In reply to Jonny2vests:
> (In reply to Trevers)
>
> What makes you think their height estimates do not change? Every time we measure any big mountain (that is not close to a coast) using a different technique, you will likely see significant differences. Nothing is actually changing (significantly), I'm simply pointing out that efforts like this are fraught with difficulties and assumption, and differences of this magnitude are expected.
>
> It wouldn't matter if I conducted a millimetric precision survey for a year, the observations may be internally consistent but that still won't tell me where MSL is underneath the mountain. Even with a gravity meter we have to make the assumption of uniform granite all the way down.
Sorry, my post was borne out of almost complete ignorance of how these things are measured. I assumed you meant that average sea levels were actually 25m higher than we had thought, which struck me as daft.