Monitoring of Geoengineering Effects and their Natural and Anthropogenic Analogues

A number of climate intervention concepts, referred to as “geoengineering,” are being considered as a potential additional approach (beyond mitigation of greenhouse gas emissions) to manage climate change. However, before governments go down the path of attempting deliberate climate intervention including precursor field-experiments, it is essential that the scientific community take the necessary steps to validate our understanding that underpins any of the proposed intervention concepts in order to understand all likely consequences and put in place the necessary strategies for monitoring the expected and unintended consequences of such intervention. The Keck Institute for Space Studies (KISS) has sponsored a project to identify specific priorities for improved scientific understanding and focused efforts to address selected priorities. This project does not advocate the deployment of geoengineering, outdoor geoengineering experiments, or monitoring systems for such proposed geoengineering field experiments, but is rather a precautionary study with the following goals: 1) enumeration of where major gaps in our understanding exist in solar radiation management (SRM) approaches, 2) identification of the research that would be required to improve understanding of such impacts including modeling and observation of natural and anthropogenic analogues to geoengineering, and 3) a preliminary assessment of where gaps exist in observations of relevance to SRM and what is needed to fill such gaps. This project focuses primarily on SRM rather than other proposed geoengineering techniques such as carbon dioxide removal from the atmosphere because there exist a number of analogues to the SRM methods that currently operate on Earth that provide a unique opportunity to assess our understanding of the response of the climate system to associated changes in solar radiation. Additionally, the processes related to these analogues are also fundamental to understanding climate change itself being of central relevance to how climate is forced by aerosol and respond through clouds, among other influences. In other words, this research has likely powerful co-benefits for climate science writ large. The study phase of the project was executed in 2011 and consisted of two workshops at Caltech (May 23-26 and November 15-18) as well as several smaller meetings and telecons. Participants in the study included individuals with an established track record of geoengineering research (primarily modeling studies), experts in the theory and observation of related physical processes, as well as engineers with expertise in risk management and systems analysis. Graduate students and post-doctoral fellows were active participants in the study. Four major topics that were identified during the workshops as priorities for subsequent research and development, particularly in regards to addressing related observational gaps: 1. Volcanoes as analogues of geoengineering with stratospheric aerosols 2. Ship tracks and cloud/aerosol interactions in general as analogues of geoengineering with marine-cloud brightening 3. Studying more targeted geoengineering interventions to counteract specific consequences of climate change, and 4. Identifying the satellite-based albedo monitoring needs that would be required for monitoring either a geoengineering test or its natural and anthropogenic analogues. Major volcanic eruptions that inject sulfate aerosol into the stratosphere cool the planet and are one of the motivating examples behind geoengineering. Much more could be learned about the intentional introduction of stratospheric aerosols through a combination of more thorough analysis of existing data, and development of a rapid-response observing strategy to maximize what we can learn from a future large eruption. Gaps in our knowledge include the evolution of aerosol size, the interaction with cirrus, water vapor, and ozone, and tropospheric chemistry more broadly. There are also attribution challenges that need to be understood, as the conditions following volcanic eruptions are not the same as those due to SRM (e.g. the presence of ash, or the discrete vs continual injection). The second main concept put forth for geoengineering is to introduce aerosols (e.g. salt) to change the optical depth of marine clouds; the current analog for this effect is ship tracks and other cloud/aerosol interactions. There is potential for further analysis of existing data to better understand these interactions and assess the science behind this SRM approach. The sensitivities of cloud albedo to specific processes and parameters are poorly understood. There are also observational gaps, such as the entrainment rate, or direct measurement of albedo, that limit our current ability to assess this approach. Third, it is important to understand what the actual goals for a possible eventual implementation of SRM might be, since SRM would quite possibly be deployed in response to a particular concern, rather than a generic desire to restore the overall climate. The highest priority identified during the study program was to focus on the high risk, high impact potential for a “tipping point” associated with Arctic permafrost melt, and the potential for geoengineering to reverse this. Other tipping points involving Arctic sea-ice and the Greenland and Antarctic ice-sheets may also warrant targeted intervention studies. Finally, one of the specific gaps in our observational capability is the ability to monitor albedo accurately enough to measure and attribute changes, with sufficient spatial, spectral, and temporal resolution. This capability is needed for all of first three SRM topics

