How do you know that carbon dioxide and other greenhouse gases are to blame, and not other factors, such as volcanoes, solar output or natural cycles?
Climate models help answer this question. Factors such as volcanic eruptions, solar radiation and changes in Earth’s orbit are fed into the supercomputer models. When they are run without the observed increases in carbon dioxide and other greenhouse gases in the atmosphere, the models do not produce a warming trend. When the greenhouse gases are added, the models reproduce the observed warming. Thus, these results show that rising levels of greenhouse gases, produced by human activities, are warming the planet. Greenhouse gases, by their nature, allow shortwave (mostly ultraviolet) radiation from the sun to pass through the atmosphere to the Earth’s surface. This radiation is re-emitted by the Earth as long-wave (infrared) radiation, which is trapped and absorbed by greenhouse gases, making the Earth’s surface warmer. So it’s logical to expect that a planet with increasing levels of greenhouse gases would become warmer. An example is Venus, which is dramatically hotter than can be acco
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