[jimmydorry]

To add to your post, where and how did they determine that 30 years was the appropriate time scale to use?

>The value we show is a 30 year rolling average of temperature change. We have chosen that long term trend because it fits the time scale of the climate and its changes.

[tonmoy]

There isn’t enough temperature record around before that timeframe to estimate an accurate global average. You can still see the effects of temperate indirectly

[User23]

Arguably, the quality record only began with the launch of satellites. How much can we really trust some weather station in the middle of Montana from 1880? And of course pre-satellite the data for the southern half of the globe is relatively sparse.

When it comes to CO2 in particular, there are things like ice cores and plant fossil stomata that gives us some understanding over geological timeframes, but that's very different from a thirty year average.

[kkjjkgjjgg]

Even if the measurements from the middle of Montana is correct, I could imagine there are different ways to extrapolate to average global temperature from just a few points of measurements. In the end, it will just be another estimate.

[User23]

That reminds me of a thought experiment. Suppose you want to accurately measure the average temperature of a company cafeteria. How many thermometers do you need and where do you place them? Do you keep them in fixed locations or move them?

That thought experiment is readily adapted to other spaces, such as a high school gymnasium or the state of Iowa.