Idiot's Guide to Climate Science.
This is far from my area of expertise and I am here trying to advance my own knowledge and understanding. The obvious place to start would be with one of the standard text books such as 'Principles of Planetary Climate' by R.T.Pierrehumbert. (That pdf appears to have many sections only summarised, possibly it was a reduced version for some online course, the full volume available via Amazon is 679 pages compared to 132 pages in the pdf.)
We could also look at the history of climate science, and go back as far as 1856 to experiments by Eunice Foote demonstrating that CO2 and water vapour absorb more energy from sunlight than normal air, followed a few years later by the work of John Tyndal, who gets most of the credit for the discovery of the 'greenhouse effect'. Strictly speaking the 'Foote Effect' was primarily caused by absorbtion of visible and ultra-violet light, by using glass containers for the gas the infra-red input was reduced.
Eventually I took a different approach, trying to simplify and clarify, without getting into all the fine details.
1: Atmospheric Carbon Dioxide
I have seen carbon dioxide described as an "insignificant 0.04%" of the earth's atmosphere. While that percentage is about right it is maybe helpful to look at a few additional figures. I have an empty coffee cup on my desk, with volume around 400ml. The air in that cup is made up of molecules, mostly nitrogen and oxygen. Air at sea level and 20 deg.C. contains around 2.2 x 1025 molecules per cubic metre, so the cup contains about 1022 air molecules. Assuming that 0.04% CO2 is a percentage of number of molecules then that represents 4 x 1018 molecules. So, my small cup contains about 4,000,000,000,000,000,000 molecules of CO2. In other words four million trillion. That sounds rather more alarming than 0.04%. And each molecule is capable of absorbing photons of infra-red radiation, with the probability of absorbtion varying with photon frequency. Initially that absorbed energy mostly just adds kinetic energy to the molecule, in effect it raises the temperature of the air, which is just an average of the kinetic energies of the molecules. Some absorbed energy is emitted by a molecule and returns as a photon, but emitted in a more or less random direction, so in effect some of the energy originally travelling upwards through the atmosphere is then directed back down. At sea level the concentration of CO2 is already sufficient to give almost complete absorbtion in the peak absorbtion frequency band in just the first 10 metres.
There is still an upward flow of energy, partly re-radiation but also convection. Where it matters more is in the top layers of the atmosphere. In equilibrium the energy being radiated out into space must equal the energy being received from the sun, and infra-red radiation is primarily radiated from the top layer, above 10km. Water vapour is also a 'greenhouse gas' and has a greater concentration in the lower atmosphere, but not so much near the top, whereas CO2 mixes well in the upper layers, so the CO2 is more significant there. If CO2 concentration is increased the layer from which energy is radiated out becomes thinner and higher. If it is higher it is also cooler, and cooler air will radiate less, so there is then no longer equilibrium, and the overall temperature of the earth will increase sufficient to increase the radiation from the top of the atmosphere and restore balance.That is obviously a simplification and not the whole story, and there are various feedback mechanisms and potential tipping points to worry about, but that is a starting point to understand the effects of changing CO2 levels.
2: Sea Level
I was looking around the internet for information about sea level rise, leading to a fascinating detour into the importance or otherwise of parrotfish. The starting point was reading an assertion that sea level rise is slowing down, and the problems with Pacific coral islands such as Tuvalu is over-fishing of parrotfish which deposit sand which prevents sinking of the land level.
Apparently Tuvalu is on average '6 feet 6 inches above mean sea level' suggesting that at the present 3mm per year rate of rise of sea level it will be safe for a long time. However, if I lived in such an area I think what would worry me more is the local maximum sea level, not the mean level. The combined effect of tides, rainfall, wind and so on must be a danger, and climate change would be expected to make some contributions worse. A peak of 11 feet occurred on 19-Feb-2015, causing extensive flood damage.
As for lack of parrotfish faeces as an explanation for 'sinking' islands, that looks implausible without further explanation. The sand produced by parrotfish is a consequence of them eating coral, which can help or hinder the coral, if the essential symbiotic coating of algea is overgrown it helps, but if it has already been diminished by for example temperature rise, then recovery can be harmed by over-grazing. I knew nothing about this, but after an hour Googling here I am claiming to know what I'm talking about.
Regarding the rate of sea level rise, the most convincing source I found is the NASA satelite altimetry data, which is supported by gravitational measurements of ocean mass plus expansion caused by temperature rise. This shows a more or less constant upward path, with just a hint of increasing rate. So where do those graphs showing a falling rate of increase come from? Maybe the most significant thing I learnt from my online searching was that there appear to be two parallel realities with alternative facts.