Field experiments on solar geoengineering: report of a workshop exploring a representative research portfolio

We summarize a portfolio of possible field experiments on solar radiation management (SRM) and related technologies. The portfolio is intended to support analysis of potential field research related to SRM including discussions about the overall merit and risk of such research as well as mechanisms for governing such research and assessments of observational needs. The proposals were generated with contributions from leading researchers at a workshop held in March 2014 at which the proposals were critically reviewed. The proposed research dealt with three major classes of SRM proposals: marine cloud brightening, stratospheric aerosols and cirrus cloud manipulation. The proposals are summarized here along with an analysis exploring variables such as space and time scale, risk and radiative forcing. Possible gaps, biases and cross-cutting considerations are discussed. Finally, suggestions for plausible next steps in the development of a systematic research programme are presented

Aerosol lidar observations of atmospheric mixing in Los Angeles: Climatology and implications for greenhouse gas observations

Atmospheric observations of greenhouse gases provide essential information on sources and sinks of these key atmospheric constituents. To quantify fluxes from atmospheric observations, representation of transport—especially vertical mixing—is a necessity and often a source of error. We report on remotely sensed profiles of vertical aerosol distribution taken over a 2 year period in Pasadena, California. Using an automated analysis system, we estimate daytime mixing layer depth, achieving high confidence in the afternoon maximum on 51% of days with profiles from a Sigma Space Mini Micropulse LiDAR (MiniMPL) and on 36% of days with a Vaisala CL51 ceilometer. We note that considering ceilometer data on a logarithmic scale, a standard method, introduces, an offset in mixing height retrievals. The mean afternoon maximum mixing height is 770 m Above Ground Level in summer and 670 m in winter, with significant day‐to‐day variance (within season σ = 220m≈30%). Taking advantage of the MiniMPL’s portability, we demonstrate the feasibility of measuring the detailed horizontal structure of the mixing layer by automobile. We compare our observations to planetary boundary layer (PBL) heights from sonde launches, North American regional reanalysis (NARR), and a custom Weather Research and Forecasting (WRF) model developed for greenhouse gas (GHG) monitoring in Los Angeles. NARR and WRF PBL heights at Pasadena are both systematically higher than measured, NARR by 2.5 times; these biases will cause proportional errors in GHG flux estimates using modeled transport. We discuss how sustained lidar observations can be used to reduce flux inversion error by selecting suitable analysis periods, calibrating models, or characterizing bias for correction in post processing.Key PointsAerosol lidar maps LA mixing depth in space (pilot mobile study) and time (2 years data)Automatic mixing depth retrieval system finds daily variability far exceeds seasonal differencePBL heights in models used for GHG monitoring show biases that will carry over to flux estimatesPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134180/1/jgrd53200_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134180/2/jgrd53200.pd

Surface observations for monitoring urban fossil fuel CO_2 emissions: Minimum site location requirements for the Los Angeles megacity

