IPCC Expert Meeting on Geoengineering

Annex 5: Breakout Group Reports
Breakout Group I.1: Solar Radiation Management Options and Methods
Chair: Govindasamy Bala
Rapporteur: Piers Forster
The summary that follows, written by the Chair and Rapporteur, characterizes the main points of the BOG I.1 discussion. It
may not reflect the personal views of the BOG’s Chair and Rapporteur. The summary is intended for consideration by <strong>IPCC</strong>
authors of the Fifth Assessment Report (AR5), but is neither endorsed nor approved by the <strong>IPCC</strong> or its Working Groups.
Participants in the BOG considered a series of questions related to geoengineering research, developed by the meeting’s
Scientific Steering Group.
Questions suggested for discussion:
What are the most important Solar Radiation Management approaches that <strong>IPCC</strong> authors might want to consider in
the AR5?
What are the most important aspects of these approaches to evaluate (e.g., physical impacts, time scales, system
boundaries, spatial scales, direct/private costs)?
Can the most important aspects of these issues be supported by reference to the peer-reviewed literature, ideally
drawing from multiple lines of independent evidence? What is the available evidence and what are relevant
references?
Introduction
This BOG discussed Solar Radiation Management (SRM) focusing on determining techniques <strong>IPCC</strong> authors might consider,
overall framework and terminology that could be employed, and ways different impacts could be assessed.
Terminology
The group briefly discussed terminology. The group felt comfortable with “geoengineering” as a term describing a variety
of mechanisms that deliberately affect climate at a large scale. The group discussed the boundaries of this term when
impacts of a given technique are more regional than global. However, the group did not see the necessity of forcing an
exact definition; a loose definition may serve the community.
As some proposed techniques, such as cirrus thinning, affect long wave radiation, the term SRM was discussed. The BOG
suggested that the term “Radiation Management” may be more appropriate.
Scope
Much discussion focused on what was and was not in the scope of approaches that <strong>IPCC</strong> authors might want to consider in
the AR5. Generally it was felt that the <strong>IPCC</strong>’s AR5 reports should be as comprehensive as possible with regard to SRM, but
focused on the most plausible schemes that are supported by the literature. Extensive discussion of speculative schemes or
those with little potential of either deployment and/or impact would be less useful for policymakers.
Approaches supported by literature that the <strong>IPCC</strong> could consider are: space mirrors/generic total solar irradiance (TSI)
experiments; stratospheric aerosol techniques via injection of gases, particles and/or special particles; cloud whitening,
especially marine stratocumulus; direct tropospheric aerosol effects from sea-salt or sulphate; reducing cirrus amount or
thickness; increasing crop albedo, land-surface albedo, or ocean surface albedo (e.g., ocean bubbles or painting roofs
white). It was felt that within these techniques, stratospheric aerosol and cloud whitening had more extensive literature.
Some suggested assessment of ideas that, although small on the global scale, may be relevant for regional adaptation and
mitigation, such as the possible role of urban surface albedo enhancement in urban heat island mitigation.
<strong>IPCC</strong> <strong>Expert</strong> <strong>Meeting</strong> on Geoengineering - 70