“Can anybody tell me how far out of orbit earth would have to move to make it inhabitable for humans? Or do we know? Either too hot or too cold.”
Solar constant is 1.361 kilowatts per square meter. The change of yearly distance from sun is 1.412 kW/m² to 1.321 kW/m²
http://en.wikipedia.org/wiki/Solar_constant
Earth orbit difference:
“Perihelion (106 km) 147.09
Aphelion (106 km) 152.10″
http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html
So if orbit changes to more circular: 147.09 million km one gets
1.412 kW/m².
If earth were further out [and more circular] to Aphelion distance
it be 1.321 kW/m².
And one compare it to average distance of solar constant of
1.361 kilowatts per square meter.
Or adding 72 watts per square meter is closer, and losing
40 watts per square meter if further away.
If believe CAGW then a 72 watts per square meter of forcing would
dramatically change earth climate.
I think an addition or subtraction of say 100 watts per square meter
would cause a slow change in climate and global temperature, and humans could easily mitigate the long term effects fairly easier, or steps could taken
to change our world in some manner if that was seen as needed in the future. If it was a matter of choice, I think the nearer to sun is better than further from the sun, mainly because where continental land mass are currently located- we would get more arable land.
Wheres cooling by 40 or 100 watts per square meter probably result in losing Canada and Europe beginning within several decades- assuming nothing was done.