EGEE 102
Energy Conservation and Environmental Protection

Greenhouse Effect


In the first lesson, we saw that energy can be transformed from one form to another, and during this conversion, all the energy that we put into a device comes out. However, all the energy that we put in may not come out in the desired form. Please watch the following 4:17 presentation:

The Greenhouse Effect
Click Here for Transcript of The Greenhouse Effect video

This diagram explains to us about the greenhouse effect. Basically what greenhouse effect is, is the sun, which emits mostly long radiation and shortwave radiation, all this radiation comes in in the morning or during daytime without any problem. The atmosphere, which has various kinds of gases like oxygen, nitrogen, little bit of carbon dioxide, et cetera, these radiations basically pass through. And the solar radiation, part of it actually gets reflected back out into the space from these clouds. Whatever reaches the Earth, here down below, part of it heats up the atmosphere or the Earth's surface, some of it is used for growing plants, some of it evaporates waters and runs the hydrological cycle. And during nighttime, all this energy that has come in during daytime generally will go back into the space as longwave radiation, which is infrared radiation. So it comes in shortwave and longwave, but all of it tries to go back or will go back in longwave radiation. Now, the gases, like CO2, in the atmosphere generally have the unique capability to trap this infrared radiation that is going out. And these gases absorb the infrared radiation, keeping a part of the radiation that would've otherwise gone out within the atmosphere. So this is called greenhouse effect, and due to this effect, because of these gases, the atmosphere right now is at an average temperature of 59 degrees Fahrenheit. Without this effect, for example if there was no CO2 in the atmosphere, no greenhouse gases, it's totally of oxygen and nitrogen, all the energy that would come in in the daytime if it had gone out in the nighttime, the Earth would be freezing at 0 degrees Fahrenheit. So at this temperature, nothing can grow on this planet, and the planet would be uninhabitable. So this greenhouse effect is what is turning this planet into a habitable planet by keeping the average temperature at about 59 degrees Fahrenheit. This temperature is the temperature that we normally see averaged over entire year at all places, including North Pole, South Pole, equator, day, night, various seasons, et cetera. So greenhouse effect is what is actually making this planet habitable by warming up little bit. Unfortunately, if we emit more and more greenhouse gases into the atmosphere like what we have been doing-- the CO2 concentration has gone up from 275 parts per million to now about 370 parts per million--if we keep on doing these kinds of things, more and more thermal energy will be trapped inside the atmosphere, and this 59 degrees temperature is likely to increase. And that's what we call global warming, or climate change, or increase in this temperature is detrimental. So the question is whether we should blame greenhouse effect for this or global warming as a bad phenomenon.

Current levels of CO2 in the atmosphere - 392 ppm in 2011. (Data shown in Excel Sheet)