Why do greenhouse gases absorb and re emit infrared light and how much of the sun's radiation energy is absorbed by the greenhouse gases to warm the planet?
Greenhouse gases absorb and re-emit infrared light because of their molecular structure. Greenhouse gas molecules have three or more atoms, and they are arranged in a way that allows them to vibrate in certain ways. These vibrations can absorb infrared photons, which are packets of energy that have the same wavelengths as the vibrations.
Once a greenhouse gas molecule has absorbed an infrared photon, it vibrates more vigorously. After a short time, the molecule releases the photon's energy by emitting another infrared photon in a random direction. This means that infrared radiation that is emitted from the Earth's surface can be absorbed and re-emitted by greenhouse gas molecules in the atmosphere, trapping some of the heat and warming the planet.
The amount of the Sun's radiation energy that is absorbed by greenhouse gases to warm the planet varies depending on the concentration of greenhouse gases in the atmosphere and other factors, such as cloud cover. However, it is estimated that greenhouse gases absorb about 100% of the Sun's incoming longwave infrared radiation.
The following are the main greenhouse gases:
- Water vapor (H2O)
- Carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)
- Ozone (O3)
Water vapor is the most abundant greenhouse gas in the atmosphere, but it is also the shortest-lived. Carbon dioxide is the second most abundant greenhouse gas, and it has a much longer lifespan in the atmosphere. Methane and nitrous oxide are less abundant greenhouse gases, but they are much more potent than carbon dioxide at trapping heat.
Human activities, such as the burning of fossil fuels, deforestation, and agriculture, are increasing the concentrations of greenhouse gases in the atmosphere. This is causing the planet to warm, and it is leading to a variety of climate change impacts, such as more extreme weather events, rising sea levels, and changes in plant and animal life.
To reduce greenhouse gas emissions and mitigate climate change, we need to transition to a clean energy economy and reduce our reliance on fossil fuels. We also need to protect and restore forests, which absorb carbon dioxide from the atmosphere.
In fact, carbon dioxide, as, absorbs energy at a variety of wavelengths between 2,000 and 15,000 nanometers a range that overlaps with that of infrared energy. As CO2 soaks up this infrared energy, it vibrates and re-emits the infrared energy back in all directions. Much of this infrared radiation does not reach space, however, because it is absorbed by greenhouse gases in atmosphere, and is then emitted as infrared radiation back toward the Earth's surface. This process is known as the greenhouse effect.Visible light passes through the gases in the atmosphere and heats the earth up to 300K. The earth emits infra-red light which does not pass through Carbon Dioxide. So Carbon Dioxide traps some of the heat which would otherwise have radiated away from Earth. Greenhouse gases reflect infrared radiation, so some of the heat leaving the Earth bounces off the greenhouse gases in our atmosphere and comes back to the Earth's surface. This is called the “greenhouse effect,” in a comparison to the heat-trapping glass on a greenhouse. Infrared as the thermal emission from our planet ass incident solar radiation hits Earth, some of this energy is absorbed by the atmosphere and the surface, thereby warming the planet. This heat is emitted from Earth in the form of infrared radiation. About a third of the Sun's energy (30%) is reflected back into space. The rest of the Sun's energy (20%) is absorbed by greenhouse gases in the atmosphere, like carbon dioxide, water vapor, and methane. Greenhouse gases in the atmosphere also absorb and hold some of the heat energy radiating back from Earth's surface. However, the amount that directly escapes to space is only about 12 percent of incoming solar energy. The remaining fraction a net 5-6 percent of incoming solar energy is transferred to the atmosphere when greenhouse gas molecules absorb thermal infrared energy radiated by the surface. About half the light energy reaching Earth's atmosphere passes through the air and clouds to the surface, where it is absorbed and radiated in the form of infrared heat. About 90% of this heat is then absorbed by greenhouse gases and re-radiated, slowing heat loss to space. As CO2 soaks up this infrared energy, it vibrates and re-emits the infrared energy back in all directions. About half of that energy goes out into space, and about half of it returns to Earth as heat, contributing to the 'greenhouse effect. A greenhouse gas is called that because it absorbs infrared radiation from the Sun in the form of heat, which is circulated in the atmosphere and eventually lost to space. CO2, CH4 and H2O absorb at infrared frequencies because the electrical field acts on the polar chemical bonds. These will excite vibration and rotational movements of the molecule, which then also radiate at these infrared frequencies. The greenhouse effect is a process that occurs when gases in Earth's atmosphere trap the Sun's heat. This process makes Earth much warmer than it would be without an atmosphere. The greenhouse effect is one of the things that makes Earth a comfortable place to live. Of the 340 watts per square meter of solar energy that falls on the Earth, 29% is reflected back into space, primarily by clouds, but also by other bright surfaces and the atmosphere itself. About 23% of incoming energy is absorbed in the atmosphere by atmospheric gases, dust, and other particles.