First, go look at this page and then come back here. The chart on the previous page shows the temperature history from a Greenland ice core representing thousands of years. That ice core is a window into natural climate change history. The above chart is the visual depiction of the extreme temperature change peaks and troughs from that ice core history. (Note: The "peaks" represent the maximum temperature increase from the preceding climate trough. The "troughs" represent the maximum temperature decline from the preceding climate peak.) What does the this peak/trough graph tell us?
One, Earth experiences significant climate changes on a cyclical basis. It goes from extreme warming, to extreme cooling, then rebounds to an extreme warming peak, followed by an extreme cooling trough, and so on, and so on. (The above chart represents only 9,000 years of this bouncing back-and-forth, which has taken place for eons.)
Two, all these extreme climate changes are natural. Humans had nothing to do with the Earth's climate bouncing back and forth, from one extreme to another.
Three, the extremes arrive, not like clockwork, but on a sporadic basis within a range. For significant peaks, the range between each has been from 500 to 1,300 years (average between peaks is 995 years). For cooling, the range between extremes is from 660 to 1,540 years (average between troughs is 980 years).
Four, prior to modern times, there have been 9 previous extreme warming peaks and 9 cooling troughs, over the last 9,000 years.
Five, the extreme peak increase from a previous trough has been +3.7°C; the extreme trough decrease from a previous peak has been -3.0°C.
What does all this climate history mean for our modern age? Well, it's obvious we are living in a "peak" period, after the extreme cooling trough that we know as the 'Little Ice Age.' Our modern climate cycle is a natural rebound from that devastating cold trough. How high could our cyclical peak go? Based on the natural peaks Earth experienced in the past, possibly another 2.5°C.
This review of climate history brings us to the very last climate "peak cone" on the extreme left side of the above chart, which is our modern climate. Our "peak cone" represents a climate change after a long line of climate changes - a combined total of 18 peaks and troughs over 9,000 years. Our current climate peak is not an exceptional peak versus past peaks, in terms of temperature change (it's only one-third the maximum change). Our modern peak is becoming somewhat old, though. Since the last peak it has been 970 years. In contrast, the average peak difference is 995 years.
Although our modern peak is very mediocre in regards to maximum temperature change, and is becoming old in terms of duration, it absolutely has become the most contentious natural climate change period ever known to humans. Why?
Go back and examine the modern "peak cone" on the left side of the chart. There is a black dash line. Below that dash line, and for all the previous peak and trough cones to the right of that cone, 100% of all scientists consider these climate peaks/troughs to be 100% natural. Above that black dash line though, many government-funded, IPCC global warming scientists consider that small portion of the peak temperature change to be "unnatural." They attribute the climate change above the dash line to be solely due to human CO2 emissions.
Despite the proclamations of IPCC-sponsored scientists, the ice core evidence reveals that the modern extreme peak is well within the range of past peak temperature change, including those temperatures above the dash line. One thing we do know for sure is that portion above the dash line has given us "Climategate," "glaciergate," the infamous "hockey stick," the IPCC, Al Gore, and all the rest, because of the instinctive need to prove that man is more powerful than nature. The only way they have found to do so is to totally disavow the natural forces that brought Earth those 18 previous peaks and troughs, as if nature has nothing to do with our climate 'cone', and through massive scientific malfeasance.
Though it is true human CO2 emissions and other human forces may have a slight influence on temperatures, especially in local/regional areas, the fact remains that modern temperature changes are not unlike the previous global temperature movements already experienced. World temperatures are predominantly driven by the dynamic natural forces that the previous 18 climate temperature changes have exhibited. That's what the ice core climate science tells us.
What per cent of global warming is natural? Based on 9,000 years of climate change history, the answer is very close to 100%.