Completely out of my domain and seat of pants rationing here, but although the impact probability is 1%, aren't we far far more certain about the /time/ at which it would strike earth? Could humanity collectively just migrate to the side of the world that will be shielded for a day?
The bad news is no, we have nothing even remotely close to the infrastructure necessary to move half the world's population. We don't have the transport, being limited to planes and boats mostly.
The good news is that, worst-case scenario, this is going to wipe out a city. And cities and their surrounding areas can absolutely be evacuated. We definitely have the cars and buses necessary for that.
But in any case, we certainly have the logistics to move populations given the timeline. Not everyone has to evacuate and return within a 3 day window.
Even without incentives, in all likelihood, those who can will evacuate early for peace of mind, and as the prediction becomes more certain on its approach through measurement, individuals will I'm sure even start to return /before/ the pass. You know everyone has their own set of 9s to chase
Even if we had three years to move everyone from one side of the earth to the other and could handle the transportation, and then another three years to move them back, how are you going to keep them fed? We're just going to double our food infrastructure on half of the world?
Where do we house them for several years? We're going to double our housing?
How are we going to find all those people jobs to sustain them for the several years they're spending on the other side of the world?
All those things would have to be part of the logistics too. Energy usage. Health care. The list goes on.
It would be a logistical and economic upheaval the likes of which the world has never seen. It would lead to political chaos and massive wars over suddenly incredibly limited resources.
Humanity would survive, but a lot of people wouldn't. It wouldn't be a question of logistics, but a complete and increasingly violent reconfiguration of society in all spheres.
Even if we had the infrastructural capacity to move hundreds of millions or billions of people for that amount of time (how many airplanes would you need? where would they all stay?) the political considerations would never be feasible. Think if the asteroid would hit Central America/Mexico, and think of the politics of moving them further north into North America.
If we run a simulation forward to, say, Jan 1 2032, our uncertainty about where the asteroid will be is not only in, let's call it, the X and Y axes, describing a flat circle of where the asteroid might be (see [1]), but also in a Z axis.
That is, our uncertainty of where the asteroid will be can be described as a 3D shape. And if it's further "behind" or "ahead" in its trajectory, then it would be passing through Earth's orbit behind or ahead of time.
Knowing the time doesn't tell you which side of the planet it will impact. The asteroid and the Earth are both moving. From the asteroid's perspective, it can get ahead of the earth and the Earth rear ends it, which from Earth's perspective is the asteroid hitting from the opposite direction that it's coming from.
Knowing humanity and its ability for planetary level solidarity, its more likely that the most powerful nations would simply displace the weaker ones. "No offence bro, but we are the salt of the Earth, so get out of here and good luck".
What about empty places? Luckily for Greenland, the calculations predict that the flux of impacts to the poles for Earth is 22% greater than the flux at the equator [1]. So nobody (in their right mind) would want to annex it as an asteroid survival backup site.
