Climate Matters•August 7, 2024
Cooling Schools in a Hotter Climate
KEY CONCEPTS
Keeping schools cool is a growing challenge as our climate warms and many places experience hotter summers and shoulder seasons.
Access to cooling is critical to ensure the health, safety, and well-being of students and school staff in our rapidly warming world.
Cooling degree days — a measure of cooling demand — have increased during the back-to-school period (late July through early September) since 1970 in nearly all (231 or 95%) of the 243 U.S. locations analyzed by Climate Central.
Over the last 10 years, back-to-school cooling demand increased by about 34% due to human-caused climate change.
The rise in cooling demand will likely continue as the planet warms, and schools will need critical building upgrades and face higher operating costs to maintain safe, comfortable temperatures.
Download local data
New school year starts with summer heat
Students across the country will soon head back to school — and in some cities, class has already been in session for weeks. In many places, summer heat lingers as students and staff begin a new school year.
As the planet warms, higher average temperatures and more frequent extreme heat increase the cooling demand to keep homes, schools, and other buildings at safe, comfortable temperatures.
Extreme heat affects children's health, development, and behavior. It can also impact students' ability to concentrate and learn. One study found that a 1°F hotter school year is associated with a 1% reduction in learning that year, based on test scores — but air conditioning can offset heat-related impacts to learning.
Learn more: Extreme Heat Risks for Children
A lack of air conditioning in schools is more than just uncomfortable. Extreme heat is the deadliest weather-related hazard in the U.S., and children are among those most vulnerable to heat-related illness. Access to air conditioned spaces provide children with a safe place to cool down after spending time playing outdoors in hot weather.
Warming climate, higher cooling demand
Cooling demand is reflected in a temperature-based metric called cooling degree days (CDD). CDD values estimate how much cooling is needed to maintain a comfortable indoor air temperature.
CDD values are the difference between a location’s daily average outdoor temperature and 65°F, an engineering standard that is considered the ideal indoor temperature.
For example, a day with an average temperature of 90°F has 25 CDD (90°- 65°).
CDD values are highest on the hottest days of the year. But any day over 65°F — including warm late summer and early fall days during the back-to-school season — has some need for cooling.
Keeping schools cool is a growing challenge as our climate warms and many places experience hotter summers and shoulder seasons.
Back-to-school cooling demand rising in 95% of U.S. cities analyzed
Climate Central used historical temperature data to analyze the change in CDD values during the back-to-school period from 1970 to 2023 in 243 U.S. locations. These trends estimate the changing local demand for energy to cool schools and other buildings as the climate has warmed since 1970.
The back-to-school period (July 17 to September 8) is based on Pew Research Center analysis of K-12 public school start dates in a nationally representative sample (see Methodology).
Nearly all (95% or 231) of the 243 locations analyzed have experienced an increase in back-to-school CDD since 1970.
On average, these 231 locations now experience 32% higher cooling demand during the back-to-school period than they did in the early 1970s.
Back-to-school CDD has more than doubled since 1970 in 10 of the locations analyzed.
On average, the largest increases in back-to-school CDD were in the West (+86%), Northwest (+62%), Northern Rockies and Plains (+40%), and Southwest (+38%).
City | Change in Back-to-School Cooling Degree Days (1970-2023) |
|---|---|
Reno, Nevada | 320% |
Eureka, California | 300% |
San Francisco, California | 240% |
Juneau, Alaska | 238% |
Helena, Montana | 196% |
Salinas, California | 180% |
Santa Maria, California | 180% |
Seattle, Washington | 152% |
Cheyenne, Wyoming | 124% |
Bend, Oregon | 102% |
Higher cooling demand due to climate change
Because CDD is a temperature-based metric, much of the rising trend in back-to-school CDD is due to warming. A key question is how much of the warming and the increase in CDD can be directly related to carbon pollution.
Climate Central used the Climate Shift Index system to estimate the back-to-school CDD that would have occurred without human-caused climate change. We then quantified how much of the increase in CDD in the last 10 years (2014-2023) was due to climate change in 245 U.S. cities. See Methodology for details.
Over the last 10 years, back-to-school cooling demand was about 34% higher due to human-caused climate change (compared to a world without carbon pollution).
The influence of climate change on CDD was felt most strongly in the Northwest and Northern Rockies and Plains regions, where the baseline back-to-school cooling demand is relatively low. Many schools in these regions may not have needed cooling in the past, making the increase even more challenging.