The contemporary global carbon cycle is dominated by perturbations from anthropogenic CO_2 emissions. One approach to identify, quantify, and monitor anthropogenic emissions is to focus on intensely emitting urban areas. In this study, we compare the ability of different CO_2 observing systems to constrain anthropogenic flux estimates in the Los Angeles megacity. We consider different observing system configurations based on existing observations and realistic near-term extensions of the current ad hoc network. We use a high-resolution regional model (Stochastic Time-Inverted Lagrangian Transport-Weather Research and Forecasting) to simulate different observations and observational network designs within and downwind of the Los Angeles (LA) basin. A Bayesian inverse method is employed to quantify the relative ability of each network to improve constraints on flux estimates. Ground-based column CO_2 observations provide useful complementary information to surface observations due to lower sensitivity to localized dynamics, but column CO_2 observations from a single site do not appear to provide sensitivity to emissions from the entire LA megacity. Surface observations from remote, downwind sites contain weak, sporadic urban signals and are complicated by other source/sink impacts, limiting their usefulness for quantifying urban fluxes in LA. We find a network of eight optimally located in-city surface observation sites provides the minimum sampling required for accurate monitoring of CO_2 emissions in LA, and present a recommended baseline network design. We estimate that this network can distinguish fluxes on 8 week time scales and 10 km spatial scales to within ~12 g C m^(–2) d^(–1) (~10% of average peak fossil CO_2 flux in the LA domain)

Detecting Urban Emissions Changes and Events With a Near‐Real‐Time‐Capable Inversion System

In situ observing networks are increasingly being used to study greenhouse gas emissions in urban environments. While the need for sufficiently dense observations has often been discussed, density requirements depend on the question posed and interact with other choices made in the analysis. Focusing on the interaction of network density with varied meteorological information used to drive atmospheric transport, we perform geostatistical inversions of methane flux in the South Coast Air Basin, California, in 2015–2016 using transport driven by a locally tuned Weather Research and Forecasting configuration as well as by operationally available meteorological products. We find total‐basin flux estimates vary by as much as a factor of two between inversions, but the spread can be greatly reduced by calibrating the estimates to account for modeled sensitivity. Using observations from the full Los Angeles Megacities Carbon Project observing network, inversions driven by low‐resolution generic wind fields are robustly sensitive (p < 0.05) to seasonal differences in methane flux and to the increase in emissions caused by the 2015 Aliso Canyon natural gas leak. When the number of observing sites is reduced, the basin‐wide sensitivity degrades, but flux events can be detected by testing for changes in flux variance, and even a single site can robustly detect basin‐wide seasonal flux variations. Overall, an urban monitoring system using an operational methane observing network and off‐the‐shelf meteorology could detect many seasonal or event‐driven changes in near real time—and, if calibrated to a model chosen as a transfer standard, could also quantify absolute emissions.Key PointsLA CH4 flux estimates differ by driving meteorology but agree when calibrated for model sensitivityAliso Canyon leak can be detected by inversions using operational meteorologyOperational meteorology driven inversions significantly detect seasonal emission changes even with only one sitePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149534/1/jgrd55279-sup-0001-Text_SI-S01.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149534/2/jgrd55279.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149534/3/jgrd55279_am.pd

Monitoring of Geoengineering Effects and their Natural and Anthropogenic Analogues

