Scientific American had an article on some research that indicates that the earth should already have entered an ice age and that this hasn't happened due to human activity, mostly agriculture that has been going on for thousands of years.
Natural cycles of the earth movement around the sun and other mechanisms are responsible for the cooling and warming cycles and I expect when the natural warming begins, along with our industrial activities, we are in for some problems.
We need to understand how these mechanisms work so that we can maintain the climate status quo. We can neither afford to ignore this problem or simply cease all industrial and agricultural activity. We must instead master it. There is no other alternative but to try.
