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4 votes
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Safer Sunscreen: Stanford researchers explore novel approach to sustainable sun protection
13 votes -
The (simple) theory that explains everything | Neil Turok
10 votes -
What cats’ love of boxes and squares can tell us about their visual perception
30 votes -
Complex systems science allows us to see new paths forward
5 votes -
On surveys
10 votes -
Argentine scientists find speedy ninety-million-year-old herbivore dinosaur
12 votes -
Lemon-scented marijuana compound reduces weed’s ‘paranoia’ effect
17 votes -
The Homo Economicus as a prototype of a psychopath? A conceptual analysis and implications for business research and teaching.
6 votes -
Does light itself truly have an infinite lifetime?
10 votes -
‘Like a film in my mind’: hyperphantasia and the quest to understand vivid imaginations
18 votes -
New Foundations is consistent - a difficult mathematical proof proved computationally using Lean
10 votes -
Introduction to the physical basis of global warming
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...
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
21 votes -
The Hydra game
6 votes -
Bizarre traveling flame discovery
11 votes -
David Dunning: discoverer of Dunning Kruger effect on overcoming overconfidence
6 votes -
Canadian science gets biggest boost to PhD and postdoc pay in twenty years
7 votes -
Energy as a conserved quantity (why it's a useful abstraction)
8 votes -
AI traces mysterious metastatic cancers to their source
4 votes -
The hazy evolution of cannabis
3 votes -
Human brains and fruit fly brains are built similarly – visualizing how helps researchers better understand how both work
7 votes -
How to succeed in a cramming-based academic system?
I'm an intuitive learner. I learn by constantly asking questions, the answers to which i can then effortlessly remember. By messing around and seeing what happens, and then asking why. Lecturers...
I'm an intuitive learner. I learn by constantly asking questions, the answers to which i can then effortlessly remember. By messing around and seeing what happens, and then asking why. Lecturers have been enthusiastic about my approach but said I'm going to struggle because the school system in my country wasn't designed for people who learn like this. I want to kill myself.
The way I see myself learning stuff:
- Here's a fresh store-bought kombucha scoby
- Here's a scoby from the same store that I've been growing for 6 weeks
- If I sequenced the DNA from equivalent cells in each of these scobys, would I find any differences? Why?
Same with my latest interest: Law. I've watched a few (mock) court cases and researched whatever questions I came up with, to get an understanding of how courts worked, and had a look at the cited laws.In physics tests I end up running out of time because whenever I forget an equation I need, I try to intuit/derive it, which I would manage given enough time.
The way we are actually expected to learn stuff:
- Listening to a lecturer talk for 12×2 hours, and/or reading the referenced literature. Anything mentioned could be on the test.
I have been trying to do it the mainstream way anyway, but I am getting such bad grades that I've had to re-take a year. Even if I found strategies to help me focus I'd still clearly have a competitive disadvantage to people to whom this approach comes naturally. This feels unfair since I know there is a way that I could learn about my field as effortlessly as other people do listening to these lectures.
How does someone like me succeed in academia instead of just scraping through?
I understand that my prefered methpd which I outlined is what you do at PhD level. I'm afraid that by force-feeding my brain all this information that it currently sees as irrelevant, I will kill my curiousity, which I don't want to do because it's the thing that's allowed me to get this far with practically no effort (I went through the archetypal Smart Kid thing in middle school).
For context, I'm in 1st year bachelor's biochemistry (repeating the year). Although I think that at least in my country, all university courses have the format I described.
Since I am also struggling with ADHD I honestly feel like giving up on Uni and going for some sort of apprentiship-style thing. I would like to have a degree though because it's sort of a requirement nowadays and I am genuinely interested in my subject area. Alternatively, what kind of professions seek my method of inquisitively deep-diving into stuff, as I described?
