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 Climate Change Indicators: Length of
Growing Season
This indicator measures the length of the growing season in
the contiguous 48 states.
Key Points
The average length of the growing season in the contiguous
48 states has increased by nearly two weeks since the
beginning of the 20th century. A particularly large and
steady increase occurred over the last 30 years (see Figure
1).
The length of the growing season has increased more rapidly
in the West than in the East. In the West, the length of the
growing season has increased at an average rate of about 2.2
days per decade since 1895, compared with a rate of nearly
one day per decade in the East (see Figure 2).
The length of the growing season has increased in almost
every state. States in the Southwest (e.g., Arizona and
California) have seen the most dramatic increase. In
contrast, the growing season has actually become shorter in
a few southeastern states (Figure 3).
In recent years, the final spring frost has been occurring
earlier than at any point since 1895, and the first fall
frost has been arriving later. Since 1980, the last spring
frost has occurred an average of three days earlier than the
long-term average, and the first fall frost has occurred
about three days later (see Figure 4).
Patterns in the timing of spring and fall frost (Figures 5
and 6) largely mirror the overall patterns in the length of
growing season (Figure 3). States that saw an increased
length of growing season had comparable changes in
frost-free days for both the spring and fall. |
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Background
The length of the growing season in any given region refers
to the number of days when plant growth takes place. The
growing season often determines which crops can be grown in
an area, as some crops require long growing seasons, while
others mature rapidly. Growing season length is limited by
many different factors. Depending on the region and the
climate, the growing season is influenced by air
temperatures, frost days, rainfall, or daylight hours.
Changes in the length of the growing season can have both
positive and negative effects on the yield and prices of
particular crops. Overall, warming is expected to have
negative effects on yields of major crops, but crops in some
individual locations may benefit. A longer growing season
could allow farmers to diversify crops or have multiple
harvests from the same plot. However, it could also limit
the types of crops grown, encourage invasive species or weed
growth, or increase demand for irrigation. A longer growing
season could also disrupt the function and structure of a
region’s ecosystems and could, for example, alter the range
and types of animal species in the area. |
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About the Indicator
This indicator looks at the impact of temperature on the
length of the growing season in the contiguous 48 states, as
well as trends in the timing of spring and fall frosts. For
this indicator, the length of the growing season is defined
as the period of time between the last frost of spring and
the first frost of fall, when the air temperature drops
below the freezing point of 32°F. This is referred to as the
frost-free season.
Changes in growing season have been calculated using
temperature data from 750 weather stations throughout the
contiguous 48 states. These data were compiled by the
National Oceanic and Atmospheric Administration’s National
Centers for Environmental Information. Growing season length
and the timing of spring and fall frosts were averaged
across the nation, then compared with long-term average
numbers (1895–2015) to determine how each year differed from
the long-term average.
Indicator Notes
Changes in measurement techniques and instruments over time
can affect trends. This indicator includes only data from
weather stations with a consistent record of data points for
the time period. Methods for producing state, regional, and
national values by year were designed to provide spatial
representativeness regardless of station density.
Data Sources
All six figures are based on temperature data compiled by
the National Oceanic and Atmospheric Administration’s
National Centers for Environmental Information, and these
data are available online at:
www.ncei.noaa.gov.
Analysis of frost timing and growing season length was
provided by Kunkel (2016).
Technical Documentation
Download related technical information PDF |
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 Figure
1. Length of Growing Season in the Contiguous 48
States, 1895–2015
This figure shows the length of the growing season in the
contiguous 48 states compared with a long-term average. For
each year, the line represents the number of days shorter or
longer than average. The line was smoothed using an 11-year
moving average. Choosing a different long-term average for
comparison would not change the shape of the data over time.
Data source: Kunkel, 20162 |
 Figure
2. Length of Growing Season in the Contiguous 48
States, 1895–2015: West Versus East
Include another us map - growing season reference map
This figure shows the length of the growing season in the
western and eastern United States compared with a long-term
average. For each year, the line represents the number of
days shorter or longer than average. The lines were smoothed
using an 11-year moving average. Choosing a different
long-term average for comparison would not change the shape
of the data over time.
Data source: Kunkel, 20163 |
 Reference
Map
Reference map for figure 2 above. |
 Figure
3. Change in Length of Growing Season by State,
1895–2015
This map shows the total change in length of the growing
season from 1895 to 2015 for each of the contiguous 48
states.
Data source: Kunkel, 20164 |
 Figure
4. Timing of Last Spring Frost and First Fall Frost
in the Contiguous 48 States, 1895–2015
This figure shows the timing of the last spring frost and
the first fall frost in the contiguous 48 states compared
with a long-term average. Positive values indicate that the
frost occurred later in the year, and negative values
indicate that the frost occurred earlier in the year. The
lines were smoothed using an 11-year moving average.
Choosing a different long-term average for comparison would
not change the shape of the data over time.
Data source: Kunkel, 20165 |
 Figure
5. Change in Timing of Last Spring Frost by State,
1895–2015
This map shows the total change in last spring frost date
from 1895 to 2015 for each of the contiguous 48 states.
Data source: Kunkel, 20166 |
 Figure
6. Change in Timing of First Fall Frost by State,
1895–2015
This map shows the total change in first fall frost date
from 1895 to 2015 for each of the contiguous 48 states.
Data source: Kunkel, 20167 |
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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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Additional Climate Change Information |
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(Beginner - Listening,
reading)
A video lesson to
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The English is
spoken at 75% of normal speed.
Great English listening and reading practice. |
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The English is
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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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