This graph shows the increase in the concentration of methane in the earth's atmosphere over the last 10,000 years (panel inset shows the increase since 1750) based on the study of ice cores. Different colors represent different studies. Radiative forcing indicates the influence a factor has on the amount of energy entering or leaving the earth's atmosphere and is an index of how important the factor is as a climate change mechanism. The higher it is, the more important it is.