UAU107M
Fall
FOR GODS SAKE ...
Haven’t you heard of global
warming?
Western powers make their contribution to resolving
evironmental issues
CLIMATE CHANGE - BASICS
What is climate?
• Need to distinguish between
weather and climate!
• No single rule, but …
• Generally climate refers to average
conditions over ~30 years.
• There are natural variations and external
factors that affect climate.
Throstur Thorsteinsson ([email protected])
Environment and Natural Resources, University of Iceland
Rising temperature
Earths atmosphere
• The atmosphere is thin
• Does not have a well
defined lid
Melting glaciers
Atmospheric
temperature
– Pressure drops with altitude
– Temperature is more
complicated
• 99% of the dry atmosphere
is two gasses
– The remaining 1% contains
various gasses, including
GHG
Throstur Thorsteinsson ([email protected])
1
UAU107M
Fall
Composition of our air
Other gasses in atmosphere
Kr CH4
0% 1%
N2
78%
He H2
1% 0%
Ne
5%
O2
21%
CO2
Ne
He
CH4
Kr
H2
N2
O2
Ar
Other
Ar
Other 1%
0%
This is for dry air.
Water vapor variable between 0 – 4%.
Lifetime of gasses
CO2
93%
Atmospheric circulation
• Some gasses stay a short time in the
atmosphere – days (water vapor, ozone, …)
– To maintain significant quantities of such gasses
they need to be continually produced
• Other gasses live longer
– Oxygen, Nitrogen, CO2, noble gasses (Ar, Xe, …)
• The atmospheric circulation mixes these
gasses
Vapor mixing
• Mixing time scale days  months
• Mixes constituents and heat
• Heat transport is from the tropics to
the poles
Breathing
• One breath of air is ~1022 molecules
• The atmosphere “contains” about 1044
molecules
– That makes about 1022 breaths
– Each breath will eventually mix with all other
• The atmosphere is a shared resource!
Throstur Thorsteinsson ([email protected])
2
UAU107M
Fall
Causing changes to radiation
balance of Earth
1. Changes in the incoming solar radiation
– Earth’s orbit, or Sun itself
2. Changing albedo
– Cloud cover, atmospheric particles
– Vegetation
Theories about ice ages
• All theories concerned with
Q  Qi (1   )  I i  I o  QH  QE




  
A
B
C
3. Altering long-wave radiation back to
space
– Greenhouse gasses
A. Changes in radiation
1. Qi
changes in the solar constant
2. Distance, tilt, eccentricity of Earth’s path
around the Sun
3. Changes in . Eruptions, …
C. Changes in sensible
and latent heat
•
B. Changes in long-wave
radiation
• Changes in Ii (changes in Io are smaller)
– Increase in CO2  warmer, uncertain change
in cloudiness
Factors influencing radiation
Changes in QH and QE
1. Changes in atmospheric circulation
2. Changes in ocean circulation
Throstur Thorsteinsson ([email protected])
3
UAU107M
Fall
Milankovitch cycles
and Glaciation
The three Milankovitch Cycles impact the
seasonality and location of solar energy around
the Earth, thus impacting contrasts between
the seasons.
Axial Tilt
Eccentricity
Earth
Axis of rotation
Equator
radiation
Sun
More elliptical
Less elliptical
Periodicity: 100,000 years
Now
summer
5250
winter
summer
Today axial tilt is ~23.5 degrees, which largely accounts for our
seasons. Because of the periodic variations of this angle the
severity of the Earth's seasons changes. With less axial tilt the
Sun's solar radiation is more evenly distributed between winter
and summer.
Milankovitch cycles
Precession
23.5°
21.5°
Periodicity: 41,000 years
Reduces, or increases, the amount of
radiation received at the Earth's
surface in different seasons
winter
24.5°
10,500
Periodicity: ~23,000 years
ε is obliquity (axial tilt).
e is eccentricity.
ϖ is longitude of perihelion. e
sin(ϖ) is the precession index,
which together with obliquity,
controls the seasonal cycle of
insolation. Q is the calculated
daily-averaged insolation at the
top of the atmosphere, on the
day of the summer solstice at
65 N latitude. Benthic forams
and Vostok ice core show two
distinct proxies for past global
sea level and temperature.
At present the southern hemisphere seasons are somewhat more extreme
than the northern hemisphere seasons, when other factors are equal.
Throstur Thorsteinsson ([email protected])
4
UAU107M
Fall
The Greenhouse effect
• Been known for a long time that the
atmosphere keeps the Earths surface
warmer than direct solar heating implies.
• This is primarily due to a few different
gasses present in the atmosphere …
– … some only in very small quantities
Black body radiation
A perfect black-body is defined as a body
that absorbs all radiation that falls on it
• The intensity of radiation emitted by a blackbody depends only on its temperature.
• Solar energy heats the surface
– If only that, then Earth ~33°C colder!
The Electromagnetic Spectrum
History
• Fourier (1827)
• Tyndall (1861): Measured
what trace gasses were
responsible for the absorption
of infra-red radiation. Chief
gasses he found were CO2 and H2O
• Arrhenius (1896): First actual attempt to
calculate the warming effects of CO2.
