The atmospheric carbon dioxide concentration has risen from about 280 parts
per million by volume (ppmv) to about 360 ppmv in the period from before
the Industrial Revolution to the present. This rise of nearly 30% in the
atmospheric concentration is a result of emissions of carbon dioxide from
human activities, both from combustion of fossil fuels and from the clearing
of forested land for agriculture and other uses. Emissions now total about 6
billion tons of carbon per year (GtC/yr). That the rise in concentrations is
occurring is confirmed by many types of measurements, including those of
the carbon dioxide concentration in the air over the past 40 years and in air
bubbles trapped in glacial ice over the past 1,000 years. The figure is from the
Working Group I contribution to the IPCC Second Assessment Report (1995).