Meeting global temperature targets the role of bioenergy with carbon capture and storage

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1 Meeting global temperature targets the role of bioenergy with carbon capture and storage Christian Azar, Daniel J.A. Johansson and Niclas Mattsson Supplementary In this supplementary material, we first briefly discuss the impact of varying three key parameters pertaining to the role of BECCS in meeting stringent temperature targets: climate sensitivity, biomass availability and carbon storage potential. For each variation, we reproduce figures 1 and 2 from the main paper. Next, we present additional sensitivity analyses with respect to the impact of allowing for a temperature overshoot to 2100 instead of 2150, the impact of forcing the model to use at least 50 EJ of coal per year that is not equipped with CCS, the discount rate, the nitrous oxide emissions associated with biomass production, the baseline energy demand scenario, and the cost of carbon capture and storage. The interplay between abatement of different greenhouse gases is explained in the next section, and emission pathways of non-co2 greenhouse gases for our base case scenarios are presented. Next, we include a comparison between our results and MAGICC-6 on the CO2 concentration and global mean surface temperature change for the 1.5 C overshoot case with base case assumptions. Finally, we offer a schematic illustration of the GET-Climate model. 1. Climate sensitivity In supplementary figures 1 and 2 we show emission, concentration and temperature pathways for the 1.5 C and 2 C ceiling and overshoot targets for a climate sensitivity of 1.5 C and 4.5 C per CO2 doubling, respectively. In supplementary figure 1 (with a climate sensitivity of 1.5 C per CO2 doubling) we see that for the 2 C ceiling and overshoot targets, availability of BECCS does not have any significant effect on the emission pathways over the next 50 years. In this case, the target is relatively easy to achieve; significant emission reductions do not need to take place until around Further delaying emission reductions beyond 2100 by means of BECCS is not possible in a large scale because there is simply not enough time for negative emissions to compensate for delayed abatement until the target must be met in However, for the 1.5 C target, availability of BECCS has a significant effect for the overshoot target, but not for the ceiling target. The mechanisms behind these results are virtually the same as for the main cases described in section 3.1 in the main paper. When climate sensitivity is 4.5 C per CO2 doubling, both 1.5 C and 2 C targets are very difficult to reach, and most of the emission pathways shown in supplementary figure 2 are close to being infeasible in our model. These pathways require very high-cost abatement options. For the 2 C targets, availability of BECCS plays an important role for both ceiling and overshoot targets. A difference compared to the results in the main paper is that we now have global net negative emissions even in the ceiling case. There are two reasons for this. First, the 1

2 temperature response to an emission pulse depends strongly on the climate sensitivity. Specifically, the time to reach peak temperature response after an emission pulse is considerably longer when climate sensitivity is high [45]. Therefore, in our scenario, net negative emissions (pulses) compensate for previous emissions (pulses) which have not yet reached their peak temperature response. Second, when BECCS is available we typically have larger CH4 and N2O emissions compared to cases when BECCS is not available. This holds for different values of the climate sensitivity as well, but this effect becomes much more important when solutions are nearly infeasible, since N2O and CH4 abatement is very costly beyond a certain level. Hence, for the 2 C ceiling target with a high climate sensitivity, BECCS can replace very high-cost abatement of CH4 and N2O emissions. For both 1.5 C and 2 C overshoot targets, the rate of temperature decline after the peak is slightly higher in the case with a climate sensitivity of 4.5 C per CO2 doubling compared to the base case. In supplementary figure 3, we explore the effect of using a higher or lower value for the climate sensitivity on mitigation costs for overshoot and ceiling targets. We find that overshoot targets below +1.5 C are technically feasible to reach with BECCS, even for a high climate sensitivity. The "temperature benefit" of introducing BECCS for overshoot targets, i.e., the reduction in temperature increase by the year 2150 for a given cost level (i.e. the horizontal distance between green and blue curves of the same line style in supplementary figure 3), is greater the higher the climate sensitivity is. The reason for this is that for a given cost level, the emission reductions achieved when introducing BECCS are essentially equal for all climate sensitivities tested. Thus, the temperature response will be higher with increasing values of the climate sensitivity. Similarly, the cost reduction achieved by introducing BECCS when aiming to meet a specific temperature target is greater the higher the climate sensitivity is. This is essentially equivalent to our observation that the value of BECCS is higher the lower the temperature target is (for a given climate sensitivity). For ceiling targets, we see in the bottom panel of supplementary figure 3 that BECCS generally has only a small temperature benefit. It is somewhat larger in the case of a high climate sensitivity. 2. Biomass availability In supplementary figures 4 and 5 we show emission, concentration and temperature pathways for 1.5 C and 2 C ceiling and overshoot targets for a maximum supply of bioenergy of 100 or 300 EJ per year, respectively. This range corresponds to the IPCC estimate of potential bioenergy deployment levels in 2050 [17, 47]. As seen in the two figures (and figure 1 in the main paper) the supply constraint on bioenergy has a profound impact on overshoot emission pathways when BECCS is available. The larger the supply of bioenergy is, the larger the nearterm CO2 emissions can be and the more negative emissions we can have beyond Also, for ceiling pathways, a larger bioenergy supply leads to slightly higher emissions in the near 2

