This is my attempt at contributing to "A Layperson's Introduction" series, here on Tildes. It's why it's here on ~science, rather than ~enviro

Many people have heard about how global warming works. “We are emitting greenhouse gases, and these trap heat, leading to further warming.” So how does this process occur in more detail? What is its physical basis? In this post, I will try to explain the physical basis of these questions in a simple way that is a bit more detailed than what is usually seen.

Electromagnetic Spectrum and Thermal Radiation

The electromagnetic spectrum is a broad spectrum that includes visible light. There are long wavelengths, such as radio waves and infrared light, and short wavelengths, such as ultraviolet light, X-rays, and gamma rays.

Visualization of the electromagnetic spectrum

Thermal radiation is the radiation emitted by the molecules of an object due to thermal movement. It can be in the visible light wavelength, shorter wavelength, or longer wavelength. The length of these wavelengths varies depending on the temperature of the object that is the source of thermal radiation. For example, the thermal radiation emitted by Earth falls into the infrared spectrum, which is at lower energy, because Earth is not as hot as a star. The shift of thermal radiation emitted by colder objects to longer wavelengths is also known as Wien's law.

Energy Budget and Stefan-Boltzmann Law

Our planet Earth has a certain energy budget. In other words, the energy coming to the planet and the energy going out from the planet are specific. The source of the energy coming to the Earth is the Sun, and on average, approximately 340 Watt/m² energy reaches the surface of the planet. In order for this energy to be balanced, the energy radiated from Earth into space must be equal to this amount. This happens in two ways. First, some of the incoming energy is reflected into space by the Earth itself. Both the atmosphere (especially clouds) and the surface make this reflection. The second part can be explained by a physical law called Stefan Boltzmann law. According to this law, each object emits a certain amount of energy as thermal radiation, and the amount of this energy increases with temperature. This increase does not occur linearly, but as the fourth power of temperature. The mathematical expression of the law is given below.

E = σT⁴

In this equation, "E" is the energy, "σ" (sigma) is the Stefan-Boltzmann constant, and "T" is the temperature in Kelvin. However, the law cannot be applied to any object in its current form. The above equation is valid for ideal bodies called "black bodies". In physics, a black body is the name given to an ideal body that absorbs and emits all incoming radiation. However, Earth differs from a black body due to reflection. Therefore, the following equation is more appropriate.

E = εσT⁴

Here, ε (epsilon) means emissivity. Emissivity is the effectiveness of the surface of a material in emitting energy as thermal radiation. For a black body, ε = 1. The Earth's mean ε is less than 1, because it is not a black body. At the same time, emissivity changes depending on which part of the Earth is examined. For example, the emissivity of a vegetated surface and a desert or glacier are different. However, it is more important for us at this point to remember that the mean ε is less than 1.

When we look at the formulae above, we see that, in accordance with the Stefan-Boltzmann law, the Earth emits thermal radiation depending on the temperature, even though it is not a black body. This constitutes the second part of the Earth's energy budget, namely thermal radiation. In summary, Earth receives energy from the Sun and radiates this energy through reflection and thermal radiation.

Radiative Forcing and Greenhouse Effect

The energy budget is very important for our planet. Any change in the budget causes Earth to warm or cool. Natural or human-induced changes that change the balance between incoming and outgoing energy are called radiative forcing. This is the mechanism by which greenhouse gases warm the planet. Some gases in the atmosphere, such as carbon dioxide (CO²) or methane (CH⁴), have physical properties that absorb the thermal radiation emitted by Earth. If you remember, Earth's thermal radiation was in the infrared spectrum. That is, these gases absorb at certain points in the infrared spectrum. As a result of this absorption, the gases emit it again in the form of thermal radiation in all directions. While some of the emitted radiation escapes into space, some of it remains on Earth, causing warming. Since the energy emitted by Earth will increase as it warms up, at a certain point, the incoming and outgoing energy becomes equal again.

CO² emissions, concentration, and radiative forcing

In the image above, in different climate change scenarios, emissions of the greenhouse gas CO²) (left), the corresponding increase in CO² concentration in the atmosphere (middle), and the increasing radiative forcing due to this increase are shown (right). Note that the radiative forcing is shown in Watts/m². It is shown this way because it is calculated based on the change in Earth's energy budget, and Earth's energy budget is shown as Watt/m².

In other words, although the incoming energy is the same, there is a certain decrease in the energy going into space due to the greenhouse effect. This leads to what we call radiative forcing. As a result of radiative forcing, the temperature of Earth increases, and as the temperature increases, the thermal radiation energy emitted by the planet increases. This causes the incoming and outgoing energy to become equal again. As a result, in the long run, radiative forcing (and the greenhouse effect) does not lead to a change in the energy budget. However, it causes solar energy to remain in the atmosphere for a longer period of time, causing a certain amount of warming. This is what we call global warming due to the greenhouse effect.

This process is, of course, more complex than described here. Since the atmosphere has a layered and fluid structure, there are factors that make the job more complicated. For example, while the increase in CO² warms the troposphere (what we call global warming), the lowest layer of the atmosphere, it causes the stratosphere, its upper layer, to cool. Despite these and similar complexities, the physical basis of global warming is still based on the mechanisms described in this post.

