The ultimate source of heat in the process of global warming is greenhouse gasses. Correct answer: D The greenhouse gasses are gasses that have the property of absorbing infrared radiation emitted from Earth's surface and reradiating it. They include water vapour, carbon dioxide, methane, nitrous oxide, ozone and some artificial chemicals such as chlorofluorocarbons (CFCs) and are the main reason for the greenhouse effect, which is a natural process that warms the Earth's surface.