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CHAPTER 11 GLOBAL WARMING AND OZONE LOSS The Two Greatest Threats 1. Global warming from fossil fuel burning and deforestation that enhances the earth’s natural greenhouse effect - it is the trophosphere (lower atmosphere) that is warmed

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chapter 11



the two greatest threats
The Two Greatest Threats
  • 1. Global warming from fossil fuel burning and deforestation that enhances the earth’s natural greenhouse effect - it is the trophosphere (lower atmosphere) that is warmed
  • 2. Depletion of stratospheric ozone, caused by our use of chlorofluorocarbons and other chemicals
the greenhouse effect and global warming
The Greenhouse Effect and Global Warming
  • Though water vapor is an important “greenhouse gas” most of it does not originate from human activities.
  • Other greenhouse gases have become more prevalent in atmosphere as a result of human activities that produce them.
  • Developed countries, especially U.S., produces most greenhouse gas
  • Ice cores show that CO2 has increased
greenhouse gases carbon dioxide
Greenhouse gases - Carbon dioxide
  • Responsible for 50-60% of global warming
  • Sources:
    • Fossil fuel burning -70-75%;
    • Land clearing with plant burning - each plant removed means more CO2 which is not used in photosynthetic reactions
  • Chart shows more CO2 during winter months - Why? Because plants without leaves are photosynthesizing less.
greenhouse gases cfcs
Greenhouse gases - CFCs
  • Contribute to global warming and deplete ozone
  • Sources:
    • leaking air conditioners and refrigerators
    • evaporation of industrial solvents
    • production of plastic foams
    • aerosol propellants
  • Use is being phased out
greenhouse gases methane
Greenhouse gases - Methane
  • Responsible for ~20% of warming
  • Produced in anaerobic reactions of bacteria decomposing dead organic matter
  • Occurs in:
    • swamps and other natural wetlands
    • rice paddies
    • landfills
    • intestinal tracts of cattle, sheep and termites
greenhouse gases nitrous oxide
Greenhouse gases - Nitrous oxide
  • Global warming and ozone depletion
  • Released from:
    • nylon production
    • burning biomass and nitrogen-rich fuels
    • smog-fighting catalytic converters on motor vehicles
    • breakdown of nitrogen fertilizers in soil, livestock wastes and nitrate contaminated groundwater
past and future changes in earth s climate
Past and future changes in earth’s climate
  • Intergovernmental Panel on Climate Change reports evidence on past and future changes such as…
  • Antarctic ice show that glacial and interglacial periods have alternated
  • Ice cores show that water vapor content has changed little, but CO2 content increased
  • Last 15 years, especially 1998, hottest
modeling climate changes
Modeling Climate Changes
  • Development of mathematical models to project increases in greenhouse gases
  • Model’s usefulness depends on:
    • design and assumptions made
    • accuracy of data
    • magnification of tiny errors over time
    • positive and negative feedback effects
    • unexpected and unpredicted event
scientific consensus future global warming
Scientific consensus ~future global warming
  • Project that 1.3 - 4.10 temperature increase between 1990 and 2100
  • Northern hemisphere will heat faster than southern hemisphere, esp. at poles
  • Current signs of warming:
    • retreating glaciers
    • fish and trees migrating northward
    • tropical diseases spread away from equator
    • coral reef bleaching
scientific consensus future global warming 2
Scientific consensus ~future global warming - 2
  • Increased water evaporation --> increased heavy rainstorms
  • Rise in sea levels
how serious is the threat
How serious is the threat?
  • How to separate “climate noise” from overall temperature change
  • Factors that might influence changes:
    • variations in solar output
    • ocean effects: uptake of CO2 and heat and effects of El Ninos, disruption of ocean currents, effect of decreases in salinity
    • water vapor and clouds both trap heat and reflect sunlight
how serious is the threat 2
How serious is the threat? - 2
  • Factors that might influence changes (cont):
    • Effect of polar ice - melting means less sunlight reflection or more snow falling
    • Air pollution might form condensation nuclei
      • pollutants could both warm and cool
      • acid rain --> decreased plant life --> decreased CO2 uptake
    • Increased CO2 levels --> increased photosynthesis --> increased methane; growth & death of forest trees forest
how rapidly could climate shift
How rapidly could climate shift?
