PNNL

The Science

Estimates of sea level rise over the coming century, particularly the upper tail of the predictions, can be an important factor for adaptation planning and vulnerability assessment. One way to estimate this upper tail is with a reduced complexity Earth system model that can provide useful constraints on sea level rise informed by historical observations. The model range reflects uncertainty about the evolution of the climate system and physical processes related to sea level, such as melting land ice. A team of researchers, including a scientist from the U.S. Department of Energy’s Pacific Northwest National Laboratory, investigated how a key climate uncertainty, Earth's long‐term temperature response to a doubling of atmospheric carbon dioxide, affected the range of 21st century sea level rise predicted using the simple climate model Hector‐BRICK. While all of the model realizations generally matched historical observations, those with a high temperature sensitivity to atmospheric carbon dioxidehad a generally higher 21st century sea level rise.

The Impact

The current uncertainty surrounding the sensitivity of Earth's equilibrium climate to increased atmospheric carbon dioxide is an important influence on climate hazard projections. While implications for projected global temperature changes have been extensively studied, the impacts of this uncertainty on sea level projections have been relatively unexplored. This study indicates uncertainties in equilibrium climate sensitivity do influence sea level rise projections in ways that could affect regional variability and the estimated timing of future exceedances.

Summary

The researchers analyzed the relationship between Earth’s climate sensitivity and historical/future sea level projections, with a particular focus on the high‐impact upper tail. They used a Bayesian calibration of key climate and sea level parameters using historical observations and the reduced complexity Earth system model Hector‐BRICK. This methodology allowed them to focus on plausible realizations of the climate system in a probabilistic framework. The researchers analyzed the effects of high‐end climate sensitivity (above 5 K) on projections and spatial patterns of sea level change. The sea level projections hinged critically on the upper tail of the climate sensitivity, especially for the highly decision‐relevant upper tail.

Funding

This research was supported by the U.S. Department of Energy Office of Science, as part of research in the MultiSector Dynamics, Earth and Environmental System Modeling Program, as well as the Penn State Center for Climate Risk Management.