to proponents, this method would counter climatic changes, take effect rapidly, have low implementation costs and be reversible.

What’s not to like about this solution? Some of the potential downsides include depletion of ozone that acts as our natural atmospheric protection against the sun’s ultra-violet radiation; reduction in water precipitation around the world; and potential health effects from tons of sulphate particles returning into the lower atmosphere. In addition, there are significant ethical and political consequences of injecting sulphide gases into the stratosphere that become unevenly dispersed and hence disproportionately impact some countries more than others.

The impact of potential geo-engineering technologies is simply untestable on a small scale, as Martin Bunzl, Director of the Rutgers Initiative on Climate and Social Policy, points out:

You can test a vaccine on one person, putting that person at risk, without putting everyone else at risk. So even though we have a lot of planetary wide goals – like eradicating smallpox – we can test them for untoward effects before full-scale implementation. Not so for geo-engineering. You can’t build a scale model of the atmosphere or tent off part of the atmosphere. As such you are stuck going directly from a model to full-scale planetary wide implementation.

Even if we could partition the atmosphere for test purposes, the evolving nature of our ecosystem makes predictions from such experiments impossible. In the words of microbiologist Sallie Chisholm at the Massachusetts Institute of Technology:

Proponents of research on geo-engineering simply keep ignoring the fact that the biosphere is a player (not just a responder) in whatever we do, and its trajectory cannot be predicted. It is a living breathing collection of organisms (mostly microorganisms) that are evolving every second — a ‘self-organizing, complex, adaptive system’ (the strict term). These types of systems have emergent properties that simply cannot be predicted. We all know this! Yet proponents of geo-engineering research leave that out of the discussion.

Other outlandish ideas such as sucking up carbon directly from the air using chemical filters or sowing vast quantities of alkaline minerals in the oceans to absorb more carbon dioxide are no better alternatives. The hard truth is that engineered negative emissions technologies do not exist on the large scale needed for scrubbing carbon from the air and yet the vast majority of IPCC scenarios assume this technology is in place.

How do we resolve this contradiction? We do have another option. There exists a proven negative emissions technology that can work on the scale we have assumed, can be deployed locally almost anywhere, costs very little and builds itself. It is called a tree. The innovation needed is not an engineered alternative to trees and plants – it is the ingenious ways we embed trees and plants into our built environment and how we change our land use practices.


Originally published on LinkedIn on June 12, 2020.