Stefan-Boltzmann law
• The radiated flux, Stefan-Boltzmann law
F  s T 4
• Where s = 5.67 10-8 W m-2 K-4
• The wavelength of maximum energy, Wien’s
law,
m  T  k  const
Sun and Earth as black bodies
• The Sun (T ~ 6000 K effective
temperature) and Earth (T ~ 300 K
effective temp.) behave as black bodies
(to a good approximation).
m (sun) ~ 0.5 mm (visible)
m (earth) ~ 10.0 mm (infra-red)
Throstur Thorsteinsson ([email protected])
5
UAU107M
Fall
Radiation – Earth & Sun
Greenhouse effect
• The Earths surface warms and radiates heat
• Clouds and atmospheric gasses absorb the
radiation, and radiate
– Back to space
– Down to Earth’s surface
Sun
Earth
99% of energy at 0.15 – 4 mm
99% of energy at 4 – 120 mm
• As a consequence, the lower part of the
atmosphere and the surface warm
• Known as the “Greenhouse effect”
Greenhouse effect
The Sun
Earth’s surface heat budget
Surface radiation budget
• All heat received on Earth’s surface is
from the Sun
• Energy falling outside the Earth’s
atmosphere, the
solar constant 1368 W m-2
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6
UAU107M
Fall
Chief greenhouse gasses
•
•
•
•
Radiative forcing
Water vapor, 36–70%
Carbon dioxide, 9–26%
Methane, 4–9%
Ozone, 3–7%
• Clouds also important
Changes in spectrum
Solar radiation spectrum
•
Spectrum of GHG radiation
Change in spectrum from 1970 to 1996 due to trace gases.
'Brightness temperature' indicates equivalent blackbody
temperature (Harries 2001).
CO2 effect
Spectrum of the greenhouse radiation
measured at the surface. Greenhouse
effect from water vapor is filtered out
(Evans 2006).
Throstur Thorsteinsson ([email protected])
7
UAU107M
Fall
Average Carbon dioxide
Concentration
Insolation
Incoming
short-wave
solar radiation
Climate models predict that an increase in
atmospheric carbon dioxide would cause a
heightened greenhouse effect, which in turn
would cause a rise in global temperatures.
Concentration now about 399 ppmv, a 40%
increase from a value of 280 ppmv that existed
some 200 years ago !
Units: W m -2
Average CO2 concentration
Carbon cycle rates
Current conditions:
CO2now.org
July 2016
404.39 ppm
Seasonal variations
by terrestrial biota
Contributions to surf. T. cahnge
Throstur Thorsteinsson ([email protected])
Climate forcing in 2011
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UAU107M
Fall
Disruptions
Changes
in
radiative
forcing
• Positive feedback – disrupts equilibrium
• Negative feedback – maintains equilibrium
WGIAR5_SPM
Feedbacks
Feedbacks
• Water vapor
– Warming  more vapor
– More vapor  more greenhouse effect
– More warming
Climate change - causes
Clouds
• Dual role
• Can cause warming
• Or cooling
• Depends on altitude, droplet size, …
Throstur Thorsteinsson ([email protected])
9
UAU107M
Fall
Cloud cover
Generally speaking, low, thick clouds tend
to cool the Earth by reflecting the sun’s
radiation and preventing it from reaching
the Earth’s surface.
Ice albedo feedback
• Ice reflects more than
ocean- or land surface.
• Warming  less ice
 less reflection
 warming
In contrast, high, thin clouds tend to
warm the planet by allowing solar radiation
to pass easily through to the Earth’s surface
while, at the same time, trapping some of
the Earth’s infrared radiation and radiating it
back to the surface.
Sea ice
Sea ice
Current conditions: http://arctic.atmos.uiuc.edu/cryosphere/
Ocean
Ocean currents
• Oceans transport heat from tropics to higher
latitudes
– May be disrupted in the Atlantic if freshwater
input to N-Atlantic increases
• Cold oceans absorb CO2.
– If they warm, they absorb less
– Positive feedback
Throstur Thorsteinsson ([email protected])
10
UAU107M
Fall
Gulf stream 5 Aug 2000
Rising sea level
Ocean conveyor belt
Climate cooling factors
Cover sea level rise later
Aerosols
• Aerosol particles influence radiative forcing directly
through reflection and absorption of solar and
infrared radiation in the atmosphere.
• The total direct aerosol radiative forcing is
estimated to be −0.5 [±0.4] W m−2.
• The direct radiative forcing of the individual aerosol
species is even less certain,
Aerosol
optical
depth
– estimates for mineral dust are −0.1 [±0.2] W m −2
• Aerosol particles also have an indirect effect on the
radiative forcing, since a subset of the aerosol
population acts as cloud condensation nuclei (CCN)
and/or ice nuclei (IN).
Throstur Thorsteinsson ([email protected])
11
UAU107M
Fall
Natural sources: FIRES
Natural sources: Eruptions
Natural sources:
Dust storms
Eruptions: Temperature
Global temperature
<|>
Feedback and turning points
Human influence
• Complex systems with many feedbacks may
undergo a “change of state”; if positive
feedbacks take over
– Tipping points, turning points, …
• “Recent” ice ages indicate that such
changes are possible
– Does not mean they will happen
Throstur Thorsteinsson ([email protected])
12
UAU107M
Fall
World Greenhouse Gasses
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