The current view of physics is that to have a supernova you need to have a sun that is at least 8 solar masses in size, thought to have a high silicon or calcium content seen in their absorption lines. One candidate that is only 150 light years away is IK Pegasi A, located at a distance of about 154 light-years away, light taking 154 years to get to us, but if it went off 154 years ago we may theoretically get the full results maybe 15 years after at the earliest, light being the immediate warning and some possible drastic effects.
A lot of what we know is very theoretical and based mainly on the standard theories of stellar evolution, but Betelgeuse, one of the most easily observed and recorded stars has shown that all is not completely known and predictable using these models, doing quite unexpected things. It’s said and calculated according to theory, that a supernova within 26 light years could strip the world of half its ozone layer (50%), but in a system that is said to be heavily effected by 1/7000th of its composition, the CO2 proportion in the atmosphere change over the last 250 years, even a 1% change may have a major impact, the higher level of the oxides of nitrogen being apparent in ice cores that are said to be from such events at much larger distances.
The James Webb Telescope has alreday started to question the theories of stellar evolution that are current in a small wy and it has only just started to show minor results. Just wait until it starts to be fully operational and had time to look at the results and ramifications, we may find the imagined security of the 8 mass star is suspect.
The red giant Betelgeuse still seems to be quite variable. It is between 200-700 light years away. An estimate of a similar distance supernova from about 2-3 million years ago and accumulations of radioactive iron on the sea bed suggests that there might be little effect if it did happen, but again this is an assumption as nobody was around to tell if it did. It’s estimated that it would need one around 30 light years away to have a drastic effect, but again that is based on no real knowledge of what will or can occur.
Supernovae are easy to spot but hard to record. The fact that many are recorded, especially when things are overcast doesn’t give a good impression. To get through clouds and that much takes at least a worrying level of light, the view is ‘if it isn’t seen and verified it didn’t happen,’ being no excuse in the real world when it comes to its effects.
I suspect that stellar events may be much more common and may influence things on our fragile earth much more that is appreciated. The earth has a cross section 7,926 miles wide and added to this an extra 16 miles wide of most of its effective atmosphere, so an energy receiving area of maybe of around 100 million square miles from one direction, althought the cross section for very fast particles may only be around 59 million square miles.
In 2009 higher levels of nitrate ions were detected in ice cores that related to the 1006 and 1054 recorded supernovae, but this was only because they were actively looking for the link. Had they not had the previous knowledge of the events they may have not noticed them at all, being lost within other changes from unknown sources. That they were found there and elevated does not suggest a completely hidden effect, the temperature cooling after this point after being quite stable and not returning to the same level until about 1930, and the world population growing much faster at about this point after being stable and low.
Simple ‘climate or environmental change’ is said to have led people who are secure and established to up and move to other areas, many discarding, destroying or burying their most revered monuments at a point in time. You do ask, ‘what would it need for something to leave the home you own and live in, give up your trade, destroy or bury your church, then move somewhere else in the world without sure knowledge of the new area, taking just what you could carry?’ The current view is that ‘it just happened.’ My view is that it would need something pretty formidable and disastrous to make me do that.
The big question is always, ‘what is driving things like climate change, and what are just driven by climate change?’ In effect, ‘what is a cause and what is just an effect of that cause, or part of the consequences?’ Belief and faith are sure, science can never be, just giving likelihoods or not, the reported truth just being changed by peoples beliefs and confidence in other peoples views and beliefs.
The current view is that we are in little danger for the next few million years from this area. But this is based on the current standard models that are starting to be worried about. Still, the odds are thought to be low and the earth has probably endured many distant such events.
If the standard star model is not correct then we can’t be sure. Stars have been observed from a distance for maybe only 200 years, our slightly unusual star maybe having a life of +10 billion years, so it has been closely observed for about 1/50,000,000th of its life, others similarly observed at various stages for that proportion. How close it is to reality is a statistical exercise.