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 • 2. Depletion of stratospheric ozone, caused by our use of chlorofluorocarbons and other chemicals
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 • 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 • 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 • 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 • 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 • 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 • 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 • 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 • Increased water evaporation --> increased heavy rainstorms • Rise in sea levels
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 • 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? • 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 • 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 • 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 • 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 • 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 • 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? • 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 • 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? • 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? • 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 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 • 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? • 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 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? • 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.