Download Carbon Dioxide Removal – Model Intercomparison Project (CDR

Carbon Dioxide Removal – Model Intercomparison Project (CDR-­‐MIP) (March 2, 2016) Project Leaders: David P. Keller, GEOMAR, Germany ([email protected]) Andrew Lenton, CSIRO, Australia ([email protected]) Vivian Scott, University of Edinburgh, Scotland ([email protected]) Naomi E. Vaughan, University of East Anglia, U.K. ([email protected]) Steering Committee: Kirsten Zickfeld, Simon Fraser University, Canada Helene Muri, University of Oslo, Norway Ben Kravitz, Pacific Northwest National Laboratory, USA Chris Jones, Met Office Hadley Centre, United Kingdom Duoying Ji, Beijing Normal University, China Ken Caldeira, Carnegie Institution, USA Website: http://www.kiel-­‐earth-­‐institute.de/CDR_Model_Intercomparison_Project.html 1. Context Continued anthropogenic greenhouse gas emissions are changing the climate threatening “severe, pervasive and irreversible” impacts. Inadequate emissions reduction had lead to increasing attention on Climate Intervention (CI) – deliberate intervention to counter or reduce the impact of climate change by either modifying the Earth’s radiation budget (Solar Radiation Management; SRM), or removing the primary greenhouse gas (carbon dioxide; CO2) from the atmosphere – Carbon Dioxide Removal (CDR). There is increasing focus and study on the potential of carbon dioxide removal (CDR) methods to enable “negative emissions” to compliment emissions mitigation efforts. CDR is employed in many IPCC WG3 AR5 scenarios, e.g. for ~90% of the scenarios which attain atmospheric CO2 ppm consistent with ≤2°C mean global surface temperature. CDR application at a large scale (~ ≥1Gt CO2) will have an impact on the global carbon cycle due to physical, chemical and biological changes on land and in the ocean. For example a reduction in CO2 in the atmosphere will reduce the rate of oceanic CO2 uptake through a reduction in the air-­‐sea flux disequilibria, while at the same time an increase in terrestrial and ocean carbon storage would be anticipated through a reduction in radiative warming. Furthermore as many of these changes will impact the ecosystem services (e.g. food production) provided by the land and ocean, there will certainly be positive and negative effects on 1 human societies, and on their responses and strategies for adaptation to a changing climate.
At present these potentially positive and negative impacts in response to CDR remain poorly quantified and elucidated. This information is urgently needed to allow us to assess: • The degree to which CDR could help mitigate climate change or reverse its effect. • The potential effectiveness and risks/benefits of different CDR proposals. • To inform how CDR might be appropriately accounted. Such work might also usefully inform on the ability of climate models to examine questions of climate reversibility. Studies of CDR to date have been undertaken in only a few Earth system models1–4. Furthermore, these studies all used different experimental designs so their results are not directly comparable. A model intercomparison study with Earth System Models of Intermediate Complexity (EMICS) that addressed climate reversibility, among other things, has also recently been published5, but the focus was on the very distant future rather than the next century. Thus, there is a need for a CDR focused model intercomparison project that also brings the scientific community together. Scientific focus The goals of CDR-­‐MIP are to use multiple models to: (i) address climate “reversibility”†: assessing the efficacy of using CDR to return high future atmospheric CO2 concentrations to lower levels. This topic is highly idealized as the technical ability of CDR methods to remove such enormous quantities of CO2 in relatively short (i.e. this century) timescales is doubtful. However, the results would provide information on the degree and rate at which a changing and changed climate could be returned to a previous state; and (ii) address the potential efficacy, feedbacks, and side effects of specific CDR methods. This topic would help to better constrain the carbon (C) sequestration potential and risks and/or benefits of selected methods. Together a rigorous analysis of the nature, sign, and timescales of these CDR-­‐related topics would provide important information for the inclusion of CDR in climate mitigation scenarios, and in resulting mitigation and adaptation policy strategies. Moreover, such studies would be a good test for the models and could be used to improve their performance/realism. † Climate reversibility needs to be carefully defined in regards to any analysis of the CDR-­‐MIP simulations as it could be focused on global properties (e.g. mean temperature) or include some degree of specified regional results (e.g. cryosphere extent). 