If carbon levels stabilized at present concentration, how warm would it get?

All the answers, in some detail, are here:

http://www.ipcc.ch/pdf/assessment-report/ar4/syr/a...

... and if you want even more detail you can read the full reports (e.g. the Physical Basis one).

In all the testing I have done co2 would have to reach 10% or more of the atmosphere to achieve even close to the same effect that 50% relative humidity has. Co2 at 4000 ppm or lower has virtually no heat retention value at all. The tests that were used to label co2 as a green house gas used containers with 100% co2 against normal air.

From just CO2 alone the warming "in the pipeline" is 0.5°C from the carbon we've already emitted. The science behind this is that we've emitted CO2 so rapidly that the climate system isn't in equilbrium and the oceans haven't had time to warm up yet.

However, there are other feedbacks when you increase CO2, such as water vapor (another greenhouse gas) also increasing. So I believe the total expected warming "in the pipeline" is 2°C.

See the link below for a more scientific explanation, particularly Step 6.

There's about a 50% chance that the Earth would warm, however if no changes occurred to greenhouse gases then there's about a 50% chance that the Earth would start to cool.

The only think we know 100% is that there is a 0% chance that the climate would be static and never change one way or the other.

Forget about it. That global warming was a farce dreamed up by Al Gore. It's a con job.