A number of climate intervention concepts, referred to as “geoengineering,” are being considered as a potential additional approach (beyond mitigation of greenhouse gas emissions) to manage climate change. However, before governments go down the path of attempting deliberate climate intervention including precursor field-experiments, it is essential that the scientific community take the necessary steps to validate our understanding that underpins any of the proposed intervention concepts in order to understand all likely consequences and put in place the necessary strategies for monitoring the expected and unintended consequences of such intervention. The Keck Institute for Space Studies (KISS) has sponsored a project to identify specific priorities for improved scientific understanding and focused efforts to address selected priorities. This project does not advocate the deployment of geoengineering, outdoor geoengineering experiments, or monitoring systems for such proposed geoengineering field experiments, but is rather a precautionary study with the following goals: 1) enumeration of where major gaps in our understanding exist in solar radiation management (SRM) approaches, 2) identification of the research that would be required to improve understanding of such impacts including modeling and observation of natural and anthropogenic analogues to geoengineering, and 3) a preliminary assessment of where gaps exist in observations of relevance to SRM and what is needed to fill such gaps. This project focuses primarily on SRM rather than other proposed geoengineering techniques such as carbon dioxide removal from the atmosphere because there exist a number of analogues to the SRM methods that currently operate on Earth that provide a unique opportunity to assess our understanding of the response of the climate system to associated changes in solar radiation. Additionally, the processes related to these analogues are also fundamental to understanding climate change itself being of central relevance to how climate is forced by aerosol and respond through clouds, among other influences. In other words, this research has likely powerful co-benefits for climate science writ large. The study phase of the project was executed in 2011 and consisted of two workshops at Caltech (May 23-26 and November 15-18) as well as several smaller meetings and telecons. Participants in the study included individuals with an established track record of geoengineering research (primarily modeling studies), experts in the theory and observation of related physical processes, as well as engineers with expertise in risk management and systems analysis. Graduate students and post-doctoral fellows were active participants in the study. Four major topics that were identified during the workshops as priorities for subsequent research and development, particularly in regards to addressing related observational gaps: 1. Volcanoes as analogues of geoengineering with stratospheric aerosols 2. Ship tracks and cloud/aerosol interactions in general as analogues of geoengineering with marine-cloud brightening 3. Studying more targeted geoengineering interventions to counteract specific consequences of climate change, and 4. Identifying the satellite-based albedo monitoring needs that would be required for monitoring either a geoengineering test or its natural and anthropogenic analogues. Major volcanic eruptions that inject sulfate aerosol into the stratosphere cool the planet and are one of the motivating examples behind geoengineering. Much more could be learned about the intentional introduction of stratospheric aerosols through a combination of more thorough analysis of existing data, and development of a rapid-response observing strategy to maximize what we can learn from a future large eruption. Gaps in our knowledge include the evolution of aerosol size, the interaction with cirrus, water vapor, and ozone, and tropospheric chemistry more broadly. There are also attribution challenges that need to be understood, as the conditions following volcanic eruptions are not the same as those due to SRM (e.g. the presence of ash, or the discrete vs continual injection). The second main concept put forth for geoengineering is to introduce aerosols (e.g. salt) to change the optical depth of marine clouds; the current analog for this effect is ship tracks and other cloud/aerosol interactions. There is potential for further analysis of existing data to better understand these interactions and assess the science behind this SRM approach. The sensitivities of cloud albedo to specific processes and parameters are poorly understood. There are also observational gaps, such as the entrainment rate, or direct measurement of albedo, that limit our current ability to assess this approach. Third, it is important to understand what the actual goals for a possible eventual implementation of SRM might be, since SRM would quite possibly be deployed in response to a particular concern, rather than a generic desire to restore the overall climate. The highest priority identified during the study program was to focus on the high risk, high impact potential for a “tipping point” associated with Arctic permafrost melt, and the potential for geoengineering to reverse this. Other tipping points involving Arctic sea-ice and the Greenland and Antarctic ice-sheets may also warrant targeted intervention studies. Finally, one of the specific gaps in our observational capability is the ability to monitor albedo accurately enough to measure and attribute changes, with sufficient spatial, spectral, and temporal resolution. This capability is needed for all of first three SRM topics

Definition, Capabilities, and Components of a Terrestrial Carbon Monitoring System

Research efforts for effectively and consistently monitoring terrestrial carbon are increasing in number. As such, there is a need to define carbon monitoring and how it relates to carbon cycle science and carbon management. There is also a need to identify capabilities of a carbon monitoring system and the system components needed to develop the capabilities. Capabilities that enable the effective application of a carbon monitoring system for monitoring and management purposes may include: reconciling carbon stocks and fluxes, developing consistency across spatial and temporal scales, tracking horizontal movement of carbon, attribution of emissions to originating sources, cross-sectoral accounting, uncertainty quantification, redundancy and policy relevance. Focused research is needed to integrate these capabilities for sustained estimates of carbon stocks and fluxes. Additionally, if monitoring is intended to inform management decisions, management priorities should be considered prior to development of a monitoring system