The Republicans love to deny the global climate change (i.e., global warming) that is happening by saying that there has always been a cycle of warming and cooling -- and that this is completely natural (and not man-made). They are partially right.
The chart above, from the NOAA/Scripps Institution (and reported by the NY Times), shows the cycle of rising a falling amounts of carbon dioxide (CO2) in the atmosphere for the last 800,000 years. CO2 is the primary cause of the global warming. It has indeed cycled up and down over that extended period.
But there is a problem with the cycle theory. Over that 800,000 year period, the amount of CO2 in the air has never exceeded 300 parts per million. But now it is for the first time reaching 400 parts per million (more than 33% higher than it has ever been). How is this happening? The obvious answer is that humans have indeed had a deleterious effect on the environment (through the overuse and abuse of fossil fuels).
Scientists now say this is very likely the last year that will report levels of carbon dioxide under 400 ppm. The El Nino weather phenomenon will help push the CO2 level well above 400 ppm, and although it has been above that level for short periods in the past, they don't think it will fall back below the 400 ppm level again. In fact, they say that even if we take action to lower the CO2 level, it may well take several generations to get it back below the 400 ppm level again.
We are letting this global climate change get out of hand -- and it's just being done to protect corporate profits (so they don't have to pay to clean up the mess they are creating). I wonder if future generations will accept that as a valid excuse. I suspect they will consider us a greedy and inconsiderate generation of fools -- uncaring people who didn't consider the future (or those who would have to live in it).