We have all learned that the earth is getting heat up because of the CO2 and CO molecules absorbing heat. However, how is heat actually kept in those molecules. When photons heat them up, their electron gets excited and goes to a higher energy level; however, we know that atoms want to remain at a low energy state and they quickly drop down to a lower energy state (correct me if I am wrong here). If that is happening, then how can heat be actually kept in a carbon-monoxide or carbon-dioxide molecule?
Is it because during the day, they get heat up and remain heated because they require more time to get to a lower energy state?
Note: This is not a duplicate to the question given as a duplicate because the other question was addressed at why is one element able to absorb heat and not the others. This question, on the other hand, is focused towards how any element is able to absorb heat at all.
Answer
We have all learned that the earth is getting heat up because of the CO2 and CO molecules absorbing heat.
@Benjohn has given you the correct answer. Here is my take.
The ultimate heat provider of the earth ( except a small percentage of heat from the magma at the center of the earth) is the sun. It pours down at the surface about 1.2 kilowatts of energy per meter square ( which btw is directly used by solar panels). The same energy falls on the surface of the moon whose surface burns up during its daytime and freezes by black body radiation at night.
The earth is fortunate to have a gas atmosphere which mitigates the extremes of the possible temperatures that the ground would reach otherwise. An example of mitigation is what happens at the sea floor. Most of the energy is picked up by the water and the floor is kept at a steady temperature with small changes day and night in the first meters from the surface, depending on the season, radiating away with the black body radiation, but the body of water has such large heat capacity that variations are small.
The gas atmosphere is a more temperamental "blanket", its heat capacity depends on several gases , called green house gases from the bad impression that agricultural green houses work that way ( they do not, they work by inhibiting heat exchange by convection but that is another story, on which there is no controversy).
The main green house gas is water , H2O. It is worth contemplating this figure :
Solar irradiance spectrum above atmosphere and at surface. Extreme UV and X-rays are produced (at left of wavelength range shown) but comprise very small amounts of the Sun's total output power.
We see that H2O has the most absorption spectrum for infrared wavelengths, (which are the wavelengths of heat )and then comes CO2. Green house gases absorb both incoming and reflected from the surface of the earth infrared, and as most of the reflected wavelengths are in the infrared they act as a slowing down of the black body radiation that would finally leave the earth. As a blanket keeps a person warmer green house gases by playing ball with infrared radiation ( the wavelengths where heat is really transferred) keep the surface of the earth into a reasonable temperature for life, lucky us.
However, how is heat actually kept in those molecules. When photons heat them up, their electron gets excited and goes to a higher energy level; however, we know that atoms want to remain at a low energy state and they quickly drop down to a lower energy state (correct me if I am wrong here).
Heat is kept collectively when kept, it is not a one atom thing but emerges statistically by the response of zillions of atoms which keep on exciting and deexciting by collisions and vibrations etc as described in the other answers.
If that is happening, then how can heat be actually kept in a carbon-monoxide or carbon-dioxide molecule?
Heat is not kept in an individual molecule but in the gas ensemble but in a sense the level of green house gases have a delaying action in the radiation of the earth to the atmpsphere, by reflecting back and forth with the surface. This keeps the temperature close to the surface from fluctuating enormously between daytime and night ( as on the moon), it is a buffer similar to the buffer of water for the floor of the ocean.
Is it because during the day, they get heat up and remain heated because they require more time to get to a lower energy state?
No, it is a collective emergent thermodynamic phenomenon as I said. No need to invoke atoms and quantum mechanics at the level of heat.
Now going back to the figure, the reason so much stress has been put on anthropogenic CO2 is because of computer modeling of the dynamics of the atmosphere. The atmosphere is not a static phenomenon, it has winds, interacts with ocean surfaces, has storms etc. The models assume that CO2 increases act as a trigger for the land and atmosphere to release more H2O, in a feedback mechanism, and thus be pivotal in contributing to the small increase in temperature since the middle of last century, but this is another story.
No comments:
Post a Comment