Climate change is widely seen as the central environmental issue of our time. The international community has been following a range of strategies for some time now aimed at reducing anthropogenic greenhouse gas emissions (mitigation) and measures for adapting to climate changes which have already occurred or are expected to occur (adaptation) in order to manage climate change and its varied impacts. Despite the various climate protection efforts, however, the rise in greenhouse gas concentrations in the atmosphere has not been halted. In principle, other potential actions are available for counteracting the associated global warming. These include targeted technical interventions in the climate system, known as geoengineering or climate engineering (CE) which covers two systematically different approaches:

• Carbon dioxide removal (CDR) technologies are aimed at removing already emitted CO₂ from the atmosphere.
• Radiation management (RM) technologies, on the other hand, seek to change the Earth's radiation balance.

Against this backdrop, the Committee for Education, Research and Technology Assessment of the German Bundestag commissioned TAB to conduct a TA study into geoengineering. The focus of the project was the question of whether and under what conditions climate engineering could or should assist in averting the threat of a climate catastrophe.

Results

Fundamentally, the technological and scientific knowledge relating to the impacts and side effects of CE technologies are still at a rudimentary stage. Decades of (experimental) research would presumably still be required to achieve substantial scientific knowledge in terms of technical developments and the assessment of climate engineering.

According to the current state of knowledge, probably none of the CDR concepts under discussion would be capable of achieving a relevant reduction in global temperatures. Nevertheless, certain measures could prove to be meaningful and, under certain circumstances, important climate protection tools to complement emission reduction action in the longer term.

Initial computer simulations indicate that certain RM options could generate a significant and rapid reduction in the temperature of the Earth, though this would have an uneven distribution around the globe. At the same time, there would be changes in other climate variables for which there is an almost complete lack of knowledge to date with regard to their quality and regional prevalence. Furthermore, all climate engineering measures which require large-scale or global application would most probably always entail sometimes serious environmental side effects and far-reaching impacts on human living conditions if implemented.

Climate engineering can therefore be regarded as a potentially highly controversial issue and its unprecedented global nature can be expected to trigger major public concern. The policy objective, therefore, ought to be to establish a discourse and communication process within society as a whole in order to achieve the broadest possible consensus on how to proceed with these technologies.