All of a sudden humans show up and we're arrogant enough to think that we caused it and somehow have to fix it?
A small proportion of humans are smart enough to have developed an understanding of fundamental physics, the chemistry that springs from it and how human activity is impacting the atmosphere. We already know we can have a large scale impact on the atmosphere from the impact of CFCs on the Ozone layer.
We now have ample evidence that heavily implicates human activity as the main cause of the rapid change in climate over the last 200 years that's moving far quicker than any cycles the planet has gone through over the prior million years. The body of scientific evidence that means we've been able to determine changes in climate the planet has experienced, both over extended periods of time and due to catastrophic events, is drawn from the same pool as that which tells us we have a large cause for concern about what humanity is doing to our atmosphere.
Science, done properly, always leaves room for doubt in the event of new evidence that challenges current knowledge but as things stand the science is telling us it's humanity driving the pace of climate change we're experiencing. The only real open question is
what affect this will have on life, particularly humanity, on earth.