A Reassessment of 20th Century Global Sea-Level Change

Abstract:

Climatic change in the 20^th century is directly and indirectly observable in multiple aspects of the climate system. Some of these changes, such as global mean surface temperature, are widely studied and understood, while others, such as global mean sea-level change (GMSL), remain uncertain. Until the mid-1990s, with the advent of satellite altimeter observations of a significant percentage of the global ocean, point observations of global sea-level change through tide gauges were the primary means of monitoring the changing height of the sea surface relative to the sea floor. Traditionally, there have been two approaches for estimating GMSL from these temporally and spatially sparse tide gauge records. The first approach uses such records to obtain a global mean value by computing and summing representative regional averages through time (e.g., Jevrejeva et al., GRL, 2008). The second approach uses the dominant spatial patterns of sea surface heights from 20 years of satellite altimetry data to interpolate between tide gauge records to reconstruct global sea level over the century (e.g., Church and White, Surv. Geophys., 2011). However, the GMSL estimates obtained using these two methods differ by ~0.5 mm/yr from the mean global rate achieved by summing the data- and model-derived estimates of the underlying contributions (e.g., thermal expansion, mass flux from land ice, etc.) (IPCC, 2014). Here we describe a third approach that estimates GMSL using two probabilistic approaches based on fingerprinting the underlying source contributions from the spatiotemporal patterns of sea-level change captured by the tide gauge records (Hay et al., Nature, 2015). Our revised GMSL rate estimate of 1.2 ± 0.2 mm/yr over 1901-1990 closes the sea-level budget and maintains a good fit with the tide gauge record over the 20^th century.