The World Meteorological Organization (WMO), in its new 2006 Greenhouse Gas Bulletin, reports:
In 2006, globally averaged concentrations of carbon dioxide (CO2) in the atmosphere reached their highest levels ever recorded … 381.2 parts per million (ppm), up 0.53 per cent from 379.2 ppm in 2005.
Note this is a one-year rise of 2.0 ppm, continuing the accelerated trend of the past decade, which is due to increases in global economic activity and carbon intensity, together with decreased efficiency of natural sinks, like the ocean.
CO2 is the single most important infrared absorbing, anthropogenic gas in the atmosphere and is responsible for 63% of the total radiative forcing of Earth by long-lived greenhouse gases. Its contribution to the increase in radiative forcing is 87% for the past decade and 91% for the last five years. For about 10,000 years before the industrial revolution, the atmospheric abundance of CO2 was nearly constant at ~ 280 ppm.
We have radically altered the composition of the atmosphere, and the bill is coming due.