“Negative emissions”: the next challenge for climate policy

Print Friendly
forest in Italy (photo Moyan Brenn)

forest in Italy (photo Moyan Brenn)

If the Paris climate objectives are upheld, policymakers will soon be facing calls to set emission-reduction targets of much more than 100 percent, write Oliver Geden of the German Institute for International and Security Affairs (SWP) in Berlin and Stefan Schäfer of the Institute for Advanced Sustainability Studies (IASS) in Potsdam. But the debate about how to achieve “negative emissions” – and who will have to achieve them – has not even begun, they note.

Global climate stabilisation targets, such as restricting global warming to 1.5 or 2 degrees Celsius (°C) above pre-industrial levels, can be translated into carbon budgets that show the total amount of emissions that would still be allowed for meeting the target. According to current calculations, the remaining emissions budget for the 2 °C target is about 800 gigatonnes (Gt) of carbon dioxide (CO2). However, for 1.5 °C, it is only about 200 Gt. Given that annual CO2 emissions currently stand at about 40 Gt, the world’s budget for 2 °C would be consumed by the mid-2030s, the budget for 1.5 °C as soon as the early 2020s.

Since completely decarbonising the world economy within a time frame of only 5 to 20 years is unrealistic, climate models build on the concept of negative emissions. By using technologies to remove CO2 from the atmosphere, the original emissions budget could initially be overshot, with the resulting deficit then being recouped over the course of the 21st century.

Almost all the technological options currently being favoured are still in the early stages of development, making their potential for successful deployment extremely uncertain

However, the looming budget deficit has now reached an alarming size. The Intergovernmental Panel on Climate Change’s (IPCC) climate models show that a total of 500 to 800 Gt in negative emissions would have to be generated by 2100 to limit global warming to 2 °C or 1.5 °C – in other words, up to twenty times the current annual CO2 emissions.

In principle, all governments accept the scientific consensus set out by the IPCC in its 5th Assessment Report (2013-2014). The report points out that negative emissions cannot be avoided if ambitious climate targets are to be met. Currently, however, there is hardly any discussion on how to bring about negative emissions. This is particularly worrying because building the necessary capacities would have to start by 2030 at the latest.

Since there is no political debate on negative emissions yet, potential conflicts of interests or public acceptance problems can only be guessed at. The possible social and ecological consequences of such a far-reaching use of technologies for CO2 removal have barely been examined. The biggest problem, however, is that almost all the technological options currently being favoured are still in the early stages of development, making their potential for successful deployment extremely uncertain.

Technological options

In its current climate-economic models, the IPCC almost exclusively refers to a technological option that combines planting fast-growing biomass, burning it in power stations to generate electricity, and capturing and storing the CO2 that is released in the process (bio-energy with carbon capture and storage BECCS). During its growth phase, the biomass absorbs carbon dioxide from the atmosphere that is then captured during combustion and subsequently stored, for instance in geological formations. This process would be constantly repeated with new biomass, thus reducing the CO2 concentration in the atmosphere.

So far, however, BECCS has barely been tested: there is only one single pilot facility in the US. Moreover, generating the amount of negative emissions that is assumed in climate-economic models would require an additional area for growing biomass that is equivalent to one-and-a-half to two times the surface area of India. Transporting the CO2 and storing it underground would also require enormous capacities. And yet the use of this technology is always already included in the calculations of climate researchers, environmental NGOs or policymakers when they insist that, based on the IPCC’s calculations, targets such as 2 °C or even 1.5 °C can still be met.

On closer inspection, however, even a universally supported measure such as afforestation raises the question of whether it can really help to limit global warming

Over half a dozen other technological options are also under discussion. They range from apparently unproblematic measures, such as afforestation, to fertilising or liming the oceans. On closer inspection, however, even a universally supported measure such as afforestation raises the question of whether it can really help to limit global warming. Especially for the boreal forests of the northern hemisphere, the darkening of the Earth’s surface that would result from an afforestation of large regions, and the attending warming effect, might more than cancel out the cooling effect that would result from binding CO2 in trees – thus achieving the very opposite of the intended outcome. By contrast, suggestions for afforestation of the Sahara or Australian outback simply seem unrealistic.

