They don't for aerosols/ozone past the 50s I dont think.
But carbon/methane/NO/etc... they get from ice samples that have trapped air bubbles from quite a long time ago. They also take a ton of samples from ice cores and the data is reproducible both in the north and south poles. I believe temperature is also learned from the ice samples.
But carbon/methane/NO/etc... they get from ice samples that have trapped air bubbles from quite a long time ago. They also take a ton of samples from ice cores and the data is reproducible both in the north and south poles. I believe temperature is also learned from the ice samples.