1. The sun and other natural forces cause global warming and cooling.
The sun provides nearly 100% of the heat reaching Earth's upper atmosphere. Many other factors (17 or more) determine how much of that heat is temporarily retained to provide warmth for an inhabitable planet. Some factors, such as the tops of low clouds, ice, and snow, reflect most of the incoming ultraviolet rays back into space before they can heat Earth's surface. Other surfaces reflect less. Greenhouse gases temporarily trap some of the heat that is absorbed into Earth's surface and is then radiated upward as infrared rays. This helps keep Earth's atmosphere warm instead of all of the radiated heat escaping to space. To see a summary of 18 factors, including CO2, that help determine Earth's climate drivers, climate and climate change, see below. Also, to view the reflectivity of Earth's various surfaces, referred to as Earth's albedo, see the chart below titled ALBEDO. To see expanded write-ups on each of the 18 drivers, refer to "Fire, Ice and Paradise" in the recommended reading list.