Geoengineering: guidance exists.

![Figure][1] CREDIT: INGA SPENCE/ALAMY In their Policy Forum “End the deadlock on governance of geoengineering research” (15 March, p. [1278][1]), E. A. Parson and D. W. Keith recognize the environmental and policy risks posed by geoengineering methods and lay out a course of action to address them. They argue that a void in international governance of research exists and that geoengineering operations are subject to no international legal control. They further assess no progress in defining the boundary between small and large activities. In fact, relevant guidance does exist. The 1977 Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques—the so-called ENMOD Convention—is an international agreement that already governs aspects of geoengineering. The Convention was the result of a several-year policy development, set in motion by interest in the national security implications of geoengineering. The U.S. government investigated geoengineering techniques ([ 1 ][2]) and used weather modification (cloud seeding) as a weapon during the Vietnam War in the late 1960s and early 1970s ([ 2 ][3]). The Convention, recognizing the issue of scale, prohibits weapons uses that would have “widespread, long-lasting, or severe” effects. An agreed Understanding specifies that, for the purposes of the Convention, these terms refer to an area of several hundred square kilometers, a duration of months or about a season, and severity as “serious or significant disruption or harm to human life, natural and economic resources or other assets” ([ 3 ][4]). Parties commit to the “fullest possible” exchange of relevant information on peaceful geoengineering and to feasible international scientific and economic cooperation. If geoengineering research, let alone experiments or possibly operations, is to proceed, the ENMOD Convention and its negotiating history provide precedents and information. The need for a moratorium on geoengineering for weapons purposes is moot. The authors' discussion of a social bargain recognizes the importance of “international norms of cooperation and transparency.” Arms control already applies to geoengineering: Fortunately, one cooperative norm is already in place. 1. [↵][5]1. S. Weart , “The Discovery of Global Warming: Climate Modification Schemes” (2011); [www.aip.org/history/climate/RainMake.htm][6]. 2. [↵][7]1. D. Shapley , Science 184, 1059 (1974). [OpenUrl][8][FREE Full Text][9] 3. [↵][10]Federation of American Scientists, Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques (1980); [www.fas.org/nuke/control/enmod/text/environ2.htm][11]. [1]: pending:yes [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: #xref-ref-1-1 "View reference 1 in text" [6]: http://www.aip.org/history/climate/RainMake.htm [7]: #xref-ref-2-1 "View reference 2 in text" [8]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.aulast%253DShapley%26rft.auinit1%253DD.%26rft.volume%253D184%26rft.issue%253D4141%26rft.spage%253D1059%26rft.epage%253D1061%26rft.atitle%253DWeather%2BWarfare%253A%2BPentagon%2BConcedes%2B7-Year%2BVietnam%2BEffort%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.184.4141.1059%26rft_id%253Dinfo%253Apmid%252F17736187%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [9]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6MzoiUERGIjtzOjExOiJqb3VybmFsQ29kZSI7czozOiJzY2kiO3M6NToicmVzaWQiO3M6MTM6IjE4NC80MTQxLzEwNTkiO3M6NDoiYXRvbSI7czoyNDoiL3NjaS8zNDAvNjEzMi81NDguMS5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30= [10]: #xref-ref-3-1 "View reference 3 in text" [11]: http://www.fas.org/nuke/control/enmod/text/environ2.htm