Royal Society - David Keith

The two major classes of geoengineering methods have
distinct characteristics, summarised in Box 5.2.
As there is now intense interest being shown in
geoengineering, there is an immediate need for the
establishment of frameworks and mechanisms by which the
public and other stakeholders can be informed and engaged,
and R&D and deployment can be responsibly considered
within the broader context of climate change action.
To help guide decisions regarding whether to proceed with
geoengineering research or deployment decision makers
are advised to consider the following (refer to Annex 8.1
for more detail):
1. Legality of the method proposed (national/regional/
international);
2. Effectiveness (proven/unproven);
3. Timeliness (of implementation and climate effect);
4. Environmental, social and economic impacts
(including unintended consequences);
5. Costs (direct financial and carbon life cycle);
6. Funding (support for R&D and security over term for
deployment);
7. Public acceptability (novelty/containability/scale of
intervention/control frameworks);
8. Reversibility (technological, political, social and
economic).
When developing climate change strategies, and
considering a potential role for geoengineering, decision
makers are advised to also consider the following:
a) The appropriate balance of the relative contributions of
mitigation, adaptation, and both CDR & SRM methods
of geoengineering;
Box 5.2 Characteristics of the two major classes of geoengineering methods
CDR methods
• treat the cause of climate change by removing greenhouse gases;
• would only slowly become fully effective (many decades);
• would reduce ocean acidification (and other CO2 related problems);
• would not suffer from the ‘termination problem’;
• would lead to reduced plant productivity (compared to the elevated level expected with high CO2 concentrations);
• for ecosystem-based methods, would likely involve major impacts on natural ecosystems, and may involve tradeoffs
with other desirable ecosystem services;
• for “engineered” methods, may require the construction of substantial infrastructure, and/or the secure disposal of
large quantities of CO 2 ;
• would probably have costs similar to (or greater than) those of mitigation;
• can mostly be tested easily at small and medium scales;
• for engineered (air capture) methods would probably not require international agreement (until the atmospheric CO2
level had declined to near the preindustrial level).
SRM methods
• could mostly be deployed relatively quickly and would take effect rapidly;
• could provide a fairly good approximate cancellation of increased temperatures, but could not generally cancel
changes of other aspects of climate (eg, precipitation) at the same time;
• would create an artificial (and only approximate) balance between greenhouse warming and reduced solar
radiation, which might have to be maintained, potentially for many centuries;
• would create a risk of severe and rapid greenhouse warming if and when they ever ceased operation suddenly
(the ‘termination problem’);
• would do little or nothing to reduce atmospheric CO2 levels, or the associated problem of ocean acidification;
• could prove to be relatively inexpensive (compared to the costs of mitigation);
• would most probably require international cooperation when conducted beyond national boundaries or when
impacts are transboundary.
The Royal Society
Geoengineering the Climate I September 2009 I 55