My 10 year old apartment has a heat pump rated for a CoP of 2.3 at a temperature of 17°F/-8°C, which is actually below the record low outdoor temperature for this area. This isn't some exotic new equipment or a model designed for cold climates; it's what was cheap and mainstream a decade ago.

The data wasn't terribly correlated to temperature, though he didn't have a mini-shed for the outside unit to protect it from snow, so it probably had to defrost more often during the less-cold, snowy days.

FWIW here in Oslo, we've been using a mini split as the main heat in our home, where it's often -15C for long stretches during winter, and can get down to -25C. It's in the main livingroom, and we do supplement the upstairs bedroom with resistive foil floor heating during the coldest periods. Other than that it's doing great, and comparing the electricity bills with friends and colleagues who don't have a heat pump it's definitely helping a lot.

[1]: https://youtu.be/fxEqVuiHhM0?t=523

You are talking about air source heat pumps. There are actually variants of that technology that work fine at -20 and below. -20 is actually quite far above absolute zero. The challenge is not that there isn't enough energy but finding and pumping liquids around that can absorb that "heat" and actually stay liquid. Efficiency indeed drops below zero. But it still works.

However, ground source heat pumps are not dependent on the air temperature at all and work anywhere you can get a decent temperature gradient from the ground. Which is pretty much anywhere except maybe on top of the arctic ice sheet in e.g. Antarctica.. Stick a few pipes in the ground and get them deep enough and you can have an nice cozy house pretty much anywhere that is not located on a few miles of ice. NY is perfect for that. No permafrost there and stable temperatures below ground throughout the year.

And again, they have been doing this for decades in places like Finland, Sweden, Norway, Greenland, etc. That's because this stuff works and is reliable and efficient enough. This is not some new kind of science fiction technology. Millions of households depend on this when it gets to minus 40C and below (about the same in C and F). And having lived in Sweden and Finland, I can tell you that they like their houses heated properly there and it really gets that cold up north. They don't use gas in houses there at all and never have. There are no gas distribution networks there. Oil based heating has been phased out in most places there a long time ago. But people forget that that stuff has to be trucked in and trucking anything in gets tricky when there's a few meters of snow on the roads. Heatpumps, resistive heating, district heating, and wood based stoves is pretty much all they use there. District heating is not common outside the more populated areas (i.e. most of the Arctic region) with the exception of the larger towns and villages.