Over the last few years, the concept of a global carbon budget has established itself as a key element of the international climate policy debate. The budget defines the total amount of carbon dioxide we can emit into the atmosphere and still keep warming below 3.6 degrees Fahrenheit, or 2 degrees Celsius, the goal set by the United Nations.
The concept of the budget is quite simple: If the total amount of remaining emissions is explicitly defined, then we will have a road map for political and economic action. To meet the budget, the Intergovernmental Panel on Climate Change estimates that we would have to reduce global greenhouse gas emissions by some 40 percent to 70 percent from 2010 levels by 2050. After that, emissions would have to fall to “net zero” by the end of the century.
But as delegates meet in Paris this week for what is expected to be the most decisive United Nations climate summit yet, we are already in danger of busting the budget. If the plans submitted by more than 180 governments are implemented, humanity will outspend its carbon budget by 2040 at the latest. Staying within the original budget outlined by the I.P.C.C. no longer seems realistic.
So what do we do? This is where magical thinking, questionable accounting and dubious expectations about future technology come into play. It is called negative emissions.
Negative emissions are the flip side of emissions. The idea is to develop technology that would remove carbon dioxide directly from the atmosphere. This would allow for significantly higher fossil fuel emissions over the next few decades. To compensate, we would start removing more and more carbon dioxide from the atmosphere to eventually reach the I.P.C.C.’s net zero emissions line by 2070 and go even lower afterward.
Climate problem solved — at least according to the climate models.
But there’s a problem with this scenario. The United Nations’ own Environment Program pointed it out in a report last year:
“Theoretically, carbon uptake or net negative emissions could be achieved by extensive reforestation and forest growth, or by schemes that combine bioenergy use with carbon capture and storage. But the feasibility of such large-scale schemes is still uncertain. Even though they seem feasible on a small scale, the question remains as to how much they can be scaled up without having unacceptable social, economic or environmental consequences.”
Climate scientists and economists are betting primarily on a new technology called bioenergy with carbon capture and storage, or Beccs. This involves cultivating fast-growing vegetation, or biomass, to absorb carbon dioxide from the atmosphere. Trees or energy crops would then be burned in power plants, and the emissions would be captured and pumped underground. Beccs could also be attached to industrial processes involving biomass, like pulp factories or ethanol plants.
But the Beccs technology does not exist at scale at present. And even if it did, the immensity of this endeavor would be unlike anything that exists today. To achieve the negative emissions that are an essential component of the I.P.C.C. models, we would have to plant around 500 million hectares of biomass crops — an area one and a half times the size of India. This would also require enormous capacities for transporting and storing the carbon dioxide extracted from the atmosphere.
This vast enterprise is being figured into the calculations of climate researchers, environmental groups and policy makers when they maintain that a 3.6 degree target can still be reached.
Including negative emissions in these models has one decisive advantage, of course: It allows climate economists to significantly increase the carbon budgets calculated by climate scientists. Both base their calculations on the same net amount of emissions. But since the economists’ budgets also include negative emissions, they allow for significantly higher fossil fuel emissions over the next few decades, thus putting the world into carbon debt. Those carbon debts accumulated by overshooting the original budget will be paid back again in the second half of the century. At least that is the hope.
The public has taken little, if any, notice of these considerations, and even policy makers are often unaware of the amount of negative emissions climate economists assume for the future. I.P.C.C. models foresee negative emissions of about 600 gigatons of carbon dioxide by 2100, which equals more than 10 years of current annual emissions. This is the amount of carbon dioxide that we will somehow have to remove from the atmosphere.
We need to be honest. This approach relies on some very dubious calculations and assumes the existence of technologies whose risks have not been adequately studied, let alone discussed publicly. Admittedly, not all of the technologies that could be used to remove carbon dioxide from the atmosphere would require enormous land areas or carbon storage capacities. But that does not mean that alternative methods, such as direct air capture or liming the oceans, would face considerably less public opposition.
We need to seriously discuss the effects of technologies designed to remove carbon from the Earth’s atmosphere — technologies whose large-scale use is now being assumed as a means for achieving ambitious climate goals — and to have this discussion not only among scientists, but on a political level as well.
Because right now, we’re on the verge of repeating the same mistake that led to the financial crisis: relying on economic models that are completely detached from what’s going on in the real world.
Oliver Geden heads the E.U. research division at SWP, the German Institute for International and Security Affairs.