Today on Fareed Zakaria GPS, economist Jeff Sachs of Columbia University added some economic detail to the earlier hurricane intensity model developed by Kerry Emanuel of MIT (here). Sachs inserted economic growth in the model and argued that glacier melting and coastal development increase hurricane impacts with higher sea level and more homes built on prime development land near the Ocean. The causal model above puts the two arguments together (click to enlarge) and shows the multiple positive impacts of economic growth on hurricane intensity and storm damage.
TECHNICAL NOTE: When reading causes off directed graphs, be aware that there are parameters associated with each arrow (discussed below) and that the parameters have either implicit positive signs or explicit negative signs. When you travel down a path, the parameters are multiplied together to determine the amount and direction of causation. For example, from CO2 Emissions -> Flooding in the graph above there are two negative signs that get multiplied together to create a positive effect.
The role of the parameters can be seen from simpler Impact Models (e.g., the IPAT equation, the Kaya Identity and the Environmental Kuznets Curve);
In Impact Models, population growth (N) leads to economic growth (Q) leads to Energy use (E) leads to CO2 emissions (C). By the rules of path analysis, N(qec) -> C where q is productivity (output per capita), e is Energy Efficiency (E/Q) and c is Emission Intensity (C/E). These can be influenced by technological change. The effect of population growth on CO2 emissions then depends on whether technological change increases more rapidly than the population growth rate.
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