The Atmosphere
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Transcript of The Atmosphere
The Atmosphere
Composition
Chemically, the Earth’s atmosphere is:
78% nitrogen21% oxygen1% argon.
Trace compounds, like carbon dioxide, comprise less than .1% of the atmosphere.
Structure
Because air is compressible, the pressure varies exponentiallywith height (as opposed to linearly if it were not compressible).
90% of the atmosphere liesbelow this line
Structure (cont.)Temperature varies with height dependingupon the trace gases and type of radiationpresent in the zone.
Thermosphere hotter at the top due to friction with incoming solar particles
Stratosphere hotter at the top due to the absorption of incoming UV by ozone
Troposphere hotter at the bottom due to absorption of outgoing IR by greenhouse gases
ConvectionMovement within the atmosphere occurs becauseof the differential heating of the Earth’s surface by the Sun.
Where the air is the hottest,it expands the most and riseshigher into the atmosphere.This causes cooler air to rush in to replace it, creatinga convection cell.
On a non rotating Earth, this is anidealized view of what that convectionmight look like.
Coriolis Effect
On a non rotating Earth, all placeson the surface would have the samehorizontal velocity, i.e. no velocity.Objects can change latitude withouthaving to change horizontal velocities and still move in a straight path.
On a rotating Earth, objects at differentlatitudes would have different horizontalvelocities. If an object does not change itshorizontal velocity as it changes latitude,it will not appear to move in a straight pathfrom an Earth reference frame.
Coriolis Effect (cont.)
This film clip demonstrates that anobject that travels in a straightpath as seen from outside of the rotating reference frame will appear to travel in a curved pathwhile observed from within.
Effect on Weather PatternsThis effect prevents convectivecell winds originating at the equator from reaching the pole,and vice versa
Due to the Earth’s size and rotation, this results in 3 different cells being formed ineach hemisphere
These cells help control the climate of different regions byby creating patterns of wind and precipitation.
Isobars
Pressure systems drivelocal wind. However, the Coriolis effect meansthat wind does not flowdirectly from high tolow. In Northern Hemisphere, wind is deflected to the right
Thus, winds go in a clockwise fashion aroundhigh pressure and in counter-clockwise fashion around lows
Winds attempt to go parallelto isobars. The closer the isobars are, the greater the wind
Global Warming
Outline
GLOBAL WARMING:Natural Greenhouse Effect
Global Warming
Controversy and GW
Possible effects of GW
Sunlight warms Earth's surface
Heat radiates back into atmosphere
Some heat reabsorbed in atmosphere
Remainder radiates into space
Sun and earth
The Natural Greenhouse Effect
IT'S NOT BAD:Heat trapping elevates temperature at Earth's surface
Allows liquid water to persist on the Earth's surface without freezing
Makes Earth warmer than it would be without it
Presence of liquid water allowed for the evolution of life
Natural G.H. Effect is necessary for life to persist
Wavelength and GH EffectTHE 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?
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:Electromagnetic radiation (EMR) travels in waves
Wavelength (l): distance from one wave crest to the next
Shorter l = more energy
l
Fig. 3.7
Wien’s Law
Wien’s Law shows the relationshipbetween the temperature of an object and the wavelength at which the most energy is radiated.
For an object as hot as the Sun(T = 6000 K), this translates intoa wavelength of .0000005 meters.This is about the color yellow in the spectrum. For the Earth (T = 300 K), this
is a wavelength of .00001 meters.This is the infrared part of the spectrum.
Fig. 3.8
Note differences
in wavelength in incoming
and outgoing radiation
Natural Greenhouse gasesGases in atmosphere trap radiation at the long
wavelength of outgoing radiation, but not at the short wavelength of incoming radiation
H2O
Water vapor & small droplets account for 97% of the natural GH effect
CO2 "Normal" levels of CO2 in
atmosphere also contribute
MOLECULES THAT TRAP HEAT IN G.H. EFFECT:
Fig. 21.8
Absorbance by H2O and CO2 is at l of emitted radiation,
not incoming
Incoming W = 0.1 - 1.5 m
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
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
Adding CO2: Human Impacts
COMPARING THE FOSSIL FUELS?Which emits the least CO2 per unit energy produced?
Natural Gas:
Lowest CO2
Coal:43% more CO2 than nat. gas
Oil:30% more CO2 than nat. gas
Fig. 21.9CO2 concentrations since 1960
Fig. 21.10QUESTION:Do increasing CO2
concentrations correlate with higher
temps?
