I think the only audience for this sort of thing are flight fanatics and the uber-rich. Aside from the climate impact, there are a number of other issues:
> the overcrowding of all airports is not getting better, so tying up a jetway time slot for a tiny number of passengers will be expensive, and the only plausible way that could work is if the terminal is completely remoted from the general flow of passenger traffic
> ditto the takeoff/landing slots -- this is more intractable, since the noise is likely to force such planes into a daylight slot, which need to be reserved for planes that carry more passengers
> the inevitability of a higher cost will limit the clientele to the rich and/or profligate -- not conducive to the general public accepting getting bumped to let such a plane into the flight schedule of the local airport

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yes, but do we want to "give" the uber rich that option ? if it means CO2 emissions that are not "required".

another day in paradise, or is paradise one day closer ?

That part will be up to the likes of Boeing and Airbus, who probably aren't that interested in onesie-twosie production runs. Boeing flirted with idea of an SST for about 6 months, i.e., they announced an intention and rescinded same.

I don't know that we have that ability to prevent someone from building one, based on CO2 alone, short of some rather drastic political changes.

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there are several start-ups in the UK interested in this, and Gulfstream (and probably the other biz jet builders) and Lockheed-Martin.

Actually, I think we have plenty of opportunity to "kill" this. Easy to make a rule "if supersonic then no CO2 emissions". Now of course they'd just go shopping for an approval (if not the US, then maybe Russia?) … which'd only create another windmill (to tilt at).

another day in paradise, or is paradise one day closer ?

I meant as political will.

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Pretty lengthy "6 months".

The simple solution for the CO2 concern is to include an appropriate CO2 tax, and then direct the resultant tax revenue towards other CO2 reduction programs, selected for effectivity.

If such a policy is designed and implemented correctly, then the overall effect can be net eco-positive.

I have a friend working on the Aerion project which seems really cool from a technical challenge standpoint. The bizjet side of things seems to fit the supersonic thing better (customers are already paying otherworldly sums for travel, and are likely to be quick to get in line for the new "one up" on their peers), but I'm still curious how they'll handle the overland noise aspect. It was my understanding that aside from fuel consumption, sonic booms were the main thing that limited the adoption of supersonic aircraft for travel purposes. I've worked near Edwards AFB and while the sonic booms were cool when they rattled the hangar, it would be way less cool rattling my house at 2AM.

I know NASA and others have worked on aerospikes etc that are supposed to make things quieter, but I hadn't heard of any major breakthroughs that would completely eliminate the boom.

Interesting point. Here's a tidbit.

NASA investigates the 'FaINT' side of sonic booms - phys.org

Private jets won't take jetway space, so that's a good thing for most overcrowded airports.

That just leaves:
> noise and air pollution
> deconfliction of landing slots -- if this results in more private jets flying into already crowded airports
> deconfliction with other aircraft -- something that's going twice as fast as you results in less time to avoid collisions
> deconfliction in air traffic control -- shorter timelines means more potential conflicts, more stress, etc.
> possible need to run SSAs at a different set of altitudes to minimize interactions with slower aircraft

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Excuse my ignorance here-what is the current requirement for spacing between commmercial aircraft flight paths?

I have to think that even if at ground level an aircraft doing mach 1.5 at 35,000 ft isn't audible that if that same aircraft is flying anywhere near a typical A320 or 737 commercial flight that it's going to scare the pants off of everyone inside. I've looked out the window on flights and seen aircraft heading the opposite direction within probably half a mile or so of the aircraft I was on. If that other plane was going supersonic I have to think you'd feel it. What kind of additional airspace requirements would be necessary?