Greenhouse Gas Endangerment Finding, Part 4:
Scientific causation
7 Jun 2009 in Regulatory Science
A careful look at parts of EPA's proposed endangerment finding show the causal chain that the Agency believes is scientifically sufficient. This causal chain has interesting implications for air pollution policy more generally.
We last posted on the distinction between effects on "public health" and "welfare," and how this distinction appears to be muddied in EPA's proposed endangerment finding. We found text in the proposal that seems to indicate that muddying the distinction between "public health" and "welfare" is a purposeful act on the Agency's part. We speculated that EPA might want to do this because "mere" welfare effects might not appear to be important enough to justify the scope, scale, and economic effects of the regulations it intends to issue to implement the finding.
We've returned to a portion of this text to look at EPA's scientific logic, which conveniently the Agency has expressed with unusual parsimony:
All public health risks and impacts described here as a result of elevated atmospheric concentrations of greenhouse gases occur via climate change. The pathway or mechanism occurs through changes in climate, but the end result is an adverse effect on the health of the population. Thus these effects from climate change are appropriately denoted public health effects (p. 18901).
Taking into account the evidence cited elsewhere in the text, we can summarize this scientific logic in a series of bullets for the most serious health effect of all -- premature death:
- Greenhouse gas emissions from US mobile sources cause climate change.
- Climate change causes increased summer temperatures.
- Increased summer temperatures cause more premature mortality.
- Premature mortality is (obviously) a public health effect.
- Therefore, greenhouse gas emissions from US mobile sources cause premature mortality.
A similar set of bullets can be crafted for each of the other indirect effects of climate change posited by EPA by modifying bullets #3 and #4 accordingly.
EPA's scientific logic is novel at least in part because heretofore it has never counted indirect effects on health as "public health" effects. One of the consequences of novelty, of course, is that its full ramifications usually are not understood until later. Nonetheless, it is easy to imagine that if EPA establishes this logical precedent, it could backfire when the time comes to promulgate regulations restricting the emission of greenhouse gases from mobile sources.
Using premature death as the public health endpoint of concern as in the example above, the regulation of greenhouse gases could be shown to cause premature mortality:
- Reducing greenhouse gas emissions from motor vehicles requires regulations that directly or indirectly increase fuel economy.
- Regulations increasing fuel economy will be implemented by reducing the size and mass of motor vehicles.
- Occupants of smaller and lighter motor vehicles are more likely to die in crashes than occupants of larger and heavier motor vehicles.
- Mortality is (obviously) a public health effect.
- Therefore, regulations to reduce greenhouse gas emissions from US mobile sources cause premature mortality.
The scientific logic is identical. The lawyers at EPA will have to figure out a way to use it to support the endangerment finding but reject it later when it comes up in the context of specific regulatory actions, and do so without being arbitrary and capricious.
