@Noflaps said in #21:
> I am transfixed by the apparently massive amount of work put into a single post by
@Thalassokrator .
>
> Well played.
Thanks, I appreciate that! They sometimes are too verbose though. All too often in fact.
> But now let me say it. Betelgeuse doesn't seem to be the sorta star around which sentient beings will hang. But it's not to be ruled out entirely. We might be about to witness the death of a civilization. A sobering thought.
I hadn't thought of that, you might be right! Pure speculation of course. I guess there's a (very) small probability that there might be sentient life on an exoplanet orbiting a star that's neighbouring Betelgeuse and is close enough for the supernova to be a threat to said life.
But there's fortunately almost certainly no sentient life living on a potential (undiscovered) exoplanet orbiting Betelgeuse itself. Not only because of its rapidly shifting habitable zone (it's a variable star and has also expanded significantly since its departure from the main sequence and development into a red supergiant) which not conducive for life.
This star is so massive and bright that it burns though its fusion fuel astonishingly quickly, much quicker than our sun does. This means that Betelgeuse is a spring chicken in cosmic terms: Only 8,000,000 to 8,500,000 years old (mere millions, a puny age, I tell ya!).
To get an idea on how slow evolution is: planet Earth is approximately 4,500,000,000 years old, yes billions with a B! At the very least 4.404 ± 0.008 billion years:
www.nature.com/articles/35051550Some of the earliest evidence for life on Earth is about 3.7 billion years old (
www.nature.com/articles/ngeo2025). All life was unicellular for 1.6 billion years at the very least. Probably for longer. Multicellular life – even though it probably existed for some time before that – only really got going (developed into large multicellular life) at the Cambrian explosion, about 540 million years ago, 3.2 billion years after some of the first evidence for life on Earth. Mammals might have appeared 225 million years ago at the earliest. And modern sharks have been around for at least 200 million years. Anatomically modern humans (Homo sapiens) emerged ≈315,000 years ago. That's how slow evolution is. The star Betelgeuse is less than 9 million years old. Fortunately that's probably not nearly enough time for complex life to evolve if Earth's history is anything to go by.
We could enjoy the cosmic spectacle knowing that it's most likely not affecting any existing sentient life forms. I agree with the sentiment that it would be kind of sad to see Orion lose his shoulder though ;-)
> I hope not to see the same thing here. Our star is probably safe. But that's hardly enough to reassure.
Our sun has less than one fifteenth of Betelgeuse's mass. So yes, it's safe. Our sun won't end in a type II-P supernova like Betelgeuse presumably will. Rather it will end up expanding into a red giant and then gently producing a planetary nebular about 5 billion years from now. Leaving behind a white dwarf star.
Life on Earth will die out (for various reasons) much sooner than that though an estimated 1.6 to 2.8 billion years from now. A bit sobering at first glance. Note that such estimates and far future predictions are not necessarily very accurate.
hal.science/hal-00297823/file/bgd-2-1665-2005.pdfThis paper gives Earth's total habitability time as 6.2 billion years and notes that complex life (like us) is only possible during a small fraction of that habitability time: 1.3 billion years, the rest of the time is only suitable for unicellular life (or already passed before complex life evolved). Complex multicellular life on Earth has about 0.8 billion or 800 million years left according to their model (while unicellular life can potentially last twice as long). Given that complex life emerged at the Cambrian explosion a bit more than 500 million years ago, it still has more than half of the way to go. Not yet time for a mid-life crisis! ;-) Again, take these numbers with a grain of salt.
Either way, you can be reassured that nothing remotely similar to a type 2 supernova will happen to our sun. Ever.
> No, I'm not losing sleep over "climate change." I'm more worried about contagious foolishness.
Anthropogenic climate change is a symptom of contagious foolishness! And maybe you should lose sleep over it. I'm obviously not advocating for insomnia, but I want to know about it.
What's worrying me most is the dramatic pace at which it happens. It's truly unprecedented within the lifetime of our entire species (315,000 years). Before I explain what I mean by that, some basics (feel free to skip ahead to the dashed line if you already know this):
CO2 is the most important greenhouse gas. It absorbs infrared radiation (heat radiation or IR for short) from the Earth at various wavelengths, importantly at 4.26 μm [2,347 cm^(−1)] (asymmetric stretching vibrational mode) and 14.99 μm [667 cm^(−1)] (bending vibrational mode). Here's an illustration:
en.wikipedia.org/wiki/Infrared_spectroscopy#Number_of_vibrational_modesAnd then reemits the IR radiation (in part) back towards Earth thereby keeping energy in the system that would otherwise have escaped to space quicker. Therefore warming the planet's atmosphere. The greenhouse effect is a bit more complicated and subtle than that, but this simplified picture has to do for now.
The fact that CO2 has these absorption characteristics is nothing special, many molecules have them. It's an inevitable consequence of the chemical bonds between the molecule's atoms being "loose" enough – so to speak – for them to bend and vibrate and distort. These vibrational modes can be driven by electromagnetic radiation of a specific (resonant) frequency.
