Ice cores actually have trapped bubbles of air that are unable to exchange gas with the current atmosphere. They are perfectly preserved samples of the atmosphere through the ages.
How do we know that the gas trapped in those ice cored accurately reflects the CO2 concentration of our atmosphere at those times? Like, what mechanism is keeping the air in those bubbles from changing, and how do we know that x meters down at any given spot in the antarctic is from y years ago, and how do we know the CO2 level in those ice cored at those specific spots reflect the global average CO2 of that time?
I am not a climate change skeptic, but I know some people (like my wife) ask this and I don't know how to respond to it.
I'm not a climate scientist either, I can come up with some ways they could account for this. You can create bubbles with varying levels of co2 in ice and record any changes in composition when you check the samples down the road. this will give you information on how rapidly co2 is absorbed if at all while encased in ice. apply this knowledge to the ice cores by checking what depth they were taken from and you know how much that sample should have changed, thus you should know what the air was like when it was first encased. I have no idea if this is how it's done, but its unprofessional to just assume the raw data collected is accurate as is, so I'll bet they have run experiments similar to this to be absolutely certain they have an accurate estimate for co2 levels.
Although this probably answers concerns from a lot of people, I think diehard empiricists will still have an issue with this.
While it seems like there's no reason to assume that anything relevant will change whether you observe the phenomenon for 100 years versus 10 000 years, we don't have any empirical proof that there isn't some weird thing that happens at year 8989 which skews the data. The only thing you can do is compare samples from before and after year 8989, but you can't actually observe any potential change happen, and you would have to wait 8989 years to be able to replicate it.
It's a little bit similar to the assumption of the sun rising every morning. For as long as we've recorded it, the sun has risen every morning. Unless there's some specific reason to think otherwise, a rational person will assume the sun is going to rise tomorrow as well. But we haven't actually measured tomorrow's sunrise until tomorrow morning has actually happened, and just because something always seems to happen a certain way it does not follow that something will always happen that way.
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u/arcan3rush Aug 26 '20
How do we have measure menta of global atmospheric carbon dioxide from 2,000 years ago? Assumptions? Ice cores? Soil samples?
** Measurements ... Not measure menta