We're in a natural warming cycle, aren't we?

 Some processes that affect Earth's temperature do go through cycles. Examples range from the El Niño–Southern Oscillation, which brings warming (El Niño) or cooling (La Niña) to Pacific waters every few years, to glacial–interglacial periods that can span tens of thousands of years.

But the pace of natural warming since the last ice age 10,000 years ago looks puny compared to the accelerated temperature increases observed in the last 50–100 years, as our industrial activities dumped more and more greenhouse gases into the atmosphere.

There is now more carbon dioxide in the air than at any time in at least 2.1 million years. Whether in prehistoric times or today, more greenhouse gases mean higher global temperatures.

Because the extra carbon dioxide produced by human activity is indeed sufficient to outweigh natural cycles, it will not be easy to reverse this process. But since human beings are causing the problem, it's up to us to figure out how to solve it. We can't do anything about natural cycles, but we can alter our own actions.