Fig. 15.8
Disappearance of the Aral Sea, during the period from 1973 to 2000.
Largely due to diversion of water from the rivers feeding the sea for irrigation.
AOSC 200LESSON 13
Human Influences on Climate
• Greenhouse effect
• Feedbacks
• Northward movement of the jet streams
• Changing Land Surfaces
• Heat Islands
• Consequences of Greenhouse Effect
Simple Greenhouse Model
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Positive Feedback
Negative Feedback
CLIMATE FEEDBACK MECHANISMS
• POSITIVE AND NEGATIVE FEEDBACKS
• WATER VAPOR - POSITIVE
• CLOUDS - POSITIVE AND NEGATIVE - MAINLY NEGATIVE
Fig. 7-27, p. 191
Positions of the jet streams
Jet Streams on March 11, 1990Sub-tropical = Blue, Polar = Red
Fig. 8-30, p. 231
Relation between jet stream and high and low pressure systems
% DAYS WHEN JETSREAM WITHIN 150 MILES OF BALTIMORE
Frontal Movement and Climate Change
• Increasing evidence that the Polar and Sub-tropical jet streams in the Northern Hemisphere are moving northward.
• This implies that the weather patterns associated with the jets (fronts) are also moving northward
• As the sub-tropical jet moves northward so do the high pressure systems associated with this jet.
• Expect drier summers• Could increase in greenhouse forcing in the
tropics lead to a stronger Hadley cell circulation, and hence to a movement of the jet?
Fig. 15.8
Disappearance of the Aral Sea, during the period from 1973 to 2000.
Largely due to diversion of water from the rivers feeding the sea for irrigation.
Aral Sea
• Government of the Soviet Union diverted waters feeding this inland lake to provide water for the growing of cotton.
• Aral Sea began shrinking rapidly
• Climate has also changed in the region
• Asian ‘Dust Bowl’
• Increased salinity destroyed fishing industry
Fig. 15.9
Roadways and buildings reduce evapor-transpiration and absorb more solar radiation than the surrounding rural regions.
Washington DC Heat Island
THE CLIMATE OF CITIES
• URBAN HEAT ISLAND• TEMPERATURES ARE GENERALLY HIGHER THAN
IN RURAL AREAS, CREATING AN 'ISLAND' OF WARMER AIR.
• CITIES ARE GENERALLY CLOUDIER, FOGGIER, WARMER, WETTER
• WHY?• ROCK-LIKE MATERIALS OF CITY HAVE HIGH
THERMAL CAPACITY• IMPERVIOUS SURFACES REMOVE PRECIPITATION
QUICKLY• LARGE SOURCES OF HEAT• ATMOSPHERIC POLLUTION TRAPS RADIATION• TALL BUILDINGS ALTER THE AIR FLOW• INCREASED PRECIPITATION• THERMALLY INDUCED UPWARD MOTIONS
Fig. 15-1, p. 442
CONSEQUENCES OF GREENHOUSE WARMING
• .WATER RESOURCES AND AGRICULTURE - CHANGES IN PRECIPITATION PATTERNS - LENGTH OF GROWING SEASON
• .SEA LEVEL RISE - .MELTING OF GLACIERS PLUS THE THERMAL EXPANSION OF THE OCEANS - HAS RISEN 10-25 CM OVER PAST CENTURY
• .NEW WEATHER PATTERNS - HIGHER FREQUENCY AND GREATER INTENSITY OF HURRICANES BECAUSE OF WARMER SEA SURFACE TEMPERATURES.
• SHIFTS IN PATHS OF CYCLONIC STORMS - PRECIPITATION PATTERNS.
• .SHIFTS OF OCCURRENCES OF TORNADOES. • .MORE INTENSE HEAT WAVES AND DROUGHTS IN
SOME REGIONS AND LESS IN OTHERS.
Air Pollution
William Shakespeare 1564-1616, from his play ‘Hamlet’
Air Pollution
Air Pollution
History of Air Pollution• Air pollution is not a new problem• In England, wood for burning became scarce, and the
populace resorted to burning coal which had a high sulfur content. The by-products were soot (carbon particles) and sulfur dioxide.
• John Evelyn in 1661 wrote about the notorious London pea-soup fog. These occur in the fall when the Thames is warm but the ground is cold. The natural fog this produces is enhanced by the extra soot particles, and the sulfur dioxide reacts in the water droplets to produce sulfuric acid.