Sources

• Schmittner, A. (2018). Introduction to Climate Science. Oregan State University
• van Vuuren, D. P., Edmonds, J., Kainuma, M., Riahi, K., Thomson, A., Hibbard, K., Hurtt, G. C., Kram, T., Krey, V., Lamarque, J.-F., Masui, T., Meinshausen, M., Nakicenovic, N., Smith, S. J., & Rose, S. K. (2011). The Representative Concentration Pathways: An overview. Climatic Change, 109(1-2), 5–31. https://doi.org/10.1007/s10584-011-0148-z
• Wild, M., Folini, D., Schär, C., Loeb, N., Dutton, E.G., König-Langlo, G. (2013). The global energy balance from a surface perspective. Clim Dyn 40, 3107–3134. https://doi.org/10.1007/s00382-012-1569-8
• Zohuri, B., McDaniel, P. (2021). Basic of heat transfer. Introduction to Energy Essentials, 569–578. https://doi.org/10.1016/b978-0-323-90152-9.00017-7

Image Sources

• Image 1: https://science.nasa.gov/ems/01_intro/
• Image 2: van Vuuren et al., 2011

Those last 10 laps or so were pretty spicy. Sure, Herta kinda ended that Dixon and Newgarden fight, but I'm not sure that Newgarden would've passed Dixon for P1 even if that hadn't happen. Dixon is a beast.

Theo Pourchaire, the reigning F2 Champion, had a great IndyCar debut, finishing P11 from P22! He apparently hadn't sat in an IndyCar until this weekend for practice and such.

Next race:
Alabama Grand Prix
Barber Motorsports Park
Sunday, April 28

This thread is posted weekly - please try to post all relevant US political content in here, such as news, updates, opinion articles, etc. Extremely significant events may warrant a separate topic, but almost all should be posted in here.

This is an inherently political thread; please try to avoid antagonistic arguments and bickering matches. Comment threads that devolve into unproductive arguments may be removed so that the overall topic is able to continue.

I am posting to get your opinions on something that happened tonight.

Music started blasting from my neighbor’s place at 12-ish with some people screaming. Our corridor has a WhatsApp group and I wasn’t 100% sure which neighbor it is so I messaged there at around 12:30am.

I chose my words to be as polite as possible… dunno if it was polite enough. Something like: hey to the people who are having the party, have fun but please adapt the noise accordingly with the time with a thanks emoji.

They replied apologetically and added that it was their birthday. Didn’t feel like it was being used as an excuse but more an explanation.

Thinking maybe I should have let it slide regardless of whether it was their birthday or not but I did wake up exceptionally early this morning and needed some sleep after a hard day’s work.

Am I being too anal about it? How would you handle such a situation with noise?

I've been doing a lot of work with my therapist and it has been suggested that I might have a mix of both Autism and ADHD.

I have always related to Autism to a certain extent but I would never say it because I felt like I didn't really fit because some things I do don't make sense it that context. I was also obsessed with learning to be human since young and have a lot of systems to deal with it and apparently that means I've been masking for a very long time.

But my therapist also brought up ADHD and that has explained a lot about some the things I'm still currently struggling with. But again, when I look it up, I don't feel like I fully fit. But also, I have developed a lot of systems over the years to deal with my issues and function like a normal human being. So a lot of the things I struggle with is hidden because I've "fixed" them.

I'm still reluctant to say I have either of those two things because I feel like an imposter. So I've just settled on Neurodivergent and think that I can always learn the tools that help people with ADHD even if I don't have it. Because if the tools work for you, then why not?

But my therapist has suggested getting diagnosed because it does change what kind of medication you might get. I'm currently on medication for anxiety and depression.

So now I'm wondering how common it is to have a mix of both ADHD and Autism. For those who have both, what is it like for you? What is your daily life like? What are your struggles and how do you deal with them? When did you realise you might have a mix of both? How do you feel about yourself and your brain?

I apologize if this isn't the right place to ask this. I don't post very often and am getting used to it.

Add awesome game deals to this topic as they come up over the course of the week!

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The kinds of change I'm referring to are hard to put into words. A few examples may be switching from one end of the political spectrum to the other, leaving one country or culture for another, religious conversions and deconversions, or leaving behind one's family. Often, these changes are caused by deeply personal events like receiving a serious medical diagnosis, conflict, the death of a loved one, midlife crisis, or merely examining one's values or beliefs. There are countless other examples of both changes and causes, many of which I've never considered.

There is shared experience between these changes: the world hasn't changed, but somehow everything is different. Everything is in a completely new light; it's as if you've moved between parallel universes. Not everyone has had or will have such a moment, but these changes seem to be the most important in catalyzing who we are. As much as we think sharing opinionated memes or arguing at Thanksgiving is going to shape or mold people around us, it is often personal experiences that actually make such change possible. And some small number of people do experience profound change: racists become antifascists, liberals become stanch conservatives, Christians become atheists. These sorts of life-altering changes are often what tell us most about who a person is.

I made this post because the discussion of these changes are among the most valuable discussions I've had with others, and people often don't get socially-acceptable opportunities to share something so personally important to them. This is potentially a heavy subject, so don't feel that you need to share or elaborate any further than what's comfortable for you.

Hi Tilderinos! I am doing a study abroad program in Bordeaux, France. I am considering buying myself a folding bike for my time there. I just started doing some online research, and Brompton, Tern, and Dahon have popped up so far. The Brompton bikes are a bit more than I really want to spend, but I could spend that much if it was worth it. Do you have any recommendations on brands, models, or things to look for? Thanks!