Definition of the Greenhouse Effect
The greenhouse effect is a natural process in which certain gases in Earth's atmosphere trap heat from the sun, warming the planet to support life. Without it, Earth's average temperature would be about -18°C instead of the current 15°C. It occurs when solar radiation passes through the atmosphere, warms the surface, and some of that heat is radiated back as infrared energy, which is absorbed and re-emitted by greenhouse gases.
Key Components and Principles
The primary greenhouse gases include water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases. These gases act like a blanket, allowing shortwave solar radiation to enter but absorbing and re-radiating longwave infrared radiation emitted from Earth's surface. This selective absorption maintains a stable climate, but imbalances can alter temperatures.
Practical Example: Earth's Energy Balance
Consider sunlight hitting Earth: about 50% is absorbed by the surface, warming oceans and land, which then emit infrared radiation. CO2 and other gases trap roughly 30% of this outgoing energy, preventing it from escaping to space. In a balanced system, this keeps temperatures habitable, as seen in Venus's extreme greenhouse effect, where runaway trapping leads to surface temperatures over 460°C.
Role in Global Warming
Human activities, such as burning fossil fuels and deforestation, increase greenhouse gas concentrations, enhancing the natural effect and causing global warming. This leads to rising average temperatures, melting ice caps, sea-level rise, and extreme weather. Since the Industrial Revolution, CO2 levels have risen from 280 ppm to over 420 ppm, amplifying the effect and contributing to about 1.1°C of warming observed since pre-industrial times.