19 votes -
Cow magnets
24 votes -
Nobel Prize-winning phycisist Peter Higgs died at 94. About sixty years ago he proposed the Higgs Boson, an elememtary particle essential in describing mass in the Standard Model of particle physics.
28 votes -
Peter Higgs, physicist who proposed Higgs boson, dies aged 94
27 votes -
Loneliness can kill, and new research shows middle-aged Americans are particularly vulnerable
31 votes -
Underrated ideas in psychology
7 votes -
Researchers map how the brain regulates emotions
1 vote -
Unraveling Havana Syndrome: New evidence links the GRU's assassination Unit 29155 to mysterious attacks on US officials and their families
40 votes -
Not every student needs Algebra 2. UC should be flexible on math requirement.
21 votes -
AI assists clinicians in responding to patient messages at Stanford Medicine
4 votes -
Beyond solid, liquid, and gas: The seven states of matter
10 votes -
Venting doesn't reduce anger, but doing calming activities does, study finds
44 votes -
Proving the Earth is round at home
I am looking for practical ways to prove the Earth is round using materials accessible to the average person. I have zero interest in disproving Flat Earth folks. I am inspired by Dan Olson's...
I am looking for practical ways to prove the Earth is round using materials accessible to the average person. I have zero interest in disproving Flat Earth folks.
I am inspired by Dan Olson's (Folding Ideas) excellent video where he is able to do this measuring the curvature of a lake near his home that has a very specific geography that lends itself to this sort of experiment. I've seen all sorts of ways to prove this measuring shadows and poles, using gyroscopes, etc. and wanted to know if there are any practical guides for proving once and for all that the Earth is round for yourself relying on nothing more than experimentation.
What I'm not looking for:
- Math relying on flight times/charts
- Video/picture evidence
- Deductive proofs built on agreed upon premises
- Expensive tests
- Extremely time consuming projects
- Underwhelming results (relying on a probabilistic argument for a round Earth from the evidence.)
What I am looking for:
- Practical experiments
- Things I could potentially do without spending much money
- Tests that aren't largely comprised of accepting someone else's research
- Potentially math-heavy evidence
- Results that are strong and conclusive
I've thought of finding some easy to test version of Eratosthenes' proof using two poles. I've also thought about using a balloon and sending something to space like what is done in this Tom Scott video. Nothing seems well documented in such a way as for me to be able to follow it at home.
TL;DR: I think it would be a meaningful experience to have the power to prove the Earth is round by myself, for myself. I can only compare this desire to the desire a child with a telescope has when wishing to observe Saturn or Mars themselves for the first time. It's not to prove anything or to settle doubts, but for the personal value of independently observing this astronomical fact oneself.
17 votes -
Reducing late-night alcohol sales curbed all violent crimes by 23% annually in Baltimore
33 votes -
Daniel Kahneman, who plumbed the psychology of economics, dies at 90
16 votes -
Mechanism keeps track of the time cells take to split, sounding the alarm on cells that may turn cancerous
11 votes -
Memories are made by breaking DNA — and fixing it (in mice)
19 votes -
More exposure to artificial, bright, outdoor night-time light linked to higher stroke risk
16 votes -
Daniel Kahneman, renowned psychologist and Nobel prize winner, dies at 90
19 votes -
Water isn't normal
24 votes -
Researchers show that introduced tardigrade proteins can slow metabolism in human cells
11 votes -
The mystery of spinors
4 votes -
When you make a mathematical knot using elastic material you get jumping loops, and challenging puzzles
8 votes -
Investigating touchscreen ergonomics to improve tablet-based enrichment for parrots
19 votes -
Science will only end once we've licked all the objects in the universe
20 votes -
Scientists studied how cicadas pee. Their insights could shed light on fluid dynamics.
7 votes -
I teach you weird animal mating facts for half an hour
13 votes -
The Dunning-Kruger effect is autocorrelation
30 votes -
Psilocybin therapy alters prefrontal and limbic brain circuitry in alcohol use disorder
17 votes