Region | Average annual back-to-school CDD (2014-2023) | Additional back-to-school CDD (2014-2023) due to climate change |
|---|---|---|
Northwest | 410 | 59% |
Northern Rockies & Plains | 356 | 55% |
Southwest | 843 | 52% |
Northeast | 468 | 42% |
Upper Midwest | 354 | 40% |
West | 643 | 35% |
Ohio Valley | 569 | 26% |
Southeast | 874 | 17% |
South | 1,012 | 14% |
Adapting schools for a warming world
Schools across the U.S. lack adequate infrastructure to cool buildings. A 2020 report by the Government Accountability Office found that around 41% of public school districts need to replace or update HVAC systems in at least half of their schools (representing about 36,000 schools nationwide).
The average U.S. public school was built nearly half a century ago, according to a 2024 survey These facilities were not built to function in our present-day climate. Regions that historically experienced milder temperatures during the school year are less likely to have air conditioning in schools. (See Figure 6 in the Environmental Protection Agency’s report, Climate Change and Children’s Health and Well-Being in the United States.)
As conditions continue to shift, schools will be exposed to more extreme weather. Rising temperatures (and therefore increased cooling demand) will mean schools are faced with necessary and expensive upgrades, as well as higher maintenance and operations costs to keep students and staff cool.
Buildings can be retrofitted with better windows and insulation to reduce energy waste, and existing fossil-fuel burning systems can be replaced with safer, more energy-efficient options. Adequate ventilation and filtration have the added benefit of improving air quality.
LOCAL STORY ANGLES
Map the influence of climate change on daily heat extremes in your area.
Climate Central’s Climate Shift Index map tool shows the influence of human-caused climate change on daily temperatures around the globe.
Check local temperature and heat risk forecasts.
HeatRisk is an interactive map tool from the National Weather Service, now available for the contiguous U.S. This color-numeric index shows current and forecast risk of daily local heat-related impacts.
Learn more about how climate change impacts children’s health – now and in the future.
Climate Central’s series Climate Change and Children’s Health details how climate change affects kids. Read about how climate change is worsening the effects of extreme heat and seasonal allergies for children. Stay tuned for future topics about children’s health, including air quality changes and flooding risks.
CONTACT EXPERTS
Joellen Russell, PhD (she/her)
Thomas R. Brown Distinguished Chair of Integrative Science
University of Arizona
Relevant expertise: Heat; heat-related illness; health effects of climate change on children
Media contact: sciencemoms@fenton.com
Serena Campas, MPA
Policy Associate
Rewiring America
Relevant expertise: education policy, electrification and clean energy in schools
Media contact: Yazmyn Pelaez yazmyn@rewiringamerica.org
Rosimar Rios-Berrios, PhD
Scientist II
National Center for Atmospheric Research
Relevant expertise: Extreme weather and climate change
Media contact: sciencemoms@fenton.com
*Available for interviews in Spanish and English
FIND EXPERTS
Submit a request to SciLine from the American Association for the Advancement of Science or to the Climate Data Concierge from Columbia University. These free services rapidly connect journalists to relevant scientific experts.
Browse maps of climate experts and services at regional NOAA, USDA, and Department of the Interior offices.
Explore databases such as 500 Women Scientists, BIPOC Climate and Energy Justice PhDs, and Diverse Sources to find and amplify diverse expert voices.
Reach out to your State Climate Office or the nearest Land-Grant University to connect with scientists, educators, and extension staff in your local area.
METHODOLOGY
Daily cooling degree day (CDD) data from 1970-2023 were obtained from the Applied Climate Information System. The annual period of analysis was limited to the “back-to-school” period, defined as July 17 - September 8, based on a 2023 Pew Research Center analysis of K-12 public school start dates for the 2023-24 school year from a nationally representative sample of 1,573 districts.
Back-to-school CDDs were calculated as the sum of the daily cooling degree days from July 17 to September 8 (inclusive) each year using a base temperature of 65°F. The percent change in back to school CDDs from 1970 to 2023 is based on endpoints of the linear regression fit.
Climate Central's CDD analysis includes 247 stations. Data summaries based on linear trends include 243 total locations due to data gaps in three stations (Dothan, Ala.; Hazard, Ky.; and Wheeling, W.Va) and negative slope values in Anchorage, Alaska.
Regions were defined based on NOAA’s U.S. Climate Regions.
Climate Central used observed temperature data and counterfactual temperature estimates (temperatures that would have occurred in a world without human-induced climate change) derived from the Climate Shift Index system to analyze CDDs during the back-to-school period for 245 U.S. cities during the last 10 years (2014-2023).