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| Heating and Cooling Degree Days |
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 Climate Change Indicators: Heating
and Cooling Degree Days
This indicator examines changing temperatures from the
perspective of heating and cooling needs for buildings.
Key Points
Heating degree days have declined in the contiguous United
States, particularly in recent years, as the climate has
warmed (see Figure 1). This change suggests that heating
needs have decreased overall.
Overall, cooling degree days have increased over the past
100 years. The increase is most noticeable over the past few
decades, suggesting that air conditioning energy demand has
also been increasing recently (see Figure 1).
Heating degree days have generally decreased and cooling
degree days have generally increased throughout the North
and West. The Southeast, with the exception of Florida, has
seen the opposite: more heating degree days and fewer
cooling degree days (see Figures 2 and 3). |
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Background
Outdoor temperatures can affect daily life in many ways. In
particular, temperature affects our comfort level and our
demand for heating and air conditioning. Collectively,
heating and cooling the spaces in which we live accounts for
48 percent of the energy that American households use every
year. As climate change contributes to an increase in
average temperatures, an increase in unusually hot days, and
a decrease in unusually cold days (see the U.S. and Global
Temperature and High and Low Temperatures indicators), the
overall demand for heating is expected to decline and the
demand for cooling is expected to increase.
One way to measure the influence of temperature change on
energy demand is using heating and cooling degree days,
which measure the difference between outdoor temperatures
and a temperature that people generally find comfortable
indoors. These measurements suggest how much energy people
might need to use to heat and cool their homes and
workplaces, thus providing a sense of how climate change
could affect people’s daily lives and finances. |
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About the Indicator
This indicator uses daily temperature data from thousands of
weather stations across the United States to calculate
heating and cooling degree days. A “degree day” is
determined by comparing the daily average outdoor
temperature with a defined baseline temperature for indoor
comfort (in this case, 65°F). For example, if the average
temperature on a particular day is 78°F, then that day
counts as 13 cooling degree days, as a building’s interior
would need to be cooled by 13°F to reach 65°F. Conversely,
if the average outdoor temperature is 34°F, then that day
counts as 31 heating degree days, as a building’s interior
would need to be warmed by 31°F to reach 65°F. This does not
mean that all people will actually heat or cool buildings to
65°F; it is just a number to allow for consistent
comparisons over time and across the country. For reference,
New York City experiences far more heating degree days than
cooling degree days per year—a reflection of the relatively
cool climate in the Northeast—while Houston, Texas, has far
more cooling degree days than heating degree days—a
reflection of the much warmer climate in the South.
Figure 1 shows each year’s average heating and cooling
degree days across the contiguous 48 states. Figures 2 and 3
show how heating and cooling degree days have changed by
state, based on a comparison of the first 60 years of
available data (1895–1954) with the most recent 61 years
(1955–2015). State and national averages were calculated by
finding the total number of heating and cooling degree days
per year at each weather station, averaging the results from
all stations within regions called climate divisions (each
state within the contiguous 48 has up to 10 climate
divisions), then calculating state and national averages
weighted by the population of each climate division. With
this population-weighting approach, average state and
national heating and cooling degree days more closely
reflect the conditions that the average resident would
experience.
Indicator Notes
Heating and cooling degree days suggest how temperature
changes affect energy demand, but they do not necessarily
reflect actual energy use. Many other factors have
influenced energy demand over time, such as more
energy-efficient heating systems, the introduction and
increasingly widespread use of cooling technologies, larger
but better-insulated homes, behavior change, and population
shifts (such as more people moving to warmer regions). All
of the population-weighting in this indicator is based on
the population distribution according to the 2010 U.S.
Census, so any changes in heating and cooling degree days
over time in this indicator reflect actual changes in the
climate, not the influence of shifting populations. A
nationally applied baseline—in this case, 65°F—has certain
limitations considering the various climate regimes across
the United States.
Data Sources
The data for this indicator were provided by the National
Oceanic and Atmospheric Administration’s National Centers
for Environmental Information, which maintains a large
collection of climate data online at:
www.ncei.noaa.gov.
Technical Documentation
Download related technical information PDF |
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 Figure
1. Heating and Cooling Degree Days in the Contiguous
48 States, 1895–2015
This figure shows the average number of heating and cooling
degree days per year across the contiguous 48 states.
Data source: NOAA, 20163 |
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EPA Page |
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This is the
EPA page for this topic. To see if the Trump
administration has changed the EPA page, simply click the
link and compare the information with this page. If you
notice changes were made to the EPA page, please post a
comment. Thanks. |
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Interactive Map
This map shows how the average number of heating degree days
per year has changed in each state over time. Click each
state to reveal the data. The map was created by comparing
the first 60 years of available data (1895–1954) with the
most recent 61 years (1955–2015). “Warmer” colors indicate
an increase in temperatures between the two periods, leading
to less of a need to turn on the heat—that is, fewer heating
degree days. “Cooler” colors indicate a decrease in
temperatures, leading to more of a need to turn on the
heat—that is, more heating degree days.
Data source: NOAA, 20164
Interactive Map
This map shows how the average number of cooling degree days
per year has changed in each state over time. Click each
state to reveal the data. The map was created by comparing
the first 60 years of available data (1895–1954) with the
most recent 61 years (1955–2015). “Warmer” colors indicate
an increase in temperatures between the two periods, leading
to more demand for air conditioning—that is, more cooling
degree days. “Cooler” colors indicate a decrease in
temperatures, leading to less demand for air
conditioning—that is, fewer cooling degree days.
Data source: NOAA, 20165 |
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Additional Climate Change Information |
Climate Change and Carbon Dioxide
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change
and carbon dioxide.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice. |
Carbon Dioxide and Climate Change
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of carbon dioxide
and climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice. |
Environmental Group Warns Earth's Health at Risk
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
A report by the World Wildlife Fund looked at thousands of animal populations
and found they have dropped significantly in 40 years. |
Sea Levels Rising at Fastest Rate in 3,000 years
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
A group of scientists say sea levels are rising at record rates. Another group
found that January temperatures in the Arctic reached a record high. |
Capturing CO2 Gas Is Not Easy
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
Most scientists agree that carbon-dioxide gas is partly to blame for climate
change: rising global temperatures. But capturing the CO2 gas released by power
stations is costly and difficult. |
Growth, Climate Change Threaten African Plants and
Animals
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
Researchers believe Africa may lose as much as 30 percent of its animal and
plant species by the end of this century. |
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