Which of the following is NOT a greenhouse gas?

Q. Which of the following is NOT a greenhouse gas? 

(A) Methane
(B) Sulphur Hexafluoride
(C) Nitrous Oxide
(D) Carbon Monoxide

Answer: Carbon Monoxide

Greenhouse Gases

Greenhouse gases reflect radiation that the Earth emits, and stop it from being lost into space. This causes the Earth's temperature to be higher than it would be without greenhouse gases. The name for this is the "greenhouse effect."

Most greenhouse gases are natural - water vapour is the most common, and causes most of the greenhouse effect on Earth.

Other greenhouse gases are carbon dioxide, methane, nitrous oxide, chlorofluorocarbon and ozone.

Perfluorocarbons (PFCs) and sulphur hexafluoride (SF6) are greenhouse gases with atmospheric lifetimes of more than 1000 years. They are powerful greenhouse gases and today's emissions will still be affecting earth's climate in the next millennium.

Carbon monoxide (CO) is only a very weak direct greenhouse gas but has important indirect effects on global warming. Carbon monoxide reacts with hydroxyl (OH) radicals in the atmosphere, reducing their abundance. As OH radicals help to reduce the lifetimes of strong greenhouse gases, like methane, carbon monoxide indirectly increases the global warming potential of these gases.

Without greenhouse gases, the earth would be on average 33 degrees Celsius colder. Life, as we know it would probably not be possible on Earth, for heat, is important for life. Natural emissions of greenhouse gases vary. For example, the great volcanic eruptions that created the Siberian Traps a quarter billion years ago may have released enough gases to partly cause the Permian–Triassic extinction event which killed most life on Earth.

However, humans are adding greenhouse gases to the atmosphere. Mainstream science believes that this has caused the planet's average temperature to rise by increasing the greenhouse effect. The most important greenhouse gas that humans add to the atmosphere is carbon dioxide which is less than 0.4% of the atmosphere. Carbon dioxide is released when people burn fossil fuels, like oil, coal, and natural gas. Carbon dioxide emissions come mostly from transportation, energy and industries. Among these, the largest contributor is from meat production. The Food and Agriculture Organization said emissions associated with livestock added up to 7.1 gigatonnes (GT) of carbon dioxide equivalent (CO2-eq) per year – or 14.5% of all human-caused greenhouse releases. This exceeds the 13% that comes from global transport (including all cars and planes) each year.

Water vapour is the most abundant of these gases but merely reacts to climate change. In other words, when the atmosphere is warm, there is more water vapour. Thus there is a higher possibility of clouds and precipitation.