Firstly, and not to start a flame war here, but very clearly 99% of the world do not believe in a god.  This is a fiction.  For a start China is communist and therefore wont believe in a god, not mention Japan or in fact anyone practicing Buddhism.

So, is there a god?  It depends what you mean and how you define such a question. 

If you mean, is there a white guy with a beard and a unnatural fixation for Jewish virgins and that you can take a deep breath and relax knowing in firm certainty that by believing one thing or another will set you up for the afterlife?; then no, probably not.

If you mean, some sort of super being that created the Universe (note caps on the U); then nobody knows for sure.  It is possible, but then so if everything you can imagine and quite a lot that you can not.  A great book for examining ideas about this is The Star Maker by Olaf Stapleton or perhaps the free online book "God's Debris" written by the Dilbert author Scott Adams.  They both show that when you get to a "power" of that "size" you could quite easily mistake it for a simple facet of nature or physics.

If however, you want cold hard scientific certainty or rigid philosophical arguments one way or the other, again nope.  Neither science nor Philosophy has successfully argued that there is or is not a god.  That is to say that arguments are in fact put forwards and laws formulated regarding standards of proof etc, but in the end they are only measuring what they know.  Not what they don't.  So here the answer is again "as far as we know" there isn't a God.  Why?  because of the lack of rigid evidence.

Edit for spelling.