What are observation-based extrapolations in the 2022 technical report and what do they tell us?

Observation-based extrapolations, or sea level rise “trajectories,” are estimates of relative sea level rise out to 2050. These are built by analyzing regional sets of tide gauge data. To create them, the rate and acceleration of sea level rise from 1970 to 2020 was calculated from sea level rise observations from regional sets of tide gauges. Filtering was done to remove some effects of natural variability that can bias trend characterizations, such as El-Nino/La-Nina cycles. For the global sea level rise extrapolation, satellite-based water elevation data (altimetry) was also included.

The 2022 technical report represents the first time observation-based extrapolations are provided for global sea level and eight coastal regions (the Northeast, Southeast, Eastern Gulf, Western Gulf, Southwest, Northwest, Hawaiian Islands, and the Caribbean). Separate extrapolations are also provided for the southern and northern coasts of Alaska and the Pacific islands but caveated with greater uncertainty due to variations in land elevation and underlying regional sea level rise processes.

These observation-based extrapolations are very similar to the model-based projections through 2050, and therefore serve as a further line of evidence for the confidence in the near-term trajectory of sea level rise. Or, put another way, with continued global heating that is expected, there is strong reason to suspect that the current acceleration in sea level rise will continue, and this response is similar in both the observation trends and the modeled scenarios.