Case study: Climate vulnerability in the USA

By Matt Burdett, 15 March 2018

On this page, we look at one of two detailed examples of societies with contrasting vulnerability to climate change, focusing on the United States of America.

Climate change in the USA: the problem

The USA is a High Income Country according to the World Bank’s classifications. As such, it has relatively high levels of income which increases the country’s coping capacity, also known as its adaptive capacity. However, it’s not simply that the USA is relatively rich – the USA is still vulnerable because of its exposure to climate change and the geographical sensitivity of its increasingly elderly and coastal population.

Environmental change

Climate change is almost certainly going to make the USA warmer. Temperatures in the USA over the 20th century have increased overall:

  • Graph showing annual average temperatures in 48 states (i.e. excluding Alaska and Hawaii) compared to 1901. Source: EPA, 2017a.

Furthermore, the extremes of temperature are likely to increase. The map below shows the increase in temperatures under two scenarios of different greenhouse gas emissions (called RCPs, or Representative Concentration Pathways). Even with a reduction in emissions, temperatures are still likely to go up.

Projected Temperature Change of Hottest Days in the US. The entire map is red, depicting a change from 7 to >15 degrees F.

  • ‘Hot day’ temperatures (those that occur once every 20 years) by 2100 compared to 1986-2005. Source: EPA, 2017b.

The situation regarding rainfall is less clear. Rainfall averages over the course of the 20th century were variable, as shown on the graph below.

  • Graph showing annual average precipitation compared to 1900 in 48 states (i.e. excluding Alaska and Hawaii). Source: EPA, 2017a.

However, the extremes of precipitation suggest a gradual increase in the amount of precipitation falling in a short space of time, as seen on the graph below:

  • Graph showing the percentage of the land area of the contiguous 48 states (i.e. excluding Alaska and Hawaii) where a much greater than normal portion of total annual precipitation has come from extreme single-day precipitation events. Source: EPA, 2017a.

A major factor affecting vulnerability is exposure to sea level change. The map below shows that several parts of the USA experience more sea-level change problems than others. This is because the land itself can also rise and fall; relative to sea level change, this means that there can be an overall change that is greater than simple sea level change.

  • Cumulative changes in relative sea level from 1960 to 2015. Source: EPA, 2017a.

Economic vulnerability

The USA is the world’s largest economy. While this increases its adaptive capacity, it also means the US has a lot to lose! GDP could be reduced by 1.2% annually if a 1°C temperature increase occurs, and lead to greater inequality due to the uneven spatial impact of the costs, with the south being hit more than the north (Hsiang et al., 2017). This is shown on the map below, showing the cost of damage from climate change. Part of the reason why the south will experience more difficulties is the cost of sea level rise (Florida especially is very low-lying) and that the elderly population is concentrated in the south, so there is less adaptive capacity.

  • Variation in economic cost of climate change. Source: Plumer and Popovich, 2017.

The most obvious economic impacts will be responding to disasters, such as flooding from tropical storms. These are already costing more over time (see graph below) but this is not necessarily because there are more disasters: as the economy increases, there is more wealth that can be destroyed by a disaster, so the figure would be expected to increase if the economy does well.

billion dollar disaster line stacked bar graph: there appears to be an increase in the number of billion dollar disasters since the graph begins at 1980, peaking at 2011.

  • The cost of disasters. Note: CPI is the Consumer Price Index. This graph therefore shows prices in ‘today’s money’, so inflation has already been factored in. Source: NOAA, 2016.

Economic inequality may be increasing too. This is partly because in general the poorer districts are in the south. These are likely to be bit more by sea level rise and significantly rising temperatures.

  • Variation in economic cost of climate change. Source: Plumer and Popovich, 2017.

Humanitarian vulnerability

The problems for people in the USA are likely to be highly dependent on their location. As seen above, the economic impacts are spatially more likely in the south; this corresponds with an increase in population that occurred since 1970. The central and northern regions have generally lost population. This is a key factor in explaining not just the economic impacts, but also the potential for climate change to harm individual people and communities.

Map showing population change in the US, from <-50% to >500%.

  • % change in population, 1970-2008. Source: EAP, 2017b.