3 term and somewhat lower emissions in the long-term. For cases without BECCS, the biomass supply constraint does not have any significant impact on the pathways. In supplementary figure 6 we examine whether our results on mitigation costs are robust if annual bioenergy availability is 100 or 300 EJ per year. For overshoot targets we find that the benefit of BECCS is significantly lower if only 100 EJ per year of biomass is available. Interestingly, the temperature benefit of increasing biomass availability for BECCS beyond 200 EJ per year is comparatively small, because the potential for net negative emissions is limited by carbon storage capacity. When high biomass availability is combined with high carbon storage capacity, very ambitious temperature overshoot targets can be reached at low cost (see "BECCS optimistic" curve in supplementary figure 6). For ceiling targets, BECCS only has a minor impact on mitigation costs, for all levels of biomass supply. In rough terms, the area requirements for 200 EJ per year of biomass can be estimated in the following way. Approximately 100 EJ per year of biomass may be achieved as residues from forestry, agricultural and municipal solid waste (see table 2.2 in [17]). Remaining biomass supply will likely come from dedicated plantations which compete with other land uses. Assuming a yield of 10 ton DM/ha/year (equivalent to 200 GJ/ha/year), results in an overall demand for land on the order of 500 Mha. This corresponds to a third of global crop land and a sixth of global pasture land. Similarly, assuming that 1 ton of biomass (dry matter) is equivalent to 20 GJ, and that half of the biomass is carbon by weight, a back of an envelope calculation gives that 200 EJ per year of biomass contains 5 GtC which if captured implies negative emissions of 18 GtCO2. 3. Carbon storage capacity In supplementary figures 7 and 8 we show emission, concentration and temperature pathways for the 1.5 C and 2 C ceiling and overshoot targets for lower and higher availability of carbon storage capacity. The global technical potential for carbon storage capacity is likely to be at least 2000 GtCO2, with a possibility of 10,000 GtCO2 of geological storage in deep saline formations [18]. We assume 2000 GtCO2 is available in our base case. Here we analyse the sensitivity of our results with respect to a lower and a higher storage capacity, 1000 GtCO2 and 8000 GtCO2. It may be surprising to note when comparing the BECCS overshoot cases of supplementary figure 7 (with a carbon storage capacity of 1000 GtCO2) and supplementary figure 8 (with a carbon storage capacity of 8000 GtCO2) that the temperature overshoot and maximum negative emission levels are similar in size, and are actually slightly larger in the scenario with less storage capacity. In the case with only 1000 GtCO2, virtually all of this storage capacity is used for BECCS. When more carbon storage capacity is allowed, most of the incremental capacity is used for fossil CCS. This explains why maximum negative emission levels are roughly comparable. 3

