evidence: Greenhouse gases - which trap the Sun's heat - are the crucial link between temperature rise and human activities. The most important is carbon dioxide (CO2), because of its abundance in the atmosphere. We can also tell it's CO2 trapping the Sun's energy. Satellites show less heat from the Earth escaping into space at precisely the wavelengths at which CO2 absorbs radiated energy. [...] They reveal there would have been little global warming - and possibly some cooling - over the 20th and 21st Centuries, if only natural factors had been influencing the climate.