On April 2, the Supreme Court ruled that the Environmental Protection Agency has authority under the Clean Air Act to regulate emissions of carbon dioxide, one of the “greenhouse gases” linked to global climate change. Some journalists and talking heads wrongly construed this as a requirement that the EPA regulate CO2 emissions.

The high court’s 5-4 ruling requires the EPA to give a reasoned scientific basis for not regulating carbon dioxide, and there are indeed legitimate reasons not to do so. Nonetheless, many are calling for the EPA to take action to regulate these emissions.

The federal Clean Air Act authorizes the EPA to regulate emissions that “cause, or contribute to, air pollution which may be reasonably anticipated to endanger public health or welfare.” Under this Act, however, there are a number of reasons why carbon dioxide emissions would be difficult if not impossible to regulate legitimately and fairly.

For one, there is no level of carbon dioxide emission that is reasonably anticipated to endanger public health. Or rather, the level of emissions known with any degree of certainty to cause human health or welfare concerns (asphyxiation, for example) is so high that regulating to this level would be meaningless: there are no sources of this level of emissions. What people are really concerned about are the effects of accelerated climate change, such as weather patterns, rising sea levels, elevated temperatures, and so forth, which global climate models link to increased concentrations of greenhouses gases such as CO2. However, there is likewise no specific level of carbon dioxide emissions that is known to be hazardous in this way. The only evidence of the dangers posed by CO2 emissions is from global climate models, and the outputs from these models vary widely. Determining a reasonable emissions level for CO2 necessary to avoid the potentially negative side effects of climate change is therefore not possible.

For this reason, establishing an emissions cap under the Clean Air Act is inappropriate. Further, these sought-after regulations would apply to single entities and sources. Carbon dioxide emissions, in terms of their relationship to climate, pose potential threats only in global sums. Thus it is not possible to assign any scientifically defensible emissions limit for an individual source.

Finally, there are many more natural sources of carbon dioxide than human sources. In fact, more than 95 percent of annual global carbon dioxide emissions are from these natural sources, including diffusion out of the oceans, respiration of biological organisms, and oxidation of soil organic matter. Other human sources of emission come from processes that would be nearly impossible to regulate. For example, agricultural tillage accelerates the release of carbon dioxide from the soil, yet the amount of emission depends on the type of tillage, weather, soil, and crops.

Attempting to set legitimate regulation of carbon dioxide emissions under the Clean Air Act would require extreme bureaucracy with no clearly identifiable benefits in the short or long term, and any level of CO2 emissions regulation under the Clean Air Act would have to be arbitrary. Arbitrariness should not be the hallmark of regulation, nor of the United States’ response to the concerns over greenhouse gases.