October 12, 2021 by Adem Delibaş
In collaboration with Climate Central, we have added sea level rise (SLR) maps to En-ROADS in the October 2021 update. To learn about these updates in more detail, join us for a special webinar on November 4 – offered at both 7am and 2pm EDT.
With SLR maps embedded in En-ROADS, users can now see the impact of mitigation policies on SLR across the world in real-time.
Sea level rise is among the most severe impacts of climate change, with far reaching potential consequences for humans and ecosystems around the world. In addition to its devastating effects on coastal habitats such as destructive erosion, wetland flooding, aquifer and agricultural soil contamination with salt, rising seas could also displace hundreds of millions of people and cause more than $300 billion worth of damage to harbors and ports across the world by the end of the century.
Year-to-year variability in sea level at a particular location or regional differences across the world’s oceans have always existed due to natural variability in the strength of winds and ocean currents. Yet, in parallel to the Earth’s warming due to human caused climate change, the global average sea level has also been rising at an ever-increasing rate since the late 1800s.
As the planet gets warmer, ice sheets and glaciers melt, and warming sea water expands. Therefore, the volume of world’s oceans increases. Through these dynamics, the global mean sea level has risen by more than 20 centimeters since 1900. The annual rate of increase since 1993 is 3.4 millimeters per year – more than twice as fast as the rate during 1900-1993.
Estimating the global sea level rise (SLR) throughout the 21st century has always been a part of En-ROADS. Building on the method proposed by Vermeer and Rahmstorf, En-ROADS calculates SLR as a function of global mean temperature. In the baseline scenario, En-ROADS estimates 1.15 meters of SLR by the end of century, compared to the year 2000. Although the global mean SLR is a useful metric in estimating the severity of potential consequences of rising seas, it does not directly indicate how much a particular coastal region could be affected. Yet, estimating where and when a given warming scenario may lead to increased flooding and permanent inundation is profoundly important for coastal planning and climate change mitigation strategies. Therefore, in the October 2021 update of En-ROADS, we have introduced a new graph, Sea Level Rise – Flood Risk Map, in collaboration with Climate Central.
The new Sea Level Rise – Flood Risk Map graph, accessible under Graphs > Impacts menu, comes in two types: 21st century map and long-term equilibrium map. Being built on the Google Earth Engine, SLR flood risk maps can be depicted for any location in the world. The location of interest is selected via the search bar – either by typing or selecting among five featured locations, shown upon clicking on the search bar. Using Climate Central’s digital elevation model, CoastalDEM, the SLR flood risk maps indicate the land areas estimated to be below the high tideline because of SLR in a future climate change scenario and therefore threatened by daily flooding.
Land at risk, shown in dark blue on the map, is the area at risk of daily flooding due to it being below high tideline in the Current Scenario. This area is also at risk in the Baseline scenario. On the other hand, land saved by actions, depicted in dark green on the map, is the land that is saved from daily flood risk due to the mitigation actions taken in the Current Scenario. In other words, this area would have been at risk given the expected sea level rise in the Baseline, but it is expected to remain above high tideline in the Current Scenario.
When the 21st century map is selected, using the Map Type dropdown below the map, En-ROADS displays a decadal SLR risk map throughout the 21st century. Although this map by default shows the land areas projected to be below the high tideline in year 2100, it is also possible to visualize the estimated risk in any decade during 2030–2100, via the Map Year slider. Below, the SLR flood risk maps of Alexandria, Egypt are shown under a 1.5 °C scenario for the years 2070 and 2100. The land shown in dark blue is estimated to be below the high tideline in both baseline and the 1.5 °C scenarios, while the area shown in dark green is the land saved from daily flooding risk by limiting the temperature increase to 1.5 °C by the end of the century.
A couple points are worth noting about the 21st century SLR flood risk maps. First of all, En-ROADS displays the 21st century sea level rise map using the 95th percentile projection of *Rasmussen et al. 2018***** method of Climate Central’s Coastal Risk Screening Tool. This is because the En-ROADS internal SLR projection method is on the less conservative end compared to Rasmussen et al. 2018 and consistent with its 95thpercentile projections. Also, in estimating the areas at risk of daily flooding, physical barriers, such as levees and other coastal protection, are not taken into the account.
Looking at the 21st century SLR risk map above of Alexandria, Egypt in the year 2100, it should also be noted that the land area saved from permanent inundation by limiting the end of century temperature increase to 1.5 °C (the area shown in dark green) is relatively small compared to the land area that would be inundated in the 3.6 °C baseline scenario (the sum of the land areas shown in dark blue and dark green). Why would such a major reduction in global mean temperature not avoid more SLR by the end of century? The answer lies in the comparison of Temperature Change and Sea Level Rise graphs in En-ROADS for the 1.5 °C scenario. As shown below, with the policy options taken at the 1.5 °C scenario, the temperature increase stops around 2040 and stabilizes at 1.5 °C around 2060. On the other hand, despite its growth rate declines after 2060, SLR keeps increasing until the end of century. Indeed, if En-ROADS simulated the global climate system beyond 2100, we would expect SLR to keep increasing for some time before it reaches a stable equilibrium. This is due to the long delay in the system before SLR fully responds to changes in global mean temperature and stabilizes.
Because it takes a long while until climate change reveals the full impact of SLR, we have also included an option in En-ROADS to display the long-term SLR flood risk using the long-term sea level outcomes maps of Climate Central’s Coastal Risk Screening Tool.** Long-term equilibrium **SLR maps depict the land areas that are projected to be at risk of daily flooding over the coming centuries due to the human-caused climate change committed during the 21st century. Therefore, the long-term equilibrium SLR maps enable En-ROADS users to visualize and compare the long-term outcomes of their climate action scenarios, even though En-ROADS does not simulate SLR post-2100. Below, for instance, are the 21st century and the long-term equilibrium SLR maps of the Alexandria region side by side at 1.5 °C global warming by 2100. As seen, not only the land projected to be at daily flood risk (the area shown in dark blue) but also the land saved from daily flooding (the area shown in dark green) is significantly larger in the long-term map on the right.
Along with SLR maps, Climate Central has also recently released Picturing Our Future – an impressive resource of imagery of coastal cities and coastline under different climate scenarios. SLR maps in En-ROADS together with the images provided by Picturing Our Future is a powerful way to highlight coastal impacts of climate change and mitigation policies.
Embed Cape Town Sea Level Rise Comparison
Take a look at the En-ROADS simulator now to create your own scenario of climate action and see the difference it makes in sea level rise across the world using the new sea level rise risk maps. Please get in touch with us if you have questions, comments or ideas.
For more information, read these FAQs:
 The UN Ocean Conference 2017 Fact Sheet
 Vermeer, Martin, and Rahmstorf, Stefan. “Global sea level linked to global temperature”. Proceeding of the National Academy of Sciences of the United States of America 2009 106 (51) 21527-21532.
 Rasmussen, D. J., et al. ”Extreme sea level implications of 1.5 C, 2.0 C, and 2.5 C temperature stabilization targets in the 21st and 22nd centuries.” _Environmental Research Letters _13.3 (2018): 034040.