Climate Change and Health Equity

Extreme Heat Days Narrative

What is the climate change challenge?

Periods of warmer temperatures and heat waves are expected to increase in frequency, intensity, and duration throughout the 21st century. In California, annual average maximum daily temperatures are expected to increase by 5.6°F (with moderate changes to greenhouse gas emissions) to 8.8°F (with no changes in emissions) by the end of the century.¹ Minimum nighttime temperatures are also projected to increase. Increased daytime temperatures, reduced nighttime cooling, and higher air pollution levels associated with urban heat islands (a phenomenon in which urban areas are warmer than the surrounding non-urban areas) can affect human health and exacerbate the impact of heat waves.² As of September 2023, the summers of 2020, 2021, and 2022 made California’s top 10 hottest summers of all time.³ A heat wave in July 2023 set and tied 358 maximum temperature records across California.⁴

Why is the climate change impact important to health?

Sustained exposure to high temperatures can cause heat-related illnesses, such as heat cramps, heat rashes, heatstroke, heat exhaustion, and even death.⁵ During a record-breaking 10-day heat wave in California in September 2022, there was a 5% increase in deaths – 395 more deaths than would have been expected.⁶ In July of 2006, approximately 147 deaths related to the California heat wave were reported by county coroners, though some models estimate there were as many as 655 excess deaths during that heat wave period.² In addition to excess deaths, exposure to higher temperatures was associated with increases in hospitalizations for acute renal failure, appendicitis, dehydration, ischemic stroke, mental health, non-infectious enteritis, and primary diabetes in California from 1999-2009.⁷ Warm temperatures and higher than normal temperatures in the cold season have resulted in an increase in emergency room admissions for mental health-disorders, self-injury or suicide, and intentional injury or homicide.⁸ Higher temperature exposures have been shown to be associated with an increase in adverse birth outcomes, such as preterm birth and low-birth weight.⁹,¹⁰ Santa Ana winds in Southern California can increase extreme heat-related events in spring, fall, and winter. Between 1999 to 2012, Santa Ana winds were linked to increased hospitalizations for ischemic stroke, dehydration, and renal failure, creating additional health and hospital burden during non-summer months.¹¹

Who is most impacted?

Populations with the greatest risk of health impacts from extreme heat, due to physical vulnerability or lack of resources to prepare or respond to heat, may include:

Older adults, particularly elderly over 65 years of age and/or living alone¹²,²⁴
Children and people who are pregnant¹³⁻¹⁵
People with pre-existing chronic health conditions (e.g., respiratory diseases, cardiovascular diseases, diabetes, cerebrovascular diseases, and acute allergies)¹⁴⁻¹⁶
People who engage in vigorous physical activity including agricultural and outdoor workers, indoor workers, athletes (especially young athletes), military personnel, and outdoor recreationists¹⁴,¹⁷⁻¹⁸
Lower-income populations²⁰
Socially or geographically isolated populations¹⁴
People with mental or physical disability²¹⁻²³
People living in cooler areas¹⁵
Residents of urban areas, living on the highest floors of apartment buildings, and without air-conditioning¹⁵,¹⁹
Racial and ethnic minoritized groups, particularly African Americans²⁰
People taking certain medications related to specific heart or mental health conditions²³⁻²⁴

How can communities build resilience to the climate impact?

Strategies that communities can use to build resilience to heat include the following²⁵⁻²⁷
Providing public and private cooling centers and offering free transportation to them on extreme heat days
Installing green roof gardens on top of buildings to provide shading, reduce roof surface temperature, and counter the urban heat island effect
Installing cool roofs, which reflect sunlight heat and can reduce the need for air conditioning during hot days
Planting trees and vegetation and restoring urban streams to provide shade and reduce the surrounding temperature
Installing new, low-emission and energy efficient air conditioning units or replacing old and damaged air conditioning units with more efficient ones
Creating a community-wide heat response plan to prepare for and respond to extreme heat related events that includes identifying conditions to activate or deactivate response plans, developing an outreach plan to reach vulnerable populations, and raising awareness about identifying and preventing heat illness
Improving community resilience by identifying data sources for characterizing and assessing vulnerability and improving infrastructure, especially for vulnerable communities
Improving health care systems extreme heat resiliency and preparedness by developing disaster medical response plans
Protecting outdoor workers against exposure to extreme heat by working with local communities to increase accessibility to resources
Creating heat warnings based on health outcomes as well as local conditions, temperature tolerance, and cooling availability
Funding weatherization or energy efficiency programs to assure vulnerable populations are protected from extreme heat

All strategies should be implemented with community involvement, especially including community members that are most vulnerable to heat, and who may historically have been excluded from disaster planning. Strategies should be feasible, accommodating to disabilities, economically accessible, available in multiple languages, and implemented in such a way that they reach community members without internet or cable. Strategies should assure that the jurisdiction is reducing greenhouse gas emissions while planning for climate change effects that are happening now and accelerating, to address the root cause of increasing heat. Without reducing emissions, it will not be possible protect health and life from the increasing severity of impacts.

Resources

What is the indicator?

Definition Indicator = Projected annual number of extreme heat days above the 98th percentile of computed maximum temperature for each location using 1961-1990 baseline data
Stratification: Time periods 2040-2060 and 2080-2099

Data Source

Historical and projected LOCA model data obtained from Cal-Adapt

Years available: 2040-2060, 2080-2099
Geographies available: County, Census Tract

Description

The data are derived from daily climate projections which have been downscaled from global climate models from the CMIP5 archive, using the Localized Constructed Analogs (LOCA) statistical technique developed by Scripps Institution of Oceanography. LOCA is a statistical downscaling technique that uses past history to add improved fine-scale detail to global climate models. An extreme heat day is defined as a day in a year when the maximum temperature exceeds the 98th historical percentile of the maximum temperatures based on observed historical data from 1961-1990 between April and October. By definition the baseline annual number of extreme heat days is 4.27 for all counties and geographic units. Projected data were provided from the four models that were selected by California’s Climate Action Team Research Working Group as priority models for research contributing to California’s Fourth Climate Change Assessment:

A warm/dry simulation – HadGEM2-ES
A cooler/wetter simulation – CNRM-CM5
An average simulation (CanESM2)
The model simulation that is most unlike the first three for the best coverage of different possibilities – MIROC5

Data were provided for each of these four models, for the RCP 8.5 scenario, for the County and Census Tract levels. The RCP 8.5 is a scenario where emissions continue to rise strongly through 2050 and plateau around 2100.

Limitations

Climate projections tell us how weather conditions are likely to change on average, but they cannot predict the weather at a particular day and time. Climate model projections illustrate how the climate system is expected to behave under specific scenarios of greenhouse gas emissions. Since our emissions of greenhouse gases depend on a variety of different social, political, and economic factors, we cannot be certain how they will change. Therefore, projected climate data may not prove to be accurate if the actual emissions pathway we follow differs from the scenarios used to make the projections. In addition, some aspects of the climate system are less well understood than others.