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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Natural Greenhouse Effect
Controversy and GW
Possible effects of GW
Sunlight warms earth's surface
Heat radiates back
Some heat reabsorbed
Remainder radiates into space
0 -15 km above surface
G.H. Effect occurs here
15 - 50 km above surface
50 - 80 km above surface
80 km and up
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
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?
Electromagnetic radiation (EMR) travels in waves
Wavelength (l): distance from one wave crest to the next
Shorter l = more energy
Note differences in l in incoming and outgoing radiation
Wien’s Law: l = 3 mm/T
Water vapor & small droplets account for 97% of the natural GH effect
"Normal" levels of CO2 in atmosphere also contribute
CO2Natural Greenhouse gases
Gases in atmosphere trap radiation at the long wavelength of outgoing radiation, but not at the short wavelength of incoming radiation
Absorbance by H2O and CO2 is at l of emitted radiation, not incoming
Incoming l = 0.1 - 1.5 m
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
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
30% more CO2 than nat. gas
43% more CO2 than nat. gas
Adding CO2: Human Impacts
COMPARING THE FOSSIL FUELS?
Which emits the least CO2 per unit energy produced?
CO2 concentrations since 1960
Do increasing CO2 concentrations correlate with higher temps?
Yes, historically. This connection is questioned by some though
Other Greenhouse gases besides CO2 that trap heat
Methane (natural gas)
Nitrous Oxide (N2O)
CO2 emissions account for 50-60% of the anthropogenic (human-induced) temperature change
12-20 % of anthropogenic GW due to methane
From natural gas leaks, livestock
Concentrations currently stable, but high
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
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
Trap heat in a wavelength not trapped by CO2
Note 8-12 m window of absorbance
NATURAL GREENHOUSE EFFECT:
Natural trapping of heat by gases in Earth's atmos.
Allows life to persist on earth
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
Controversy #1: Recent temp. change
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
Some claim temp. readings are inaccurate due to "urban heat island effect", and temps. aren't really rising
Controversy #2: Correlation between CO2 and temp.
Reconstruct past climate from air bubbles trapped in glaciers. Finds CO2 levels and temp. to be correlated
CO2 data solid, but temp. estimates are suspect. Contend there is no relation between CO2 levels and temperatures
Controversy #3: Predicting temperature changes
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
Climate models higher speculative. Earth's climate too complex to be modeled.
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?
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
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
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
ocean temperatures elevate too much
THREE SCHOOLS OF THOUGHT:
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.
Act now, while you have the chance. Research will never prove connection, so why wait?
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
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.