[T]aking the world’s temperature is not as easy as it sounds. Different parts of the planet warm at different rates, as do different layers of the atmosphere, so all sorts of corrections have to be applied to arrive at a single number. A truly simple, and arguably better, approach would be to use concentrations of greenhouse gases—the cause of the warming—as putative maxima. These gases mix rapidly into the atmosphere, so are easily sampled in ways that brook little dissent. Goal difference, 'the Economist, 5 December
I disagree, partly because greenhouse gases are not the sole cause of warming: we do not know, for instance, how big are the relative contributions of deforestation (through changes in albedo as well as carbon emissions) or different cloud types. Some proportion of climate change also comes from natural (non-anthropogenic) events. At least as importantly, our views about the greenhouse gases' relative contributions change dramatically with our growing scientific knowledge. There would, then seem to be a pragmatic basis, as well as the case for broader public engagement, for instead targeting for reduction the impacts on human, animal and plant life of adverse climatic events.
Climate Stability Bonds could set such impact reduction goals. If, in time, and with the market's incentives on offer, bondholders decide that the best way of achieving such goals is to reduce certain greenhouse gas emissions, then that is what they will do. But it would seem hubristic and inefficient for governments or UN bodies to assume that that this is the best way of achieving meaningful reductions in those impacts. There are too many uncertainties, and the science upon which such a policy is based is inescapably ossified. See also my other recent posts on this question.