IPCC Expert Meeting on Geoengineering

Annex 4: Poster Abstracts
Categorization of policy responses to climate change with a focus on
geoengineering
Olivier Boucher 1 * and Piers Forster 2
1
Laboratoire de Météorologie Dynamique, IPSL / CNRS / Université P. et M. Curie, Paris, France
2
University of Leeds, United Kingdom
Potential policy responses to anthropogenic climate change can be broadly classified into four categories: additional
research into climate sciences and carbon-free or carbon-neutral sources of energy, mitigation (i.e. reduction in
anthropogenic emissions of greenhouse gases), adaptation (i.e. reduction of the impacts of climate change on natural and
societal systems), and geoengineering.
Geoengineering is usually defined as the intentional large-scale manipulation of some element of the Earth system, in an
attempt to counteract the effects of anthropogenic climate change. It is sometimes also referred to as climate intervention,
climate engineering or planetary engineering. To qualify as geoengineering, an intervention into the Earth system has to
deliberately attempt to tackle climate change by a method that does not seek to reduce anthropogenic emissions of
greenhouse gases or other warming agents. For instance, the emission of anthropogenic aerosols from burning fossil fuels,
although responsible for a cooling effect, is not considered to be geoengineering because it is a by-product of our industrial
and transportation systems rather than a deliberate action. The intervention, although it can be localized, also has to have
a large-scale effect on the climate system. This clearly distinguishes geoengineering from, e.g., weather modification or
other sorts of environmental engineering which attempt to modify the atmosphere or the land surface on a much smaller
scale.
A number of geoengineering schemes have been proposed in the scientific literature. Their technological maturity,
effectiveness, scalability, residual impacts, unintended consequences and cost vary a great deal and remain uncertain. The
Royal Society report (2009) on geoengineering categorized geoengineering schemes into solar radiation management
(SRM) and carbon dioxide removal (CDR) techniques. SRM schemes seek to artificially modify the solar radiation budget to
cool the planet. CDR schemes seek to artificially remove carbon dioxide from the atmosphere and store it in some form.
While the distinction between SRM and CDR is useful, it does not cover all potential geoengineering schemes one can think
of. For instance, it has been suggested that the terrestrial radiation budget could also be artificially modified through
changes in cirrus clouds and/or atmospheric water vapor in order to decrease the greenhouse effect. Carbon dioxide is not
the only long-lived greenhouse gas in the atmosphere, and air removal can also be envisaged for methane (Boucher and
Folberth, 2009) or other gases.
Figure A.4.2 lists a large number of approaches to climate change and attempts to refine their groupings into distinct
categories. It appears that there is not always a clear division between geoengineering and adaptation or between
geoengineering and conventional mitigation. For instance, it has been suggested that the Earth’s albedo could be artificially
increased over land by increasing the reflectivity of human dwellings (Akbari et al., 1999) or cropland (Ridgwell et al.,
2009). These modifications may actually be more relevant to local and regional adaptation to climate change than
geoengineering. Furthermore the frontier between geoengineering and mitigation is not very clear when it comes to
biofuels. The large-scale exploitation of biofuels associated with carbon capture and storage (CCS) has the potential to
remove CO 2 from the atmosphere and qualifies as a CDR scheme, even though biofuels and CCS on their own are usually
considered as conventional mitigation tools.
In conclusion we argue that it is important to develop a clear terminology on policy responses to climate change, while
recognizing that the frontier between these responses is not always clear-cut. We will provide in this presentation a first
attempt at developing such a terminology. This will help to decide how geoengineering should fit (or not) in the portfolio of
existing climate change policies. Multiple factors have to be considered when comparing these policy responses, including
their technological maturity, effectiveness, scalability, timescale for implementation, risk, residual climate change,
unintended consequences, degree of interference with the climate system, the policy and governance challenges they pose,
and their cost.
References
Akbari H., S. Konopacki, and M. Pomerantz, 1999: Cooling energy savings potential of reflective roofs for residential and
commercial buildings in the United States. Energy 24, 391–407.
<strong>IPCC</strong> <strong>Expert</strong> <strong>Meeting</strong> on Geoengineering - 45