It's not actually. Water vapor is the only significant green house gas on Earth.
The Fourth National Climate Assessment (
USGCRP, 2017:
Climate Science Special Report: Fourth National Climate Assessment, Volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 470 pp, doi:
10.7930/J0J964J6.) is a summary review of the current state of climate research. It illustrates the chaotic state of current climate studies.
The executive summary reflects this chaos in its useless and self evident opening sentence:
"The climate of the United States is strongly connected to the changing global climate. "
The climate is changing. Thus the report acknowledges something that has been occurring for the last nine billion years and there is no reason to think it will not continue to occur for the next nine billion. What we would like to know is whether human activity is affecting the rate of climate change; in what direction, and to what extent. Climate modeling has not contributed anything of value toward answering that question, and it is doubtful it will, unless of course there is a breakthrough in our ability to model chaotic, multivariable systems. Other studies have, however, contributed to our understanding; yet we are still far away from the answers we seek. Let the research continue, and perhaps one day we will know the answers.
Sadly. the executive summary is silent where an important contribution to scientific progress might have been made. The summary misses the opportunity to call for less political interference.