Ragtime wrote:
There is no clear evidence that humans cause a significant amount of global warming, or even that unidirectional global warming exists. Remember, just a few decades back, people were up in arms about "global cooling"!

i wasn't around then but i've heard a lot about it.
i don't think we should ever rule out the possibility of us adding to a problem...even if it's a fraction of a percent...with how the smallest things can add to an exponential increase elsewhere, it'd be foolish to simply throw out all together that our contribution didn't do something.
think of it like a balancing act and right now we're pushing on it and offsetting the balance. the earth isn't exactly gonna overcompensate...because that isn't what the earth does...it compensates to get back to the middle. if we keep pushing, it will eventually result in a compensation that will adversely affect us....so...we need to study it more. there is a decent bit of evidence, though, to support the side that humanity has had influence in our current environmental situation. how much is yet to be determined, though.