We cannot interact with the outer universe and don't know if the laws of physics as we know in our universe, hold in this region. Think of it as our observable universe being an air bubble floating in the larger ocean which is the actual universe.
For some reason I thought Mars was larger than Earth...
It's pretty hard to debate at this point that humans are having a huge impact on our climate though.
If you are going to take a position that is in opposition to scientific consensus and common sense, then come armed with something stronger than "we can't be sure". Post evidence at the very least.
You can always find "a" scientist that disagrees, or several; but the overwhelming consensus (which represents our best current model) is that climate change, as we see it occurring now, is primarily caused by human activities.
If greenhouse effect is to blame, then fine; but to claim that the greenhouse effect is responsible *rather* than humans would be like a drunk driver claiming that it was simply a transfer of momentum and rapid acceleration that killed the family of four, "not me." I would argue increased CO2 emissions is a valid answer for a cause of climate change.
It's not asking for the lowest value of temperature. If you read about your link more you'll find that even though they created a state with negative Kelvin values, that state is hotter than positive temperatures due to the definition of the Kelvin scale.
It goes from +0 to +∞ to -∞ to -0 with increasing "hotness".