Carbon dioxide climate trends. Animated graph showing the effects on the Earth磗 climate of increasing levels of atmospheric carbon dioxide between 1980 and 2005. The year is across bottom, with petagrams of carbon per year PgC/yr at left. The first curve yellow is fossil fuel emissions the known amount of carbon dioxide released into the atmosphere. The second curve red is the atmospheric increase measured in the atmosphere. The green region is the difference between the two, the 磗ink?representing carbon dioxide taken out of the atmosphere by natural processes not all of which are fully known. The sequence ends with the addition of the El Nino Southern Oscillation ENSO Index blue, numbers at right with bars indicating when each El Nino occurred. This graph shows strong correlation between the ENSO Index and the spikes in atmospheric carbon dioxide increase. This may be due to a reduction in the carbon sink processes. Carbon dioxide is a greenhouse gas that contributes to global warming and climate change.