Fertilising the oceans is based on the idea that algae growth in some maritime regions is limited by a lack of nutrients, especially iron. A targeted addition of iron could provoke algae growth, removing CO2 from the atmosphere: when the algae die and sink to the seabed, the CO2 stored in them would be permanently sequestered there. In 2009, the German-Indian iron-fertilisation experiment LOHAFEX attracted international attention to the idea of ocean iron fertilisation. From a climate-policy perspective, however, the results were disappointing. The algae growth primarily caused a local population of crustaceans to multiply. The amount of CO2 that was removed from the atmosphere was very small.

Another possibility is liming the oceans. This involves adding calcium oxide powder (lime) to sea water to increase its pH value. Since water that is more alkaline absorbs more CO2 from the air, this method could extract carbon dioxide from the atmosphere. At the same time, it could ease the acidification of the oceans. However, the effectiveness of this option is once again questionable: producing calcium oxide powder is a CO2-intensive process, and transporting it would also generate emissions.

New distributional conflicts

In climate research, at least, the potentials and risks of the individual technological options are now beginning to be explored. By contrast, the political implications of a negative emissions climate policy have not yet been elucidated. The United Nations’ (UN) policy to protect the climate has so far relied on allotting differentiated levels of responsibility to individual groups of states that will converge in the long term – at the very latest when all states have reduced their emissions to zero.

Because of their historical responsibility and greater economic capability, the ‘old’ industrialised nations have to substantially reduce their emissions. Some of them, such as the northwestern member states of the EU, have claimed a pioneering status for themselves. Here, the so-called “zero line” – reducing emissions by 100 percent – has been the conceptual reference point. Some EU countries will reach the zero line earlier than others, but member states from Central and Eastern Europe will be obliged to follow suit. This is also true for large emerging economies like China and India. Convergence towards zero thus means a pioneering role for a limited period of time. The assumption that such a role will bring positive economic effects rests not least on the idea that the countries initially lagging behind will have to follow suit eventually, and will do so using technologies developed by the pioneers.

If the EU agrees to a reduction target of, say, 150 percent, we should also expect to see conflicts within the Union

However, should the limit of what is currently conceivable in emissions mitigation be removed, new conflicts about burden sharing would be inevitable. Possibilities for differentiating national climate targets would greatly increase, and the pioneers would have to play their part for much longer.

For the year 2100, the IPCC considers net negative emissions of around 10 Gt to be feasible. This would correspond to a global emissions-reduction target of around 125 percent against the base year 1990. If this became a point of reference in the UN climate negotiations, key emitters like China or India, and most of the developing countries would likely argue that the industrialised nations organised in the Organisation for Economic Co-operation and Development (OECD) should continue to take on more far-reaching responsibilities.

For instance, emerging economies and developing countries could demand that OECD countries invest more in carbon-dioxide removal whilst they themselves might not even reduce their own emissions to zero. If the EU agrees to a reduction target of, say, 150 percent, we should also expect to see conflicts within the Union: the latecomers from Central and Eastern Europe will be keen to maintain the EU’s internal distribution of responsibilities.

Similar conflicts should also be expected between different economic sectors. If BECCS becomes the world’s preferred carbon-removal technology, the electricity sector would be the very first to be called upon to generate negative emissions. The sector is already the focal point of emissions- mitigation efforts and is likely to reach the zero line long before the transport or buildings sector.

A necessary strategic decision

If climate policy pioneers like the EU and Germany do not want to prematurely abandon the temperature targets decided in Paris, they will have to start developing strategies for CO2 removal soon. As we have indicated, global emissions budgets for 1.5 °C and 2 °C will be consumed within five to 20 years. This means that the EU’s and Germany’s reduction corridor of 80 to 95 percent by 2050, can only be an adequate contribution to meeting global temperature targets if emissions in the second half of the century are pushed substantially below the zero line. To date, neither the EU nor Germany has declared itself ready to aim for long-term reduction targets of more than 100 percent. And even if they did, it remains unclear whether such a policy would be technologically and economically feasible, and if it would find sufficient socio-political support.

