Gobal climate change
temperature
atmospheric CO2
sea level

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In discussions of Global Warming, CO2 is
regularly discussed. What is the problem
associated with CO2?
Based upon your knowledge, how would you
rank the current concentration of CO2 in the
atmosphere (highest ever, high, moderate, low,
lowest ever)?
What are sources of CO2 to the atmosphere?
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Sea level rise
> 60 meters
(would
happen over
several
thousand
years)
We are in an interglacial period; still have permanent ice caps (for the
moment) so technically we are still in an Ice Age.
Glacial-interglacial cycle is about 120,000 years
Now look at CO2 for the same period
Note high CO2 levels
coincide with
interglacials
Glaciers retreated from upper midwest ~10,000 years ago
Last ~8,000 years have had relatively stable temperatures
Vikings settled
Greenland
Vikings abandoned
Greenland
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Medieval warming period
Not everywhere has the same temperature trend, but on
average the planet's surface is heating up
Seasonal changes reflect
uptake of CO2 by plants
(photosynthesis)
(Last 160,000 years).
Clearly the
"Greenhouse Effect" is
very real and acts on a
short timescale
What about other
greenhouse gases?

Greenhouse Gases
Carbon Dioxide (CO2)
 Methane (CH4)
 Nitrogen oxide (N2O)
 Chlorofluorocarbons
(CFCs)

A planet's climate depends on its mass, distance from the sun and
atmospheric composition. Without greenhouse gases, Earth's average
temperature would be roughly –20°C.
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
(i) Naturally occurring:
Water
H2O
~ 0 to 4 % variable
Carbon dioxide
CO2
~ 0.03 % increasing
Methane
CH4 doubled in 200 years
Nitrous oxide
(ii) Other very powerful
greenhouse gases include
CFCs (anthropogenic)
N2O
Each greenhouse gas differs in its ability to absorb heat in
the atmosphere.
CFCs 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)
Some Global Warming Potentials (100 y timescale)
Gas
Carbon dioxide (CO2)
Methane (CH4)
Nitrous oxide (N2O)
HFC-23
GWP (set at CO2 = 1)
1
21
310
11,700
CF4
6,500
C2F6
9,200
SF6
23,900
these four are
totally
anthropogenic
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.
The most
important
greenhouse gases
are CO2 and CH4.
So we need to
understand the
carbon cycle
Fossil fuel
emissions are
small relative to
natural fluxes
Why do they have
so large an
effect?
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Projected 40% increase in next 13 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
Note change
will be rapid
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)