The rest has been matched and synchronized to it using other sources. I’m not a climate scientist, but I would guess the best sources are ice samples from polar regions where it accumulates from top and melts from bottom. CO2 dissolves in water and when snow falls and turns into permanent ice in such places, it captures a snapshot of that period’s atmospheric gas content, among that the CO2 level.
Lots of different independent methods and sources that correlate, along with some approximations. Actual measured readings aren’t as accurate or match up in the early periods, which is why the IPCC decided to use 1980 as a baseline to start from for consistent and abundant data to compare with. This continues to be a side argument about if we’re really past 1.5C or not, since the graphs start differently. The “good” news is that as time goes on, that argument becomes less relevant because the differences shrink and catastrophic converges.
So how do we have readings going so far back, like even in the late 1800s? Is this just an assumed average for back then?
Here is the Mauna Loa data line from 1958, matching the top figure.
https://upload.wikimedia.org/wikipedia/commons/c/c5/Mauna_Loa_CO2_monthly_mean_concentration.svg
The rest has been matched and synchronized to it using other sources. I’m not a climate scientist, but I would guess the best sources are ice samples from polar regions where it accumulates from top and melts from bottom. CO2 dissolves in water and when snow falls and turns into permanent ice in such places, it captures a snapshot of that period’s atmospheric gas content, among that the CO2 level.
Tree rings are another used source for historical estimates
Usually measurements in ice core drillings.
Oh yea…didnt think of that. But i have heard of that method for lots of things!
old trapped air
Lots of different independent methods and sources that correlate, along with some approximations. Actual measured readings aren’t as accurate or match up in the early periods, which is why the IPCC decided to use 1980 as a baseline to start from for consistent and abundant data to compare with. This continues to be a side argument about if we’re really past 1.5C or not, since the graphs start differently. The “good” news is that as time goes on, that argument becomes less relevant because the differences shrink and catastrophic converges.