Because there is no CONCRETE scientific evidence that global warning is the result of human actions.Many of the problems said to be a result of man made global warming have been proven to not be true ie.shrinking of Arctic coastlines.Do some research with an open mind and see what you discover.
Stop believing the alarmists. The earth stopped warming 16 yrs ago. Do your own research and stop with the "green" crap. It takes a really big ego to think we can ruin the earth. Remember the last oil spill, we were told we were all gonna die. The ocean fixed itself in what 2 months.
There are too many variables to determine what is causing the warming and cooling cycles. The "evidence" reported was proven to be fabricated. To jump to the conclusion that warming is man-made, is a philosophical fallacy.
Have you ever seen valleys or mountains? Big giant glaciers that melted formed those for the most part. How did that ice melt thousands of years ago? Dont you think that that big giant heat source in the sky would have any effect on temp rises and cooling? It is all natural dont stress out. The earth is very powerful and CO2 is a trace gas that plants love.