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Thematic Guide to Integrated Assessment Modeling
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How Integrated and Over What Dimensions?
Many assessments try to integrate "end-to-end," looking together at the causes and consequences of atmospheric change. In effect, they try to perform benefit-cost analysis of proposed emission controls, to estimate the optimal level of emissions control (balancing emissions abatement with other measures such as adaptation or geoengineering) and the optimal means of carrying it out. This goal requires end-to-end assessment: looking simultaneously at emissions and opportunities to abate them, and at the cost of climate change and measures to adapt to it.But no policy-maker has responsibility for this entire job. Most real decision problems are more limited, either because an abatement target has been established and the only decisions to make concern finding cost-minimizing measures to meet it, or because some climate change is bound to fall on a specified place, group, or sector, and the only decisions to be made concern finding optimal ways to adapt and respond. For people whose responsibilities take either of these forms, end- to-end integration is not necessary, because one side of the benefit-cost equation is fixed.
On the other hand, the highest level political decisions cannot consider climate change in isolation, so end-to-end integration might not be sufficient either. To help the highest level of decisions, assessments would have to consider climate change together with other environmental issues and human concerns. Perhaps the most effective way to integrate assessments to inform such decisions would be to consider broad sectoral areas of activity such as energy or agriculture, and assess their impacts on multiple environmental issues.
But even broader integration may be necessary. The most basic question about climate change is "How important is it?" Helping senior policy-makers deal with this question requires not just integration across environmental issues but across the aggregate set of other impacts on human well-being that are liable to occur over the same time horizon. Expressing projected consequences in universal metrics like economic losses or lives at risk is an attempt to achieve such universal comparability, but is only partly successful.
The next section is Integrated Assessment and Integrated Models.