'The human health benefits of the President's plan do not largely stem from the reduction in carbon dioxide emissions. After all, carbon dioxide is a colorless, odorless gas that is not dangerous to breathe. Instead, they are to come from the "co-benefits" of reducing some forms of air pollution that are emitted when fossil fuels are burned. But these by-product emissions are already subject to existing regulations and are being double-counted by the President. Further, direct health impacts from climate change are difficult to pin down -- and ethereal -- as adaptive measures can more than erase them.'