so humans must be causing global warming because smog doesn't look natural??? please explain the intermediate steps in reasoning that led you do that conclusion. smog is a local effect for which we know the cause. there are also many more types of pollution that can be even more harmful than smog and should certainly be reduced or eliminated. but focusing on a non-pollutant like co2 only takes the attention off of more important environmental issues.
global warming, even if it is caused by humans, will not be the end of the world. longer growing seasons, fewer deaths and illnesses resulting from cold weather, and more food for arctic wildlife are not bad things. the supposed ill effects of global warming are far from proven. it would take an aweful lot of ice melting to cause a significant rise in sea level. increased "storminess" is a heavily contentious idea even within the church of global warming. so it really makes no sense to make such a big deal about something that we probably can't change, and probably won't be all that bad anyway.