4 In supplementary figure 9 the sensitivity of our mitigation cost results with respect to alternative storage capacities is shown. For overshoot targets we find that the temperature benefit of overshoot targets with BECCS when storage capacity is high is significantly higher than in our base case, whereas the opposite holds for the case with only 1000 GtCO2 of storage capacity. Our base case value for the storage capacity, 2000 GtCO2, is binding when meeting ambitious temperature targets, i.e., the model uses all available storage capacity. Increasing the storage capacity makes it possible to use more fossil CCS (and somewhat more BECCS, although this is primarily limited by biomass availability), and thus lower costs as shown in supplementary figure 9. The potential economic value of carbon storage capacity is also apparent in this figure. For overshoot targets between 1.5 C and 2.5 C, increasing storage capacity from 2000 GtCO2 to 8000 GtCO2 decreases abatement costs by around 0.5% of future discounted global GDP. For ceiling targets, availability of BECCS has a relatively minor impact on mitigation costs for all levels of storage capacity examined. 4. Overshoot target year In supplementary figures 10 and 11 we examine the impact of changing the target year for overshoot scenarios from 2150 to 2100, thus significantly reducing the available time for BECCS to compensate for delayed emission reductions. The most striking difference from our base case is that the temperature overshoot for the 2 C target disappears for cost-effective emission pathways, and is considerably smaller for the 1.5 C target. Nevertheless, there is a minor deferral of abatement that generates a small economic benefit, as can be seen in supplementary figure Coal 50 EJ Next, we wish to assess whether BECCS retains its value when there are non-abatable emission sources in the energy system. In supplementary figures 12 and 13, we force the model to use at least 50 EJ of coal per year in total (30 EJ in the power sector and 20 EJ for industrial use) that is used without CCS. The results are very similar to our base case, with only a slight reduction in temperature overshoot. As expected, if BECCS is not available, the forced use of 50 EJ per year of coal leads to additional emissions of about 5 GtCO2 per year near the end of the century (as base case emissions approach zero). This constraint limits the potential to achieve global net negative emissions, hence the reduction of temperature target overshoot. In supplementary figure 13, we see that mitigation costs for overshoot targets below 1.5 C become considerably higher, and overshoot targets below 1 C become infeasible. Finally, we see in supplementary figure 13 that availability of BECCS now has a larger effect on costs for ceiling targets. In the base case, the availability BECCS did not have any significant impact on the mitigation costs for ceiling targets, while if we force the model to use 50 EJ per year of coal that is not fitted with CCS, BECCS can be used to compensate for these emissions leading to lower overall mitigation costs. 4

5 6. Additional sensitivity analyses In supplementary figures 14 and 15 we vary four additional key assumptions: first, we double nitrous oxide emissions resulting from bioenergy production compared to our base case assumptions (i.e. from 10 to 20 g N2O-N per GJ); second, we double the investment cost increment for all CCS technologies in our model; third, we use a baseline energy demand corresponding to IIASA A2r projections (thus an increase of demand compared to the B2 scenario used in the main paper); finally, we examine the impact of lowering the model discount rate from 5 percent to 3 percent per year. For all of these cases, we restrict our analysis to mitigation costs. Our main conclusion remains robust for all parameter variations examined. We see in supplementary figures 14 and 15 that the fundamental features from the base case are unchanged (c.f. figure 2 in the main paper). The benefit of introducing BECCS is considerable for overshoot temperature targets (supplementary figure 14), but is relatively insignificant for ceiling targets (supplementary figure 15). Substantially lower overshoot targets become feasible with BECCS, and the technology offers large potential cost reductions when considering ambitious overshoot targets. It may be useful to compare how costs change when compared to the base case. For example, the cost of reaching the 2 C overshoot case with BECCS is 1.14% of discounted global GDP in our reference case (figure 2 in the main paper). When N2O emissions from biomass are doubled, the cost increases to 1.19%. Similarly, when CCS costs are increased as described above, costs increase to 1.17%. Although the changes are important for the assessment of these individual technologies, the overall impact is small. For the A2r energy demand scenario, the cost of reaching the 2 C overshoot case with BECCS is 1.81% of discounted global GDP. Finally, for a discount rate of 3% per year, the cost increases to 2.67%. The reason why the net present value of abatement costs relative to the net present value of GDP is higher when the discount rate is lower is that annual abatement costs grow faster than GDP. 7. Methane and nitrous oxide emissions In supplementary figures 16 and 17, methane and nitrous oxide emissions and concentrations are shown for 2 C and 1.5 C targets, using our base case assumptions (c.f. figure 1 in the main paper for the concomitant CO2 emissions). Note that methane and nitrous oxide emissions are higher in the BECCS cases with overshoot compared to cases with only fossil CCS during most of this century. Since BECCS makes it easier to meet any given temperature target, the required greenhouse gas prices are lower, and thus less abatement of methane and nitrous oxide is cost-effective than in cases without BECCS. For the 2 C overshoot target the overall impact of this on the cumulative CO2 emissions until 2150 is very small (the difference between the BECCS and the fossil CCS case is only 87 GtCO2). 5

