Parallel Session: Putting the ‘Engineering’ in Solar & Carbon Climate Engineering Approaches

14:00 - 15:30

Modifying Earth’s climate is one of the largest proposed activities in history. Designing, constructing, and managing such a large endeavor will require engineering. We explore engineering questions from both a systems and deployment perspective and how they can inform the science of SRM and CDR climate engineering.



  • David Keith - Engineering radiative forcing by stratospheric aerosols
    • If the objective is to achieve specified short wave radiative forcing by increasing the loading of stratospheric aerosol, then one needs to choose (a) the aerosol, (b) the means of delivery, (c) the means of monitoring the aerosol distribution, and (d) a system to combine observations with forward models to provide feedback by which the aerosol delivery is adjusted to achieve the specified radiative forcing.
      I will review methods of control particle size for sulfates such as delivery of H2SO4 in an aircraft plume, and discuss methods of producing the required precursors from elemental sulfur on board an aircraft. I will review options for solid aerosols, including new laboratory work on the surface chemistry of solid aerosols that may react to reduce ozone depletion.
      I will review the options for monitoring aerosol loading including the possibly of using new low-cost limb sounders, upward looking instruments on high altitude aircraft or commercial jet transports, and in situ aerosol observations using new lightweight aerosol instruments.
      Finally, I will speculate about the engineering design challenge of integrating these elements into an operational system.
  • Simone Tilmes
    • The state-of-the art global climate model CESM-WACCM has been used to demonstrate for the first time that a relatively simple feedback-control algorithm coupled to WACCM can be applied to counteract anthropogenic climate change through stratospheric SO2 injections. The feedback-control algorithm is designed to meet specific climate objectives, for instance to keep surface temperatures to specific levels. Before, this type of geoengineering has only been demonstrated in more simple and less interactive climate models, while dimming the solar constant (Kravitz et al., 2016). We demonstrated that global mean temperatures and hemispheric temperature gradients could be kept at 2020 conditions, while following the RCP8.5 emission scenario until 2100, using different point locations of stratospheric SO2 injections that are determined annually by the feedback-control algorithm. We have performed a 20-member ensemble to identify robustness of impacts und advance our process understanding of strategic geoengineering.
  • Wake Smith - Deployment Tactics and Costs for Early Phase Stratospheric Aerosol Injection
    • SAI would deploy aerosols high in the atmosphere to deflect a small fraction of the sunlight the earth would otherwise absorb, thereby slightly cooling the earth. Among the many unanswered questions about SAI is how to actually get the aerosols to their intended locations around the globe and in the atmosphere. This is a non-trivial aviation problem because the desired injection altitude is 65,000 feet above sea level.
      Previous research assumed that this mission could be achieved with modified versions of conventional aircraft, such as Gulfstream business jets. However, such aircraft cannot achieve the required altitudes. Another overly simplistic prior assumption was that the deployment solution would be an all-new, purpose-designed aircraft, but the tens of billions of dollars necessary to design and certify this exotic new aircraft will not be financially feasible for year 1, before the feasibility and desirability of SAI has been established. My paper therefore considers the array of alternative deployment solutions for year 1, and they are currently meager. Nonetheless, if we don’t know the deployment solution, then we don’t the cost, and without the cost, we can’t do sensible cost/benefit analysis on SAI.
  • Hugh Hunt - An engineer's perspective of SRM and SPICE
    • Much has been said about SPICE, but very little from those involved directly.  As leader of the 1km
      testbed outdoor experiment I can reveal quite a few details that have not been spoken about before
      - and perhaps it's interesting that no-one has ever bothered to ask!  The message is that the
      engineering issues of SRM are largely ignored even though the enormity of scale and harshness of
      environment are exceptional challenges.  If SRM is ever deployed at scale safely and responsibly it
      will have taken decades of careful engineering R&D to get there, and we haven't really started.
Convened by: 

Ben Kravitz

Pacific Northwest National Laboratory
United States

Ben Kravitz is a climate scientist in the Atmospheric Sciences and Global Change Division at the U.S. Department of Energy's Pacific Northwest National Laboratory.  His research involves using climate models to understand climate response to perturbations on a variety of timescales.  Ben's focus is on climate model simulations of geoengineering.  He is the coordinator of the Geoengineering Model Intercomparison Project (GeoMIP), an international effort to understand the robust responses of climate models to standardized scenarios of geoengineering.

