Climate MattersAugust 4, 2021

2021 Cooling Degree Days

2021 Cooling Degree Days


  • As temperatures continue to rise due to climate change, our need for air conditioning will increase as well.

  • Cooling Degree Days (CDDs) describe how much cooling is needed to maintain a comfortable indoor temperature and can help determine changing energy demands. About 95% (235 of 246) of locations had an increase in the number of CDDs since 1970, indicating that cooling demand has risen in these places. We also see more homes being built with central air conditioning across the U.S.

  • Higher usage of air conditioning raises several challenges. Air conditioners contain potent greenhouse gases, rely on fossil fuel-intensive power grids, and cost us money. Improving building and air conditioning efficiencies would reduce wasted energy. And replacing coal and natural gas with renewables, like wind and solar, will allow us to stay cool without making the planet warmer.

More Homes Built with Central AC - 2021 Cooling Degree Days
More Homes Built with Central AC
Local Cooling Degree Days - 2021 Cooling Degree Days
Local Cooling Degree Days

As our climate gets hotter, our cooling demand rises.
On those hot and muggy days, it's second nature to turn our air conditioning on full blast. As temperatures continue to rise due to climate change, cooling demands will increase as well. We can see this with last month's heatwave in the Pacific Northwest. The unprecedented heat forced many residents to purchase their first air conditioner to stay cool.

Tracking our energy use: What is a Cooling Degree Day?
To analyze cooling demand in the U.S., Climate Central used a data metric called Cooling Degree Days (CDDs). CDDs measure the difference between the 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 CDDs (90°- 65°). Since CDDs describe how much cooling is needed to maintain a comfortable indoor temperature, we can use them to determine changing energy demand to cool homes and buildings in a given location across time.

Take a look at the numbers to see how cooling demands have risen over time:

  • Climate Central collected CDDs data from 246 U.S. locations since the 1970s. About 95% (235) of locations had an increase in the number of cooling degree days over 51 years. The rise in CDDs is due to the average temperatures in those areas getting hotter.

  • According to the U.S. Survey of Construction, the U.S. has seen an increase in the number of newly built single-family homes with central air conditioning. The increasing trend since 1973 shows the growing need to cool our buildings as temperatures, especially in the summer months, become warmer due to climate change.

The burdens of high cooling demand:

  • In a greener world, increased demand for cooling wouldn’t be a problem. But in today's world, the energy needed to cool our buildings relies primarily on fossil fuels. That means we will emit more heat-trapping emissions that lead to even more warming.

  • The growing demand for more air conditioning can strain our aging power grids, leading to reliability concerns. This can become a dangerous situation, especially if a power grid fails during a heatwave.

  • Refrigerant chemicals used in air conditioners, like hydrofluorocarbons (HFCs), are extremely powerful greenhouse gases. HFCs have a global warming potential greater than carbon dioxide but a much shorter lifespan in the atmosphere.

  • Air conditioners can emit heat back outside to the immediate environment. In a city where millions of air conditioners are running at once, the combined heat can increase the heat island effect.

  • Minority and low-income communities disproportionately lack access to air conditioning, which can be fatal in the summer months. In addition, higher cooling demands will mean a higher energy bill, which can be a significant financial burden to low-income households.

Solutions: According to the Energy Information Administration, air conditioning consumption is expected to increase by 59% in U.S. homes and 17% in commercial spaces by 2050. The best solution to curb this high demand would be to transition to a cleaner electrical grid that replaces fossil fuels with renewable energy, like solar and wind. Other improvements include:

  • Retrofitting current buildings with better windows and insulation to reduce energy waste.

  • Updating to more advanced and energy-efficient air conditioners and central air systems.


How can I find information about the most energy efficient air conditioners or where I can dispose of or recycle an old air conditioner?
Check out the Environmental Protection Agency’s Partner Database for Incentives and Joint Marketing Exchange (DIME) or enter your zip code, select the "Room Air Conditioner" box, and click the "locate special offers/rebates" button to find a room air conditioner recycling program in your area.

How costly is air conditioning near me?
The Energy Information Administration (EIA) estimates that air conditioning accounts for 12% of homeowners’ energy bills on average in the U.S., but these can vary greatly by region. EIA publishes the average monthly price of electricity for businesses and residents in all states here.


The SciLine service, 500 Women Scientists or the press offices of local universities may be able to connect you with local scientists who have expertise on cooling demand and climate change. The American Association of State Climatologists is a professional scientific organization composed of all 50 state climatologists.


Ankit Kalanki
Building Sector Lead, Third Derivative
Senior Associate, Rocky Mountain Institute

Ariel Drehobl
Local policy manager, Energy Equity
American Council for an Energy-Efficient Economy (ACEEE)
Media contact to set up interviews: / 202-658-8129


Cooling Degree Days data was gathered via the Applied Climate Information System. Cooling degree days were calculated using the sum of the daily cooling degree days each year. Change in the number of days is based on linear regression. Climate Central's local analyses include 247 stations. However, for data summaries based on linear trends, only 246 stations are included due to large data gaps in Wheeling, West Virginia.

Data on newly built homes with central air conditioning was gathered from the Survey of Construction on the U.S. Census website. Region divisions are based on the U.S. Census Regions.

The stories below are served through a new pilot program from our partners at the Solutions Journalism Network, and were not created by or with Climate Central.