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Climate Change, Health Care, Public Health

Summer temperature variability and long-term survival among elderly people

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Extreme weather events such as hurricanes, droughts and heat waves are likely to increase in frequency in the coming years because of climate change, directly threatening human lives. At the same time, global warming has the potential to affect human health through less dramatic, but equally serious, changes.

A 2012 study published in Proceedings of the National Academy of Sciences, “Summer Temperature Variability and Long-Term Survival among Elderly People with Chronic Disease,” explores the relationship between the unusually high temperatures associated with climate change and geriatric mortality. The researchers, based at the Harvard School of Public Health and the University of Michigan School of Public Health, analyzed Medicare data from more than 10 million individuals over age 65 suffering from chronic obstructive pulmonary disease (COPD), diabetes, congestive heart failure or myocardial infarction (MI, or heart attack) from 135 U.S. cities between 1985 and 2006. Mortality rates were then correlated with local year-to-year variations in summer temperatures.

The study’s findings include:

  • For each 1° Celsius increase in summer temperature, elderly individuals suffering from diabetes are 4% more likely to die than their healthy counterparts; similar outcomes were found for individuals suffering from MI (3.8%), COPD (3.7%) and congestive heart failure (2.8%).
  • The probability of mortality due to summer temperature variability — typically between 0.5°C and 5°C — is higher in cities with hotter climates and with those 75 and older.
  • Heat waves do not explain increases in mortality, suggesting that increased temperature variability impairs health and survival even when hot weather does not officially qualify as a heat wave.  “We are not simply looking at the long-term effects of heat waves…. Adaptation and intervention strategies solely targeted to heat waves may miss an important opportunity to improve public health.”
  • Summer temperature variability is less strongly associated with mortality in cities with higher percentages of green land and college-educated populations, and more strongly associated with mortality in cities with higher population density, poverty levels and percentages of nonwhite residents.
  • Ozone levels are similarly associated with both heat variability and mortality. “Our recent study applying the same survival analysis approach found that long-term ozone exposure alone is associated with increased risk of death in Medicare subjects with the same specific chronic conditions as in the present study.”

The authors suggest that an additional 1°C increase in temperature variability would result in a 5% increase in mortality rates in the population studied. “Our findings suggest that long-term increases in temperature [standard deviation] may increase the risk of mortality in different subgroups of susceptible older populations, although further investigation of appropriate adaptation measures is needed.”

Related research: A 2011 study published in Environmental Health Perspectives, “Heat Waves in the United States: Mortality Risk during Heat Waves and Effect Modification by Heat Wave Characteristics in 43 U.S. Communities,” found that “Nationally, mortality increased 3.74% … during heat waves compared with non-heat wave days. Heat wave mortality risk increased 2.49% for every 1°F increase in heat wave intensity and 0.38% for every 1-day increase in heat wave duration.” Another 2011 study in that journal, “Toward a Quantitative Estimate of Future Heat Wave Mortality under Global Climate Change,” estimates that “under three different climate change scenarios for 2081–2100 and in the absence of adaptation, the city of Chicago could experience between 166 and 2,217 excess deaths per year attributable to heat waves, based on estimates from seven global climate models.”

Tags: aging, poverty, global warming

    Writer: | Last updated: June 18, 2013

    Citation: Zanobettia, Antonella; O'Neillb, Marie S.; Gronlundb, Carina J.; Schwartza, Joel D. “Summer Temperature Variability and Long-Term Survival among Elderly People with Chronic Disease,” Proceedings of the National Academy of Sciences, April 2012. doi: 10.1073/pnas.1113070109.

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    Read the study-related Science Daily article titled "Summer Temperature Variability May Increase Mortality Risk for Elderly With Chronic Disease."

    1. What key insights from the article and study should reporters be aware of as they cover issues relating to climate change and elderly populations with chronic illnesses?

    Newswriting and digital reporting assignments

    1. Write a lead, headline or nut graph based on the study.
    2. Spend 60 minutes exploring the issue by accessing sources of information other than the study. Write a lead (or headline or nut graph) based on the study but informed by the new information. Does the new information significantly change what one would write based on the study alone?
    3. Compose two Twitter messages of 140 characters or fewer accurately conveying the study’s findings to a general audience. Make sure to use appropriate hashtags.
    4. Choose several key quotations from the study and show how they would be set up and used in a brief blog post.
    5. Map out the structure for a 60-second video segment about the study. What combination of study findings and visual aids could be used?
    6. Find pictures and graphics that might run with a story about the study. If appropriate, also find two related videos to embed in an online posting. Be sure to evaluate the credibility and appropriateness of any materials you would aggregate and repurpose.

    Class discussion questions

    1. What is the study’s most important finding?
    2. Would members of the public intuitively understand the study’s findings? If not, what would be the most effective way to relate them?
    3. What kinds of knowledgeable sources you would interview to report the study in context?
    4. How could the study be “localized” and shown to have community implications?
    5. How might the study be explained through the stories of representative individuals? What kinds of people might a reporter feature to make such a story about the study come alive?
    6. What sorts of stories might be generated out of secondary information or ideas discussed in the study?

    Study analysis

    Read the study titled “Summer Temperature Variability and Long-Term Survival Among Elderly People with Chronic Disease.”

    1. What are the study's key technical term(s)? Which ones need to be put into language a lay audience can understand?
    2. Do the study’s authors put the research into context and show how they are advancing the state of knowledge about the subject? If so, what did the previous research indicate?
    3. What is the study’s research method? If there are statistical results, how did the scholars arrive at them?
    4. Evaluate the study's limitations. (For example, are there weaknesses in the study's data or research design?)
    5. How could the findings be misreported or misinterpreted by a reporter? In other words, what are the difficulties in conveying the data accurately? Give an example of a faulty headline or story lead.