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Global Warming GLOBAL WARMING: Natural Greenhouse Effect Global Warming Controversy and GW Possible effects of GW Outline Sun and earth Sunlight warms earth's surface Heat radiates back into atmosphere Some heat reabsorbed in atmosphere Remainder radiates into space

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GLOBAL WARMING:

Natural Greenhouse Effect

Global Warming

Controversy and GW

Possible effects of GW

Outline


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Sun and earth

Sunlight warms earth's surface

Heat radiates back

into atmosphere

Some heat reabsorbed

in atmosphere

Remainder radiates into space


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EARTH'S ATMOSPHERIC LAYERS

TROPOSPHERE

0 -15 km above surface

G.H. Effect occurs here

STRATOSPHERE

15 - 50 km above surface

Ozone layer

MESOSPHERE

50 - 80 km above surface

"Middle sphere"

IONOSPHERE/THERMOSPHERE

80 km and up


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ANSWER:

The wavelength of the energy changes, and this is the reason for the difference in entry and exit

To help you understand this, let's examine wavelengths in more detail...

Wavelength and GH Effect

THE QUESTION:

But if the energy passed through the atmosphere on the way to the earth's surface, why does it get trapped on the way out?


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l

WAVELENGTH:

Electromagnetic radiation (EMR) travels in waves

Wavelength (l): distance from one wave crest to the next

Shorter l = more energy

Fig. 3.7


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Note differences in l in incoming and outgoing radiation

Wien’s Law: l = 3 mm/T


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MOLECULES THAT TRAP HEAT IN G.H. EFFECT:

Water vapor & small droplets account for 97% of the natural GH effect

H2O

"Normal" levels of CO2 in atmosphere also contribute

CO2

Natural Greenhouse gases

Gases in atmosphere trap radiation at the long wavelength of outgoing radiation, but not at the short wavelength of incoming radiation


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Absorbance by H2O and CO2 is at l of emitted radiation, not incoming

Incoming l = 0.1 - 1.5 m


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So what's the problem?

HUMAN ACTIVITIES AFFECT SYSTEM:

Affect system so it traps more heat than it normally would

This raises temperatures at the Earth's surface

WHAT CAUSES THIS?

(1.) Increasing CO2 concentrations in atmosphere, trapping more heat

(2.) Adding other gases ("greenhouse gases") to atmosphere that also trap heat


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Adding CO2: Human Impacts

WHAT ADDS CO2 TO THE ATMOSPHERE?

Burning fossil fuels for energy

Combustion of coal, oil, and natural gas produces CO2

Overwhelms system's capacity to remove CO2 from atmosphere

CO2 builds up, traps more heat, temperatures increase


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Oil:

30% more CO2 than nat. gas

Coal:

43% more CO2 than nat. gas

Natural Gas:

Lowest CO2

Adding CO2: Human Impacts

COMPARING THE FOSSIL FUELS?

Which emits the least CO2 per unit energy produced?


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CO2 concentrations since 1960


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QUESTION:

Do increasing CO2 concentrations correlate with higher temps?

ANSWER:

Yes, historically. This connection is questioned by some though


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WHERE'S THE OTHER 40-50% FROM?

Other Greenhouse gases besides CO2 that trap heat

Chlorofluorocarbons (CFCs)

Methane (natural gas)

Nitrous Oxide (N2O)

Greenhouse gases

GLOBAL WARMING:

CO2 emissions account for 50-60% of the anthropogenic (human-induced) temperature change


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METHANE (Natural Gas):

12-20 % of anthropogenic GW due to methane

From natural gas leaks, livestock

Concentrations currently stable, but high

CHLOROFLUOROCARBONS (CFCs):

15-25 % of anthropogenic GW due to CFCs

Used as coolants (freon), formerly as propellants

Atmospheric concentrations growing by 5% annually

NITROUS OXIDE (N2O):

5 % of anthropogenic GW due to N2O

From fertilizer use, burning coal, vehicle exhaust

Concentrations growing by 0.2% annually


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Greenhouse gases

PROBLEM #1:

Compared to CO2 molecule, each molecule of these gases traps:

CFCs: 1,500 - 7,000 times as much heat

Methane: 25 times as much heat

Nitrous Oxide: 230 times as much heat

PROBLEM #2:

Trap heat in a wavelength not trapped by CO2


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Note 8-12 m window of absorbance


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Recapping

NATURAL GREENHOUSE EFFECT:

Natural trapping of heat by gases in Earth's atmos.

