Defining dangerous anthropogenic interference.

Dangerous Anthropogenic Interference The United Nations Framework Convention on Climate Change (UNFCCC) commits signatory nations (which includes all major nations including the United States) to stabilizing greenhouse gas concentrations at levels short of DAI. To properly define DAI, one must take into account issues that are not only scientific, but, as I have argued elsewhere (2), economic, political, and even ethical in nature. Defining DAI begs the question, for example, ‘‘Dangerous to whom?’’ It amounts to the tacit adoption of some level of risk, risk that will not be shared equally among all nations and people. The Intergovernmental Panel on Climate Change (IPCC) is charged by the United Nations Environment Program (UNEP) to assess climate change risks in a way that informs, but, importantly, does not prescribe the government policies necessary to avoid DAI. It is therefore not surprising that the IPCC stops short of defining what DAI actually is, let alone advocating policies designed to avoid it. The determination of climate change risk involves the process of ‘‘integrated assessment’’ (3), that is, taking theoretical climate model-based projections of future climate change, using appropriate approaches to assess the likely environmental, societal, and economic impacts, then attributing a level of risk to society and/or our environment presented by these potential impacts. Uncertainties exist at each step, and propagate through this process. Despite claims often heard to the contrary, however, uncertainty is hardly an excuse for inaction. Indeed, careful economic analyses indicate that the current uncertainties surrounding climate change render sizeable near-term investments to mitigate greenhouse gas emissions a sound economic strategy, due to the possibility of low-probability, high-impact events that cannot be ruled out (4–7). In the IPCC third assessment report, Smith et al. (8) first presented the now famous ‘‘burning embers diagram,’’ a graphic, easily digested representation of the level of threat or risk associated with future projected anthropogenic climate change with respect to five different categories or ‘‘reasons for concern’’ (RFCs) which include: (i) risk to unique or threatened systems (e.g., the loss of endangered species, unique ecosystems, indigenous communities, and island nations), (ii) risk of extreme weather (e.g., more extreme heat waves, f loods, and droughts, and more intense tropical cyclones), (iii) distribution of impacts (i.e., the degree to which impacts are differentially harmful to different nations,