evidence: Natural processes on Earth constantly create and destroy GHGs. For example, plant and animal matter decay produce carbon dioxide, which plants then absorb during photosynthesis. This natural cycle stabilizes atmospheric levels of carbon dioxide. Climate change scientists at the National Aeronautics and Space Administration (NASA) and other federal and international agencies recognize that natural factors, including volcanic activity and shifts in the planet's crust, continue to play a role in climate change. However, they generally agree that these factors alone do not explain the substantial rise in Earth's temperature. Natural causes of climate change are referred to as naturogenic, while causes of climate change related to human activity are called anthropogenic. [...] Increased levels of other GHGs, such as nitrous oxide and methane, have also resulted from human activity. Several agricultural and industrial processes, such as the use of certain fertilizers in farming, produce extensive amounts nitrous oxide. Methane emissions come from fossil fuel production, landfills, and livestock. Though much smaller quantities of these gases exist in Earth's atmosphere, some scientists believe they cause more harm than carbon dioxide. Methane, for example, is about twenty-one times as potent as carbon dioxide at trapping heat. Humans have also created and released GHGs that do not occur in nature. These include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). These gases, released during industrial processes such as aluminum production and electrical transmission, trap thousands of times more heat in the atmosphere than carbon dioxide.