There are many different greenhouse gases, the most well-known of which is carbon dioxide. Different greenhouse gases affect the climate in different ways. Some remain in the atmosphere for a long time, but do not cause as much warming per kilogram of emissions as carbon dioxide, for example.  Others, such as methane, warm the Earth greatly but do not stay in the atmosphere for very long. There is a certain exchange rate that allows for comparison of different gases.  The exchange rate expresses how many kg of carbon dioxide emissions warm the climate as much as 1 kg of another greenhouse gas. The exchange rate is called the global warming potential and is usually abbreviated as GWP. By knowing the GWP of different gases, the overall climate impact of a product can be summarized in a single unit: kilograms of carbon dioxide equivalents (kg CO₂e).