A grid is overlayed over the Earth and a temperature is calculated for each cell. Over the continental US and Europe most of the numbers are determined using weather stations but where sensor data is unavailable, like most of the oceans, a temperature is calculated indirectly using satellite data and a bunch of other sources.

The grids for the northern and southern hemisphere are averaged separately and then combined with a weight to eliminate bias towards the northern hemisphere (since most of the weather stations are concentrated in the northern half of the planet).

There are lots of different models for this calculation and different agencies use ones tailored to their needs

But how can this method be accurate due to mass urbanization/concretization as that increases heat instead of eg a forest?

This would then apply that it's not "global warming" but merely the effect of concrete heat capture and emission and not CO2 related?

How can they then say this is "human gas pollution related"?

Where am I wrong (serious question)?

Let's really assume you are asking in good faith.

Please start using the internet for more than just hackernews.

Good to start is always Wikipedia: https://en.wikipedia.org/wiki/Climate_change?wprov=sfla1 after that you can read all sources.

It's hard to answer your question any other way. General speaking the CO2 behavior is quite well understood by now. We know that we make so much CO2 because we measure CO2 in Hawaii for ages https://de.wikipedia.org/wiki/Messstation_Mauna_Loa?wprov=sf...

This isn’t the beginning and end of the data. The connection between emissions is established elsewhere.