Preparing Climate Engineering Responses to Climate Emergencies II: Impact Detection/Attribution and Field Testing

Through a one-week intensive study, the authors of this abstract explored the question: What program of comprehensive technical research over the next decade would maximally reduce the uncertainties associated with climate engineering responses to climate emergencies? The motivations underlying this question, our group's focus on climate engineering concepts for manipulating incident short-wave solar radiation, and our in-depth consideration of stratospheric aerosol interventions as a case example are all described in a previous presentation (Keith et al. in this session). This second of two presentations on our study group's findings concentrates specifically on our technical evaluation of the issues associated with climate impact detection and attribution. Our analyses begin by examining the natural variability (noise) and equilibration timescales (temporal response) of a number of specific climate parameters (e.g. surface radiative flux, surface temperature, atmospheric ozone concentrations, etc.) at both the global and regional scales. First, using the assumption of immediate response for all climate parameters, order-of-magnitude signal-to-noise ratio calculations are used to estimate the minimum intervention durations and amplitudes needed for climate impacts of predicted magnitude to be attributably detected. Next, a number of relevant processes (physical, chemical and biological) within the climate system are evaluated to provide order-of-magnitude estimates for the actual temporal response of these climate parameters (e.g. delay in global temperature response due to ocean heat capacity). Cumulatively, these first-order quantitative estimates reveal a number of basic limits to the timescale over which equilibrium climatic parameter impacts of a climate engineering intervention could be detected. Building from these basic results, we examine current climate monitoring capabilities across four broad categories of climate parameters: (1) radiative; (2) geophysical; (3) geochemical; and (4) ecological. The utility of present monitoring capabilities (e.g. the AeroNet network and ARM) for field-tests are considered, including the proposal and quantitative evaluation of methods for achieving maximal understanding from minimal amplitude tests (e.g. intermittent interventions with phase-sensitive "lock-in" detection methods to maximize sensitivity). Finally, large gaps between current monitoring capabilities and the basic detection limits are identified in each of these categories, and new detection systems are proposed to fill those gaps.