Five categories of climate impacts have been added to En-ROADS in the September 2021 update. To learn about these updates in more detail, join us for a special webinar on Sept. 23 at 11am EDT.
Just in the past couple of months, we have observed a series of record-breaking extreme weather events throughout the world. A days-long heatwave in the Pacific Northwest killed hundreds of people. Devastating floods in western Europe took many lives and caused more than 10 billion euros of property damage. Wildfires in Southern Europe, Siberia, and the Pacific Northwest have burned millions of acres of forest area.
Extreme weather events with increased frequency and intensity are not the only kind of impacts we are expected to face due to climate change. Various health risks, economic loss, reduction in crop yield, biodiversity loss, and major retreat in summer sea ice coverage of the Arctic Ocean are among the other impacts reported by different climate studies.
After introducing economic impacts of climate change and social cost of carbon in previous releases of En-ROADS, we now add five categories of climate impacts in the September 2021 release: Population Exposed to Sea Level Rise, Probability of Ice-free Arctic Summer, Decrease in Crop Yield from Temperature, Species Losing More than 50% of Climatic Range, and Additional Deaths from Extreme Heat.
Building on five peer-reviewed journal articles, we included the relationship between global mean temperature and these impact metrics. En-ROADS simulates how these metrics change as users create different climate action scenarios.
The new climate impact graphs are accessible in En-ROADS under Graphs > Impacts menu. Each impact graph, presented in the form of bar charts, displays the snapshot values of one or more impact metrics (often for the year 2100). Below, I elaborate on each of these impact graphs and metrics; and discuss how each metric changes in a 1.5-degree Celsius scenario compared to the En-ROADS baseline.
Population Exposed to Sea Level Rise
Taking the global average sea level rise projection one step further, En-ROADS now also simulates the global population exposed to sea level rise and coastal flooding. Two impact metrics are introduced to measure this exposure by the year 2100:
Population at risk to annual flooding estimates the number of people living on land that is below annual flood levels, while population living below high tide line measures how many people live on land below the high tide line (the point on land where the tide reaches its highest point). Following the approach taken by the source study, these metrics use population data of coastal communities from 2010. Future populationgrowth, migration, and urban development are not considered due to uncertainty in where the growth will happen.
As seen below, population exposed to annual flooding increases from 269 million today (visible when hovered over the grey Today bar in the chart) to 454 million by 2100 in the baseline scenario. On the other hand, in the 1.5-degree scenario, population vulnerable to flooding reaches only at 421 million by the end of century (8% decline compared to the baseline scenario). Similarly, population living below the high tide line by the year 2100 goes from 300 million in the baseline down to 257 million in the 1.5-degree scenario (15% decline).
It is worth noting that despite the major reduction in global mean temperature by the end of century (from 3.6 degrees to 1.5 degrees), population exposed to sea level rise and coastal flooding improves only slightly. This is primarily due to the long delay in the ocean system before the sea level rise responds to any changes to global mean temperature. In other words, had we extended the simulation period beyond the year 2100, we would expect to see a larger difference between the 1.5-degree scenario and baseline in terms of population exposed to sea level rise and coastal flooding.
Probability of Ice-free Arctic Summer
Increased likelihood of summer ice-free conditions in the Arctic Ocean is an important anticipated impact of climate change. An ice-free Arctic summer is defined to occur when the average September sea ice coverage of the Arctic Ocean is less than one-million square kilometer (approximately 7% of the Arctic Ocean area).Such conditions are expected to have far-reaching consequences for the global climate system. In addition to impacts on ecology and human activities, ice-free conditions in the Arctic Ocean would also have a reinforcing effect on climate change. As the sea ice melts, darker ocean water absorbs more of the sun’s heat than the white ice, and further warms up the Earth.
The Probability of Ice-free Arctic Summer graph in En-ROADS presents three snapshot values for the likelihood of ice-free conditions in the Arctic: probability of having an ice-free Arctic summer in year 2050, probability of having an ice-free Arctic summer in year 2100, and probability of having at least one ice-free Arctic summer by the end of century.
