There are many uncertainties regarding the magnitude of future climate change, its consequences and the costs, benefits and implementation barriers of possible solutions. Future emissions to the atmosphere are inherently uncertain and can only be explored on the basis of scenarios. The change in concentration of GHGs that would result from a given emission rate is much less uncertain. But the timing, extent, and distribution of climate change and sea level rise for a given concentration of GHGs is not well known due to limitations in modelling climate change at the regional level. The impacts of climate change on ecosystems and humanity is known with limited certainty. The potential for an unspecified, low-probability, but catastrophic turn of events haunts the problem.
While uncertainties are great, they are not distributed evenly throughout the problem. The cost implications of emissions mitigation are better known than the more distant (in time) potential benefits from mitigation. In part this is because of temporal proximity, but it is also because most of the costs associated with emissions mitigation pass through markets, whereas many of the benefits do not. Some uncertainties will remain unresolved regardless of the decisions made. This follows directly from the fact that there is only one observed history. All the other potential histories are counterfactual, and therefore constructs from analytical tools that are limited in their veracity. In decision making terms the problem of climate change mitigation requires decision making under uncertainty. Given the long lead times of mitigation action, fully resolving uncertainties would make an adequate response infeasible.
Many global biogeochemical processes have long time scales. Sea level changes as a consequence of changes in mean global temperature can take more than 1000 years to play out. Similarly, changes in the concentration of GHGs can rise rapidly, but decline slowly. And, even if concentrations can be reduced, the nature of the climate system is such that it might not return to the same climatic state associated with an earlier concentration.
The UNFCCC has been ratified by more than 170 parties and entered into force in 1994. It provides the institutional foundations upon which international climate change negotiations occur. It sets as its ultimate objective the stabilization of the concentration of GHGs in the atmosphere at levels that prevent dangerous anthropogenic interferences with the climate. However, the UNFCCC establishes a process and does not create the institutions for implementing the objective. The objective has not yet been quantified. The term dangerous is left open to interpretation by the parties.
The Kyoto Protocol of December 1997, described in Chapter 1, represents a further important step in the international regime formation under the UNFCCC. The Kyoto Protocol has brought a number of new elements and broadened the context of the decision-making process regarding implementation of climate change policy. Ultimately, further institutional development is needed for the UNFCCC to meet its final objective.
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