The most important global warming pollutants are: carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and the halocarbons (CFC's and their various substitutes). These compounds are present in minute quantities in the atmosphere, measured in parts-per-million (ppm), parts-per-billion (ppb), or even parts-per-trillion (ppt). Despite these small concentrations, their impact is large.

The three dominant gases (CO₂, CH₄, and N₂O) are naturally present in the atmosphere. To understand the impact of human pollution, we need to compare current concentrations with prior levels.

Carbon dioxide has increased from about 280 ppm to 382 ppm. It is increasing about 1.5 ppm/year. CO₂ is the most significant greenhouse gas, responsible for about 60% of global warming.

Methane has increased from about 700 ppb to 1,745 ppb. It has been increasing about 7 ppb/year. Recently that rate appears to have slowed.

Nitrous oxide has increased from about 270 ppb to 314 ppb. Its rate of increase is about 0.8 ppb/year.