Are we experiencing it or not?
From the 'Yes' side:
Global warming is occurring: The graph in the past has peaked and then immediately fallen as a pattern. Currently the graph is remaining static around -/+ 2° C for longer than it has in the past, indicating a difference in today’s climate. This may indicate a leveling off of warmer temperatures. The Carbon dioxide levels follow a similar pattern, perhaps causing the rise in temperatures.
From the 'No' side:
Global warming is NOT occurring: The graph shows a clear pattern of peaks and falls, with a period of about 75,000 years. Currently the graph is nearing another peak, and according to the pattern should fall again during the coming years. This indicates that global warming is not occurring, as we are just in another part of the cycle.
From Petit, J. R. et al. (1999) Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica, Nature, vol 399, pages 429-436.
Clearly the graph is different currently than in the past, so the past patterns cannot be a predictor here. The graph is leveling off at a temperature toward the higher end of the previous cycles, so it is getting warmer and staying warmer. Furthermore, the clear consistency of the similar pattern in the CO2 levels indicate that there is a definite correlation between the two, maybe even indicating that the rising CO2 levels are causing global warming.