It took about 24 hours of computation time on a very serious supercomputer.
The world is a very big place, the vary few climate interaction sub models that have been characterized are also very non liner.
It's really tough to say about the interactions between the multitude of the climate interactions mechanisms that we don't yet realize exist along with the other mechanisms that we have a hazy realization of but have no realistic characterization or model pretty much makes any realistic analysis intractable.
I am not quite as arrogant as the Global Warming gurus so I have to admit I have absolutely no idea what realistic boundary conditions on a world wide scale might be or how to properly apply them. Given the complexity and scope of the problem and enormous size of the world, a slightly more humble perspective might be in order for some of the more vocal researchers.
The biggest factors are the amount of solar radiation energy that hits the earth and how much of that energy is either radiated or reflected back into space.
The amount of solar energy from the sun hitting the earth is constantly changing, we have no control over the sun, and very little ability to accurately predict what the sun's output will be over any extended length of time.
The amount of the sun's energy the Earth radiates and reflects back into space are not constants and the parameters that govern the reflection and radiation have not been sufficiently characterized to provide the input for an accurate, and possibly not even realistic basis for climate analysis.
The problem for the Global Warming gurus is that humble people do not get grants.
People that admit that they are just whistling in the dark don’t get grants. Unless you can tell some bureaucrat that you can produce tangible and useful results you don’t get a grant.
Given the over production of people with degrees in the last few decades the competition for a paying job in science is getting fierce. These people want money and the big money is in scaring people. For climatologist the easy money is in scaring people with Global Warming.
Cheers!