posted May 5, 2017, 7:13 AM by Barry McMullin
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updated May 5, 2017, 8:04 AM by Paul Price
]
A centrepiece of Irish action on climate change is the Climate Action and Low Carbon Development Act, 2015. Under the terms of the Act, the Government is now required to prepare (and regularly update) a "National Mitigation Plan" which lays out the short, medium and long term pathway and policy actions for Ireland to "mitigate" its contribution to global climate change. In effect, this means a plan to reduce (or, better, eliminate completely) our collective emissions of greenhouse gases: especially carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). CO2 arises mainly from energy use (in electricity, transport and heating). Emissions of CH4 and N2O are primarily associated with our agricultural system (especially beef and dairy production).
Of course, climate change is a global problem and needs a global response: but some of us contribute much more than others to the problem, and also have a much greater capacity (material wealth, infrastructure etc.) to act. Accordingly, some will need to play a much bigger role in the response than others. Given that, on a per capita basis, Ireland's total annual emissions are currently among the highest in the world, fairness and justice suggests that we have a particular obligation to work harder (and earlier!) at reducing them. We are also, of course, exposed to the looming impacts of climate disruption (both direct and indirect): if mitigation action is inadequate over the next immediate, relatively small, number of years, these impacts may prove overwhelming (beyond human or technological capacity to "adapt to" in any managed, equitable, way, either locally or globally).
- There is no doubt that deep reductions in greenhouse gas reductions are now unavoidable if we are to have an effective, managed, response to global climate change over the next small number of decades. But this is very challenging precisely because our current "developed world" patterns of production and consumption are so deeply entwined with processes that intrinsically generate these emissions. For that reason, it seems that even if we reduce ongoing emissions very rapidly (which we must do), this may not be sufficient on its own. In that case, we will also have to try to proactively remove some, or a lot, of the greenhouse gases that are already accumulating to dangerous levels in the atmosphere: that is, through achieving some level of "negative emissions". This is true on a global basis, but is especially true for countries like Ireland that have very high current (per capita) emissions. It is well understood that the draft Irish mitigation plan does not (yet) lay out nearly a sufficient level of reductions of (positive) emissions to balance our "fair share emissions budget" over the immediate years (and decades) ahead: in fact, there is a very big gap between our current policies and our (well-intentioned) ambitions and aspirations. Accordingly, while the draft Irish mitigation plan does not currently mention this issue of negative emissions technologies, we recommend that, before the plan is finalised, it should be revised to make clear whether, or how much, negative emissions the Government is assuming can be achieved (to balance its emissions budget) in the short, medium and long terms.
- One of the most commonly proposed approaches to negative emissions is based on the use of so-called "bioenergy" crops, at large scale. Because all plants naturally absorb CO2 as they grow, they automatically remove it from the atmosphere - at least temporarily. The problem is that usually the plants then die naturally (and decay), or are harvested and eaten (by people or as animal feed), or are otherwise "consumed" (e.g. burned for heating or cooking). In all cases, that means that their embodied carbon is quickly released back to the atmosphere as CO2 again. However, if we intervene in this cycle, and instead process the plant material (the "biomass") in a controlled way, we can still exploit the energy embodied in it, but, at the same time, (re-)capture the CO2 that is released, and put it into some kind of stable, long term, storage. Such an arrangement is called "BioEnergy with Carbon Capture and Storage" or BECCS. While the various elements are certainly possible in principle, it is very unclear whether this arrangement can be effectively scaled up, or at what cost. In particular, it potentially involves a progressively larger allocation of land area for cultivation of bioenergy crops, and would therefore potentially conflict with other land uses, especially food production.
- An issue with any proposed expansion of bioenergy is the choice of crop. This is obviously constrained significantly by local soil and climate conditions, and varies significantly even within Ireland. The crop choice is further complicated by the fact that CO2 removal from the atmosphere may be happening on a very different timescale from that at which the bioenergy is exploited: e.g., forests may take decades to grow, but timber might be harvested and burned in a matter of a few weeks. Certainly, in the case of "unabated" bioenergy use (without CCS), there is a clear advantage to focusing on short rotation energy crops (e.g., miscanthus, willow etc.).
- Separately, consideration would have to be given to whether bioenergy cultivation can or should displace existing farming systems. However: current Irish agriculture is dominated by beef and dairy production, which are intrinsically greenhouse gas intensive (relative to nutritional output). Accordingly, a significant shift of land use from beef or dairy to bioenergy (or, more especially, to BECCS) might offer a "win-win" of both reducing emissions of methane and nitrous oxide while simultaneously achieving nett removal of CO2.
- In any case, it is clear that the bioenergy resource (nationally and globally), will be finite and constrained. In order to get the maximum climate benefit from that resource, it would make sense to ensure that it is developed in a way that is compatible with BECCS. This is an important immediate policy consideration because BECCS is only feasible where the combustion (direct or indirect) of the biomass happens in large scale plants, where it is practical to install carbon capture and storage technology. Normally that means use in electricity generation or other large scale industrial settings - which would specifically argue against allocation to small scale or mobile combustion (small scale heating or transport use in the form of "biofuels"). This runs counter to certain assumptions in the draft National Mitigation Plan.
- A second possible approach to negative emissions is to replace the role of plant photosynthesis in BECCS with machinery that is capable of filtering and concentrating CO2 from air directly. This is called "Direct Air Capture [of CO2]" or DAC. Of course, this must also be combined with long term storage, i.e., "Direct Air Carbon Capture and Storage" or DACCS. In principle, DACCS could operate without the use of large land areas (air might be drawn into a relatively small, fixed, area using large fans). However, unlike BECCS, instead of yielding usable energy output, DACCS would require very significant nett energy input: so unless this energy is available from extremely low carbon sources (renewables or, perhaps, nuclear) then it will not result in nett CO2 removal. Even if it can be supplied with suitable low carbon energy, the energy requirement alone will tend to make it relatively high cost: so a business model to support it would have to be created. Nonetheless, for a country like Ireland with a large renewable energy resource (particularly off-shore wind), DACCS might offer an excellent way of dynamically balancing the intermittency of such resources if it could be deployed as a large scale "dispatchable" load (where the energy being consumed can be quickly ramped up or down to compensate for variability in renewable generation, so that the marginal cost of the low-carbon energy used for DACCS could still be relatively low, with co-benefits in facilitating very high penetration of renewable energy sources into overall electricity generation). Ireland may thus have a particular, strategic, national interest in promoting and leading DACCS deployment.
- There are a variety of other candidate ideas for achieving negative emissions: increasing natural accumulation of carbon in soils, or using biomass to produce a form of charcoal called biochar that can then be added back into soils, or "enhanced weathering" where crushed silicate minerals might be spread on land surface and would naturally absorb CO2. While all of these merit study for their potential in Ireland, they are generally either more speculative or have more limited capacity for scaling up compared to BECCS or DACCS.
It is clear that there is some potential for development and deployment of negative emissions technologies; nonetheless, it is also clear that they are currently at very early stages of investigation, with large uncertainty about scalability, costs, and potential interactions or conflicts with other critical activities (especially food production). While the National Mitigation Plan should make clear what the current assumptions and plans are for NETs in Irish policy, it would be extremely unwise to rely on early, large scale, deployment. The precautionary principle clearly applies, and, at this point, the working policy assumption should be that adequate mitigation (consistent with the Paris agreement temperature targets) must be achieved without significant contributions from NETs.
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