Carbon Dioxide (CO₂) is a confounding adversary: 

• It is almost always invisible, odorless, and feels weightless—it is imperceptible except as bubbles and dry ice, until it reaches a concentration of about 1%.
• It is an essential nutrient for plants and is part of the breath we exhale.

• Small amounts matter a lot—before coal, oil and gas were discovered it made up less than 0.03% (about 280 parts per million) of the atmosphere.   Raising that concentration to even 0.05% would dramatically alter climates and ecosystems.  The current level is about 0.0385% (385 parts per million).
• The carbon dioxide released by burning fossil fuels, especially coal, petroleum, and natural gas, comes from carbon that was buried by natural processes over millions of years.
• Once in the atmosphere, it lasts for decades before being absorbed again by these natural processes.
• Other gases also contribute to global warming and are tabulated by their effect using their “CO₂-equivalent impact (CO₂e).”  Methane and nitrous oxide are the most significant of these other gases.  Both are mostly by-products of agricultural practices and waste disposal.  An equal mass of methane has a 72 times more powerful impact, and nitrous oxide a 289 times greater impact, over a 20-year period than carbon dioxide (Methane is often shown to have a 21 or 23 times impact, but that is over a 100 year period.  Methane does not last as long in the atmosphere as CO₂ so its immediate impact is more intense than the 100-year value would indicate.  )