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Gobal climate change
Reading: Keller chapter 16, p. 490-498 and 513-531
temperature
atmospheric CO2
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Studying Global Change
Geologic record: what
happened in the past
Real-time monitoring:
what is happening now
Mathematical models:
predicting the future
(also tested against the
geologic record)
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Climate Change
Climate = average of weather conditions over
seasons, years or decades
e.g. Missouri's climate now is "humid continental"
Depends on latitude, proximity to ocean, etc.
Climate changes over geologic time as continents
drift and as Ice Ages come and go
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The atmosphere
Nitrogen
N2
~ 78
%
Oxygen
O2
~ 21
%
Argon
Ar
~ 0.9 %
Carbon dioxide
CO2 ~ 0.03 %
Others
< 0.07 %
Water contents vary from ~ 0 to 4% within the
troposphere (lowest 10 km of the atmosphere)
Water and CO2 contribute to the greenhouse effect
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A planet's climate depends on its mass, distance from the sun
and atmospheric composition. Without greenhouse gases,
Earth's
would be roughly –20°C.
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2003 average temperature
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Greenhouse gases
(i) Naturally occurring:
Water
H2O ~ 0 to 4 % variable
Carbon dioxide
CO2 ~ 0.03 % increasing
Methane
CH4 doubled in 200 years
Nitrous oxide
N2O
Ozone
O3
(ii) Other very powerful greenhouse gases include
HFC's, PFC's and SF6 (all anthropogenic)
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The greenhouse effect
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Light waves
velocity = frequency x wavelength
Wavelengths ~ 0.4 to 0.7 µm are visible
(most sunlight)
1 µm = 1 millionth of a meter (1 x 10-6 m)
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Greenhouse
Effect
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Temperatures: last 800,000 y
We are in an interglacial period; still have permanent ice caps
(for the moment) so technically we are still in an Ice Age.
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Temperatures: last 150,000 y
Glacial-interglacial cycle is about 120,000 years
Now look at CO2 for the same period
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Atmospheric CO2: last 160,000 y
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Temperatures: last 150,000 y
Note high CO2 levels coincide with interglacials
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Temperatures: last 18,000 y
Glaciers retreated from upper midwest ~10,000 years ago
Last ~8,000 years have had relatively stable temperatures
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Temperatures: last 1,000 y
Vikings settled
Greenland
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Vikings abandoned
Greenland
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Sea temperature in Medieval times estimated ~4 ˚C warmer than today
text
Medieval warming period
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Temperatures: last 140 y
Not everywhere has the same temperature trend,
but on average the planet's surface is heating up
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Atmospheric CO2, 1958 to present
Seasonal changes reflect
uptake of CO2 by plants
(photosynthesis)
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CO2 and
climate
(Last 160,000 years).
Clearly the
"Greenhouse Effect"
is very real and acts
on a short timescale
What about other
greenhouse gases?
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Greenhouse gases
Each greenhouse gas differs in its ability to
absorb heat in the atmosphere.
HFC's and PFC's are most heat-absorbent.
Nitrous oxide traps ~ 270 times more heat per
molecule than CO2; methane traps ~21 times more.
Estimates of greenhouse gas emissions are often
given in units of millions of metric tons of carbon
equivalents (MMTCE), which weights each gas by
its Global Warming Potential (GWP)
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Greenhouse gases
Some Global Warming Potentials (100 y timescale)
Gas
GWP (set at CO2 = 1)
Carbon dioxide (CO2)
1
Methane (CH4)
21
Nitrous oxide (N2O)
HFC-23
310
11,700
CF4
6,500
C2F6
9,200
SF6
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these four are
totally
anthropogenic
23,900
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Greenhouse gases
a,bRate
of change is in parts per billion per year (ppb/y) except
SF6 (concentration and rate of change in parts per trillion)
Atmospheric Lifetime = residence time in years
Atmospheric CO2 will double relative to pre-Industrial levels
in the next 100 years or so. Methane already has doubled.
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Greenhouse gases
Greenhouse gases are global in their effect upon
the atmosphere.
The main greenhouse gases have long residence
times in the atmosphere, and therefore accumulate
over time (unlike many local air pollutants)
Greenhouse gases are generally well mixed in the
atmosphere, so their impact is mostly independent
of where they were emitted.
Hence the emission of greenhouse gases should be
addressed on a global (i.e., international) scale.
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Recent CO2 emissions
The US currently emits
~ 25% of anthropogenic
CO2, mostly from
burning fossil fuels
In 1990 the US emitted 5 billion
tons of CO2 (~20 tons per person)
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CO2 emissions by country
text
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Future estimates of CO2 emissions
Projected 40% increase in next 17 years
In 2001 the US backed out
of the Kyoto treaty (designed
to cut CO2 emissions to
below 1990 levels by ~2010) for economic and political reasons
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Future CO2 concentrations
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Some conclusions
1.
"Naturally occurring" climate change has occurred in
the past on many timescales, and will continue in the
future. Several times in the past, Earth has been hotter or
colder than today
2.
Anthropogenic activities have greatly increased (and
continue to increase) the concentration of greenhouse
gases in the atmosphere
3.
In the past, high levels of CO2 (greenhouse gas) have
correlated with high temperatures
4.
So we should expect global warming to continue in the
future (noticeable on a human timescale)
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Global climate change
Reading: Keller chapter 16, p. 490-498 and 513-531
temperature
atmospheric CO2
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Greenhouse gases
The most
important
greenhouse
gases are CO2
and CH4.
So we need to
understand the
carbon cycle
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Fossil fuel
emissions are
small relative to
natural fluxes
Why do they
have so large
an effect?
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Title
text
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Melting ice increases sea level
Sea level rise is
occurring today
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Submergent coastlines
Melting glaciers and ice caps increases sea level
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Retreating
Glaciers
Positive feedback
relationship between
warming and melting
There are also negative
feedback relationships,
e.g. more CO2 encourages
more plants which
consume CO2
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Sea level rise
text
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What if the remaining ice caps melt?
• Over 2% of the world’s water is in glaciers
• Antarctic ice sheet
– Eighty percent of the world’s ice
– Nearly two-thirds of Earth’s fresh water
– Covers ~1.5 times area of United States
– If melted, sea level would rise ~65 meters (200 ft)
(Missouri river is at c. 565 ft above sea level at Boonville)
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What if
the ice
melts?
Sea level
rise > 60
meters
(would
happen over
several
thousand
years)
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Title
Note change
will be rapid
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Future sea
level rise
(models)
Expect about 0.5 m
in the next century.
Longer range
predictions are less
certain.
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Changes in rainfall
text
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Oceanic circulation
Without the circulation, northern Europe would be much colder.
Global warming may shut down the Gulf Stream; this would freeze N. Europe
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Normal conditions
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El Niño conditions
Suppressed
upwelling
changes
atmospheric
circulation, leads
to storms, etc.
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Effects of El Niño, 1997-98
Global warming leads to more and stronger El Niño years:
For the US, this means floods and storms near S and E coasts.
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What is a normal Earth Temperature?
"Snowball"
Earth
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Greenhouse
Earth
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What is a normal Earth temperature?
Note we are
actually way
below average
for the last 100
million years.
So why worry?
1) we were not around last time it was hot!
2) we are perturbing Earth systems much faster than
most natural processes
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