6 For the overshoot 1.5 C target the same mechanism applies but the difference in cumulative CO2 emissions become larger, see figure 1 in the main paper. The reason for this is that when negative carbon emissions are not available the model must resort to more substantial reductions of methane and nitrous oxide in order to reach the stringent target. 8. Model result comparison In order to corroborate our climate model we compare our results on CO2 concentration and global mean surface temperature for the 1.5 C overshoot case with CCS and BECCS with the results we get from MAGICC-6 when using the same CO2, CH4 and N2O emissions. Since MAGICC-6 has been thoroughly calibrated to more advanced climate models [48], this model is a useful benchmark for evaluating the functioning of our model. Other climate forcers than CO2, CH4 and N2O follow the RCP-3PD pathway in both models. The climate sensitivity is set to 3 C for a doubling of the CO2 concentration in both models, other parameters governing the energy balance model and the gas cycles differ between the models. Our parameter value choices and model structure are presented in the main paper, and MAGICC-6 is described in Meinshausen et al. [48]. For the calibration of MAGICC-6, we used the RCP default setting [49]. As seen in supplementary figure 18, the CO2 concentration pathway is virtually identical in the two models, while the global surface temperatures differ to some extent. However, the temperature response is still similar and shares the main characteristics. The difference in the temperature response pertains to differences in aerosol forcing, and that diffusivity and upwelling rate are temperature dependent in MAGICC-6 while they are not in GET-climate. Given that our temperature and carbon cycle response is very similar to that of MAGICC-6 and the fact that our simple climate model is based on well-known sub-modules and parameterisations (see model description in the appendix of the main paper), we conclude that the climate model in GET is suitable for our analysis. References [47] Creutzig F et al Reconciling top-down and bottom-up modelling on future bioenergy deployment Nature Climate Change [48] Meinshausen M, Raper S C B and Wigley T M L 2011 Emulating coupled atmosphere-ocean and carbon cycle models with a simpler model, MAGICC6: Part I Model Description and Calibration Atmospheric Chemistry and Physics [49] Meinshausen M et al The RCP greenhouse gas concentrations and their extensions from 1765 to 2300 Clim. Change

7 2 C target 1.5 C target Supplementary figure 1. Lower climate sensitivity. CO2 emissions, CO2 concentration and mean surface temperature increase for scenarios with a climate sensitivity of 1.5 C per CO2 doubling, for 2 C targets (left) and 1.5 C targets (right). Cases shown are: fossil CCS with ceiling targets (light blue), fossil CCS with overshoot targets (dark blue), fossil CCS and BECCS with ceiling targets (light green) and fossil CCS and BECCS with overshoot targets (dark green). Common assumptions: biomass availability 200 EJ/year, total carbon storage potential 2000 GtCO2. 7

8 2 C target 1.5 C target Supplementary figure 2. Higher climate sensitivity. CO2 emissions, CO2 concentration and mean surface temperature increase for scenarios with a climate sensitivity of 4.5 C per CO2 doubling, for 2 C targets (left) and 1.5 C targets (right). Cases shown are: fossil CCS with ceiling targets (light blue), fossil CCS with overshoot targets (dark blue), fossil CCS and BECCS with ceiling targets (light green) and fossil CCS and BECCS with overshoot targets (dark green). For the 1.5 C target, ceiling cases and the fossil CCS with overshoot case are infeasible in our model. Common assumptions: biomass availability 200 EJ/year, total carbon storage potential 2000 GtCO2. 8

9 Overshoot targets Ceiling targets Supplementary figure 3. Impact of climate sensitivity. Abatement costs in percent of discounted future GDP as a function of temperature target for multiple model runs, for scenarios with fossil CCS and BECCS (green) and fossil CCS only (blue). Line styles indicate different values for the climate sensitivity: 1.5 C (for 2xCO2, dots), 3 C (solid) and 4.5 C (dashes). All temperature targets are overshoot targets. Common assumptions: biomass availability 200 EJ/year, total carbon storage potential 2000 GtCO2. 9

10 2 C target 1.5 C target Supplementary figure 4. Lower biomass availability. CO2 emissions, CO2 concentration and mean surface temperature increase for scenarios with a biomass availability of 100 EJ, for 2 C targets (left) and 1.5 C targets (right). Cases shown are: fossil CCS with ceiling targets (light blue), fossil CCS with overshoot targets (dark blue), fossil CCS and BECCS with ceiling targets (light green) and fossil CCS and BECCS with overshoot targets (dark green). Ceiling cases for the 1.5 C target are infeasible in our model. Common assumptions: climate sensitivity 3 C (for 2xCO2) and total carbon storage potential 2000 GtCO2. 10

