[pipodeclown]

Yes, but atmospheric co2 sticks around for 300-1000 years and the resulting temperature spike should therefore definitely be detecteable. They might not be able to pin point the exact period of 100 years we started to industrialise but it will definitely be able to see the change and determine that this took place over a timeline 100-1000 times shorter than previous similar changes.

Furthermore, there will be massive cooroborating evidence in the form of fossile records showing a mass extinction event and ice core samples (assuming we will still have icesheets) showing the accompanying rise in co2 levels as ice layers are deposited on a yearly basis.