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. Burning fossil fuels and chopping down trees lead to the release of this greenhouse gas. Both activities exploded after the 19th Century, so it's unsurprising that atmospheric CO2 increased over the same period.