En-ROADS Updated with New Sea Level Rise Estimates in Light of Latest Science

March 3, 2022 by Adem Delibaş

In the March 2022 update of the En-ROADS climate solutions simulator, we have updated our global sea level rise (SLR) estimates for the 21st century in light of the latest science regarding historical SLR since 1900 and the Working Group I contribution to the IPCC’s Sixth Assessment Report (AR6).

With these revisions, the 2100 SLR simulated by En-ROADS in the Baseline scenario is updated to 71 cm (from 115 cm before these revisions). Users can also now test different assumptions about the contributions to global SLR from ice sheet melting in Antarctica and Greenland, within an uncertainty range covering the full spectrum of AR6 scenarios. Moreover, we have introduced a new SLR map type to help users visualize the additional risk of flooding due to storm surges.

Watch this video where Climate Interactive Director Andrew Jones shares the highlights of these sea level rise updates:

Why is the estimated future sea level rise lower than before? 

Simulating 21st century global sea level rise (SLR) has always been a part of En-ROADS. To accomplish this, the En-ROADS model first approximates the relationship between global temperature and SLR. We compare this approximation generated by the model with the historical SLR data to see how closely En-ROADS simulates history and adjust the model as needed. Then, with this calibrated model, En-ROADS estimates future global SLR for a particular scenario.

Prior to the March 2022 update, the En-ROADS SLR model used the sensitivities of SLR to an increase in global temperature proposed by Vermeer and Rahmstorf (2009)[1] and was tested against the historical SLR data composed of a reconstruction of the 20th century tide gauge data provided by Jevrejeva et al. (2008)[2] and relatively limited satellite data.

With the continued scientific progress over the last decade two areas of evidence have changed:

Imagen 1 Slr
Figure 1. 1993-2021 global sea level rise estimates relative to 1993 in the old calibration of En-ROADS and new (2022) calibration compared to NASA satellite data.

To address these two issues, we have recalibrated the relationship between global temperature and SLR to the new historical data composed of: (1) 1900-1993 tide gauge reconstructions by Dangendorf et al. 2019; and (2) 1993-2021 NASA satellite observations. The figure below displays both the fit between the estimated SLR and the measured data for the 1900-2021 period and the estimated SLR until the end of this century, after this recalibration.

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Figure 2. 1900-2021 global sea level rise estimates relative to the year 2000 by the new En-ROADS calibration (“SLR: Simulated”) vs. historical data (“SLR: Data (Tide Gauge & Satellite)”) and the mid-range projections of AR6 SSP3-7.0 scenario.

The following points are worth noting:

The 21st century SLR (compared to year 2000) estimated by En-ROADS in the Baseline scenario is now 71 cm.

Table 1. The global sea level rise estimates of the En-ROADS Baseline scenario vs. the AR6 SSP3-7.0 scenario (relative to the 1995-2014 average). Values in parentheses represent the likely range, 100-66% probability.

YearAR6 SSP3-7.0 SLR
(relative to 1995-2014 average)
Recalibrated En-ROADS Baseline SLR
(relative to 1995-2014 average)
20300.10 m (0.08 — 0.12)0.11 m
20500.22 m (0.19 — 0.28)0.24 m
20900.56 m (0.46 — 0.74)0.58 m
21000.68 m (0.55 — 0.90)0.70 m

What if ice sheets melt faster than we thought?

Contributions to SLR from ice sheet melting in Antarctica and Greenland remain the largest sources of uncertainty in estimating how much the Earth’s oceans will rise in the future. While the methods outlined above give us confidence in the estimates of sea level rise from thermal expansion, the dynamics of future ice sheet melting from climate change could be very different than the past 100-150 years. To account for this uncertainty, En-ROADS includes two new Assumptions sliders to capture how much ice sheet melting in Antarctica and Greenland contributes to global SLR.

Unlike in prior versions of En-ROADS, these two sliders are connected to the SLR outputs. In other words, if users want to change the En-ROADS default assumption of a 11 cm contribution to global SLR from ice sheet melting in Antarctica by the end of the century, they can increase it and the Sea Level Rise graph, the Sea Level Rise–Flood Risk Maps, and the Population Exposed to Sea Level Rise table will respond to this change.

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Figure 3. New ice sheet melting assumption sliders in En-ROADS.

