When a scale tips over too far towards one side, placing more weight on the other side will help to balance it out again. That is exactly what is meant by “Negative Emissions”. It means that to restore the global carbon balance, heavily perturbed by anthropogenic (carbon) emissions, humankind needs to create or enhance processes that draw down carbon [dioxide] from the atmosphere. The Earth itself is quite capable of balancing the fluxes of carbon into and down from the atmosphere, but does so at a slow, geological pace. Over time scales that run in the thousands, if not millions of years, more CO2 in the atmosphere will lead to more dissolution of rocks and minerals, thereby effectively consuming the CO2 and so working towards another balance. However, our Industrial Revolution is only 200 years old, and when it comes to carbon emissions, we have been industrious indeed. We have been emitting so much carbon in such a short period of time, that the Earth’s climate system is starting to react accordingly. Certainly, without any intervention, transport of CO2 to the deep oceans and more mineral dissolution would restore the carbon balance over the next centuries. But those are time scales, which rather exceed our normal frame of reference. Growth and development (of our society, our “ecosystem”, if you will) can prosper in more stable and predictable environments, whereas the climatic events to be expected -should the currents trends continue- will be a far cry from those stable conditions. It would thus be a proper expression of self-preservation to prevent such extreme and potentially dangerous climate change from happening, correct ?
If we would be so inclined to reverse the current trend, Mother Earth would need a little hand in re-setting the carbon balance. One way is obviously to turn down our emissions, by deep de-carbonisation of our economy, fast. However, the surplus carbon emissions already present in the atmosphere, will continue to cause climate change, until the balance is again set. But, as discussed above, that would exceed our normal working time frame, and leave us moreover feeling rather powerless in the face of imminent climate change. The other way is to increase the uptake of carbon from the atmosphere, and render the CO2 inert. While re-designing our economy, and creating incentives for industrial and societal collaboration for low- or no-carbon energy, we may simultaneously sequester as much CO2 as is needed. Negative emissions may thus buy us some time, and avert the point of no return. In fact, the latest Assessment Report (AR5) of the International Panel on Climate Change explicitly states (paragraph SPM.4.2.2, page 21 in the Summary for Policy Makers) the need for negative emissions to steer Earth’s climate back to a cooler state, with significantly less CO2 in its atmosphere. A recent peer-reviewed scientific publication in the journal Environmental Research Letters discusses the research efforts into negative emissions, concluding that a fast up-scaling is needed, which in turn depends on (greatly) increased research efforts.
Now, I am not an explicit advocate of one or the other climate change mitigation approach. But I am a fervent supporter of increased research efforts in that direction. If we do not start researching the consequences and potential pitfalls of climate engineering from this very moment onwards, we will never be able to expect our leaders to make well-informed and (most importantly) evidence-based decisions in the (near) future. In the UK, a 8.6 million-pound (9.8 million euro or $11.5 million USD) national research programme has been initiated, to investigate the “potential, as well as the political, social and environmental issues surrounding [the] deployment” of negative emissions technologies (NETs). We wish the researchers involved much success and good luck in their work, and are of course hoping to collaborate in the future.