For 10 points, name this elevation that is "rising" due to global warming.
The start of the Bølling-Allerød interstadial coincided with the MWP-1A event that caused a rapid change in this quantity. The first global, precise measurements of this quantity were done by the joint NASA/CNES TOPEX/Poseidon mission, whose followup is the currently-operating OSTM/Jason-2 mission. The zero level of this quantity - due only to the influence of Earth's gravity and rotation - is represented by the geoid. The displayed atmospheric pressure on weather maps is benchmarked to this level rather than the local elevation. Local changes in this quantity occur in transgressions and regressions, while its global change is known as "eustasy". For 10 points, name this elevation that is "rising" due to global warming.
The start of the Bølling-Allerød interstadial coincided with the MWP-1A event that caused a rapid change in this quantity.
mean sea level [or sea surface height; or mean ocean surface]