OK, so 800 kyr is about the limit for ice core data. Those are pretty much the deepest parts of Antarctica, since glaciers move, we can't get anything older with short term (~2-5 year) data. Incidentally, the ice cores near Summit in Greenland only go back about 400 kyr but they generally have annual data as snow is much more regular there. Source: some of my fellow grad students who took ice cores up there.
Before that, your carbon proxies are pretty much entirely soils and rocks. Except for extreme events, your resolution shoots up to about 50 years at best, and more likely in the tens of thousands of years. We can also get temperature in all of these samples because of isotope ratios -- heavier isotopes of oxygen are more likely to evaporate in warmer weather.
So that graph doesn't tell the whole story. As a way to be somewhat less alarmist, our carbon dioxide levels are heading towards the levels we saw during the Miocene, when there were in fact primates alive. So all is not lost. We have had much higher levels before, although the Sun is more intense now. We think. Though this doesn't explain how Mars had liquid water.
Before that, your carbon proxies are pretty much entirely soils and rocks. Except for extreme events, your resolution shoots up to about 50 years at best, and more likely in the tens of thousands of years. We can also get temperature in all of these samples because of isotope ratios -- heavier isotopes of oxygen are more likely to evaporate in warmer weather.
So that graph doesn't tell the whole story. As a way to be somewhat less alarmist, our carbon dioxide levels are heading towards the levels we saw during the Miocene, when there were in fact primates alive. So all is not lost. We have had much higher levels before, although the Sun is more intense now. We think. Though this doesn't explain how Mars had liquid water.
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