Well there is 'recorded history' (generic) and 'recorded weather' (specific). The latter came a bit later, the former arguably started in ancient Egypt (my 5,000 years ago or 3000 BCE) but some will put it earlier in Sumeria. There is an argument to be made that records of crop yields or floods in the Nile river basin are legitimate indications of weather conditions at the time (certainly droughts and floods).
The other reason to pick 5,000 rather than 150 as a starting point is that folks will argue with you about written history starting at 150 years ago but are willing to concede that beyond 5,000 years there isn't a lot of information to extract. The point to be made is that geologically speaking, 5,000 years is a trifling. Even when you consider the 65M years since the dinosaurs left us, we're looking at .008% or a mark a mere 8mm wide for 1meter at 65M years.
The other reason to pick 5,000 rather than 150 as a starting point is that folks will argue with you about written history starting at 150 years ago but are willing to concede that beyond 5,000 years there isn't a lot of information to extract. The point to be made is that geologically speaking, 5,000 years is a trifling. Even when you consider the 65M years since the dinosaurs left us, we're looking at .008% or a mark a mere 8mm wide for 1meter at 65M years.