2 Specifically some of the questions addressed will include: 1) What components of the Earth’s climate system exhibit “reversibility” when CO2 increases and then decreases? On what timescales do these “reverses” occur? If reversible, is this complete reversibility or just on average (are there spatial and temporal aspects)? 2) Which changes are irreversible? 3) What role does hysteresis‡ play in these responses? 4) What consequences might these changes have on societal strategies for climate change mitigation and adaptation§? 5) How much CO2 would have to be removed to return to a specified level e.g. present day or pre-­‐industrial? 6) How quickly could CDR remove atmospheric CO2? 7) What are the short term C-­‐cycle feedbacks (e.g., rebound) associated with the method? What are the consequences for accounting for C removed? 8) What are the short-­‐ and longer-­‐term physical/chemical/biological feedbacks and side effects of the method? What are the consequences for accounting? And, for societal adaptations to climate change? 9) Where is the C stored (land and ocean) and for how long? What are the consequences for accounting and the reward for the removed C? 2. Experiments: It is anticipated that this be the first stage of a continuing project exploring CDR. CDR-­‐MIP will allow and encourages development of other (future) experiments and scenarios. Potential future experiments could include Bioenergy with Carbon Capture and Storage (BECCS) or ocean fertilization. It is also anticipated that scenarios will be ultimately developed that will combine Solar Radiation Management (SRM) and CDR in the future. The following experiments have been designed to be relatively simple to implement, and to enable comparison of how models respond to significant CDR perturbations. We anticipate these experiments to be run by groups using full Earth System Models (ESMs) and Earth System Models of Intermediate Complexity (EMICS). For models with interannual variability, e.g., the ESMs and some EMICS, multiple (at least 3) ensemble members should be undertaken. The first experiments of this project (C1 & C2) will be idealised to best assess and quantify questions related to climate reversibility and carbon cycle feedbacks. Subsequent experiments (C3 & C4) will investigate specific CDR techniques. ‡ The dependence of the climate system depends not only on its current environment, but also on its past environment. Irreversibility implies hysteresis, but hysteresis does not necessarily imply irreversibility. § As a crude example how would the option of “reversibility” impact discussion on the relocation of agricultural production? 3 Idealised experiments: Preliminary experiments with a small group of models will be undertaken in late 2015 to test these experiment protocols and generate initial results (see Timetable section below). C1. Carbon Cycle Reversibility experiment. This experiment will start from the existing CMIP Diagnostic, Evaluation, and Characterization of Klima (DECK) prescribed 1% yr-­‐1 CO2 increase experiment** until 4xCO2 (140 years into the run), and then prescribe a 1% yr-­‐1 removal of CO2 from the atmosphere to pre-­‐industrial levels (~140 years of removal), followed by holding CO2 at pre-­‐industrial for a minimum of 60 years in ESMs. EMICS are encouraged to extend runs another 1000 years total to investigate long-­‐term climate system reversibility. Extending the existing CMIP DECK prescribed 1% yr-­‐1 CO2 increase experiment should provide a relatively straightforward opportunity to explore the reversibility of the Earth system to CO2 removal. ** CMIP5 (cmip-­‐pcmdi.llnl.gov/cmip5) experiment 6.1: 1% per year increase in atmospheric CO2 concentration from 280ppm in 1850 for 140 years to 1120ppm in 1990. 