Furthermore, the south-east is the area of the USA with the oldest population. This is partly because of the migration to retirement communities in the south-east, and also because of the generally increasingly aged population in the US. By 2050, the proportion of the population aged over 65 is expected to grow to 20%, from just 13% in 2010 (EPA, 2017b).

These older people are much less likely to cope with climate change, as they are more physically sensitive to increasing temperatures, and they are less adaptive as they can move less easily. This results in the cumulative impact on elderly people in the south, making many cities in the Florida more vulnerable to coastal flooding by 2050. By comparing the two tables below, we can see that the most vulnerable cities are in the same state (Florida) as the most vulnerable populations.

  • Vulnerable cities and populations in the USA. Source: Climate Central, 2017

  • Vulnerable cities and populations in the USA. Source: Climate Central, 2017

This extra vulnerability – due to increased sensitivity and increased exposure – could result in more deaths due to climate change factors. The graph below shows two climate change scenarios, and in both of them there is an increase in deaths (shown by the black line). This increase in deaths is especially caused by an increase in summer temperatures, which (as shown earlier up the page) are expected to be more extreme in the future. The blue bars show the expected decrease in deaths due to warmer temperatures in the winter, but these do not balance out the expected increase from warmer temperatures in the summer.

  • Increase in deaths overall (black lines) due to an increase in summer deaths (orange bars), despite a decrease in winter deaths (blue bars). The graph on the left shows a climate model of significant warming; the one on the right shows less warming. Source: USGCRP, 2016.


Sources

Climate Central, 2017. These U.S. Cities Are Most Vulnerable to Major Coastal Flooding and Sea Level Rise http://www.climatecentral.org/news/us-cities-most-vulnerable-major-coastal-flooding-sea-level-rise-21748 Accessed 15 March 2018.

EPA, 2017a. Climate Change Indicators: U.S. and Global Temperature. https://www.epa.gov/climate-indicators/climate-change-indicators-us-and-global-temperature Accessed 15 March 2018.

EPA, 2017b. Climate Impacts on Society. https://archive.epa.gov/epa/climate-impacts/climate-impacts-society.html Accessed 15 March 2018.

Hsiang et al, 2017. Estimating economic damage from climate change in the United States. In Science, 30 Jun 2017: Vol. 356, Issue 6345, pp. 1362-1369. DOI: 10.1126/science.aal4369. http://science.sciencemag.org/content/356/6345/1362 Accessed 15 March 2018.

NOAA [National Center for Environmental Information (NCEI)], 2016. U.S. Billion-Dollar Weather and Climate Disasters (2016). https://www.ncdc.noaa.gov/billions/time-series Available at

https://archive.epa.gov/epa/climate-impacts/climate-impacts-society.html Accessed 15 March 2018.

Plumer and Popovich, 2017. As Climate Changes, Southern States Will Suffer More Than Others. https://www.nytimes.com/interactive/2017/06/29/climate/southern-states-worse-climate-effects.html Accessed 15 March 2018.

USGCRP [The U.S. Global Change Research Program], 2016. Our Changing Planet: The U.S. Global Change Research Program for Fiscal Year 2017. https://www.globalchange.gov/browse/reports/our-changing-planet-FY-2017 Accessed 15 March 2018.


Case study: Climate vulnerability in the USA: Learning activities

Questions

  1. Describe the climate of the USA. [2]
  2. Using statistical evidence, outline how the climate is likely to change in the future. [4]
  3. Describe the spatial variation in impacts of climate change in the USA. [4]
  4. Explain why some areas will be more vulnerable than others. [6]
  5. Which do you think is the most important factor in determining the USA’s vulnerability to climate change: exposure, sensitivity or adaptive capacity? Explain your answer. [6]

Other tasks

Complete this table:

USA

Other country

Climate change predictions

Potential problems of climate change

Mitigating strategies

Going further

Look at https://www.epa.gov/climate-indicators/weather-climate and establish the trends in other climate indicators. What does this suggest about the USA’s vulnerability to climate change in the future?


© Matthew Burdett, 2018. All rights reserved.

All secondary material on this site is clearly referenced and may be subject to copyright restrictions by the original authors. All original material on this page is subject to copyright.

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