Find a carpool in Michigan, USA:

The measurable climate change in recent decades and projected future that has seen temperatures of the Earths atmosphere rise considerably. It is believed that abnormaly high levels of carbon dioxide and other greenhouse gasses in the Earth's atmosphere are a cause of global warming.

Cars are a major contributor to carbon dioxide in our attmosphere. Carpooling is one effort that results in lower carbon dioxide production by reducing the number of cars used to carry passengers on their commutes.

An explanation of how global warming works