Composition Chemically, the Earth’s atmosphere is: 78% nitrogen 21% oxygen 1% argon. Trace compounds, like carbon dioxide, comprise less than.1% of the atmosphere.
Structure Because air is compressible, the pressure varies exponentially with height (as opposed to linearly if it were not compressible). 90% of the atmosphere lies below this line
Structure (cont.) Temperature varies with height depending upon the trace gases and type of radiation present 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
Convection Movement within the atmosphere occurs because of the differential heating of the Earth’s surface by the Sun. Where the air is the hottest, it expands the most and rises higher into the atmosphere. This causes cooler air to rush in to replace it, creating a convection cell. On a non rotating Earth, this is an idealized view of what that convection might look like.
Coriolis Effect On a non rotating Earth, all places on the surface would have the same horizontal velocity, i.e. no velocity. Objects can change latitude without having to change horizontal velocities and still move in a straight path. On a rotating Earth, objects at different latitudes would have different horizontal velocities. If an object does not change its horizontal velocity as it changes latitude, it will not appear to move in a straight path from an Earth reference frame.
Coriolis Effect (cont.) This film clip demonstrates that an object that travels in a straight path as seen from outside of the rotating reference frame will appear to travel in a curved path while observed from within.
Effect on Weather Patterns This effect prevents convective cell 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 in each hemisphere These cells help control the climate of different regions by by creating patterns of wind and precipitation.
Isobars Pressure systems drive local wind. However, the Coriolis effect means that wind does not flow directly from high to low. In Northern Hemisphere, wind is deflected to the right Thus, winds go in a clockwise fashion around high pressure and in counter- clockwise fashion around lows Winds attempt to go parallel to isobars. The closer the isobars are, the greater the wind
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 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? 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 (): distance from one wave crest to the next Shorter = more energy Fig. 3.7
Wien’s Law Wien’s Law shows the relationship between 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 into a 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 gases Gases in atmosphere trap radiation at the long wavelength of outgoing radiation, but not at the short wavelength of incoming radiation H2OH2O Water vapor & small droplets account for 97% of the natural GH effect CO 2 "Normal" levels of CO 2 in atmosphere also contribute MOLECULES THAT TRAP HEAT IN G.H. EFFECT:
Fig. 21.8 Absorbance by H 2 O and CO 2 is at 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 CO 2 concentrations in atmosphere, trapping more heat (2.) Adding other gases ("greenhouse gases") to atmosphere that also trap heat
Adding CO 2 : Human Impacts WHAT ADDS CO 2 TO THE ATMOSPHERE? Burning fossil fuels for energy Combustion of coal, oil, and natural gas produces CO 2 Overwhelms system's capacity to remove CO 2 from atmosphere CO 2 builds up, traps more heat, temperatures increase
Adding CO 2 : Human Impacts COMPARING THE FOSSIL FUELS? Which emits the least CO 2 per unit energy produced? Natural Gas: Lowest CO 2 Coal: 43% more CO 2 than nat. gas Oil: 30% more CO 2 than nat. gas
Fig. 21.10 QUESTION: Do increasing CO 2 concentrations correlate with higher temps? ANSWER: Yes, historically. This connection is questioned by some though
CO 2 : Deforestation CO 2 accumulates because system can't remove it fast enough Why not? Amazonian slash and burn agriculture TROPICAL DEFORESTATION: Trees remove CO 2 from atmosphere and store it in their tissues. Deforestation (particularly in tropical forests) decreases amount of CO 2 removed.
Greenhouse gases GLOBAL WARMING: CO 2 emissions account for 50-60% of the anthropogenic (human-induced) temperature change WHERE'S THE OTHER 40-50% FROM? Other Greenhouse gases besides CO 2 that trap heat Chlorofluorocarbons (CFCs) Nitrous Oxide (N 2 O) Methane (natural gas)
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 (N 2 O): 5 % of anthropogenic GW due to N 2 O From fertilizer use, burning coal, vehicle exhaust Concentrations growing by 0.2% annually METHANE (Natural Gas): 12-20 % of anthropogenic GW due to methane From natural gas leaks, livestock Concentrations currently stable, but high
Greenhouse gases PROBLEM #1: Compared to CO 2 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 CO 2
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 CO 2 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 1860 Since 1860, temps have risen about 0.9 o F (0.5 o 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 CO 2 and temp. PAST CLIMATE: Reconstruct past climate from air bubbles trapped in glaciers. Finds CO 2 levels and temp. to be correlated THE CONTROVERSY: CO 2 data solid, but temp. estimates are suspect. Contend there is no relation between CO 2 levels and temperatures PROFESSOR’S OPINION: Past estimates are estimates, but it does appear (and makes sense) that CO 2 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 3.6 o F (2.0 o 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 CO 2, 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 GW KYOTO, JAPAN (DEC. 1997) Treaty needs congressional approval in U.S. Will it ever pass?Not very likely. WHY? Reductions cost money in short-term Economy could suffer short-term Global competitors like China have advantage Political suicide for congressmen
Ozone Hole For the last several decades, a thinning of the stratospheric ozone layer has been detected, most notably over the Antarctic. This thinning is most likely due to CFC emissions, which breakdown ozone. This is important, as stratospheric ozone absorbs high energy UV radiation, which has been linked to skin cancer and crop failures.
CFC’s and Ozone CFC is an extremely stable molecule. In the upper stratosphere, UV radiation breaks down CFC in chlorine and other by-products Free chlorine then breaks down ozone. NOTE: CFC is also a greenhouse gas in the TROPOSPHERE. This is the only relationship between ozone thinning and global warming, i.e. GLOBAL WARMING AND OZONE HOLE ARE TWO ENTIRELY DIFFERENT ISSUES!!!!
Other Pollutants Sulfur dioxide (SO 2 ) - reacts with water to produce sulfuric acid; produced by burning coals and gas high in sulfur Nitrogen oxides (NO x ) - produces photochemical smog; reacts with VOC’s to produce ground-level ozone; reacts with water to produce nitric 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.)