Learning about marine cloud brightening: detectability of field experiments, benefits and risks of implementation

• Main Author: VIJAYAN NAIR, ASWATHY
• Other Authors: Universität Leipzig
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2017
• Subjects: marine cloud brightening; detectability; field experiments; risks and benefits; info:eu-repo/classification/ddc/530; ddc:530; Arctic; Pacific; Climate change
• Online Access: https://nbn-resolving.org/urn:nbn:de:bsz:15-qucosa2-210857; https://ul.qucosa.de/id/qucosa%3A21085; https://ul.qucosa.de/api/qucosa%3A21085/attachment/ATT-0/

The main objectives of the thesis are to learn about the detection of a hypothetical marine cloud brightening (MCB) field experiment and to assess the benefits and risks of an actual implementation using model simulations. The first aim of the thesis is to assess the detectability of MCB from the natural variability of clouds using satellite data. The analysis uses two approaches, i) an analytical method, assessing the radiative forcing by aerosol-cloud interactions for an idealised perturbation of the droplet concentration and ii) a stochastic method, including the radiative forcing and the cloud adjustment effects of perturbing the cloud droplet number concentration. One of the main findings of the study is that in the analytical method, detection of an MCB experiment in the North Pacific region requires longer duration, larger domain and larger intensity of the Nd perturbation than in the South Pacific and the South Atlantic regions. In the Stochastic method, larger domain size as well as longer duration are required for the detection of the hypothetical field experiments compared to the analytical method. We found that increasing the duration of the experiment and intensity of Nd perturbation has more influence in detectability than increasing the domain size. Secondly, we analyse the detection of MCB using ECHAM GCM simulations. Two methods are used for the analysis, i) a temporal method, using temporal reference of nine years for the analysis, and ii) a spatial method, where a surrounding unperturbed regions are used as a reference for the analysis. In the temporal method, the detectability of the MCB experiment over the North Pacific region is most difficult. Our calculations suggest that for an experiment to be cost effective, it is preferable to design an experiment of longer duration with smaller domain sizes as well as less intensity of perturbation of Nd. Finally, we investigate the effectiveness of MCB in alleviating the changes in the mean and extremes for surface air temperature and precipitation. We compare these results with another climate engineering technique, namely stratospheric aerosol injection. The study is based on an existing multi model simulation of three Earth system models. The main conclusion from the study is that the two solar radiation management techniques are rather effective in mitigating the climate change driven increases in the mean and extremes of temperature and precipitation according to the climate simulations. However, the potential to mitigate differs around the globe and seasonally. The strong increases in lower temperature extremes, especially in the Arctic, are not well dampened with the solar radiation management implementation.