So what about this gem of "truth" in the first post in this thread
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Summary-- the ratio of the C12 isotope to C13 isotope in the atmosphere has not changed for at least 500 yrs
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Really interesting stuff.. Carbon is found in three isotopes: C12, C13 and C14. C12 and C13 are stable but C14 is not and will decay over time.
Plant photosynthesis favors C12 and the carbon molecules in plants have more C12 and relatively devoid of C13 and since fossil fuel is from plants, fossil fuel is also devoid of C13.
In this case, we are looking at the ratio of C13 to C12.
If we were NOT burning fossil fuel, the natural biological process would INCREASE this ratio simply because photosynthesis is removing C12 from the atmosphere but not C13. If we have a concentration and look at the ratio of C13 to C12, removing C12 should cause this ratio to INCREASE.
However, if we burn fossil fuel which is relatively devoid of C13 and add it to the concentration, we would be adding C12. I.e., C12 is increasing but C13 stays the same so this would cause the ratio of C13 to C12 to DECREASE.
So what is actually being measured with the ratio of C13/C12? (referred to as &13C in the paper below)
This link has a plot of the measured C13/C12
https://gml.noaa.gov/ccgg/isotopes/c13tellsus.html
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The relative proportion of 13C in our atmosphere is steadily decreasing over time. Before the industrial revolution, δ13C of our atmosphere was approximately -6.5‰; now the value is around -8‰.
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If you look at the first plot, the dark blue plot is the C13 to C12 ratio and it has a yearly wiggle but is on a steady downwards trend.
Remember that if we ONLY consider photosynthesis, C12 is being removed from the atmosphere so the curve would tend up. This is why the curve has the upwards yearly wiggle.
Now add in our burning of fossil fuel which does the opposite of photosynthesis and ADDS C12 to the atmosphere, This would cause the C13/C12 ratio to go down.
So the actual measured data showing the downwards trend is only explained by our adding C12 to the atmosphere by burning fossil fuel and the C12 added by burring fossil fuel is dominating over the removal of C12 by photosynthesis. Without burning fossil fuel, this curve would tend up which is clearly not the case. For someone who studies this subject, please read at least some of the link, really very interesting.
Now comes along GLM's paper in the first post.
The goal here is to show (from the abstract)
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unidirectional, potentially causal link between temperature as the cause and carbon dioxide concentration ([CO2]) as the effect.
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Remember that you have to stick you head in a deep hole and ignore a whole slew of othere questions like what caused the warming in the first place etc.
First thing is that these guys took the very straight forward actual plot showing C13/12 decreasing which can only be explained by our burning fossil fuel and created a plot that was flat. I just want to point out the process they had to go to change the straight forward original plot to show what they wanted. Here is the process they used..
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Local average of input isotopic signatures δ13CI
calculated from the indicated Mauna Loa time series for periods with a varying length, ending at the indicated year in the horizontal axis, and a constant increase in [CO2], equal to the standard deviation of each of the time series.
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What the heck.. the plot was very straight forward to begin with. But these folks did all sorts of manipulations until the plot looked like what they wanted to see.
Then they create a model. But note that one of inputs is the actual data of CO2 measurements (which by the way is ONLY explained by our burning fossil fuel)
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The model we use is none other than the simple Equation (12), applied sequentially, each time using past and present data for [CO2]
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Hmm... should not their model be calculating the yearly rise in CO2 instead of using it as an input..
Was this article actually peer reviewed?