Were a similarly intense geomagnetic storm to occur today, it would likely seriously damage the electrical power grid, causing widespread outages and blackouts, as well as disrupting satellite communications.

Is this really true? I’m suspicious for a few reasons:

1. If it were true, I expect it would be a national security concern, and quickly remedied

2. While there is a lot more dependence on electrical connections, there’s also many more sources of disturbance now. So I suspect some of the failure modes are tested by “normal” human activity

3. EMI is a known risk, in my previous job we actively tested and built for it. I suppose if the limits are inappropriately set , or if this sort of testing isn’t wide spread, it could still be an issue.

4. As long as there’s a neutral line, i think any common mode should be rejected, in which case this should be fine?

Not sure that I can speak to everything, but I did take a course specifically on space weather + its impacts on Earth and have some context I can maybe share. For your first point, you are correct it is a national security concern. There are standards already in place that aim to address/mitigate potential disruptions from solar storms/ space weather, but the concern is/would be if these standards are sufficient for an extreme event like Carrington or this 1840s example. From a national security perspective, it's also not a risk that comes from an adversary, it's not something Russia/China/Iran/[insert country] can do to us, it's just an environmental consideration, and could happen to anyone (and if any one country is effected in a significant want, it's likely that others would be facing some consequences of the storm as well - especially w.r.t. satellites). From a strategy perspective, it's similar to if an earthquake destroyed the 3 gorges dam - it's obviously a risk but it's categorized a bit differently. It's more about how quickly can you re-establish normal operations rather than how do you fully prevent it. Obviously mitigation is part of that, but it changes where it gets prioritized.

And to segue into your later points, the reason it's unknown if the current standards would be sufficient is because these sort of events, and how they interact with a continent-sized electrical/ transmission systems (the grid), is a pretty complex problem. It's also one that we can't exactly test in a lab or controlled environment beforehand with a super high degree of confidence given the scale that the phenomenon takes place at (the whole planet). EMI testing that occurs for most tech products today isn't super focussed on the currents induced by a solar storm, which are low frequency/quasi-DC/much less predictable (the effects vary geographically and in time-scales/patterns that "typical" EMI/EMC does not).

Some googling lead me to a NOAA doc that says GIC's "quasi-DC ... currents flow through transmission lines and enter/exit the power grid through grounded transformer neutrals" which to me reads that simply having a neutral line isn't sufficient, but I'm not an EE and could be misunderstanding what you're saying and what this doc is speaking to.

The good news is that events like this are relatively rare, confined (generally) to certain parts of the 11-year solar cycle.