Carbon dioxide surface, warming the surface and the lower atmosphere. Less energy reaches the upper atmosphere, which is therefore cooler because of this absorption. Increases in atmospheric concentrations of and other long-lived greenhouse gases such as methane, nitrous oxide and ozone have correspondingly strengthened their absorption and emission of infrared radiation, causing the rise in average global temperature since the mid-20th century. Carbon dioxide is of greatest concern because it exerts a larger overall warming influence than all of these other gases combined and because it has a long atmospheric lifetime (hundreds to thousands of years). Not only do increasing carbon dioxide
ExoMars Trace Gas Orbiter be a strong indication that biological processes are involved. However, if methane is found in the presence of gases such as sulfur dioxide (), that would be an indication that the methane is a byproduct of geological processes. The nature of the methane source requires measurements of a suite of trace gases in order to characterise potential biochemical and geochemical processes at work. The orbiter has very high sensitivity to (at least) the following molecules and their isotopomers: water (), hydroperoxyl (), nitrogen dioxide (), nitrous oxide (), methane (), acetylene (), ethylene (), ethane (), formaldehyde (), hydrogen cyanide