It's not so much that I don't believe that humans have altered the atmosphere ( but one volcanic eruption would do more IMO ), rather that I think it's impossible to change it now, whatever we do. The damage is done and can't be rectified, so just learn to live with it- stop building in fire zones and flood areas, build sea walls, stop polluting the oceans with our trash, breed resistant varieties of food plants etc. Most importantly though, stop overpopulating the planet.