Emissions of greenhouse gases from human activities have increased the proportion of the atmosphere occupied by carbon dioxide by one-ten-thousandth part since 1750 (Keeling & Whorf, 2004, updated). This minuscule perturbation may cause a small, harmless, and beneficial warming (Monckton, 2008). Greenhouse gases also include water vapor, the most significant greenhouse gas because of its volume, and methane, of which the atmospheric concentration ceased to increase in 2000 and is now declining (IPCC, 2007). Greenhouse gases are not pollutants, but occur naturally in quantities greater than those emitted from fossil fuel combustion and industrial and agricultural processes.
The evidence is incontrovertible: global cooling is occurring (GISStemp, HadCRU, RSS, UAH, NCDC). Though a natural warming trend of ~0.5 øC per century began in 1700, long before humankind could possibly have had any significant effect on global temperature (Akasofu, 2008), there has been no new record year for global temperature since 1998 and, since late 2001, there has been a downtrend. The cooling between January 2007 and January 2008 was the sharpest since records began in 1880.
Therefore no action need be taken to mitigate "global warming", for there is no evidence in the instrumental record that humankind has caused any significant increase in the 300-year-long natural warming rate, and no theoretical reason why future greenhouse-gas emissions should prove harmful. In any event, mitigating actions would be orders of magnitude less cost-effective than adaptation as, and if, necessary (all economists except Stern, 2006). The atmospheric concentration of carbon dioxide was ~18 times today's in the Cambrian era (IPCC, 2001). Humankind was not responsible - we were not there. The planet came to no harm. Significant disruptions in the Earth's physical and ecological systems, social systems, security and human health are unlikely to occur.
Because the complexity of the climate makes accurate long-run prediction impossible (Lorenz, 1963), the APS urges caution in relying upon computer models when making long-term climate predictions. There is no basis for the oft-repeated contention that the effects of human activity on the Earth's climate are likely to be great enough to influence the future climate. The APS therefore urges governments and peoples to provide the technological options for meeting real short-term and long-term environmental challenges, of which "global warming" from greenhouse-gas enrichment is not one. The APS also urges governments, universities, national laboratories and its membership to support policies and actions that will reduce the current official misinformation and unscientific alarmism about emission of greenhouse gases.