In response to my post Erroneous Claim in an AP News Article, I have been asked if I consider if the human addition of CO2 is a first order climate forcing. The answer, of course, as I have consistently emphasized in my research papers and presentations, and on my weblog, is a categorical YES (e.g. see, see, see and see).
The human addition of CO2 is a positive radiative forcing as well as a biogeochemical forcing. It is a first order human climate forcing.
The AP statement itself has two parts:
1. “ the vast majority of scientists agree that global warming is occurring
2. “that the primary cause is a buildup of greenhouse gases in the atmosphere from the burning of fossil fuels, such as oil and coal.”
Item 1 is correct if the time scale is over the last century. Global warming since mid-2003, however, based on the diagnosis of the upper ocean heat content, has halted, at least up through mid 2009.
Item 2 is the “myth”. Even with respect to global warming during the last 100 years, the addition of CO2 is just one of a number of positive radiative forcings (e.g. see), and natural forcings appear to be more significant than previously understood (e.g. see). The statement that the “primary cause” of global warming is a buildup of greenhouse gases is incomplete and, therefore, incorrect.
Thus, while I agree that the human addition of CO2 is a first order climate forcing, the claims that it is the primary human climate forcing is not supported by the science. This means that attempts to “control” the climate system, and to prevent a “dangerous intervention” into the climate system by humans that focuses just on CO2 and a few other greenhouse gases will necessarily be significantly incomplete, unless all of the other first order climate forcings are considered.
Moreover, as I have written on extensively, climate change is much more than global warming and cooling (e.g. see and see). Human caused climate change can occur even in the absence of global warming (such as from land use change). This makes attempts to mitigate climate change a much more daunting problem than assuming that all we need to do is control the human emissions of CO2 from fossil fuel combustion into the atmosphere.
For the summary overview of my perspective see Main Conclusions.
Climate Science: Roger Pielke Sr. 