Who was one of the first scientists to realize the effects of CO2 in the atmosphere? When did he do this?

How was it measured?

Where?

Who: Svante Arrhenius.

When: Claimed in 1896 that fossil fuels has a negative effect on our atmosphere.

How: Svante Arrhenius proved that fossil fuels had a negative effect by calculating the output of buildings that emit fossil fuels, and lead to the conclusion by his calculations that the industry might one day bring global warming.

Where:

I cannot find any source that mentions the where. What do you mean by where?

I hope my other information help you. I apologies to only be able to answer partially.