Transcript EVSC 305: Climate Change – the Science and

EVSC 305: Climate Change – the
Science and Local Impact on a Global
Environmental Crisis
EVSC 305…
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This introductory course will give
students an integrated overview of the
science of climate change and an analysis
of the implications of this change for
patterns of daily life in their own
circumstance and around the world
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EVSC 305
Your reader…
 Additional readings…
 The website
(www.greenresistance.wordpress.com)
 Set up your own research database
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EVSC 305
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4 objectives
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Science of Climate Change
Impacts of Climate Change
Policy Analysis
Mitigation Objectives
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Writing Assignment
2 page paper on recent news of climate change.
Reference. Grammar.Your analysis.
Due via email on Friday October 8
EVSC 305: Climate Change – the
Science and Local Impact on a
Global Environmental Crisis
Chapters 1 and 2
The start…
Climate is dynamic
 Nothing simple about how the climate
changes: the behavior of the Earth’s
climate is governed by a wide range of
factors all of which are interlinked in an
intricate web of physical processes
 What are the factors that most matter?
 What is climate change?
 What is climate?
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Weather and Climate: what is the difference?
◦ “Weather is what we get; climate is what we
expect. Weather is what is happening to the
atmosphere at any given time; climate is what
the statistics tell us should occur at any given
time of the year”
◦ Emphasis on average conditions
◦ In considering climate change: we are concerned
about the statistics of the weather phenomena
that provide evidence of longer term changes
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Climate variability – climate change
Climate variability - the way climatic variables (such as temperature and
precipitation) depart from some average state, either above or below
the average value. (Although daily weather data depart from the
climatic mean, we consider the climate to be stable if the long-term
average does not significantly change.)
 Climate change - a trend in one or more climatic variables
characterized by a fairly smooth continuous increase or decrease of the
average value during the period of record.
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Climate variability – climate change
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One basic interpretation: climate variability is a
matter or short-term fluctuations; climate change:
longer-term shifts.
Potentially oversimplifying
(1) no reason why the climate should not
fluctuate randomly on longer timescales; major
challenge is to recognize this form of variability
(2) climate change may occur abruptly
Detecting fluctuations in the climate involves
measuring a range of past variations of
meteorological parameters around the world
over a wide variety of timescales
Unfortunately – variety in quality
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Connections, timescales and
uncertainties
Golden rule: do not oversimplify the workings of the climate
 Need to understand feedback processes (a perturbation in
one part of the system may produce effects elsewhere that
bear no simple relation to the original stimulus) – positive
and negative feedback processes
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◦ Positive: warming  reduction in snow cover in winter  more
sunlight absorbed at the surface  more warming
◦ Negative: warming  more water vapor in the atmosphere  more
clouds  more sunlight reflected into space  less heating of the
surface
[supporting material on feedback systems on
http://greenresistance.wordpress.com/climate-change-evsc-305/]
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Challenge: which processes matter most
involves: (1) knowing how a given alteration
may disturb the climate; (2) knowing how
different timescales affect the analysis of
climate
 Thus: need to know how changes occur and
how they are linked to one another
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◦ Continental drift – crucial when interpreting
geological records; more immediate
consequences (volcanism) more dramatic impact
on interannual climate variability
◦ Fluctuations in the output of the Sun
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Big picture…
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Everything in the system is connected to
everything else
There is no simple answer to any issue
associated with climate change
How do the changes in every aspect of the
Earth’s physical conditions and
extraterrestrial influences combine?
◦ Atmospheric motions (ever-changing); variations
in land surface (…); sea-surface temperatures;
pack-ice extent in polar regions; deep-ocean
currents; ocean productivity; carbon dioxide
levels in the atmosphere; and…
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Chapter 2: Radiation and the Earth’s
energy balance
Essential driving process: supply of energy
from the Sun
1. Properties of solar radiation and how the
Earth re-radiates energy to space;
2. How the Earth’s atmosphere and surface
absorb or reflect solar energy and also
re-radiate energy to space;
3. How all these parameters change
throughout the year and on longer
timescales
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Solar and terrestrial radiation
Radiative balance of the Earth: over time
the amount of solar radiation absorbed by
atmosphere and the surface beneath it is
equal to the amount of heat radiation
emitted by the Earth to space
 Global warming: retains some solar
energy in the climate system
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What is radiation?
electromagnetic waves
 Characteristics of a wave …
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What are typical wavelengths of
radiation?