Limiting the temperature increase by the end of century to 1.5 degrees as opposed to 3.6 degrees in the baseline, significantly reduces the likelihood of an ice-free Arctic summer. The probability of having an ice-free Arctic summer in year 2050 goes from 22% down to 7%. Similarly, the probability of having an ice-free Arctic summer in year 2100 is 4% in the 1.5-degree scenario as opposed to 97% in the baseline scenario. Finally, the likelihood of having at least one ice-free Arctic summer between now and the end of century is only a fifth of what would otherwise be in the baseline scenario.
Decrease in Crop Yield from Temperature
As the world gets warmer, global yields of major crops are expected to decline. Building on findings of the source study, En-ROADS simulates how global yields of maize, wheat, rice, and soybean – which provide two-thirds of human caloric intake – change due to temperature increase.
The reported percentages represent the estimated change in yield due to temperature increase, relative to a reference period of 1981-2010. The source study focused on the impact of temperature and did not estimate the impact that changes in rainfall or other climatic effects would have on crop yield.
In the 1.5-degree scenario, the yield-decrease for all four crops go down compared to the baseline. But the improvement is much more significant for maize and wheat. As opposed to 21% decrease by the end of century in the baseline, the maize yield declines only by 6% if we manage to limit the temperature increase to 1.5 degree. Similarly, the wheat yield decreases by 5% in the 1.5-degree scenario as opposed to 17% in the baseline.
Species Losing More than 50% of Climatic Range
The next climate impact metric simulated by En-ROADS measures global biodiversity loss. En-ROADS estimates the proportion of species in a particular group that is expected to lose more than half of their climatically determined range (the geographic area they can be found) due to temperature increase by 2100.
As seen below, the loss in the climatically determined ranges of each group of species declines significantly in the 1.5-degree scenario compared to the baseline. However, the improvement is especially significant for invertebrates, plants, and insects, for each of which the loss in the climatic range goes from 50+% in the baseline down to 6-8% in the 1.5-degree scenario.
Additional Deaths from Extreme Heat
The last climate impact metric reported by En-ROADS measures the percentage increase in deaths attributable to extreme heat due to climate change, projected across various geographical regions. Percentages represent the proportion of all deaths that are attributable to hotter temperatures (i.e., excess mortality from heat divided by the average total deaths during 1986-2005, by region).
Simulations suggest that the excess mortality in Southeast Asia is estimated to increase from 1.9% today (compared to the reference period) to 9.1% by the end of century in the baseline scenario. The 1.5-degree scenario, however, limits the additional deaths from extreme heat to 2.6% above the reference period, by the end of century. Similarly, limiting the temperature increase significantly reduces the additional deaths from extreme heat in Southern Europe, South America, Central Europe, and Central America.
It is worth noting that the source study analyzed 23 countries but did not include any countries in Africa or the Middle East because data were reported to be unavailable. However, many populations in Africa and the Middle East are highly vulnerable to extreme heat today and further heat due to climate change is expected to impact these areas disproportionately compared to other regions of the world.
Take a look at the En-ROADS simulator now to create your own scenario of climate action and see the difference it makes in climate impacts. If you would like to read about the mathematical implementation of climate impacts, see the En-ROADS Reference Guide. Please get in touch with us if you have questions, comments or ideas.
 Kulp, Scott A., and Benjamin H. Strauss. “New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding.” Nature communications 10.1 (2019): 1-12.
 Sigmond, Michael, John C. Fyfe, and Neil C. Swart. “Ice-free Arctic projections under the Paris Agreement.” Nature Climate Change 8.5 (2018): 404-408.
 Zhao, Chuang, et al. “Temperature increase reduces global yields of major crops in four independent estimates.” Proceedings of the National Academy of Sciences 114.35 (2017): 9326-9331.
 Warren, R., et al. The projected effect on insects, vertebrates, and plants of limiting global warming to 1.5 C rather than 2 C.” Science 360.6390 (2018): 791-79.
 Source: Vicedo-Cabrera, Ana Maria, et al. “Temperature-related mortality impacts under and beyond Paris Agreement climate change scenarios.” Climatic change 150.3-4 (2018): 391-402.