In its Proposed Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Sections 202(a) of the Clean Air Act , the Environmental Protection Agency (EPA) places six greenhouse gases into one basket. All are treated as equal, primary culprits in the anthropogenic enhancement of the earth’s greenhouse effect, and thus the EPA proposes to find that they “endanger the public health and welfare of current and future generations.” The six are carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.
But for many reasons, one of these gases is not like the others and should be considered separately. That gas is carbon dioxide.
The Green Greenhouse Gas
Carbon dioxide (CO2) is essential to life on earth as we know it. It is a necessary ingredient in the photosynthetic recipe that produces the oxygen that we breathe as well as the carbohydrates that we eat. The more CO2 in the atmosphere, the better plants grow. And better-growing plants are, obviously, a boon for the planet’s animal life (including humans).
Interestingly, not only does carbon dioxide make plants grow better and be more productive, but it makes them more resistant to other environmental stressors. More CO2 reduces the negative impacts on plants from air pollution including low-level ozone concentrations (EPA sees low-level ozone concentrations rising under global warming). More CO2 improves the water-use efficiency of plants, that is, they require less water to go about their business (EPA sees global warming as placing a growing burden on our water supply). More CO2 also enables plants to survive (or, in some cases, even thrive in) higher temperatures (the EPA sees future temperatures rising).
(For a long, long list of scientific references in support of my claims concerning CO2 and plants, and for other positive impacts I failed to mention, please visit the CO2 Science webpage – far and away the web’s most thorough documentation of the interaction between carbon dioxide and the earth’s plant species)
So, not only does CO2 directly improve the productivity of the earth’s plant life, but it also helps mitigate many of the impacts of environmental changes identified by the EPA—and both of these responses lead to positive downstream impacts on the rest of the planet. So regulations aimed at reducing atmospheric CO2 levels also are aimed at reducing these benefits.
These effects are unique to carbon dioxide among the EPA’s collection of GHGs. Thus CO2 should not be grouped together with the other five GHGs, and instead it should be judged independently as to its impacts on public health and welfare. Atmospheric CO2 increases have overwhelmingly positive impacts on the earth’s ecology which lead to similarly positive impacts on public health (e.g., better producing food crops) and welfare (which the Clean Air Act defines as including “effects on soils, water, crops, vegetation, man-made materials, animals, wildlife, weather, visibility, and climate…”—of which better-growing plants positively impacts many of the listed items).
So the far-reaching benefits from increasing atmospheric CO2 would have to be weighed against any negative consequences—i.e., oceanic acidification (see here for why this concern is on wobbly legs), and presumably those arising from its role in enhancing the global greenhouse effect and the resulting impacts on the climate—to which the EPA has built a rather long list (even though scientific support for many of the items on the list is far less than EPA establishes, see here for example).
But let’s look a little closer at CO2’s role in climate change and climate change impacts.First, consider that CO2 makes up less than one-half of the total warming pressure (positive climate forcing) attributed to anthropogenic activities. According the IPCC’s numbers (which are relied upon by the EPA) the total positive anthropogenic climate forcing increase (which includes not only GHGs, but also the impacts from black carbon aerosols, tropospheric ozone, and stratospheric water vapor) since pre-industrial times totals about 3.16 W/m2, of which CO2 makes up 1.66W/m2, or 53%.
But, new research (highlighted in the Proposed Endangerment) by Ramanathan and Carmichael concluded that the warming impact of black carbon aerosols was underestimated by the IPCC. Incorporating the results of Ramanathan and Carmichael, the total positive forcing from anthropogenic activities becomes about 3.86 W/m2, which means CO2 only makes up 43% of the total. By extension, therefore, CO2 is only responsible for a modest 43% of the total climate change.
This has direct consequences to EPA’s Proposed Endangerment, for in it the EPA admits that:
The Administrator also acknowledges that warming temperatures may bring about some health benefits. Both extremely cold days and extremely hot days are dangerous to human health. But at least in the short run, modest temperature increases may produce health benefits in the U.S. (and elsewhere).
The Administrator acknowledges that as for human health, so too for welfare: moderate temperature increases may have some benefits, particularly for agriculture and forestry over the short term…
And “modest” or “moderate” temperature increases are all the CO2 alone has to offer!
Of note is that the EPA keeps repeating “in the short-term” not to refer to the benefits from modest warming, but to indicate that the EPA doesn’t think that the temperature increase will be modest for very long—but if they only considered CO2, it probably would be.
According to the Proposed Endangerment, the EPA Administrator has to find that an air pollutant “may reasonably be anticipated to endanger public health or welfare” in order to take regulatory action. However, making this case for CO2 presents the EPA with a far greater task than is the case now when CO2 is thrown into the same basket as methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.
To make a fair and scientifically just finding, the EPA must consider its Golden Egg on its own merits. If it were forced to do so, the EPA would be faced with a situation in which the benefits of enhanced atmospheric CO2 concentrations quite possibly overcome any negative conseqences.
IPCC, 2007. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Solomon, S., et al. (eds), Cambridge University Press, Cambridge, U.K., 996pp.
Ramanathan, V., and G. Carmichael, 2008. Global and regional climate changes due to black carbon. Nature Geosciences, 1, 221-227.