In the previous post, I showed why certain gases in the atmosphere acted as a blanket, and slowed down the cooling of the ground. The next question is, is there any observational evidence that this is happening? After all, there are a number of people who view statistics and argue that this is not happening because the temperatures are not rising the way you might expect from the models. So, what is the truth? The critical evidence is from the oceans, which have been measured as receiving 0.64 Watt per square meter. That may not seem to be much, but consider the number of square meters in the oceans. Without any doubt whatsoever, the planet is receiving a net heat input.
Some may protest that statistics show there has been none of the expected temperature raise since 2000 AD. This is difficult to account for with certainty. Temperatures fluctuate greatly from year to year, and arguments that there has been little net temperature rise since 2000 may simply mean that a negative fluctuation has been cancelled with net heat. The second reason might be that the ice caps are melting. If you heat a mix of ice and water, as long as you stir, there is no net rise of temperature until all the ice melts. The heat goes into melting the ice. The heat may be lost to the deep oceans. Finally, some places may get a significant rise in temperature but others do not, and statistics at one place may be misleading. It is very easy to get stupid answers from the misuse of statistics. It also may not matter. After all, if the Sahara or Death Valley get twenty degrees hotter and everywhere else stayed the same, would it matter? Even if the world got a few degrees hotter, would it matter? That depends on what happens to the spare heat.
So, the ground gets hotter, but what happens next? I mentioned in the previous post that the absorption of infrared radiation by greenhouse gases does not, in itself, heat the gas. There is an indirect method by which it can, though. If the excited state molecule undergoes a collision with another molecule, there can be an exchange of energy, and now neither molecule is in a stationary state, and this results in the energy being dissipated, usually as heat. Whether this happens depends on a quantum probability, and as far as I am aware, this probability is unknown, so I cannot answer whether this happens. The probability of a collision during the lifetime of the excited state depends on the overall gas pressure, and Earth’s pressure is such that whether a collision occurs is a bit of a toss-up. On the other hand, Martian pressure would be too low, and Venusian pressure would almost guarantee a collision. However, the reverse also happens. If a gas molecule collides with a molecule of greenhouse gas, heat may be converted to excited state vibrational energy, again with a certain quantum probability, and that may be radiated away. The very top of Earth’s atmosphere, called the thermosphere, has an absence of such molecules, and an effective temperature of something like 1400 degrees. The thermosphere of Venus, which is mainly made of carbon dioxide, and which receives twice the sunlight as Earth, has a temperature of a mild summer’s day.
Three are two mechanisms to warm the air. Contact between ground and air heats the air and cools the ground, whereupon the warmer air rises and mixes with the general air. A more effective mechanism is where ocean water cools by evaporating water, and when this condenses as clouds, heat is transferred to the air. It also tends to be dumped in one place, which raises the pressure of the local air, which in turn leads to air movement. The more water being condensed in a small volume, the more likely a storm will eventually result.
However, the biggest cause of temperature differences is ocean currents. Everybody knows that but for the Gulf Stream, Europe would be a miserable place, and ice ages are probably accompanied by a redirection of that Gulf Stream. And herein lies our real problem. The oceans are carrying sufficient heat to melt very significant amounts of polar ice, and this will led to major sea level rise. However, the issue regarding greenhouse gases now becomes more confused, because in the last four interglacials, there is clear evidence that without our industrial output of greenhouse gases, the Greenland ice sheet melted and sea levels were about 7 meters higher. Our problem is, if this is really inevitable this time, and with even more net heat input, more of Antarctic ice should melt. Now, look at Google Earth, and check the location of major coastal cities and see how much of their area is less than 10 meters above sea level. See how much prime agricultural land is less than ten meters above sea level. Now, work out how civilization can continue in our current ways if we continue to keep our population expanding the way it is?
See how difficult it is to get the future right in your novels?