  • Adaptations could occur if changes are slow
  • If changes occur within decades, changes in agriculture and homes will not happen in time and populations will die; not just Man
  • Current projections could be halved or doubled
possible effects of warmer world
Possible effects of warmer world
  • Global temperature change differs from local weather changes
  • Effect on food production:
    • disruption due to storms and soil drying
    • climate belts shift toward poles
    • increase in insects - pests
    • lowlands flooded
    • CO2 level effect on photosynthesis C3 vs C4
possible effects of warmer world 2
Possible effects of warmer world -2
  • Effect on water supplies:
    • lakes, streams, aquifers dry up
    • intense rainfall --> flooding
  • Effect on forests:
    • migrate toward poles leaving grasslands
    • seed distribution would affect adaptation
    • some forest diebacks could occur
    • wildfires
possible effects of warmer world 3
Possible effects of warmer world -3
  • Effect on biodiversity
    • species which do not migrate would suffer
    • high altitude species would suffer
    • wildlife preserves & other habitats would suffer
  • Effect on sea levels
    • flooding of coastal regions and lowlands
    • loss of beaches, estuaries, wetlands & coral reefs; effect on barrier islands
possible effects of warmer world 4
Possible effects of warmer world -4
  • Effect on weather:
    • extremes of weather more likely --> disruption of banking and insurance industries & govts
  • Effect on human health
    • heat related illnesses and deaths
    • food and water supply interruptions
    • spread of tropical diseases
    • respiratory problems
  • Environmental refugees
dealing with the threat
Dealing with the threat
  • Should we do nothing; a few scientists claim there is no problem - they are getting a lot of press.
  • Some would make so many changes that national & global economies would suffer.
  • Some propose a precautionary strategy - take informed preventive action before there is overwhelming scientific knowledge to justify acting.
how can we slow global warming
How can we slow global warming?
  • Increase efficiency
  • Use nuclear power, but what about cost and danger?
  • Use natural gas, but methane may leak
  • Phase out fossil fuel subsidies and phase in carbon taxes
  • Agree to global and national limits on greenhouse gas emissions; emission permits
how can we slow global warming 2
How can we slow global warming?2
  • Transfer renewable energy technologies to developing countries
  • Remove CO2 from emissions or liquify it
  • Reduce deforestation, go to sustainable agriculture; would reduce CO2 - so what about massive global reforestation?
  • What are 3 “radical” possible solutions?
what has been done
What has been done?
  • A goal of reducing CO2 emission was made at the 1992 Earth Summit - but there was no requirement
  • Kyoto - treaty restricts emissions in 38 developed countries; allows emissions trading - restrictions are inadequate; U.S. did not ratify treaty because of lack of restrictions on developing countries
ozone depletion a serious threat
Ozone depletion: a serious threat?
  • Loss due to human produced chemicals is real and a serious threat to plants and animals
  • Chlorofluorocarbons - cheap, chemically stable, odorless, nonflammable, nontoxic and noncorrosive - perfect for coolants, cleaners, fumigants, sterilants and foam - but remain in the trophosphere
ozone depletion a serious threat37
Ozone depletion: a serious threat?
  • UV light breaks down CFCs --> Cl release
  • Clorine catalyzes O3 to O2 and O
  • 100,000 ozone molecules destroyed/1 CFC
  • Discovered in 1974; no action for 15 years
  • 1988, problem acknowledged by DuPont
  • Other chemicals: Halons, Methyl bromide, Carbon tetrachloride, Methyl chloroform, HCl
seasonal ozone thinning over poles
Seasonal ozone thinning over poles
  • 1984, satellite data showed 40-50% ozone loss over Antarctica - the ozone hole; now the hole is larger than N. America
  • Very cold temperatures --> Cl + O --> ClO (chlorine is unavailable to react with O3)
  • Warm temperatures release the Cl so ozone is destroyed
  • Ozone depleted air moves northward - some at the North pole
is it a serious problem
Is it a serious problem?
  • Some have claimed the problem a hoax
  • What damage can be done?
    • Sunburn
    • cataracts --> increased blindness
    • skin cancer --> increased #s of cases
    • suppression of immune system
    • photochemical smog
    • damage to plants etc
is it a serious problem42
Is it a serious problem?
  • What about possibility of widespread, long-lasting, unpredictable ecological disruptions in species adapted to current levels of UV radiation?
  • So we must protect the ozone layer; find substitutes for CFCs
  • Technofixes - blimps and lasers
what is being done
What is being done?
  • 1987, Montreal Protocol- treaty to cut CFC emissions --> 85% drop in CFC production
  • Methyl bromide will be banned - substitute fumigant found
  • Ozone treaty set good precedent - but evidence for global warming is less clearcut.