carbon dioxide

Take a deep breath and exhale slowly. Your body just released carbon dioxide, a colorless gas that's essential to life on Earth. Carbon dioxide is one of the greenhouse gases that absorbs and holds heat in Earth's atmosphere, keeping our planet warm enough for life to exist. But humans are increasing carbon dioxide levels in the atmosphere above natural levels. As carbon dioxide levels rise, so do global temperatures.

Image credits: main image, © AMNH/Stephanie Fotiadis.