However, real facts can have real consequences, and if in the future we see water flooding the streets and thousands die in the heat, there will be no alternative reality in which it is cool and dry. Those sort of consequences are already happening in some places, over 1300 died in 50deg temperatures during the 2024 annual pilgrimage to Mecca, and wildfires have become a regular feature around the world. That sort of thing may need to become far more widespread and severe before some people accept that there is a serious problem. Even then many will refuse to believe, prefering to invent alternative explanations, such as wildfires caused by 'space lasers' and typhoons created and directed by the government to attack their opponents.On average at present, depending on our definitions it can be argued that cold causes more deaths than heat, but what matters is not the relative numbers but the gradients, so a +1C change may give a greater increase in heat deaths than the decrease in cold deaths. The minimum death rate is at around 20C, but an increase of 5C causes about the same death increase as a reduction of 21C. It's all rather more complex, and not something I want to get into in detail, a good account is at Climate Brink which includes some differing views in the comments section.
Meanwhile, according to a report on Ember China leads the world in the manufacture of solar panels. The current estimated annual manufacturing capacity is around 1000 GW. For comparison, the total UK electricity generation today (3-10 pm, 16-Feb-2025) is just 40GW, and only 1.6 GW of that is solar, 12.5 GW is wind, and 4.3GW nuclear. The cost of solar panels halved during 2023 because of supply exceeding demand. One current problem of course is storage, the hours of sunlight and wind are limited. Solutions do exist, e.g. Dispatchable Hydropower.
The Chinese manufacture of clean energy sources seems to conflict with their unfortunate continued use of coal. New coal-fired power stations are being built there at an alarming rate. That need not be a contradiction, solar and wind energy are cheaper, and coal is to some extent just being used as a backup, with only intermittant use. A more thorough coverage of this matter can be found at Sustainability by numbers.
3: Why Warm Air Rises.
I wanted to try a different approach looking at the behaviour of individual gas molecules rather than the usual statistical methods of thermodynamics. For example we could look at the relationship between temperature and density and say that the less dense hot air will rise, but why would a high energy molecule know which way is up and be more likely to head in that direction compared to a low energy molecule? Looking from this point of view may lead to a better understanding of the mechanisms involved.
Before trying to understand something as complex as the earth's climate it may help to start with the basic physics of an ideal gas in a gravitational field. Maybe start with a puzzle, we know warm air rises, i.e. convection, but we also know that here on earth air temperature falls at high altitude. So what happens to that rising thermal energy? The atmosphere also of course has an input of energy from the sun, and also radiates energy out into space. Let's start with a simplified model, ignoring radiation and energy input and internal energy of the gas molecules, and also restricted to one vertical dimension. Imagine a long cylindrical tube containing simple non-interacting gas atoms. That is true for a monatomic gas such as helium. Stand the cylinder vertically in a gravitational field. If the atoms had no kinetic energy, i.e. at very low temperature, they would simply fall to the bottom of the tube, and form a liquid. (Or maybe a solid, but just assume it is a liquid). Above the liquid surface will be a vacuum. Then add thermal energy, i.e. heat the liquid, and then the atoms gain kinetic energy, moving around in random directions, but not all at the same speed, there will be a distribution, most with something near the average, but some with higher energy. Some of these higher energy atoms will have enough vertical velocity to escape from the liquid, overcoming any short range binding forces. These become a gas and, assuming the gas density is low enough to avoid significant interaction between the gas atoms, each atom will head upwards at ever reducing speed as it loses energy in the gravitational field, and eventually stop and accellerate back down to rejoin the liquid. The gas atoms therefore have high kinetic energy low down near the surface, and low energy, corresponding to lower temperature, higher up. That appears to answer our initial puzzle, that the warmest gas rises but temperatures fall at high altitude. The reduction of temperature with height is only true up to around 16km - the 'tropopause' - after which it increases slightly, but this is above the height from which infra-red radiation into space becomes possible, around 10km.
Let's see what happens in 3 dimensions and with higher gas density so that collisions occur between molecules. There will be some average distance between collisions, so a slow moving molecule will on average take longer and accelerate downward more in the gravitational field before its next collision. It will then be scattered in some random direction, and may aquire higher or lower speed. A faster moving molecule has on average less time to accellerate downward. There will therefore be a tendency for the slowest, i.e. coolest, to fall more in the field. The density will increase lower down as molecules fall in the field, and eventually the mean distance between collisions will become shorter in the downward direction, so falling molecules will tend to be stopped from falling so far by the increased chances of a collision. This is in effect a 'back pressure' counteracting the downward force of gravity, and eventually there will be some equilibrium reached with the warm air still rising, cooling and falling again.
The heating near ground level is caused partly by radiation from the sun. Most of the sun's energy reaching the outer atmosphere is in the visible and ultra-violet range, and a lower level as infra-red. The absorbtion of energy from visible and UV sunlight on its way to the earth's surface accounts for about 79W/m2, so not entirely insignificant. Looking back to the top of the page, this could be regarded as an example of the 'Foote Effect'.
REFERENCES:
A Timeline Of Earth's Average Temperature
The Scariest Climate Plot in the World
Climate skeptics favourite graph
To be continued. Maybe.
