Waves are an important topic, not least because all life on Earth depends upon them. The Earth depends totally on the radiation from the Sun, which is a ceaseless blast of energy spread over a vast range of wavelengths.
Other articles in this series and more series by the same author:
In this article, John Watkinson explores waves from the sun and explains why and how broadcasters can improve their green credentials.
Electromagnetic radiation can travel in a vacuum; it needs no medium. One way of looking at it is that the electrical component forms the medium for the magnetic component to travel in and vice versa.
Electromagnetic radiation has wave/particle duality, which means that we will find both types of behaviour depending on what we look for. Electromagnetic radiation is subject to quantum theory, which means that is consists of photons whose energy is proportional to the frequency. This means that the distribution of energy has the same fantastic range as the range of frequencies.
Above a certain frequency, the energy of a photon is sufficient to detach electrons from atoms. This is known as ionizing radiation and is generally destructive. Fortunately, the Earth has a magnetic field that extends far into space and deflects most of the ionizing radiation from the Sun. That allows the Earth to have an atmosphere and water, which would otherwise be stripped off.
The atmosphere in turn makes life possible, as well as allowing certain types of broadcasting. The atmosphere is a wonderful thing because of the number of ways in which it nurtures life. Of these, possibly the most important are the protection from meteorites, which mostly burn up before reaching the ground, the supply of oxygen, which animal life requires to burn its food and the “greenhouse” action which sets the temperature of the Earth to a reasonable level.
The Earth comes to thermal equilibrium when the heat radiated, and the heat arriving are the same. Fig.1a) shows that the heat trying to reach the Earth from the sun follows the spectrum of a black body radiator at about 5500 degrees Kelvin. Heat trying to leave the Earth has the spectrum of a radiator with a temperature of about 290 degrees Kelvin (Kelvin is absolute temperature, where zero Celsius is 273 Kelvin).
In both cases the heat flow is impeded by some feature of the atmosphere. In practice the heat leaving is impeded more than the heat arriving, so the Earth is warmer. In other words the atmosphere acts like a greenhouse built with the most complicated glass you could imagine and containing complex heat transport and feedback mechanisms, both positive and negative.
Fig.2 shows the dominant filtering effects of the atmosphere. At the shortest wavelengths, incoming radiation suffers Rayleigh scattering, which is where the wavelengths are of the same order of size as the molecules obstructing them. Oxygen causes Rayleigh scattering, for example. As wavelengths get longer, absorption begins. This is where the electric field of the radiation has the same frequency as physical resonances in molecules that cause charges to oscillate.
Molecules having one type of atom, such as O2 and N2, resonate at frequencies that are too high to affect things, whereas molecules of dissimilar atoms, such as H2O and CO2 have resonances in the bands of interest. Water vapor is the most powerful of these, having over ten different vibration modes, making it the dominant greenhouse gas. CO2 is next in line with four major modes, two of which are masked when water is present.
Fig.1b) shows all of the effects of Fig.2 added together. On the sunny side, there is a window between the Rayleigh scattering and the water absorption that is fortuitously aligned with the peak of the solar energy. Plants evolved to use that energy and life evolved vision in that range of wavelengths. Rayleigh scattering makes the sky appear blue.
Chlorophyll has a number of resonances that allow solar energy to be absorbed at wavelengths that humans would describe as red and blue. Between them is a window where light is reflected and that is why most plant life appears to be green.
Fig.1a) The dominant spectra involved in global warming are the energy arriving from the sun, left, and the energy being radiated by the Earth, right. Fig.1b) The effects of water vapor, CO2 and scattering superimposed on the dominant energy spectra. Most energy now arrives around the visible light region and leaves at around 10 micrometers in the infra red.
The dominant window for outgoing radiation is at about 10 micrometres and consists of a large window in the absorption spectrum of water that is near the peak of the Earth’s radiation spectrum. The numerous other windows in the water vapour spectrum are not significant because the incoming and outgoing radiation are both small there.
The 10 micrometer window is made a little narrower by the presence of the CO2 absorption at about 11 micrometers. That’s the one that all the fuss is about. The reason for the fuss is that it reveals a mechanism by which the concentration of CO2 in the atmosphere could change the balance of heat gain and heat loss. This certainly qualifies CO2 to be classified as a greenhouse gas, but not as powerful as water vapour.
The Earth is getting warmer and the concern is that a recent increase in the amount of CO2 in the atmosphere caused by human activity may be preventing heat loss at 11 micrometers. No amount of CO2 can close the window at 10 micrometers.
