The document discusses the greenhouse effect, carbon cycle, and rising global temperatures. It notes that scientists have debated whether temperature rise is natural or human-caused. The 2007 IPCC report concluded global warming is very likely due to human activities like fossil fuel use that emit greenhouse gases like carbon dioxide, disrupting the natural carbon cycle. The greenhouse effect occurs as certain gases trap infrared radiation emitted from the Earth's surface, and rising CO2 levels from activities such as deforestation and burning fossil fuels are enhancing the greenhouse effect.