You intuitively know resonant frequencies from pushing a child on a swing:
When you don't push frequently enough (or too frequently, i.e. often push, when the child isn't even within your arm's reach, or push against the motion when the child is still moving towards you before the apex) the swing will not go any higher (and you'll soon have an unhappy child). It's only when you time your pushes just right, such that you push when they are at their highest point (apex), that you get the swing to go "HIGHER!" and "HIGHER!". That's how you know you've hit the resonant frequency of that particular swing (other swings might be longer or shorter and have a different resonant frequency)! The same is true for molecular vibrations and changing electric fields due to electromagnetic waves (i.e. IR radiation) that give the atoms a push. You need the correct frequency to get the molecular vibration going. And the frequency differs from molecule to molecule.
The trouble with CO2 and other greenhouse gases is that their resonant frequencies lie near the most common frequency of IR radiation emitted by the Earth. Any chemistry or physics student that's worth their salt can sit down and calculate these resonant frequencies based on the geometry of the molecule and the strength of the molecular bonds. Or measure them in a laboratory experiment. It's fairly basic physics at the intersection of mechanics, statistical mechanics, thermodynamics and electrodynamics.
So the fact that CO2 concentrations and temperatures of the atmosphere go hand in hand is not only directly observable, but also based on sound physics.
commons.wikimedia.org/wiki/File:Temperature-change-and-carbon-dioxide-change-measured-from-the-EPICA-Dome-C-ice-core-in-Antarctica-v2.jpg---------------------------------------------------------------------------------------------------------------------------------------------
So as we've seen high CO2 concentrations roughly correspond to high atmospheric temperatures (more accurately: there's a feedback between CO2 and temperature). Knowing this, have a look at these:
[1]
www.climate.gov/media/13493 (CO2 concentration in Earth's atmosphere in the last 800,000 years)
[2]
commons.wikimedia.org/wiki/File:CO2_40k.png (CO2 concentration in Earth's atmosphere in the last 40,000 years)
As of November 2023 the CO2 concentration in the atmosphere is at 420.46 ppm, where ppm stands for parts per million (1000ppm = 0.1%). That might not seem like a lot, but the global average temperature (anomaly) is extremely sensitive to changes in this concentration. Around 180-200 ppm is a typical glacial (commonly known as an ice age). While interglacials (warm periods) usually have CO2 concentrations of 240-300 ppm (around 100 ppm more). The highest the CO2 concentration has been within the past 800,000 years (a period nearly three times longer than the existence of Homo sapiens) was 300 ppm. But now it's 140,2% higher than that previous record.
What's even more worrying is the astounding pace at which this change has taken place due to human activity. A simple look at the data in [1] or [2] makes it obvious that something very unnatural must very recently have happened to Earth's atmosphere. It's the Industrial Revolution and the subsequent release of millions of year of ancient carbon uptake within just a few hundred years.
The 21,000 years average rate of change between the last glacial and the preindustrial interglacial is about 0.0045 ppm/yr. That's the natural rate of change. Even looking at the steepest part of the curve in [2] (between 15,750 and 17,570 years ago) we only get rates of change of 0.017 ppm/yr. That's the most extreme rate of climate change nature can provide, emerging from a glacial and rapidly changing into an interglacial. During interglacials and during glacials the rate of change is much lower. Considering the preindustrial data (up to the year 1750) we are currently already in an interglacial. So the rate of change should naturally be close to zero. Right? Right? But it isn't:
The current rate of change is 2.48±0.25 ppm/yr. Remember that 100 ppm can mean the difference between a glacial (complete with a kilometer thick ice sheet covering Northern Europe ) and preindustrial warm climate. What nature usually does in 20,000 years we currently do in 40 years (100ppm divided by 2.48 ppm/yr ≈ 40 yr). If you're born now and planning on living to the ripe old age of 40 years, be ready to experience CO2 concentration changes that are equal to the 100,000 year glacial interglacial cycle. On top of already being in a record warm interglacial.
[3]
mlg.eng.cam.ac.uk/carl/words/carbon.htmlThat's a change 150 times (!) faster than the fasted natural rate in the past 40,000 years. And 550 times (!!!) faster than the typical average rate of change (averaged over 20,000 years) during the transition between glacials and interglacials within the last 800,000 years. Earlier in this post we've seen how slow evolution is. Do you think the animals and plant life (including us) can keep up with such insane rates of change in their environment's temperature for long? Does CO2 acidify the oceans? Do chorals bleach?
WE are spring chickens! Homo sapiens has been around for only a few hundred millennia (83 ppm of the history of life on Earth). Sure, the climate has always changed. But it did so slowly (since we are around). Never at this rate. Now we are actively changing the climate at a rate that's at the very least 150 times faster than anything our species has ever experienced naturally in its short existence. And even the rate of change is steadily growing (it's up 0.02 ppm/yr since I made a previous post 10 months ago). Maybe we should lose some sleep.
I've written a post providing some details I've left out here a few months ago (shameless repost of the link):
lichess.org/forum/off-topic-discussion/a-page-called-ask-any-questions-about-climate-change?page=5#44A video [4] says more than a thousand words:
www.youtube.com/watch?v=gbxEsG8g6BA 
