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My understanding of the anthropomorphic global warming theory is that human burning of fossil fuels is increasing atmospheric carbon dioxide and causing unprecedented increases in temperature by a greenhouse effect.
My understanding of Milankovitch cycles is that the Earth's temperature is affected by its relationship with the sun in about a 100,000 year cycle. All of human civilization has existed in a 10,000 to 20,000 year interglacial warm period of this 100,000 cycle. The melting of polar ice looks less impressive on a background of the entirety of Canada being under snow and ice year round during the 80,000-90,000 cold period (evidenced by such glacial river valleys in places I have lived such as Edmonton and Toronto).
So unprecedented warming has to be examined on a background of what is usual for the stage we are at in the Milankovitch cycle. So where do we get carbon dioxide and temperature data for Milankovitch cycles? From ice cores (and also sediment layers). Technically, you could also look at tree ring data that has been correlated with ice core data, but you cannot look at surface temperature data (or even satellite temperature data) because these data do not go back very far and do not correlate with proxies such as tree ring data (the so called "divergence problem"). The problem of the hockey stick graph is that it was tacking on modern temperature data of the past 100 years to a 1000 years of proxy data, an apples to oranges comparison (The blade of the graph disappears with proxy data used all through).
Here's the thing: There is ice core data that goes back a long way and that also extends into the industrial age. It's called the Law Dome ice core. People even use the carbon dioxide data from this very core to show an unprecendented increase in atmospheric carbon dioxide.
https://www.bas.ac.uk/data/our-data/publication/ice-cores-and-climate-change/
But what has not been published to my knowledge is the temperature data from that same ice core (as has been done for other ice cores, such as the Volstok ice core, from which we derive Milankovitch cycles also known as real climate science).
In the spoiler image above, you can see that the temperature proxy from ice cores is called delta-18O, and you can read about how it is derived here:
https://en.wikipedia.org/wiki/Δ18O
https://globalchange.umich.edu/globalchange1/current/labs/Lab10_Vostok/Vostok.htm
So I think the most compelling evidence for an unprecedented increase in global temperature is to be found in the delta-18O of the Law Dome ice core. If the carbon dioxide data is good enough from that ice core then surely the best temperature data to correlate with this carbon dioxide data must come from the same ice core.
What do you think?
Great post, first note though is that you keep using the word 'unprecedented' which I don't agree with, I believe the earth has warmed and cooled in the past at much greater rates than what we are seeing now, but I digress. I think two separate positions need to be established in order to discuss this topic:
1) Human influence on the earth' s CO2 levels
Below is the graph plotted by the NOAA using ice core data which shows an obvious anomalous spike around the time period of the west's industrialization. For me the correlation is obvious and I believe it would be more than reasonable to conclude causation. Is this something you would agree with?
2) If this influence has effected global temperature rise
This will be a little more difficult to ascertain as I do not believe CO2 levels and temperature are always directly correlated. Other factors such as solar activity and geological activity do play a part in temperature fluctuation. What we do know is that CO2 is a green house gas and modern measurements with satellite data (for however brief a period) have so far corroborated the hypothesis. If one wants to say that a larger set of direct measurements is needed I'll grant that but I believe It is a reasonable to conclude that given that data that we have, AGW is real.