Precise accounting rules for negative emissions need to be set out, undesired side effects need to be avoided, and specific incentive schemes for using CO2 removal technologies have to be created

In principle, a negative-emissions strategy can only be realised if climate, energy and research policy rapidly set the process in motion. Not only would it be necessary to invest substantially in research and development, but also to start a broad political and societal debate, and initiate regulatory considerations. In many respects, these considerations concern challenges that also had to be solved (or still remain to be solved) in deploying conventional emissions-mitigation technologies. For example, precise accounting rules for negative emissions need to be set out, undesired side effects need to be avoided, and specific incentive schemes for using CO2 removal technologies have to be created. It would seem logical to clarify these points as part of the existing regulatory framework, such as the EU emissions trading directive or the EU’s sustainability criteria for biomass.

Politically, the most sensitive issues in any potential German strategy for negative emissions are linked to the fundamental decisions that have already been taken on Germany’s energy transition. Would Germany be prepared to rethink its energy transition planning for the electricity sector if BECCS emerged as the technology with the greatest potential at the global level? Would the federal government be willing to change course drastically on biomass and on carbon capture and storage, even at the expense of the decentralised expansion of wind and solar power? Or would it primarily encourage measures whose deployment would barely impact on the structure of the national energy system, such as liming the oceans?

There is still time for a broad discussion on the unconventional forms that an ambitious climate protection policy might take, and for pursuing the corresponding technological options. The longer it takes to open such a debate, the greater is the risk that the Paris climate targets will slip out of reach.

Editor’s Note

Dr Oliver Geden is Head of Research Division EU/Europe at the German Institute for International and Security Affairs (Stiftung Wissenschaft und Politik, SWP), Berlin. Dr Stefan Schäfer is Programme Leader at the Institute for Advanced Sustainability Studies (IASS), Potsdam. This article is based on a paper published by SWP in December 2016.


  1. Bas says

    Considering the direction our by far biggest polluter (USA) is going, this seems to me at least one step to far.
    Or as the Dutch saying goes: “bringing water to the sea”.

    It’s far more effective to introduce an EU climate import tax on all products and services from countries who:
    – don’t take substantial action to battle climate change; and
    – pollute more per person than EU average.
    The tax being dependent on the CO2eq emission related to that product / service.

  2. Jim C says

    Changes in agricultural & forestry practices have the potential of increasing carbon sequestration significantly. The research in these areas has not received much publicity. See the Marin Carbon project for one research stream which is being pursued by ranchers in Marin County and researchers from the University of California at Berkeley.

  3. Ger Groeneveld says

    “Almost all the technological options currently being favoured are still in the early stages of development, making their potential for successful deployment extremely uncertain”
    Terra Preta (https://en.wikipedia.org/wiki/Terra_preta) is an old technique with a good track record. Adding bio-chars to soil, the type too ‘polluted’ with fertilizers, does enhance soil fertility quit a bit. One can add up to 2.5 to 4 tons per ha without problem, storing the carbon for at least a 35 to 70 years.
    Combined with torrefaction and washing of the torrefacted biomass one does create bio-coal (low in ash/nutrients) and leach-ate (full of nutrients) which one can add to high ash, severly torrefacted containing biomass to create a organic fertilizers of excellent value.

    Both techniques (terra preta, torrefaction or mild, slow pyrolysis) are market ready (for decades already, Henry Ford was using this together with ethanol to build and drive his cars).

    So there is no real burden of making changes, apply what is there already in a sensible way. Nature works in a circulair way, so should we do.

    • Andre van Hooren says

      Hansen and Sato calculate in their “Young People’s Burden: Requirement of Negative CO2 Emissions” (2016) that the solutions Ger describes can do the job of limiting temperature rise to 1.5 C.

  4. Jessee McBroom says

    You may find an article “Researchers find a way to turn carbon into rock at Iceland Power Plant” of interest. I briefly discussed this method with a PNNL professor as he was working on this very process himself some 2 years ago.

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>