11 2 C target 1.5 C target Supplementary figure 5. Higher biomass availability. CO2 emissions, CO2 concentration and mean surface temperature increase for scenarios with a biomass availability of 300 EJ, for 2 C targets (left) and 1.5 C targets (right). Cases shown are: fossil CCS with ceiling targets (light blue), fossil CCS with overshoot targets (dark blue), fossil CCS and BECCS with ceiling targets (light green) and fossil CCS and BECCS with overshoot targets (dark green). Ceiling cases for the 1.5 C target are infeasible in our model. Common assumptions: climate sensitivity 3 C (for 2xCO2) and total carbon storage potential 2000 GtCO2. 11

12 Overshoot targets Ceiling targets Supplementary figure 6. Impact of biomass availability. Abatement costs in percent of discounted future GDP as a function of temperature target for multiple model runs, for scenarios with fossil CCS (blue) and fossil CCS and BECCS (green and orange). Line styles indicate varying amounts of annual biomass availability: 100 (dashes), 200 (solid) and 300 (dots) EJ per year. All temperature targets are overshoot targets. Common assumptions: climate sensitivity 3 C (for 2xCO2) and total carbon storage potential 2000 GtCO2 (unless otherwise specified). 12

13 2 C target 1.5 C target Supplementary figure 7. Lower carbon storage potential. CO2 emissions, CO2 concentration and mean surface temperature increase for scenarios with a carbon storage capacity of 1000 GtCO2, for 2 C targets (left) and 1.5 C targets (right). Cases shown are: fossil CCS with ceiling targets (light blue), fossil CCS with overshoot targets (dark blue), fossil CCS and BECCS with ceiling targets (light green) and fossil CCS and BECCS with overshoot targets (dark green). Ceiling cases for the 1.5 C target are infeasible in our model. 13

14 2 C target 1.5 C target Supplementary figure 8. Higher carbon storage potential. CO2 emissions, CO2 concentration and mean surface temperature increase for scenarios with a carbon storage capacity of 8000 GtCO2, for 2 C targets (left) and 1.5 C targets (right). Cases shown are: fossil CCS with ceiling targets (light blue), fossil CCS with overshoot targets (dark blue), fossil CCS and BECCS with ceiling targets (light green) and fossil CCS and BECCS with overshoot targets (dark green). Ceiling cases for the 1.5 C target are infeasible in our model. 14

15 Overshoot targets Ceiling targets Supplementary figure 9. Impact of carbon storage potential. Abatement costs in percent of discounted future GDP as a function of temperature target for multiple model runs, for scenarios with fossil CCS (blue) and fossil CCS and BECCS (green and orange). Line styles indicate varying amounts of global carbon storage capacity: 1000 (dashes), 2000 (solid) and 8000 (dots) GtCO2. All temperature targets are overshoot targets. Common assumptions: climate sensitivity 3 C (for 2xCO2) and biomass availability 200 EJ/year (unless otherwise specified). 15

16 2 C target 1.5 C target Supplementary figure 10. Overshoot target year: CO2 emissions, CO2 concentration and mean surface temperature increase, for 2 C targets (left) and 1.5 C targets (right). Cases shown are: fossil CCS with ceiling targets (light blue), fossil CCS with overshoot targets (dark blue), fossil CCS and BECCS with ceiling targets (light green) and fossil CCS and BECCS with overshoot targets (dark green). Ceiling cases for the 1.5 C target are infeasible in our model. Ceiling cases for the 2 C target are feasible, but are virtually identical to the corresponding overshoot cases. 16

17 Overshoot targets Ceiling targets Supplementary figure 11. Overshoot target year: The value of BECCS with overshoot targets (top) and ceiling targets (bottom). Abatement costs in percent of discounted future GDP as a function of temperature target for multiple model runs. Cases shown are: no CCS with overshoot targets (dark red), fossil CCS with overshoot targets (dark blue), fossil CCS and BECCS with overshoot targets (dark green), no CCS with ceiling targets (light red), fossil CCS with ceiling targets (light blue) and fossil CCS and BECCS with ceiling targets (light green). 17

