Final answer:
Greenhouse gases absorb outgoing infrared radiation from the Earth, trapping heat and causing warming, known as the greenhouse effect. This does not cancel out the effects of incoming sunlight because the Sun's peak emission is in the visible spectrum, while the Earth's is in the infrared.
Step-by-step explanation:
When discussing greenhouse gases and infrared radiation, we are considering the way these gases influence the energy balance of the Earth's atmosphere. Incoming sunlight has a temperature of approximately 5800 K, peaking in the visible spectrum, while Earth emits radiation at about 300 K, peaking in the infrared spectrum. Greenhouse gases absorb and re-emit this outgoing infrared radiation, effectively trapping heat and warming the planet.
However, while greenhouse gases do block both the incoming and outgoing infrared radiation, these effects do not cancel each other out. This is because the sunlight that reaches Earth is not primarily infrared; it's mainly visible light which passes through the atmosphere relatively unimpeded. The Earth, however, radiates energy back into space in the infrared spectrum, which greenhouse gases are effective at absorbing. This imbalance leads to more energy being retained within the atmosphere, thus causing a net increase in temperature, known as the greenhouse effect.
The key concept here is the blackbody radiation laws, which tell us that an object emits radiation across a spectrum of wavelengths based on its temperature. The Earth and the Sun, acting as blackbodies, emit different spectrums, thereby interacting differently with greenhouse gases. This differential interaction contributes to the warming of our planet.