Disclaimer! I am not a solar radiation scientist, just doing about an hours worth of research here, I may be wrong about some of this!

So, this is the most in depth explanation of how Solar Flares and CMEs are measured that I can find.

https://curious-droid.com/1349/how-prepared-are-we-for-a-carrington-level-solar-storm/

So, if the reading from NOAA of G2 is accurate… and it is only a solar flare, then basically that is nothing to worry about. The G2 reading is NOAA’s way they demark the Kp index, which in summary, is a measure of geomagnetic activity on and near Earth. G2 corresponds to a Kp index of 6, a moderate storm. Not world ending, relatively common.

The problem is that the actual magnitude or strength of CMEs cannot be accurately detected until approximately 15 minutes before they impact the Earth’s magnetic field.

The estimates for the Carrington event, of the 1800s, which caused telegraph sets to spark and shock their operators, and even set some telegraph stations on fire, is apparently estimated to have been -900 to -1750 nanoTeslas, but that is by a different measurement method called DST or the Disturbance Storm Time index, which I am unable to figure out how to correlate with the Kp value without paying to directly access scientific studies of that topic.

From abstracts, I have been able to see that the Kp score is considered by some scientists in the field to be outdated, both because it has a low time resolution of 3 hours, and is also a capped index where it is possible to have extremely high values far higher than the threshold for the highest possible Kp value. Those scientists proposes a new measurent index called Hpo, which has a time resolution of 30 minutes and does not have a maximum capped value.

For what its worth:

https://wdc.kugi.kyoto-u.ac.jp/dst_realtime/202312/index.html

This looks to be a realtime measurement of the DST index from a scientific organization in Kyoto. Again, it is apparently not really possible to know the DST value more than 15ish minutes before a CME impacts Earth, but I guess if there are aurorae down to california and power stations around the world start lighting on fire, and you somehow are able to check this website and see a value lower than -800 or so, you can uh, have confirmation that yes indeed a CME has ended modern civilization.

Basically, the Kp index measurers seem mostly to be focused on the X Ray emmissions from Solar Flares and their propensity to screw up stuff on Earth and Near Earth. CMEs on the other hand are associated with basically heavy solar flare activity, but that correlation is an inexact science at the moment.

While a Solar Flare is basically a surface level event of the Sun’s outer magnetic field lines warping such that a burst of energy is released… a Coronal Mass Ejection is a far more extreme scenario where the magnetics and other processes going on on and in the Sun actually cause the Sun to sort of belch or throw a chunk of the Sun’s more inner layer (the Corona itself) at the outward, and generally speaking this involves extremely high energy particles that can cause far more havoc than just a solar flare.

Apparently in 2012 an extreme CME was only 7 days away from hitting Earth. The Sun’s surface rotates as does the Earth rotate around the Earth, and basically CMEs just travel straight out radially from the surface of the Sun: If that particular CME had erupted 7 days earlier, it would have been a direcr hit on Earth instead of a glancing blow that really hit only some of our highest orbiting satellites.

Anyway, Ive researched the CME ending the world scenario in the past enough to know that yes, it /could/ happen, and no, there is no publically known way to predict the possibility of this.

While it is possible to harden power grids against such a scenario, the reality of the situation as I understand it is still basically this:

Above ground power lines would basically be supercharged with electricity, most common transformer substations I am aware of in America at least would likely be overwhelmed by a Carrington level event, and basically catch on fire/explode.

You can say that hardened and/or deep underground systems would remain intact, and I can say that well, one, a lot of the research on what you actually have to do to pull that off is hard to find or classified, and that that doesnt change the fact that the vast majority of at least the American power grid is not that kind of military grade hardened… and there can always be a CME more powerful than the Carrington Event.

So yep, it sadly is possible that a huge CME could basically take out huge swathes of power grids around the world, leading to mass chaos as powered heating stops, commerce stops, communications stop, and the only way to fix all this is step one to somehow start producing orders of magnitude more transformers than are currently produced each year globally to replace all the ones that have failed… all while there is no power or communications in the places that need those things to manufacture the replacement transformers.

Basically maybe parts of militaries would survive with their hardened tech and lead to something like the brotherhood of steel, i dunno.

Not exactly the stone age, but yes, a large enough CME could absolutely fry a good portion of our tech and it would end up killing billions of people due to disruptions to communications, agriculture(primarily), healthcare, and logistics. There is equipment that would survive, there are items that could be repaired, and most of our knowledge wouldn’t be lost.

It would not be fun.