Douglas MacMartin

Cornell University, California Institute of Technology
United States of America

Douglas MacMartin splits his time between Mechanical & Aerospace Engineering at Cornell University, and Computing + Mathematical Sciences at the California Institute of Technology.  His research lies at the intersection between engineering feedback analysis and climate dynamics, with a primary focus on solar geoengineering – working to develop the knowledge base for society to make informed decisions.  In addition to applying engineering analysis to climate dynamics, he is also involved in control design for the Thirty Meter Telescope.  He received his Bachelors’ degree from the University of Toronto in 1987, and Ph.D. in Aeronautics and Astronautics from MIT in 1992; prior to joining Caltech in 2000, he led the active control research and development program at United Technologies Research Center.


David Keith

Harvard University
United States of America

David Keith has worked near the interface between climate science, energy technology, and public policy for twenty-five years. He took first prize in Canada's national physics prize exam, won MIT's prize for excellence in experimental physics, and was one of TIME magazine's Heroes of the Environment. David is Professor of Applied Physics in Harvard’s School of Engineering and Applied Sciences and Professor of Public Policy in the Harvard Kennedy School, and founder at Carbon Engineering, a company developing technology to capture of CO2 from ambient air to make carbon-neutral hydrocarbon fuels. Best known for work on the science, technology, and public policy of solar geoengineering, David is leading the development of an interfaculty research initiative on solar geoengineering at Harvard. David’s work has ranged from the climatic impacts of large-scale wind power to an early critique of the prospects for hydrogen fuel. David’s hardware engineering projects include the first interferometer for atoms, a high-accuracy infrared spectrometer for NASA's ER-2, and currently, development of CO2 capture pilot plants for Carbon Engineering. David teaches courses on Science and Technology Policy and on Energy and Environmental Systems where he has reached students worldwide with an online edX course. He has writing for the public with A case for climate engineering from MIT Press. Based in Cambridge, David spends about a third of his time in Canmore Alberta.

Simone Tilmes

National Center for Atmospheric Research

Dr. Simone Tilmes is a Project Scientist II at National Center for Atmospheric Research (NCAR) and the liaison for the Community Earth System Model (CESM) chemistry-climate working group. Her scientific interests cover the understanding and evaluation of chemical, aerosol and dynamical processes in chemistry-climate models. She has investigated past, present and future evolution of the ozone hole in both hemispheres based on models and observations. Further research includes interactions in tropospheric chemistry, aerosols, air quality, long-range transport of pollutants, and tropospheric ozone. She also studies the impact of geoengineering on the Earth’s climate system, the hydrological cycle, and the impact of solar radiation management on dynamics and chemistry in both troposphere and stratosphere.

Wake Smith

New State Capital Partners LLC

Wake Smith is preparing a paper on the lofting solutions and costs of the first decade of Stratospheric Aerosol Injection deployment.  Mr. Smith is a Senior Industry Partner at New State Capital Partners, a New York-based middle market private equity firm, where he specializes in buy-outs in the field of commercial aviation.  He also teaches an undergraduate finance course at Yale University.  Prior executive positions include President of the flight training division of Boeing, Chief Operating Officer of Atlas Air Worldwide Holdings, and CEO of Pemco World Air Services.  He holds a BA from Yale and an MBA from Harvard.

Hugh Hunt

Cambridge University

Dr Hugh Hunt is a Reader in Engineering Dynamics and Vibration at Cambridge University. His research centres on the control of noise and vibration from underground railways, but he is also interested in geoengineering. He was Co-Investigator on the SPICE project, 2010-15, which looked at various aspects of SRM. He was responsible for an outdoor experiment, the 1km testbed, which was intended to evaluate the influence of wind on the motion of a tethered balloon.
He is now also interested in techniques for the removal of non-CO2 greenhouse gases, in particular methane and N2O.
Hugh is a regular presenter on television documentaries on Channel 4, PBS Nova and SBS, including "Dambusters: Building the Bouncing Bomb", "Attack of the Zeppelins", "Escape from Colditz" and "Guy Martin Wall of Death". He is Keeper of the Clock at Trinity College, a clock which is demonstrably the most accurate tower clock in the world. He has an impressive collection of boomerangs which he uses to inspire students in the study of dynamics and mechanics.