Why does that require adjustments? You're supposed to be measuring local temperatures, why in the actual fuck would you need to adjust for different atmospheric conditions when that is exactly what you're supposed to be measuring?

I should've known when you said carbon dioxide scatters light that this would be an uphill battle

If I am taking a precise temperature in calm air, and then take temperature in the same place, but with a fan blowing on it, the reading will be different. Yes, that bit of heat transfer induced by forced convection MATTERS when reading a temperature. Surprise.

meaning? different types of instruments? different types of sensors?

Duh. Differences in accuracy (different from precision so please piss off before you knock that), differences in system response, etc. etc. etc.

That doesn't require any adjustments. you have 1200 stations, some take measurements every hour, others take measurements every 4 or 6 hours, or whatever. Pick a time and get the temps for each station at that local time, or the closest measurement to that time.

The scientific community, while it collaborates, is an amalgam of organizations. They share data, but there is no one single entity that produces ALL THE DATA. What you are suggesting is absurd.

What needs to be calibrated exactly? They're all measuring the same fucking thing (temperature), so what needs to be calibrated or adjusted to compare temps from one dataset to another? If you've got an accurate sensor/thermometer, it shouldn't matter where or when you take a reading, you should get an accurate temp for that time and place.

Do you know anything at all about scientific equipment?