Your question is worth responding to because it highlights two major problems in the public climate discourse: (1) lack of scientific knowledge and (2) the disinformation campaign by interest groups.

(1) That the CO2 rise in the atmosphere is caused by human emissions is well established since the early 1960s from isotope measurements, as the isotope composition of cabon in fossil resources (coal, oil...) differs from that of carbon circulating in the natural Earth system. If isotope analysis is unfamiliar to you, you can also look at a simple budget calculation. We know how much we emit, and it is more than enough to explain the entire CO2 increase in the atmosphere. In fact, the accumulation in the atmosphere represents only 57% of our emissions. So there can be no question about this CO2 increase coming from somewhere in the natural Earth system, because to the contrary, the natural Earth system is taking up almost half of our emissions. This is all basic knowledge that you can look up e.g. at Wikipedia if you are really interested in knowing this: http://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atmosphere. Or check out the carbon budget here: http://www.globalcarbonproject.org/carbonbudget/index.htm

(2) What exactly is wrong with the "hockey stick" climate reconstruction in your opinion? It has been confirmed many times over by independent groups of scientists. The latest massive effort in paleoclimatology is the PAGES 2k project which has produced a global temperature reconstruction for the past two millennia - check out my article on it here: http://thinkprogress.org/climate/2013/07/08/2261531/most-comprehensive-paleoclimate-reconstruction-confirms-hockey-stick/ Their results look identical to the original "hockey stick" reconstruction of 1999. The only thing that is so special about the "hockey stick" is that it was subject to a massive disinformation campaign by politically motivated "climate skeptics" - but all their allegations have long been disproven. The authors of the original "hockey stick" reconstruction and their work are extremely highly regarded in the scientific community, as seen from the fact that they won important awards from the world's two largest geoscience organisations, the American Geophysical Union and the European Geosciences Union. Again, you can get solid information from Wikipedia if you are really interested: http://en.wikipedia.org/wiki/Hockey_stick_controversy



The key thing about the climate discussion is: be very careful where you get your information, since there are many who dislike the political consequences of confronting climate change and they are working very hard to cloud the facts.