18 2 C target 1.5 C target Supplementary figure 12. Forced use of 50 EJ of coal without CCS. CO2 emissions, CO2 concentration and mean surface temperature increase, for 2 C targets (left) and 1.5 C targets (right). Cases shown are: fossil CCS with ceiling targets (light blue), fossil CCS with overshoot targets (dark blue), fossil CCS and BECCS with ceiling targets (light green) and fossil CCS and BECCS with overshoot targets (dark green). Ceiling cases for the 1.5 C target are infeasible in our model. 18

19 Overshoot targets Ceiling targets Supplementary figure 13. Forced use of 50 EJ of coal without CCS. The value of BECCS with overshoot targets (top) and ceiling targets (bottom). Abatement costs in percent of discounted future GDP as a function of temperature target for multiple model runs. Cases shown are: no CCS with overshoot targets (dark red), fossil CCS with overshoot targets (dark blue), fossil CCS and BECCS with overshoot targets (dark green), no CCS with ceiling targets (light red), fossil CCS with ceiling targets (light blue) and fossil CCS and BECCS with ceiling targets (light green). 19

20 doubled N2O emissions from biomass increased capital costs for CCS higher energy demand (A2r) lower discount rate (3%) Supplementary figure 14. Cost of reaching overshoot targets (c.f. figure 2 in main paper). Abatement costs in percent of discounted future GDP as a function of temperature target for multiple model runs. Additional sensitivity analyses for four cases: doubling the N2O emission factor for biomass (top left), doubling the capital cost increment for all carbon capture and storage technologies (top right), increasing baseline energy demand according to the IIASA A2r scenario (bottom left), and lowering the model discount rate from 5% to 3% (bottom right). Base case assumptions in all cases: climate sensitivity 3 C (for 2xCO2), biomass availability 200 EJ/year (unless otherwise specified) and total carbon storage potential 2000 GtCO2. 20

21 doubled N2O emissions from biomass increased capital costs for CCS higher energy demand (A2r) lower discount rate (3%) Supplementary figure 15. Cost of reaching ceiling targets (c.f. figure 2 in main paper). Abatement costs in percent of discounted future GDP as a function of temperature target for multiple model runs. Additional sensitivity analyses for four cases: doubling the N2O emission factor for biomass (top left), doubling the capital cost increment for all carbon capture and storage technologies (top right), increasing baseline energy demand according to the IIASA A2r scenario (bottom left), and lowering the model discount rate from 5% to 3% (bottom right). Base case assumptions in all cases: climate sensitivity 3 C (for 2xCO2), biomass availability 200 EJ/year (unless otherwise specified) and total carbon storage potential 2000 GtCO2. 21

22 2 C target 1.5 C target Supplementary figure 16. Methane emissions and concentration for 2 C targets (left) and 1.5 C targets (right). Cases shown are: fossil CCS with ceiling targets (light blue), fossil CCS with overshoot targets (dark blue), fossil CCS and BECCS with ceiling targets (light green) and fossil CCS and BECCS with overshoot targets (dark green). Base case assumptions in all cases: climate sensitivity 3 C (for 2xCO2), biomass availability 200 EJ/year (unless otherwise specified) and total carbon storage potential 2000 GtCO2. 22

23 2 C target 1.5 C target Supplementary figure 17. Nitrous oxide emissions and concentration for 2 C targets (left) and 1.5 C targets (right). Cases shown are: fossil CCS with ceiling targets (light blue), fossil CCS with overshoot targets (dark blue), fossil CCS and BECCS with ceiling targets (light green) and fossil CCS and BECCS with overshoot targets (dark green). Base case assumptions in all cases: climate sensitivity 3 C (for 2xCO2), biomass availability 200 EJ/year (unless otherwise specified) and total carbon storage potential 2000 GtCO2. 23

24 Supplementary figure 18. Comparison between MAGICC-6 and GET-Climate. Upper panel shows the CO2 concentration in MAGICC-6 and GET-climate when using emissions from our 1.5 C overshoot case with fossil CCS and BECCS. Lower panel shows the temperature response for the same case. 24

25 Supplementary figure 19. Schematic overview of the climate module, its feedbacks and interactions with the energy system. See model description in the appendix of the main paper for more information. (Note that the box representing the energy system model is disproportionately small. In terms of number of generated equations, the energy system module is larger than the entire climate module illustrated here.) 25