Almost all motorized transportation today involves the combustion of fossil fuels, which produces energy to be transformed into motion. This combustion is the reaction of the hydrogen and carbon present in the fuels with oxygen in the air to produce–in the ideal world–water vapour (H2O) and carbon dioxide (CO2). Neither of these products is damaging to human health. However, CO2 is the principal gas responsible for the “greenhouse” effect, an increase in the average temperature of the planet resulting from the trapping of solar energ y, with which the increased presence of this gas in the atmosphere is.
