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Hurricanes, Earthquakes, Wildfires—a Primer on Extreme Event Attribution &
Climate
Epidemiology |
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Author: Madeline Roberts, PhD, MPH If the recent number of once-in-a-generation events has left you anywhere on the gamut from deep concern to cognitive overwhelm, you are certainly not alone. July was the hottest month on record for planet Earth. This month, tropical storm Hilary made landfall in Southern California and parts of Mexico, something not seen since September of 1939. An earthquake occurred in Southern California while people were sheltering from the storm. Abnormally dry conditions factored into the devastating fires in Lahaina, which resulted in the highest death toll from a wildfire in modern history. Climate epidemiology is an emerging subfield based on close collaboration between epidemiologists and climate scientists to study climate-related exposures and their implications for population health, as well as to inform policy in this area. Health issues that may arise from climate change and related events include changes in the distribution of disease vectors and related illnesses (i.e., mosquitoes and malaria), waterborne diseases, heat-related illness, and agricultural production leading to food supply issues. One of the most critical (and sometimes overlooked) elements of public health and epidemiology is risk management and mitigation; this falls within the scope of climate epidemiology as well, in the form of implementing warning systems and preparedness plans that combine weather forecasting with epidemiology. While there is no precise, hard-and-fast definition of an extreme weather event, it is often identified by distance from the historical (observable) mean, typically an event that falls in the highest or lowest 1, 5, or 10 percent of historical measurements. An extreme event can also be identified by, for example, absolute thresholds for a variable like temperature, beyond which we begin to see health impacts. Extreme weather falls into two main subcategories: weather-related (think events of relatively shorter duration—floods, hurricanes) and climate-related (think cumulative events over time—drought, wildfires). Climate patterns (e.g., El Niño, La Niña) and climate variability are expected and can result in extreme weather. It is important to note that under natural climate variability extreme weather events would still occur independently of human activity. Anthropogenic climate change, by contrast, is connected to burning fossil fuels and greenhouse gas emissions by humans. Extreme event attribution science is a relatively new field. One of the earliest studies was published in 2004, evaluating anthropogenic influence on a European heatwave during the previous year. The field is devoted to determining the causes of specific extreme weather events. Study within this field aims to differentiate between anthropogenic global warming and expected variability in weather patterns and to quantify the degree to which each contributed to a specific event. To do this, attribution science employs computational and statistical modeling. In some instances, this can include running models with a climate change or anthropogenic greenhouse emissions feature and then running counterfactual models that exclude the feature of the anthropogenic greenhouse emissions. In analyzing the differences in the models, scientists can measure the impact of anthropogenic climate change. This is similar to the epidemiologic concept of attributable risk. One particular challenge to this approach is that extreme events are rare and few by definition, and with fewer observations comes greater statistical uncertainty. As the field of climate epidemiology develops, one growth opportunity would be an extension of attribution science to encompass health impacts and causal inference.
Looking forward to 2100, scientists have projected a “virtually certain” increase in the number of unusually warm and cold days and nights at the global scale and a “very likely” heatwaves. Also projected is a likely increase in the frequency of heavy precipitation and total rainfall, especially in high latitudes and tropical regions. The implications of extreme weather events are of great consequence, ranging from the preservation of life to human displacement and the economic impact of rebuilding after an event. For example, Hurricane Katrina displaced approximately 1 million people from the Gulf Coast region, some permanently, and the federal government spent approximately $120 billion on recovery efforts. Over the past several decades, in addition to the devastation experienced by affected persons and families, the cost of wildfire damages has often exceeded one billion dollars, adjusting for inflation.
The past 40 years have seen the number of extreme weather events double, according to the World Meteorological Organization. Attribution science can help inform decisions about risk management, including land management and the development of infrastructure and floodwalls. Implementing and improving multi-hazard warning systems coupled with prevention and preparedness strategies can help mitigate the health impact of extreme events, be they from natural climate patterns or anthropogenic causes. ■ |
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