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units of
micrometers are
often used to
characterize the
wavelength of
radiation
1 micrometer =
10-6 meters
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Radiation laws
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Any object not at a temperature of
absolute zero (-273.16 C) transmits
energy to its surroundings by
radiation in the form of
electromagnetic waves travelling at
the speed of light and requiring no
intervening medium
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Black body: a body which absorbs
all the radiation and which, at any
temperature, emits the maximum
possible amount of radiant energy; no
actual substance is truly ‘black’
◦ Snow absorbs very little light but is
highly efficient emitter of infrared
radiation
object does not have to appear
"black"
 sun and earth's surface behave
approximately as black bodies
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Radiation laws
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Spectrum:
wavelength
dependence of the
absorptivity and
emissivity of a gas,
liquid, or solid
◦ Radiative properties of
the Earth are made up
of the spectral
characteristics of the
constituents of the
atmosphere, oceans,
and land surface
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Black body…Stefan-Boltzmann law
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Black body: the
intensity of radiation
emitted and the
wavelength
distribution depend
only on the absolute
temperature
Expression for emitted
radiation is the S-B
law: flux of radiation
from a black body is
directly proportional
to absolute
temperature
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E=sT4
◦ E/F = flux of radiation
◦ T = absolute
temperature (K) of
object
◦ s= constant called the
Stefan-Boltzman
constant = 5.67 x 10-8
Watts m-2 K-4
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Consider the earth and sun:
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Sun: T = 6000 K
◦ so E = 5.67 x 10-8 Watts m-2 K-4 (6000 K)4 = 7.3 x
107 Watts m-2
◦ Q: is this a lot of radiation??? Compare to a 100
Watt light bulb.....
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Earth: T = 288K
◦ so E = 5.67 x 10-8 Watts m-2 K-4 (288 K)4 = 390
Watts m-2
◦ Q: If you double the temperature of an object,
how much more radiation will it emit?
◦ A: 16 times more radiation
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Wien displacement
law:
◦ Wavelength at which a
black body emits most
strongly is inversely
proportional to the
absolute temperature
◦ the hotter the body,
the shorter the
wavelength of peak
emission.
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Most objects emit
radiation at many
wavelengths
However, there is one
wavelength where an
object emits the
largest amount of
radiation
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Weins law
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This wavelength is
found with Weins Law:
lmax = 2897 mm / T(K)
At what wavelength
does the sun emit
most of its radiation? –
0.5 micrometers
At what wavelength
does the earth emit
most of its radiation? –
10.0 micrometers
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Radiative equilibrium
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If the temperature of an
object is constant with time,
the object is in radiative
equilibrium at its radiative
equilibrium temperature (Te)
Q: What happens if energy
input > energy output?
A: object will be warmer
Q: What happens if energy
input < energy output?
A: object will be cooler
Q: Is the earth in radiative
equilibrium?
A: Earth’s global average is
constant with time
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So…
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If the Earth were a black body and the Sun
emitted radiation as a black body of temperature
6000 K, then a relatively simple calculation of the
planet’s radiation balance produces a figure for
the average surface temperature of 270 K
Observed value is about 287 K
Why?
Earth does not absorb all the radiation from the
Sun; in principle, should be even cooler – at
around 254 K – i.e. FROZEN
Reason for the difference: properties of the
Earth’s atmosphere, aka Greenhouse Effect
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How does the build up for radiatively active gases in
the atmosphere alter the temperature?
To understand that…
As the density of the atmosphere decreases rapidly
with altitude, any absorption of terrestrial radiation
will take place principally near the surface
Since the most important absorber is water vapor,
which is concentrated in the lowest levels of the
atmosphere, the greatest part of the absorption of
terrestrial radiation emitted by the Earth’s surface
occurs at the bottom of the atmosphere
In achieving balance between income and outgoing
radiation  the surface and lower atmosphere are
warmed and the upper atmosphere cooled
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Interaction of Long Wave
Radiation and the Atmosphere
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Some of the long-wave radiation
emitted by the earth escapes to
space
Some of the long-wave radiation is
absorbed by gasses in the
atmosphere
These gasses then re-emit some of
the long wave radiation back to the
ground
The additional long-wave radiation
reaching the ground further warms
the earth
This is known as the "greenhouse
effect"
The gasses that absorb the LW
emitted by the earth are called
"greenhouse gasses"
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Greenhouse Gases
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Methane (CH4)
Carbon Dioxide (CO2)
Ozone (O3)
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Water Vapor (H2O)
Nitrous Oxide (N2O)
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the wavelengths over which the Sun and Earth emit most of their radiation.
