Solar radiation, changes in Earth's orbit (it has been proved to be chaotic, longterm, AFAIK), microvawe from space hitting steam in atmosphere, volcanic production. There are few things that come to my head and might be connected to the problem. Some of this may sound as fringe. Nevertheless I would like to see credible debunking, using data and logic. May include calculus. If I see worth, I will relearn calculus. Heck, it may include whatever that will make me want to think about it - models, tables, photos.

Given the gravity of the problem and weight on future if there is miscalculation, I claim this should be taken out of politicians' hands. Wikipedia style.

The hockeystick scandal did not help, either.

And last but not least: what made the last glaciation melt and what caused it in first place? Model, please. Something I can compile on my computer. Twenty five years ago, maybe twenty, it would have easily placed itself among first ten fastest supercomputers (if I am correct). I am sure this machine can handle some computation. Even if not, give me a source code and let me worry how to run it.

EDIT: Ok, I would prefer a bunch of equation, differential too, rather than source code.

EDIT2: As of "being caused at least to a considerable degree by human activity", I am already rather certain that humans did their best to be part of the problem. The question I am trying to answer is "to what degree", not "if".