What I have learned in this workshop:
The course was hosted on the Coursera website by Professor David Archer of the University of Chicago.
First, basic topics about different units such as energy and heat and how to calculate were given. Then, the topics of light, magnetic field and blackbody radiation were discussed.
Then, various explanations about climate models began, and the first model was the model of the naked planet, in which we look for conditions in which the energy inside the earth is equal to the output energy and we can estimate the temperature of the earth, but according to this model, The temperature of the earth is very cold and other factors such as greenhouse gases must be added to it.
Then, we come to the effect of greenhouse gases in which we suspend a glass above the ground and the glass has the property that sunlight can pass through it without any obstacles and is not absorbed by the glass. But every infrared that comes from the earth is absorbed by that glass, and the glass itself shines in both infrared and downward directions due to its temperature. According to calculations, sunlight is absorbed in the atmosphere and does not go to the earth and has a great effect on the earth’s temperature. Because gases are so selective about the type of light they absorb, we find that CO2 absorbs light strongly during the wavelength of light reaching the earth, and there is another area called the atmospheric window, where nothing much is absorbed. So, when you look down from space. You see some light coming from above in the cold part of the atmosphere and another light coming from below near the ground. This is because the temperature in the real atmosphere is regulated by convection. This is the process by which hot gas rises near the ground and raises its heat in the atmosphere, and then cold matter rises above.
There is a very important issue, and that is that the high temperature in the atmosphere is different from the temperature of the earth, and so we are trying to find out why, and this temperature difference is what causes the greenhouse effect, because we absorb light from the warm Earth and replace the light from the cold upper atmosphere. It seems that the reason is convection. If we add convection, the temperature difference between the top and bottom is not so strong, and then by adding water vapor, it brings our ideas much closer to reality. This is what really governs the temperature of the atmosphere. So sunlight injects energy into the Earth, which drives convection, the gas expands because it’s a compressible medium and therefore cools, which cools it as it rises. But cooling causes water vapor to condense because if water is really cold, it doesn’t like to vaporize and prefers to be in a condensed state like a fluid, a liquid. So the water condenses. But when it rains, it leaves behind the heat that came with the water vapor, to begin with. So the process that appears to be real is what is called moist convection. So that’s what determines the intensity of the greenhouse effect on Earth, and if there’s something that can change that, like a change in the amount of water vapor in the atmosphere or something like that, it can feed back and water and change the earth’s climate.
In the next steps, to simulate the climate model more realistically, we added the vortex, water vapor, clouds and suspended particles to get closer to the current conditions of the earth. Aerosols are droplets much smaller than cloud droplets, typically eight to ten microns in size. So these little things, because they’re comparable in size to the wavelengths of visible light, are really good scatterers, and they’re really good at reflecting sunlight back into space.
The next important topic was the carbon cycle and its effect on the climate, where we learned that the oceans are one of the main players in the Earth’s carbon cycle and also exchange carbon with the atmosphere. Basically, there is a lot of carbon dissolved in the ocean, much more than in the atmosphere. And some parts of the ocean release CO2 into the atmosphere. Therefore, CO2 is somehow degassed or even evaporated from the oceans. Elsewhere, the ocean is absorbing carbon dioxide, for example where the water is colder, so the CO2 dissolves more easily in the water than in warm water. Therefore, the carbon back and forth flows between the atmosphere and the ocean are very large. Also, the oceans are thought to be responsible for changes in atmospheric CO2 through glacial-interglacial cycles, documented from records preserved in ice cores in Antarctica and Greenland. So, from the tiny bubbles of air in which the ice cores are trapped, we know that atmospheric CO2 concentrations are typically about 280 parts per million in warm times like today, during interglacial periods, and then in cold times, like the last glacial maximum of 20,000 years. Before, the C02 concentration was lower, about 200 parts per million.
The Earth’s carbon cycle is mainly governed by plants. Plants grow in spring and summer and absorb CO2. And then in the fall and winter, they drop their leaves, which decompose or turn back into CO2 and release it back into the atmosphere. Thus there is a very strong seasonal cycle in atmospheric CO2 concentration driven by the land surface. It rises in winter and falls in summer.
Different fuels such as coal and gasoline were also investigated and the effects of incomplete combustion of fuels were also investigated and we realized that they introduce a large amount of carbon dioxide into the atmosphere.
Finally, the methods of measuring the temperature in the earth, the oceans and their accuracy, and then the methods of comparing climate changes in different years (such as the use of tree ring width, frost cycles or sunlight) were discussed.
To sum up, The impacts of global warming on people will be greater than average temperature change, and on Earth, the strongest climate impacts are likely to be regional impacts rather than global average changes. Global warming causes droughts and storms in some areas, which are very harmful for vegetation and agriculture, and on the other hand, it causes more rain in other areas.
Also, the rise of the sea level can be considered as one of its most destructive consequences, that in low-lying areas where the level is very close to the sea level, if the sea level rises and the salt water gets too close to the surface, it can poison agriculture. Or there will be a storm in many areas.
