Estimate composition of the Earth's atmosphere

The atmosphere is a layer of gas that surrounds the earth, and its current composition is one of the primary factors that allows for the existence of life on our planet. The atmosphere protects the earth's surface from solar radiation, it traps heat that maintains livable conditions in the absence of sunlight, and its current pressure allows for the existence of liquid water on the planet's surface. Over 99 percent of the earth's atmosphere is comprised of nitrogen (78 percent) and oxygen (21 percent), while argon makes up most of the rest at over 0.9 percent.

The <0.1 percent

For humanity's survival, it is the composition of gases that make up less than 0.1 percent of the atmosphere that are currently posing the greatest challenges. In particular, the human consumption of fossil fuels has resulted in the large-scale emissions of carbon dioxide (CO₂) and methane (CH₄) into the atmosphere, which is creating an imbalance in the world's carbon cycle and accelerating climate change at an unnatural rate. Although CO₂ makes up just 0.04 percent of the atmosphere and methane's share is just 0.00017 percent, the size of the atmosphere means that these exist in vast quantities.

Heat retention

In its most simple terms, heat enters the earth's atmosphere as waves of sunlight, is absorbed or reflected by the earth's surface, and reflected heat tries to leave the atmosphere as infrared waves. Nitrogen (N₂) and oxygen (O₂) exist in the atmosphere as molecules of two of the same atom and are not affected by either set of waves. In contrast, carbon dioxide and methane are made up of compounds of three and five atoms respectively, and have the ability to absorb infrared heatwaves reflected form the earth's surface due to their larger size. As methane compounds are larger than carbon dioxide, methane is considered a much more potent greenhouse gas, although its potency deteriorates over time as it breaks down more quickly. This potential for heat retention is measured as "global warming potential" (GWP) - methane has a GWP of 86 over 20 years, which means that one ton of methane traps the same amount of heat as 86 tons of CO₂, before it drops to a GWP of 34 over 100 years.