It's a sure sign that summer is over and winter is on the way--leaves that were once deep green turn red, yellow and bright orange.
It
's
a
sure
sign
that
summer
is
over
and
winter
is
on
the
way
--
leaves
that
were
once
deep
green
turn
red
,
yellow
and
bright
orange
.
It happens every autumn.
It
happens
every
autumn
.
But did you ever wonder why?
But
did
you
ever
wonder
why
?
The leaves start changing color when the nights start getting longer and the temperature starts getting cooler.
The
leaves
start
changing
color
when
the
nights
start
getting
longer
and
the
temperature
starts
getting
cooler
.
Some scientists think that as the number of daylight hours shrinks the leaves stop making chlorophyll which makes plants green.
Some
scientists
think
that
as
the
number
of
daylight
hours
shrinks
the
leaves
stop
making
chlorophyll
which
makes
plants
green
.
The reason is that the process of making chlorophyll requires sunlight.
The
reason
is
that
the
process
of
making
chlorophyll
requires
sunlight
.
But according to horticulture educator Susan Rose from Colorado State University, it turns out leaves don't really change color at all.
But
according
to
horticulture
educator
Susan
Rose
from
Colorado
State
University
,
it
turns
out
leaves
do
n't
really
change
color
at
all
.
"The fall colors are actually there all along," she said.
``
The
fall
colors
are
actually
there
all
along
,
''
she
said
.
"But they are covered by the green chlorophyll.
``
But
they
are
covered
by
the
green
chlorophyll
.
As the chlorophyll stops being produced, the other colors can shine through."
As
the
chlorophyll
stops
being
produced
,
the
other
colors
can
shine
through
.
''
The kind of color that the leaves are going to change to is determined by the plant's genetic background.
The
kind
of
color
that
the
leaves
are
going
to
change
to
is
determined
by
the
plant
's
genetic
background
.
In some places, the leaves start changing color in September--before autumn even officially begins.
In
some
places
,
the
leaves
start
changing
color
in
September
--
before
autumn
even
officially
begins
.
In other places, they don't change until late October or even November.
In
other
places
,
they
do
n't
change
until
late
October
or
even
November
.
Some scientists say the leaves have been changing color later than usual in recent years.
Some
scientists
say
the
leaves
have
been
changing
color
later
than
usual
in
recent
years
.
And they think global warming has something to do with that.
And
they
think
global
warming
has
something
to
do
with
that
.
In one study, researchers found that the growing season in the Northern Hemisphere was nearly a week longer, on average, in 2008 than it was in 1982.
In
one
study
,
researchers
found
that
the
growing
season
in
the
Northern
Hemisphere
was
nearly
a
week
longer
,
on
average
,
in
2008
than
it
was
in
1982
.
And a professor from Harvard University found that the leaves, west of Boston, Massachusetts, are changing color about three days later than they used to.
And
a
professor
from
Harvard
University
found
that
the
leaves
,
west
of
Boston
,
Massachusetts
,
are
changing
color
about
three
days
later
than
they
used
to
.
However, other scientists disagree with the global warming theory.
However
,
other
scientists
disagree
with
the
global
warming
theory
.
Susan Rose said the leaves in her part of Colorado are changing "right on schedule."
Susan
Rose
said
the
leaves
in
her
part
of
Colorado
are
changing
``
right
on
schedule
.
''
But the leaves in other parts of that state are running a little late.
But
the
leaves
in
other
parts
of
that
state
are
running
a
little
late
.
"The lateness in the mountains may have something to do with the really warm late summer and early fall," she said.
``
The
lateness
in
the
mountains
may
have
something
to
do
with
the
really
warm
late
summer
and
early
fall
,
''
she
said
.
"But I'm afraid that's just a guess."
``
But
I
'm
afraid
that
's
just
a
guess
.
''
It's a sure sign that summer is over and winter is on the way--leaves that were once deep green turn red, yellow and bright orange. It happens every autumn. But did you ever wonder why?  The leaves start changing color when the nights start getting longer and the temperature starts getting cooler. Some scientists think that as the number of daylight hours shrinks the leaves stop making chlorophyll which makes plants green. The reason is that the process of making chlorophyll requires sunlight. But according to horticulture educator Susan Rose from Colorado State University, it turns out leaves don't really change color at all. "The fall colors are actually there all along," she said. "But they are covered by the green chlorophyll. As the chlorophyll stops being produced, the other colors can shine through."  The kind of color that the leaves are going to change to is determined by the plant's genetic background. In some places, the leaves start changing color in September--before autumn even officially begins. In other places, they don't change until late October or even November. Some scientists say the leaves have been changing color later than usual in recent years. And they think global warming has something to do with that.  In one study, researchers found that the growing season in the Northern Hemisphere was nearly a week longer, on average, in 2008 than it was in 1982. And a professor from Harvard University found that the leaves, west of Boston, Massachusetts, are changing color about three days later than they used to. However, other scientists disagree with the global warming theory. Susan Rose said the leaves in her part of Colorado are changing "right on schedule." But the leaves in other parts of that state are running a little late. "The lateness in the mountains may have something to do with the really warm late summer and early fall," she said. "But I'm afraid that's just a guess."