Allows life to persist on earth

GLOBAL WARMING:

Human activities accelerate heat trapping

Average global temperatures rise

Due to CO2 from fossil fuels, greenhouse gases

Global warming theory is controversial

Let's look at the controversy


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Controversy #1: Recent temp. change

RECORDED DATA:

Data only goes back to 1860

Since 1860, temps have risen about 0.9o F (0.5o C)

This past year (1999) was warmest on record

THE CONTROVERSY:

Some claim temp. readings are inaccurate due to "urban heat island effect", and temps. aren't really rising


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Controversy #2: Correlation between CO2 and temp.

PAST CLIMATE:

Reconstruct past climate from air bubbles trapped in glaciers. Finds CO2 levels and temp. to be correlated

THE CONTROVERSY:

CO2 data solid, but temp. estimates are suspect. Contend there is no relation between CO2 levels and temperatures


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Controversy #3: Predicting temperature changes

CLIMATE MODELS:

Create model of earth's weather, input variables and observe changes in the model. Suggests that average temp. could rise 3.6o F (2.0o C) by 2100

THE CONTROVERSY:

Climate models higher speculative. Earth's climate too complex to be modeled.


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What's the consensus?

HUMAN vs. NATURAL:

Are current temp. increases human-induced or natural?

Consensus: At least partly caused by human activities

HOW MUCH WILL IT INCREASE?

Consensus: Who knows? Earth's climate simply too complex to be accurately modeled

Assuming temperatures rise as expected, what would be the results?


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Possible effects of global warming

SEA LEVELS RISE:

Rising temps. melt ice caps and cause oceans to expand

Together these result in higher sea levels

Could rise 19 in (48 cm) by 2100

Highly populated coastal areas become unihabitable

Arable land decreases; less food production

Wealthy countries build dikes, poor countries flood


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American breadbasket becomes Canadian breadbasket

Global yields down 10-70%

Possible effects of global warming

GRAIN BELT SHIFT:

Crops (corn, wheat, etc.) grow optimally at temps in Midwest U.S.

Midwest becomes warmer, optimal temp. range shifts northward


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Possible effects of global warming

EXTREME WEATHER:

Temperature drives weather patterns

Higher average temps. means more extreme weather (floods, drought, high/low temps.)

Some are wondering if current weather extremes are due to climate change


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Ocean "conveyor belt" - could break down if

ocean temperatures elevate too much


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What should we do now?

THREE SCHOOLS OF THOUGHT:

Nothing:

Contend GW is a hoax and overstated. No action is necessary

Wait and see:

Need more definitive research to link human activities with temperature increases. Study now and act later.

Precautionary strategy:

Act now, while you have the chance. Research will never prove connection, so why wait?


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International treaties on GW

KYOTO, JAPAN (DEC. 1997)

Treaty calls for reductions in CO2, methane, nitrous oxide, and three others that damage ozone

38 industrialized nations required to reduce their emissions from 1990 levels by 2012.

E.U.  8%; U.S.  7%, Japan  6%

Developing countries, including China and India, would have voluntary limits, no set standards


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WHY?

Reductions cost money in short-term

Economy could suffer short-term

Global competitors like China have advantage

International treaties on GW

KYOTO, JAPAN (DEC. 1997)

Bush Administration refuses to sign it.

Will it ever pass?

Not very likely.


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