It is also worth noting that the same rate of increase in ice sheet melting in Antarctica or Greenland will have different effects on different parts of the world. Therefore, knowing where the accelerated ice sheet melting is expected is as important as the rate of that acceleration.

The lower and upper bounds of the sliders controlling the contribution to SLR from ice sheet melting in Antarctica (2-56 cm) and Greenland (0-59 cm) are set such that users can experiment with the uncertainty ranges of any scenarios considered in AR6. The table below—adapted from the AR6 report—lists contributions to global SLR by the end of the century (relative to the  1995-2014 average) under the range of AR6 scenarios. The associated uncertainty range is shown in parentheses next to each entry. The SSP3-7.0 scenario is highlighted as it is the most consistent scenario with the En-ROADS Baseline in terms of future temperature projections.

Table 2. Contributions to global sea level rise under different scenarios. Values in parentheses represent likely probability ranges. Source: Table 9.9 Working Group I contribution to the IPCC’s Sixth Assessment Report.

Table 2 Slr

With no additional policy actions, pulling these sliders to the upper-bounds of the uncertainty indicated by the SSP5-8.5 Low Confidence scenario, 0.56 meters for Antarctica and 0.59 meters for Greenland, increases the 21st century SLR estimate of En-ROADS to 1.64 meters – 0.93 meters above the Baseline.

Imagen 4 Slr
Figure 4. Sea Level Rise estimate reaches 1.64 meters if contributions from ice sheet melt are assumed to be at the upper-bound of the uncertainty range.

Sea level rise maps in En-ROADS can now visualize the effect of storm surges

Embedded SLR maps were added to En-ROADS in October 2021. In this March 2022 release, we introduce a new map type: 21st Century with Storm Surge. This map responds to the new Storm Surge slider in the map to depict the additional risk of flooding due to storm effects.

To access the map, open the Sea Level Rise—Flood Risk Map under the Graphs > Impacts menu and select 21st Century with Storm Surge in the Map Type dropdown menu. Use the Storm Surge slider to add the additional risk of flooding due to storm effects.

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Figure 5. New 21st Century with Storm Surge map in En-ROADS.

Several points are worth noting about this new map type and storm surges:

Take a look at the En-ROADS simulator now to create your own scenario of climate action and see the difference it makes in the sea level rise and related impacts. If you would like to read about the mathematical implementation of climate impacts, see the En-ROADS Technical Reference. Please get in touch with us if you have questions, comments, or ideas.

[1]  Vermeer, M. & Rahmstorf, S. (2009). Global sea level linked to global temperature. Proceedings of the National Academy of Sciences of the United States of America, 106 (51), 21527-21532. https://doi.org/10.1073/pnas.0907765106

[2] Jevrejeva, S., Moore, J.C., Grinsted, A., & Woodworth, P.L. (2008). Recent global sea level acceleration started over 200 years ago? Geophysical Research Letters, 35 (8). https://doi.org/10.1029/2008GL033611

[3] Dangendorf, S., Hay, C., Calafat, F.M., Marcos, M., Piecuch, C.G., Berk, K., & Jensen, J. (2019). Persistent acceleration in global sea-level rise since the 1960s. Nature Climate Change, 9, 705–710. https://doi.org/10.1038/s41558-019-0531-8

[4] Frederikse, T., Landerer, F., Caron, L. Adhikari, S., Parkes, D., Humphrey, V.W., Dangendorf, S., Hogarth, P., Zanna, L., Cheng, L., & Wu, Y.-H.  (2020). The causes of sea-level rise since 1900. Nature, 584, 393–397. https://doi.org/10.1038/s41586-020-2591-3

[5] National Hurricane Center. (n.d.). Storm Surge Overview: Notable Surge Events. National Oceanic and Atmospheric Administration. https://www.nhc.noaa.gov/surge/

[6] Islam, M., & Takagi, H. (2020). Typhoon parameter sensitivity of storm surge in the semi-enclosed Tokyo Bay. Frontiers of Earth Science, 14 (3), 553-567.

[7] Soria, J. L. A., Switzer, A. D., Villanoy, C. L., Fritz, H. M., Bilgera, P. H. T., Cabrera, O. C., … & Fernandez, I. Q. (2016). Repeat storm surge disasters of Typhoon Haiyan and its 1897 predecessor in the Philippines. Bulletin of the American Meteorological Society97 (1), 31-48.