The Gulf Stream plays a significant role in maintaining the climate of the US
East Coast and Western Europe. “We conclude with a high degree of confidence
that Gulf Stream transport has indeed slowed by about 4% in the past 40 years.”
The full study is Here
[https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023GL105170]
if it's slowing by ~1%/decade, how many decades will it take to have a significant impact that the everyday person would notice?
You are assuming a linear progression. Climate effects are likely accelerating.