I think it is necessary to look at water and CO2 in perspective. All life on Earth is based on both of these. Plants take up CO2 using photosynthesis and emit oxygen. Without CO2 there could be no plant life. Plants are made of water and carbon. Animals eat plants and drink water and incorporate the materials into their own bodies. They inhale oxygen to burn the carbon to release energy and they exhale CO2 and water vapour. This has been going on for millions of years, most of which took place without human intervention.
Looking in perspective also requires us to consider the other ways in which the environment is being damaged by human activity. The consumption of resources, destruction of habitats, cutting of migratory routes, pollution of aquifers and over-fishing form but a tiny part of the list. In the presence of those other pressing problems, to focus on and to demonize CO2 and accuse it of all manner of ills when life depends upon it doesn’t seem to be particularly logical, especially when there are other reasons for global temperature change, such as Milankovitch cycles, vulcanism, deforestation, variations in the Sun’s intensity and so on.
It seems that in the distant past the concentration of CO2 in the atmosphere was greater than it is now. If there was some positive feedback mechanism that caused the temperature of the Earth to go out of control, then surely one of the many stimuli throughout Earth’s history would have triggered it. Yet the planet has not become toast or a snowball.
The fact that life survived suggests strongly that there must be some kind of negative feedback mechanism(s) that deals with high carbon levels. It is one thing to know they exist, but that does not mean they are understood. It is known, for example, that elevated CO2 levels increase the rate of plant growth and that plants form a carbon sink.
I think before taking any remedial action some understanding of the problem should be demonstrated. There is clearly some correlation between CO2 and global heat balance, but where that lies between coincidence and causality is not understood.
Records from the Vostok ice cores are about the best information we have about conditions in the past and the data are widely available. A casual look at the temperature and CO2 level curves reveals that they have pretty much the same shape. However, a less casual look reveals that the peaks in CO2 level lag the temperature peaks by several thousand years. It is difficult to argue causation when the stimulus lags the effect by such a length of time. It is also known that an increase in the temperature of the oceans causes them to release CO2. If anything the Vostok cores demonstrate that.
Very accurate records of global temperature and sea level are available for the last thirty or forty years. There are literally hundreds of models created by various research establishments and not one of them can replicate those records. Another interesting factor is that sea levels are rising significantly slower than the modelers predicted. Given that the models cannot replicate what is known to have happened, it is simply unscientific to use those models to predict what is going to happen in the future.
Science works by observing nature and trying to find general rules that predict it. When experiments show the predictions are correct, the rules may be correct, but when they don’t, something is wrong with the predictions. A true scientist considers the data and remains sceptical about the accuracy of his models. As Bertrand Russell put it: “Those who are certain are certainly wrong.”
Today we no longer have that. There is only one truth and there are no more sceptics. Instead they are called deniers. The first victim of global warming has been science.
One result of concerns about global warming has been a push towards electrification. Electrical power is, of course, clean at the point of use, and we have to gloss over that the electricity might have been generated by burning trees, lignite or various non-sustainable hydrocarbons.
The broadcaster is quite well placed to claim green credentials because broadcasting relies almost completely on electricity. However, the ideal world of universal clean electricity is not with us and electricity still has a substantial carbon content. The best a broadcaster can do is to increase efficiency, so the same jobs are done with less energy. This has a double effect because less waste heat needs less air conditioning.
The present energy crisis that emerged from events in the Ukraine has been partly dealt with by a reduction in demand. Large numbers of people across Europe turned down their heating systems and used other conservation measures because they had been encouraged to do so by television broadcasts.
You might also like...
We present the first in a series of articles on 5G Broadcast, starting with its history and why it is rising up the agenda for broadcasters. Future articles will delve deeper into the technology and standardization, including interaction with existing…
At the moment it is far from clear exactly how the OTA TV landscape will evolve in the US over the next few years… the only sure thing is that we are in a period of rapid change.
Why keeping control of wi-fi and other devices within a broadcast facility to ensure there is no interference with critical devices is essential.
Here we look at codecs and encoding for digital RF modulation such as ATSC 3.0, DVB and other digital OTA standards, and network requirements for encoding and delivering streaming internet video.
This is the fourth of a multi-part series exploring the science and practical applications of RF technology in broadcast. Here we discuss codecs & encoding, the need to carefully manage the proliferation of RF devices within facilities and the future…