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The Sun being a much hotter body emits most of its radiation in the shortwave
end and the Earth in the longwave end of the spectrum.
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The division between shortwave and longwave radiation occurs at about 3
micrometers.
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Terrestrial radiation
The principal atmospheric gases (oxygen
and nitrogen) do not absorb appreciable
amounts of infrared radiation
 Radiative properties of the atmosphere
are dominated by certain trace gases
(water vapor, carbon dioxide, ozone) –
which interact with infrared radiation in
their own way  modifying surface
radiation by absorption and re-emission in
the atmosphere
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Remember…Greenhouse Gases
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Methane (CH4)
Carbon Dioxide (CO2)
Ozone (O3)
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Water Vapor (H2O)
Nitrous Oxide (N2O)
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How to quantify the impact of the
naturally occurring radiatively active
gases? What is their contribution to the warming
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of the Earth above the figure of 254 K?
Water vapor  21 K
Carbon dioxide  7 K
Ozone  2 K
Note: if the climate warms - the amount of
water vapor in the atmosphere will increase.
A positive feedback.
Methane, oxides of nitrogen, sulphur dioxide
and CFCs also modify the radiative
properties of the atmosphere
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Terrestrial radiation
Where are these greenhouse gases – how
are they distributed in the atmosphere?
 Most trace constituents are relatively
uniform;
 water vapor and ozone have a more
complicated distribution
 Hydrological cycle…
 Photochemical process…
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Hydrological cycle
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Questions re: H20 cycle
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What is the extent to which global warming
will alter the [ ] of water vapor in the
atmosphere?
Water vapor is dependent on the surface
temperature of the Earth  expected to
impact future warming (+ive feedback) –
depends on whether in a warmer world the
increase in water vapor will occur
throughout the troposphere
Also: most complicated absorption spectrum
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Ozone
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Majority of ozone is created by
photochemical action of sunlight on oxygen
in the upper atmosphere
Depends on the amount of sunlight – thus
have a marked annual cycle (esp at high
latitudes); + pollution in urban areas can
produce conditions for photochemical
production of ozone  significant
widespread increases in lower atmosphere
over much of the more populated parts of
the world
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Energy balance of the Earth
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Earth’s orbit
around the Sun
Earth’s own
rotation about
its tilted axis
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Energy budget
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Overall – the total incoming flux of solar
radiation is balanced by the outgoing flux
of both solar and terrestrial radiation
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Energy budget
Key: amount of energy absorbed or reflected is
dependent on the surface properties
◦ Snow: high proportion of incident sunlight reflected
◦ Moist dark soil: efficient absorber of sunlight
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Snow: selective absorption
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Snow is a
poor absorber
of solar
radiation, but
is a great
absorber and
therefore
emitter of
long-wave
radiation
during the
daytime snow surface
stays cool
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Selective Absorption - Snow
during night time
during night time,
snow is only emitting
long wave radiation,
and is doing it very
effectively
 so, snow covered
surface gets quite
cold at night
 ski areas in the spring
 thin snow cover in
the late fall
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Energy budget
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Albedo: amount of solar radiation reflected or scattered
into space w/o any change in wavelength (global albedo =
~30%) [yes, know table 2.1]
◦ Eg: what are the implications of this new discovery? – twice as
much sunlight is reflected back to space by snow-covered
croplands and grasslands as is reflected by snow-covered
forests
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Solar radiation is absorbed differently on land and at sea
◦ Land: most of the energy absorbed close to the surface, warms
up rapidly, increases amount of terrestrial radiation leaving the
surface
◦ Sea: solar radiation penetrates deeper; more than 20% reaching
10 m depth; more energy stored in top layer of ocean; less lost
to space
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Clouds and Climate Change
Some clouds help cool the Earth, but other clouds help keep Earth warm
– in part depending on how high up they are in our atmosphere.
