"Recorded history" and "records of average temperature taken in real time" are two very different things to say only go back 150 years.
"Recorded history" only going back 150 years implies that the US was basically the start of recorded history.
"real time temperature measurements" only go back 150 years means you don't trust the science that allows us to make estimates of climate based on things like ice core samples.
I find the fact that we find greatly preserved animal bodies and also paths from ancient civilisations below the melting ice even more convincing that Earth had much warmer periods in the past.