Final answer:
The concentration of greenhouse gases determines the altitude at which IR radiation last interacts with these molecules before escaping to space. With higher concentrations of greenhouse gases like CO₂, this interaction point moves to a higher altitude; due to cooler temperatures at that level, the Earth's surface becomes warmer to maintain thermal equilibrium.
Step-by-step explanation:
When the concentration of greenhouse gases increases, most of the infrared (IR) radiation that escapes to space last interacted with a greenhouse gas molecule at a higher altitude. This phenomenon is critical to understanding the concept of global warming. As the concentration of CO₂ in the atmosphere increases, it captures more of the IR radiation that Earth emits. Since IR radiation absorption by CO₂ and other greenhouse gases warms the atmosphere, an increase in their concentration means that their warming effect becomes stronger. Because of the increased absorption, the point from which IR radiation can finally escape into space moves to a higher altitude.
In the troposphere, the temperature generally decreases with altitude, resulting in the radiation escaping from a cooler region when originating from a higher altitude. This causes the rate of emission to space to decrease, meaning that to maintain the balance between incoming solar radiation and the outgoing emission, the surface of the Earth must warm up further. The relationship is not linear but logarithmic, indicating that further increases in CO₂ concentration will continue to raise the effective emission altitude and consequently the surface temperature of Earth. This intricate balance plays a major role in the concept of the greenhouse effect, which keeps the Earth's surface warmer than it would be without an atmosphere.
Greenhouse gases like water vapor, carbon dioxide, methane, and ozone all contribute to this greenhouse effect. Since the Industrial Revolution, human activity, especially the burning of fossil fuels, has rapidly increased the levels of CO₂ and other greenhouse gases causing significant changes in the Earth's climate. Consequently, as the surface temperature rises, so does the water vapor pressure in the atmosphere, leading to a feedback loop that further increases the surface temperature.