 So: what is the role of low-cloud cover?
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◦ Will climate change dissipate clouds, which would effectively speed up the
process of climate change, or increase cloud cover, which would slow it down?
◦ One study (July 2009, Science) level clouds tend to dissipate as the ocean
warms — which means a warmer world could well have less cloud cover. … A
positive feedback
Remember water vapor? The transition betw clouds and vapor …
 “The physics of clouds is the greatest obstacle to improving predictions of
climate change.”
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◦ Data from satellites (data only a few decades old)
◦ Human observations (data back to the 1950s)
◦ Read the scientific article
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Clouds and Climate Change
a growing consensus among climate modelers is that
clouds will increase, rather than hold back, the
warming triggered by greenhouse gases. That’s largely
because water vapor itself is a powerful greenhouse
gas, which means that clouds should trap more heat
than they are likely to reflect back into space.
 But uncertainty remains
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◦ what types of clouds will form and at what altitude?
◦ what particles will the clouds form around?
◦ how can modelers go from predicting the ways any given
bank of clouds might behave as opposed to forecasting
how the effects on systems of clouds on a regional or
global scale?
◦ Plus incomplete cloud observations
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Role of particulates
Better reflectors of sunlight than they are
absorbers of terrestrial radiation
 Impact: reduce the net amount received
 cooling effect
 [eg: dust from drought-prone areas]
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Role of oceans
Not separate from the atmosphere
 Continual exchange of energy
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◦ In the form of heat,
◦ momentum as winds stir up waves,
◦ moisture in the form of both evaporation
from the oceans to atmosphere, and
◦ precipitation from atmosphere to oceans
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Solar variability
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Sunspots: darker areas – seen at lower
latitudes between 30 N and 30 S crossing
the face of the Sun as it rotates – cooler
than surrounding chromosphere
◦ Chromosphere?
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The Sun explained...
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Core The energy of the Sun comes from nuclear fusion
reactions that occur deep inside the core
Radiative zone The area that surrounds the core.
Energy travels through it by radiation
Convective zone This zone extends from the radiative
zone to the Sun’s surface. It consists of “boiling”
convection cells
Photosphere The top layer of the Sun. It is this that we
see when we look at the Sun in natural light
Filament A strand of solar plasma held up by the Sun’s
magnetic field that can be seen against its surface
Chromosphere A layer of the Sun’s atmosphere above
the photosphere, around 2000km deep
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Solar variability
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Sunspots: darker areas – seen at lower latitudes between 30
N and 30 S crossing the face of the Sun as it rotates – cooler
than surrounding chromosphere
◦ Vary in size, number, and duration
◦ Sunspots are dark, cooler patches on the Sun’s surface that
come and go in a roughly 11-year cycle, first noticed in 1843.
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Output of the Sun did rise and fall during the sunspot cycle.
◦ the Sun's activity waxes and wanes over an 11-year cycle and
that as its activity wanes, the overall amount of radiation
reaching Earth decreases.
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More sunspots  more output  more heat
◦ during an 11-year solar cycle the Sun’s output changes by only
0.1 per cent
◦ Much of this change is concentrated in the UV part of the
spectrum; absorbed by oxygen and ozone molecules
◦ Useful to know how solar UV energy affects upper atmosphere
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Variability on solar variability
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assumed that as solar activity – indicated by the number of
sunspots on the Sun's surface – increases, then so does the amount
of solar radiation coming to the Earth to heat the planet.
a study based on satellite data of the Earth's atmosphere has
shown there is a complicated interaction between the varying
amounts of radiation from the Sun and the amount of ozone in the
atmosphere.
A decline in solar activity does not necessarily mean a cooler Earth
This latest study looked at the Sun's activity over the period 20042007, when it was in a declining part of its 11-year activity cycle.
the amount of energy reaching Earth at visible wavelengths
increased rather than decreased as the Sun's activity declined,
causing this warming effect.
researchers behind the study believe it is possible that the inverse
is also true and that in periods when the Sun's activity increases, it
tends to cool, rather than warm, Earth.
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