The El Niño Southern Oscillation (ENSO) has a global influence on weather and climate. Over most of the equatorial Pacific, where ENSO is focused, variations in sea surface height, such as measured by satellite, are strongly influenced by vertical displacements of the ocean thermocline. We show that linearly removing this influence leads to a time series of sea surface height that capture ENSO dynamics in the central Pacific, where ENSO variability has become more active in recent decades.