The Kyoto Protocol limits sinks credits against targets to those due to 'direct human-induced . . . change'. In retrospect, this may be among the most problematic passages on sinks in the agreement. As we reviewed in Section 8.3, strong interactions of nature and management mean clearly that separating carbon uptake into these two categories is impossible. Felzer et al. (2005) estimate the tropospheric ozone damage effect to be substantial, and while the extent remains controversial, CO2 fertilization as usually modelled strongly enhances vegetation growth and carbon uptake. Climate change itself will affect plant growth. These are probably what the framers of the Protocol considered 'indirect' effects and thus meant to exclude. However, it does not seem as easy to dismiss the US interpretation, where simply protecting property rights is a direct human action that might lead to carbon sequestration, or at least prevent deforestation and carbon release.
Even if one were to take a very narrow definition of actions - a specific forest established with the express intent of sequestering carbon - and one could somehow assess 'intent', the 'direct human-induced' language would seem to require the ability to attribute some part of the carbon sequestered to the direct human action. It would mean subtracting out that due to indirect actions (nitrogen deposition, CO2 fertilization), or even giving credit for more than was sequestered if some indirect action (e.g. tropospheric ozone) damaged vegetation which would have otherwise taken up carbon. One would need to at some level confront the reality that once trees are planted, it is mostly nature that takes over and grows them, and so the distinction of what is due to direct human action and what to nature or indirect action is necessarily fuzzy. In reality, vegetation growth is a collaborative effort of humans and nature, where the result is not uniquely attributable to either collaborator. Trying to create rules and then measure and attribute carbon uptake to different causes would seem to be a distraction, adding to the cost of monitoring and, if anything, creating cost inefficiency. With clear property rights for land, and the ability of the landowner to sell allowances for anything sequestered on it above the established baseline, or pay for emissions above (or sequestration less than) the baseline, that landowner (or the country in the case of national targets) has an incentive to fix the problems that lead to damage. Again drawing the comparison with forest and agricultural products, products harvested by the landowner can be sold and are not subject to a test of whether the products were 'human-induced'. The public good nature of the 'indirect' human effects such as air pollution requires collective action to solve, and including all carbon sequestration or emission within an incentive structure would not automatically solve these problems. But, with landowners losing or gaining depending on whether these other environmental problems are solved, it would at least provide a motivation for them to support collective action on pollution.
As previously noted, the concern of limiting sinks to direct human action as in Kyoto would appear to arise from the fact that negotiators focused first on emissions and reduction goals, and having agreed to those, tried to bring sinks into the format. With that approach, making sure sinks credits were for uptake beyond 'business as usual' was a necessary consideration. In retrospect, however, this gave rise to language that has proved nearly impossibly to implement. The problematic language could be avoided if the caps are reformulated as caps on total emissions from fossil and land use net of sinks. This will mean, however, rethinking the targets because, as shown in Table 8.1, a given percentage below 1990 emissions will have very different implications if applied to all emissions and sinks than if only applied to fossil emissions.
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