4 C2. Carbon-­‐ cycle feedbacks experiment More detailed protocol coming soon. C3. Afforestation This experiment will be driven from the pre-­‐industrial with observed emissions and using future emissions from a high SSP emission scenario (determined in consultation with ScenarioMIP), a land use change scenario from an alternative RCP-­‐SSP combination that has greater afforestation than the original land use projection will be imposed. The control simulations would follow high SSP emissions until 2100. Detailed experimental design, including management of ESMs with/without dynamic vegetation to be finalized later. Our proposed afforestation experiment is the same as the LUMIP (Land Use Model Intercomparison Project) Phase Two (Tier 1) experiment (https://www2.cgd.ucar.edu/research/mips/lumip). C4. Ocean alkalinization During high SPP emission scenario starting 2020 add 0.25 Pmol Total Alkalinity (TA) yr-­‐1 to the upper grid box of the ocean model. The control simulations would follow high SSP emissions until 2100. Optional: C4-­‐S. In 2070 the alkalinity addition would cease, and the simulations would continue for another 30 years until 2100. The additions are limited to ice free, year-­‐round ship accessible waters, which for simplicity are assumed to be between 70°N and 60°S. For many models this will in practice result in an artificial TA flux at the air-­‐sea interface with realized units that might, for example, be something like µmol TA s-­‐1 cm-­‐2. Adding 0.25 Pmol TA yr-­‐1 is equivalent to adding 9.26 Pg yr-­‐1 of an alkalizing agent like Ca(OH)2 or 8.75 Pg yr-­‐1 of forsterite (Mg2SiO4), a form of olivine (assuming theoretical net instant dissolution reactions which for every mole of Ca(OH)2 or Mg2SiO4 added sequesters 2 or 4 moles, respectively, of CO26,7). The amount of any particular alkalizing agent that could be mined, processed, transported, and delivered to the ocean in a form that would easily dissolve and enhance alkalinity is poorly constrained 6,8. Therefore, the amount of alkalinity that is to be added is set to be large enough to have an effect on atmospheric CO2 (based on the results of previous studies) but still within the total global shipping capacity3,6. As all models do not include marine iron or silicate cycles, the addition of these nutrients, which would occur if some form of olivine were used as the alkalizing agent, is not considered. 3. Logistics & Technical details All groups will be encouraged to undertake all simulations, although individual groups may not be able to complete some experiments and this would not preclude participation. We also encourage those running Earth system models of intermediate complexity (EMICS) to participate and contribute where applicable. The potential to modify or extend the simulations to harness the 5 capability of EMICs to conduct multiple or longer time-­‐scale simulations is open for discussion. It is anticipated that the model simulations will be publically available and hosted on the Earth System Grid Federation (ESGF). To date several modeling groups have been approached and have indicated that they are interested and willing to participate in such a project. Endorsement This project will initially seek endorsement from the World Climate Research Program and the Global Carbon Project (GCP). Timetable Spring 2016: C1 & C2 experimental protocol details finalised. Summer 2016: C3 & C4 experimental protocol details finalised. Sept. 20-­‐22, 2016: 3 day project workshop at the Institute for Advanced Sustainability Studies (IASS) in Potsdam, Germany. References 1. Boucher, O. et al. Reversibility in an Earth System model in response to CO 2 concentration changes. Environ. Res. Lett. 7, 024013 (2012). 2. MacDougall, A. H. Reversing climate warming by artificial atmospheric carbon-­‐
dioxide removal: Can a Holocene-­‐like climate be restored? Geophys. Res. Lett. 40, 5480–5485 (2013). 3. Keller, D. P., Feng, E. Y. & Oschlies, A. Potential climate engineering effectiveness and side effects during a high carbon dioxide-­‐emission scenario. Nat. Commun. 5, 1–11 (2014). 4. Tokarska, K. B. & Zickfeld, K. The effectiveness of net negative carbon dioxide emissions in reversing anthropogenic climate change. Environ. Res. Lett. 10, 94013 5. Zickfeld, K. et al. Long-­‐Term Climate Change Commitment and Reversibility: An EMIC Intercomparison. J. Clim. 26, 5782–5809 (2013). 6. Köhler, P., Abrams, J. F., Völker, C., Hauck, J. & Wolf-­‐Gladrow, D. A. Geoengineering impact of open ocean dissolution of olivine on atmospheric CO2 , surface ocean pH and marine biology. Environ. Res. Lett. 8, 14009 (2013). 6 7. Ilyina, T., Wolf-­‐Gladrow, D., Munhoven, G. & Heinze, C. Assessing the potential of calcium-­‐based artificial ocean alkalinization to mitigate rising atmospheric CO 2 and ocean acidification. Geophys. Res. Lett. 40, 5909–5914 (2013). 8. Renforth, P., Jenkins, B. G. & Kruger, T. Engineering challenges of ocean liming. Energy 60, 442–452 (2013). 7