Future archaeologists and ice core samplers would definitely find a "wtf" layer in all their ice cores: higher radioactivity! If they attempt carbon-dating there will be a huge discontinuity in the results.
Probably also a microplastics layer.
I'm far from an expert on this. Assumedly the damage we are seeing currently and expecting in the near future due to our current warming would be detecteble over a a very large time scale. We seem to be able to detect much more subtle changes going very far back with our current techniques.
https://earthscience.stackexchange.com/questions/8746/is-thi...
One could read your comment as “we haven’t detected temperature variation in past data that’s similar to the recent rise”, but what you are trying to say (and what the link says) is that we’ve seen the variation before, we just can’t tell exactly how quickly it happened.
"no temperature variability is preserved in our reconstruction at cycles shorter than 300 years"
This means if there was temperature variation in past data current methods couldn't detect it, so the absence of spikes in the data is not proof of absence. In other words, if global warming was reversed and 200 years from now temperatures went back to pre-industrial levels it would be undetectable 10000 years into the future with our current methods.
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.
I.e. if we (or someone a million years from now) tried to estimate the 21th century's temperatures using the same techniques used to estimate temperatures a million years ago, would we be able to detect that 4 degree change?
Conversely, can scientists today detect or rule out that there was an outlier century a million years ago in which temps varied as much as today?