According to this book Ch 3 we should be approaching another ice age, but because of man's influence over the last 100 yrs, we have almost reversed the cycle.

http://www.yeomansplow.com.au/priority-one-contents.htm

This book doesn't promote green types or the "Global Warming anarchists" but it does approach it with some interesting facts that based over time has contributed to what we are now experiencing..

There are so many factors involved in the overall scheme of things that a lot get missed and those that have agendas, only focus on what it is they are promoting (Greens vs Big Oil), but if you take into consideration everything you will come away with a better perspective of the whole picture...I would say man is definately responsible for speeding up the process of warming.