NASA:
World of Change - Global
Temperatures
Go to the
website for a very informative,
simple interactive
graphic.
NASA
February 24, 2011
http://earthobservatory.nasa.gov/Features/WorldOfChange/
decadaltemp.php?src=features-recent
NASA:
World of Change - Global
Temperatures
The world
is getting warmer. Whether the
cause is
human
activity or natural
variability-and the
preponderance
of evidence says it's
likely
humans-thermometer
readings all around the
world
have risen
steadily since the beginning of
the
Industrial
Revolution. (Click on dates above
to
step
through the decades.)
According
to an ongoing temperature
analysis
conducted
by scientists at NASA's
Goddard
Institute
for Space Studies (GISS) and
shown in
this series
of maps, the average
global
temperature
on Earth has increased by
about
0.8°Celsius
(1.4°Fahrenheit) since
1880.
Two-thirds
of the warming has occurred
since
1975, at a
rate of roughly 0.15-0.20°C
per decade.
But why
should we care about one degree
of
warming?
After all, the temperature
fluctuates by
many
degrees every day where we
live.
The global
temperature record represents
an
average
over the entire surface of the
planet.
The
temperatures we experience
locally and in
short
periods can fluctuate
significantly due to
predictable
cyclical events (night and
day,
summer and
winter) and hard-to-predict wind
and
precipitation
patterns. But the
global
temperature
mainly depends on how much energy
the
planet
receives from the Sun and how
much it
radiates
back into space-quantities that
change
very
little. The amount of energy
radiated by the
Earth
depends significantly on the
chemical
composition
of the atmosphere, particularly
the
amount of
heat-trapping greenhouse
gases.
A
one-degree global change is
significant because
it takes a
vast amount of heat to warm all
the
oceans,
atmosphere, and land by that
much. In the
past, a
one- to two-degree drop was all
it took
to plunge
the Earth into the Little Ice
Age. A
five-degree
drop was enough to bury a large
part
of North
America under a towering mass of
ice
20,000
years ago.
The maps
above show temperature anomalies,
or
changes,
not absolute temperature. They
depict
how much
various regions of the world have
warmed
or cooled
when compared with a base period
of
1951-1980.
(The global mean surface
air
temperature
for that period was estimated to
be
14°C
(57°F), with an uncertainty
of several
tenths of a
degree.) In other words, the
maps
show how
much warmer or colder a region
is
compared to
the norm for that region
from
1951-1980.
The data
set begins in 1880 because
observations
did not
have sufficient global coverage
prior to
that time.
The period of 1951-1980 was
chosen
largely
because the U.S. National Weather
Service
uses a
three-decade period to define
"normal" or
average
temperature. The GISS
temperature
analysis
effort began around 1980, so the
most
recent 30
years was 1951-1980. It is also
a
period when
many of today's adults grew up,
so it
is a common
reference that many people
can
remember.
To conduct
its analysis, GISS uses
publicly
available
data from 6,300 meteorological
stations
around the
world; ship-based and
satellite
observations
of sea surface temperature;
and
Antarctic
research station measurements.
These
three data
sets are loaded into a
computer
analysis
program-available for public
download
from the
GISS web site-that calculates
trends in
temperature
anomalies relative to the
average
temperature
for the same month during
1951-1980.
The
objective, according to GISS
scientists, is
to provide
an estimate of temperature change
that
could be
compared with predictions of
global
climate
change in response to atmospheric
carbon
dioxide,
aerosols, and changes in solar
activity.
As the maps
show, global warming doesn't
mean
temperatures
rose everywhere at every time by
one
degree.
Temperatures in a given year or
decade
might rise
5 degrees in one region and drop
2
degrees in
another. Exceptionally cold
winters in
one region
might be followed by
exceptionally
warm
summers. Or a cold winter in one
area might
be balanced
by an extremely warm winter
in
another
part of the globe.
Generally,
warming is greater over land than
over
the oceans
because water is slower to absorb
and
release
heat (thermal inertia). Warming
may also
differ
substantially within specific
land masses
and ocean
basins.
In the past
decade (2000-2009), land
temperature
changes are
50 percent greater in the
United
States than
ocean temperature changes; two
to
three times
greater in Eurasia; and three to
four
times
greater in the Arctic and the
Antarctic
Peninsula.
Warming of the ocean surface has
been
largest
over the Arctic Ocean, second
largest
over the
Indian and Western Pacific
Oceans, and
third
largest over most of the Atlantic
Ocean.
In the
analysis, the years from 1880 to
1950 tend
to appear
cooler (more blues than reds),
growing
less cool
as we move toward the 1950s.
Decades
within the
base period do not appear
particularly
warm or
cold because they are the
standard
against
which all decades are measured.
The
leveling
off between the 1940s and 1970s
may be
explained
by natural variability and
possibly by
cooling
effects of aerosols generated by
the
rapid
economic growth after World War
II.
Fossil fuel
use also increased in the
post-War
era (5
percent per year), boosting
greenhouse
gases. But
aerosol cooling is more
immediate,
while
greenhouse gases accumulate
slowly and take
much longer
to leave the atmosphere. The
strong
warming
trend of the past three decades
likely
reflects a
shift from comparable aerosol
and
greenhouse
gas effects to a predominance
of
greenhouse
gases, as aerosols were curbed
by
pollution
controls, according to GISS
director
Jim
Hansen.
.
References
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J., R. Ruedy, M. Sato,
and K. Lo
(2010). Global surface
temperature
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Advancing the Science of Climate
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Accessed
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NASA
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