We can argue r-squareds and p-values all day long, but there are several solid concepts behind the hypotheses that initiated the climate change debate. (I have included links as jumping off points)
Atmospheric CO2 concentration is either rising, or it is not (
The Keeling Curve).
The mean and varaince of global near-surface temeprature is either rising or it is not (
Deliberations continue).
Sea temeprature and chemistry are either changing, or not (
Yes, and yes.).
Carbon formerly sequestered in fossil fuels and other areas (methane in the tundra as cited by Anvil-X, etc.) is either being released in ever-increasing quantities, or it is not (
it is.).
CO2, CH4, O3, H2O(g), et al. either reflect certain portions of the electromagnetic spectrum, or they do not (they do, reference any chemistry textbook).
Atmospheric CO2 concentration is either correlated with historical temperature shifts, or it is not (
it is.).
We are either seeing shifts in plant phenology and species distribution on (latitudinal and altitudinal bases), or we are not (
yes,
yes, and yes).
It's not a question of if we have the data, but rather of the interpretation. Climate is, literally, the most complex and interdependent system on earth, so the claims, motivation, and reasoning of anyone making definitive claims about the whither-to and why-for of the changes we see should be subject to the very highest of scrutiny. Certainly, policies developed from a field which evolves as rapidly as climate science should be designed to be as flexible as possible.