So I am a little confused. The title and premise of the article is that we now have news that the oceans are rising at the fastest rate over the last 2,800 yea

So I am a little confused. The title and premise of the article is that we now have news that the oceans are rising at the fastest rate over the last 2,800 years. Is the specific news event a) that the rate last year was the highest ever or b) that scientists have better calculations of the rate of rise for the last century, and these new calculations show the rise is faster than previously believed. I assumed (a), which was why I was looking in the article for what the actual rare of increase was for last year. When the article says, "lately reaching a rate of about a foot per century" is that based on recording the rise over the last century? Or is that based on multiplying last year's rise by 100? I'm also curious -- how do we know, within plus or minus a foot -- what the sea level changes were in centuries that happened millennia ago?