London Killer Smog
SMOG
• Word coined by Dr. Harold Des Veaux, a London physician in 1903.
• SMOKE + FOG = SMOG
• He meant London smog – sulfurous fumes from coal burning + large water droplets formed around smoke particles (soot)
• 1952 – Killer smog – 4000 deaths. Another episode in 1956 led to 1000 deaths.
• Similar events have also occurred in the US.
• Large industrial cities such as St.Louis and Pittsburg also suffered from ‘London’ smog, as the use of coal increased.
PHOTOCHEMICAL SMOG
• In 1940 vegetable crop damage began to be seen in the Los Angeles basin. Pine trees began to lose their needles.
• Haagen-Smit and colleagues at the University of California, Riverside studied this effect using smog chambers - large plastic tents into which pollutants could be injected and their reactions investigated.
• They showed that the effect was due to ozone in the atmosphere.
• The ozone was produced by a series of reactions involving the oxides of nitrogen and organic compounds (e.g. gasoline), both of which are emitted by automobiles.
• It is this form of smog that gives the pollution seen in the Baltimore/Washington corridor.
Sources and Types of Air Pollutants
• can be grouped into two categories: primary and secondary.
• Primary pollutants are emitted directly from identifiable sources. They pollute the air immediately upon being emitted.
• Secondary pollutants are produced in the atmosphere when certain chemical reactions take place among primary pollutants.
• Sources. Two types of sources are identified fixed sources and mobile sources.
N2
O2
Ar
O3
Inert gasesCO2
H2
←SO2, NO2,CFC’s, etc
PM
COCH4
N2O
Composition of the Earth’s Troposphere
Denver, Colorado on a clear day
Denver, Colorado when particulate matter reduced visibility
Fine Particles or Particulate Matter (PM)
• PM is made up of suspended particles of either solid or liquid pollutants.
• PM is grouped by size: under 10 microns is called PM10, under 2.5 microns is called PM2.5.
• PM causes increased mortality and morbidity.
• Examples of PM include diesel soot, acids, dust, sulfates, nitrates, and organics.
Photochemical SMOG
Radical Hydroxyl theasknown is
2
:vapor
er with watreacts atomoxygen excited Then the
:oxygen of atom
excitedan give osunlight t with reacts Ozone
2*
2*
3
OH
OHOHO
OOhO
SMOG Chemistry
MOMOO
ONOhNO
NOOHCNOOHC
OHCOHC
HC
OHHCOHHC
32
2
252252
252252
52
252 62
:by followed
sunlightby apart broken then is dioxidenitrogen The
DIOXIDE; NITROGEN
form toOXIDE NITRIC with reactsen oxidant th This
:OXIDANTan produce
toOXYGEN MOLECULAR with combines then
(Ethane)
nshydrocarbo from ATOM HYDROGEN a stripcan OH
Schematic of ozone production from a Volatile Organic Compound (VOC)
SMOG
• NEEDS
• Hydrocarbons and nitrogen oxides
• Strong sunlight to start reactions
• Warm temperatures to maintain reactions – the higher the temperature the faster the rate.
• Peak ozone will be when temperature is highest – in the afternoon.
Daily Ozone Cycle
Sunrise Sunset
Time of day
Ozone Concentration
Ozone productionfollows a dailycycle with maximumconcentrations typically observedin the late afternoon.
This cycle is a signature of the dynamic processes of atmospheric air pollution
Highly Polluted Areas
In highly polluted areas the concentration of nitric
oxide can be large. In this case nitric oxide can react
with ozone :
NOO3 NO2 O2
This reaction removes ozone and short circuits the ozone
formation chain of reactions.
In highly polluted areas the ozone concentration
falls off as the level of nitric oxide increases.
Ozone vs NOx for Non Methane HydroCarbon level of =0.6 ppmc
High Pollution days• The figure illustrates one of the problems in the
abatement of pollution. The ozone concentration is used as the standard, and yet one can reduce the nitrogen oxides by a significant fraction and see no change, or even an increase in the ozone level.
• Most of the pollution is emitted in the cities, which typically puts the atmosphere at the right of the figure. As the pollutants move away from the city center their concentration gets smaller, and the atmosphere is moved toward the left, and the ozone increases.
• Hence the suburbs can see more ozone than the cities.
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