Four Comments to the AGU draft policy statement
„Geoengineering Responses to Climate Change Require Enhanced Research, Consideration of Societal Impacts, and Policy Development„
I) As reflected in the wording of the draft statement, the issues summarized under the label ‚geoengineering‘ go well beyond sound understanding of the non-linear dynamics of the Earth climate system. However too little emphasis is given that how climate change may affect various socio-ecological systems is incompletely understood including how governance  may handle surprises, sudden changes and irreducible uncertainties. Furthermore, the non-linear dynamics and particular features of the socio-ecological systems will render obsolete handling strategies that are engineering-like . Other handling strategies are available for such ‚wicked problems‘, which are reflexive, resilient, responsive, revitalizing and rescaling . The policy statement should express through its language that that ‚engineering-like approaches‘ could not handle adequately climate change issues. Furthermore, the stamen should strengthen its wording regarding research into ‚historical, ethical and social implications‘ of any handling strategies including any engineering-component.
II) When considering engineering-components as part of a more comprehensive handling strategy then a distinction should be made between technologies that tackle the problem ‚at-the-start-of-the pipe‘, ‚at-the-end-of-the-pipe‘, or ‚modify-other-parts-of-a-complex- system‘. Technologies for ‚carbon dioxide removal‘ belong to the second category and ’solar radiation management‘ to the third. When considering how environmental problems (e.g. acid rain, stratospheric ozone destruction) were handled in the past, successful approaches involved technologies ‚at-the-start-of-the pipe‘. In the context of climate that are technologies, which capture carbon at moment of combustion to store it away. The policy statement should refer to such technologies (‚at-the-start-of-the pipe‘), including their preference as ‚common sense‘.
III) Carbon dioxide emissions cause warming of the globe and acidification of the world ocean . ‚Solar radiation management‘ addresses only one of these major threats; ‚Carbon dioxide removal‘ addresses both. The policy statement should mention this structural difference between the approaches for geoengineering that the statement addresses.
IV) As reflected in the wording of the draft statement, the current limited success of adaptation and mitigation policies indicates a weakness of the current governance systems; a weakness that is found at global, regional and local scale. Research is needed how to strengthen governance across scales and among actors [1, 5]. Governance is a key-issue for anthropogenic change  including intended change like geoengineering of any kind and in particular for ’solar radiation management‘. It would be surprising that governance of geoengineering policies would function when governance of adaptation and mitigation policies has deemed weak. The policy statement should strengthen its argumentation regarding research of ethical legal and social implications.
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