Solar heat reaches Earth in the form of visible and UV light. Some of this light is reflected back into space by clouds and light-scattering particles before it reaches Earth’s surface. Most of the light does reach Earth's surface, providing warmth for sunbathers and energy for photosynthesis in plants.
Once this energy warms the planet, it is then reflected off of Earth and back towards space in the form of longwave energy, or infrared light. Some of this infrared energy escapes into outer space, and some will be absorbed by molecules in the atmosphere. Most molecules in the atmosphere, such as nitrogen and oxygen, can not absorb this infrared energy. Greenhouse gases (CO2, H2O, and CH4) are "tuned" to absorb energy at infrared wavelengths. Absorbing energy "excites" these greenhouse molecules.
The excited molecule can either reemit the infrared wavelength. Or, the energy is released from "excited" greenhouse molecules through collisions with other molecules. Such collisions will transform the energy to heat; some of the heat is lost to space, some is directed downwards and warms earth's surface even more.
The concentration of CO2 has increased by about 38% since industrialization, from about 280ppm to 388ppm. Humans have burned enough fossil fuels to raise the concentration of CO2 to its present level. Only by including the raising concentration of greenhouse gases CAN we account for the recent rise in global temperatures.
The Earth also has a natural greenhouse gas effect. If the atmosphere completely lacked greenhouse gases, then the global temperature would then be about 30°C (55° Fahrenheit) cooler. Water would be locked away as ice, and life would probably not be possible.
Once this energy warms the planet, it is then reflected off of Earth and back towards space in the form of longwave energy, or infrared light. Some of this infrared energy escapes into outer space, and some will be absorbed by molecules in the atmosphere. Most molecules in the atmosphere, such as nitrogen and oxygen, can not absorb this infrared energy. Greenhouse gases (CO2, H2O, and CH4) are "tuned" to absorb energy at infrared wavelengths. Absorbing energy "excites" these greenhouse molecules.
The excited molecule can either reemit the infrared wavelength. Or, the energy is released from "excited" greenhouse molecules through collisions with other molecules. Such collisions will transform the energy to heat; some of the heat is lost to space, some is directed downwards and warms earth's surface even more.
The concentration of CO2 has increased by about 38% since industrialization, from about 280ppm to 388ppm. Humans have burned enough fossil fuels to raise the concentration of CO2 to its present level. Only by including the raising concentration of greenhouse gases CAN we account for the recent rise in global temperatures.
The Earth also has a natural greenhouse gas effect. If the atmosphere completely lacked greenhouse gases, then the global temperature would then be about 30°C (55° Fahrenheit) cooler. Water would be locked away as ice, and life would probably not be possible.