Reference: Gronlund C, Cameron L, Shea C, O’Neill M. Assessing the magnitude and uncertainties of the burden of selected diseases attributable to extreme heat and extreme precipitation under a climate change scenario in Michigan for the period 2041-2070. Environmental Health. (2019) 18:40 https://doi.org/10.1186/s12940-019-0483-5
Global climate change. You’ve probably heard of it. You may be worried about it. And certainly, the sheer scale of this worldwide phenomenon can be intimidating. How can one person or one community wrap their heads around it? How can that community prepare for the public health impacts of climate change?
Luckily, public health officials can look to examples from the past and combine them with models of the future to make informed predictions about how changing climate conditions in their regions may affect health outcomes in their communities. They can use these predictions to identify individuals at greatest risk and put plans into action today to help lessen those hazards tomorrow.
Researchers at the University of Michigan just published the results of their models and estimations for the state of Michigan. They learned a lot about how extreme heat and extreme precipitation events might become more frequent in their state with climate change, and how those weather events might be expected to impact public health.
Technique for Estimating Local Impacts of Climate Change
When Michigan researchers set out to tackle this question, they turned to technical guidance from the U.S Centers for Disease Control and Prevention. The CDC published a guide to walk local health departments through the process of this assessment. Essentially, the procedure boils down to six steps:
- Identify the cause and effect relationship between a climate condition (in this case, extreme heat and precipitation) and health outcomes;
- Use climate models to estimate how those climate conditions might change in the future in your region;
- Determine the historical prevalence of the health outcomes of interest in your community;
- Assess the historical relationship between exposure to the climate condition and the health outcomes in your community;
- Predict how the expected climate conditions of the future might affect health outcomes in your community; and
- Evaluate potential sources of error and uncertainty in your predictions.
How do Heat and Precipitation Affect Health?
For step #1, Michigan researchers were able to turn to a wealth of scientific findings demonstrating that extreme heat is associated with increased hospitalization and deaths, generally due to the impact of heat on kidney and lung function. Extreme precipitation can of course cause flash floods, which can lead to accident-related injuries and deaths, but additionally, lots of rain can also overwhelm sewer systems and increase run-off of pesticides and fertilizers from farms, all of which make our water less clean. Even with advanced public water treatment services in the U.S., waterborne diseases can and do still occur. Gastrointestinal issues from unclean water are a health concern from extreme precipitation events.
So extreme heat and precipitation can be dangerous. How might the frequency, intensity, and duration of these events change in Michigan in the future? Climate models help us make educated guesses.
How Might Heat and Precipitation Trends Change in Michigan’s Future?
There are all kinds of climate models out there. Some estimate what will happen if we cut back on emissions by half by 2050, or by 25% by 2030, etc. These researchers decided to use a more conservative model, which assumes that emissions continue to increase throughout the 21st century. The model predicts climate conditions in the years 2041-2070 and estimates the number of days Michigan will experience extreme heat (over 90°F and over 95°F) and extreme precipitation (heaviest 2% of precipitation events).
Do Heat and Precipitation Affect Everyone the Same Way?
Now the researchers knew how extreme heat and precipitation can affect health, and how often we might see those events in Michigan’s future. But these events don’t impact all people equally. Some people, for example, are more tolerant of high temperatures than others. Socioeconomic status and age can impact an individual’s likelihood to suffer exposure to extreme weather. And factors of the neighborhood itself can also play a role—for example, 90°F heat baking an asphalt-covered street radiates a lot more heat into the area than the same 90°F heat in a forested park. So how will Michiganders, specifically, be affected by heat and precipitation events in the future? Analysts are able to estimate this by looking at how Michigan communities have fared in these sorts of weather events in the past.
Findings Predict Increased Burden on the Healthcare System
Having studied all the pieces—how extreme weather can affect health, how often extreme weather might happen in the future, and how extreme weather has impacted Michigan residents in the past—the researchers could now assemble a picture of the future—how Michiganders’ health may be affected by extreme heat and precipitation in 2041-2070.
They learned a lot! Their work predicts that Michigan will experience increased heat-related illness and death, if emissions continue to increase through the 21st century. They estimate that 2.9 people out of every 100,000 will suffer a heat-related death, which is a six-fold increase from the 0.46 deaths per 100,000 people experienced historically. And while historically Michigan has seen 12 visits to the emergency room per 100,000 people due to extreme heat, they expect that to increase to 68 visits in the future. That translates to about 7,800 visits to the ER due to the heat—and $14 million in costs. Most of those visits are expected to be for adults over age 65.
Extreme precipitation is predicted to have more moderate impacts on ER visits – increasing from 1.7 extreme precipitation-associated visits per 100,000 people historically to 1.9 visits. An important note here is that most people who experience gastrointestinal distress from exposure to germs don’t generally go to the ER unless it’s quite serious—most people take care of themselves at home. It’s more difficult to measure historical burden and predict future impacts in these sorts of scenarios.
What are the Limitations of the Study?
Of course, these estimates are only as good as the model, and the model is only as good as the data used. The estimates are limited because they assume the health burden Michigan residents have historically experienced in the face of extreme heat and precipitation is a constant value, when in fact it may diminish over time if people build up heat tolerance or make other changes to increase their resilience. For example, outdoor laborers who have historically suffered heat-related illnesses may adapt their behavior and shift their schedules to start earlier in the day, avoiding the hottest times. Because the analysis doesn’t account for these sorts of adaptations and because it uses a ‘worst case scenario’ climate model, it may overestimate the burden Michigan might experience. However, it also likely underestimates the true burden of the changed climate, because it doesn’t account for the impact more moderate (but still hot) temperatures might have, or for health outcomes that aren’t serious enough to go to the ER (but are still unpleasant), or for the other, more subtle and interwoven impacts the changing temperature and precipitation might have.
What can we do with this Research?
Despite the limitations, these models and estimations give public policy makers some sense of what the future might hold. These predictions can help them make informed decisions to direct finite state resources toward the measures that will have the greatest impact in protecting public health. Michigan policy makers can look to these predictions and see that older adults are expected to suffer substantially more from extreme heat in the future and prioritize adaptations to lessen the impacts. For example, they can focus on increased access to air conditioning for the elderly and add more green spaces to urban areas to decrease the amount of heat radiating off asphalt and buildings.
Climate change is a global problem that requires large scale interventions, but local communities can still take ownership for their futures. We can learn from the past and make educated predictions about the future, and plan ahead to protect those who are most vulnerable.