ANSWER:Yes, historically. This
connection is questioned by some
though
CO2: Deforestation
CO2 accumulates because system can't remove it fast enough
Why not?
Amazonian slash and burn agriculture
TROPICAL DEFORESTATION:
Trees remove CO2 from atmosphere and store it in their tissues. Deforestation (particularly in tropical
forests) decreases amount of CO2 removed.
Greenhouse gasesGLOBAL WARMING:CO2 emissions account for 50-60% of the anthropogenic (human-induced) temperature change
WHERE'S THE OTHER 40-50% FROM?Other Greenhouse gases besides CO2 that trap heat
Chlorofluorocarbons (CFCs)
Nitrous Oxide (N2O)
Methane (natural gas)
CHLOROFLUOROCARBONS (CFCs):15-25 % of anthropogenic GW due to CFCsUsed as coolants (freon), formerly as propellantsAtmospheric concentrations growing by 5% annually
NITROUS OXIDE (N2O):5 % of anthropogenic GW due to N2OFrom fertilizer use, burning coal, vehicle exhaustConcentrations growing by 0.2% annually
METHANE (Natural Gas):12-20 % of anthropogenic GW due to methaneFrom natural gas leaks, livestockConcentrations currently stable, but high
Greenhouse gasesPROBLEM #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
Fig. 21.8Note 8-12 m window of absorbance
RecappingNATURAL GREENHOUSE EFFECT:Natural trapping of heat by gases in earth's atmos.Allows life to persist on earth
GLOBAL WARMING:Human activities accelerate heat trappingAverage global temperatures riseDue to CO2 from fossil fuels, greenhouse gases
Global warming theory is controversial
Let's look at the controversy
Controversy #1: Recent temp. change
RECORDED DATA:Data only goes back to 1860Since 1860, temps have risen about 0.9o F (0.5o C)Recent years are warmest on record
THE CONTROVERSY:Some claim temp. readings are inaccurate due to "urban heat island effect", and temps. aren't really rising
PROFESSOR’S OPINION:Temp. increases since 1860 are real. Can correct for urban heat island effect and also use satellite data
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
PROFESSOR’S OPINION:Past estimates are estimates, but it does appear (and makes sense) that CO2 levels and temp are related
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 highly speculative. Earth's climate too complex to be modeled. Past models have been wrong. PROFESSOR’S OPINION:Models are suspect, but they are getting better as we learn more about how our atmosphere operates.
Controversy #3: Predicting temperature
changes
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?
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 uninhabitable
Arable land decreases; less food production
Wealthy countries build dikes, poor countries flood
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
American breadbasket becomes Canadian breadbasket
Global yields down 10-70%
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
Fig. 21.6
Ocean "conveyor belt" - could break down if ocean temperatures elevate too much
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?
KYOTO, JAPAN (DEC. 1997)
International treaties on GW
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
International treaties on GWKYOTO, JAPAN (DEC. 1997)
Treaty needs congressional approval in U.S.
Will it ever pass? Not very likely.
WHY? Reductions cost money in short-termEconomy could suffer short-termGlobal competitors like China have advantagePolitical suicide for congressmen
Ozone HoleFor the last several decades, a thinning of the stratospheric ozonelayer has been detected, most notablyover the Antarctic.
This thinning is most likely due to CFC emissions, which breakdown ozone.
This is important, as stratosphericozone absorbs high energy UVradiation, which has been linkedto skin cancer and crop failures.
CFC’s and OzoneCFC is an extremely stable molecule.
In the upper stratosphere, UV radiationbreaks down CFC in chlorine and other by-products
Free chlorine then breaks down ozone.
NOTE: CFC is also a greenhouse gas in the TROPOSPHERE. Thisis the only relationship between ozone thinning and global warming,i.e. GLOBAL WARMING AND OZONE HOLE ARE TWO ENTIRELY DIFFERENT ISSUES!!!!
Other PollutantsSulfur dioxide (SO2) - reacts with water to produce sulfuric acid; produced by burning coals and gas high in sulfur
Nitrogen oxides (NOx) - produces photochemical smog; reacts withVOC’s to produce ground-level ozone; reacts with water to producenitric acid; produced by burning fossil fuels at high temperatures
Carbon monoxide (CO) - inhibits respiration; consumed in the formation of ground-level ozone; produced by the incomplete combustion of fossil fuels
Particulates - small particles (less than 2.5 m) cause lung damage
VOC’s - implicated in ground-level ozone; some are toxic and cancer causing (benzene, MTBE, etc.)