Climate Change and Ozone LossChapter 18

Past climate change and the natural greenhouse effect

• Climate changed throughout Earth’s history– Sometimes over millions of years– Other times over a few decades

• Over the past 900,000 years average temperature of atmosphere near the Earth’s surface has undergone prolonged periods of – Global cooling – thick glacial ice covered land for about

100,000 years– Global warming – warmer interglacial period of melting

lasting 10,000 to 12,500 years (last 10,000 years has been interglacial

Global effect and its significance• For Earth to retain at a constant temperature– Incoming solar energy (visible light) must be balanced

with outgoing energy (longer-length, lower energy infrared radiation) that cools the earth

– In addition to incoming sunlight, a natural process called the greenhouse effect, warms the earth’s lower troposphere• Molecules of greenhouse gases (mainly water vapor and

carbon dioxide) warm the earth by absorbing some heat radiated by the earth’s surface.• Causes their molecules to vibrate and transform the absorbed

energy into longer-wavelength infrared radiation (heat) in the troposphere

• Atmosphere does not behave like a real greenhouse since closed windows in a car or greenhouse keep air from being carried away by convection to outside–Heat released by molecules of greenhouse gases

in the atmosphere is spread through the atmosphere by convection – Thus it should be called tropospheric heating

effect• If natural greenhouse effect acted by itself, the

average temperature on earth’s surface would be 130o F

• However, a natural cooling process occurs on the suface• Large quantities of heat are absorbed by evaporation of liquid

surface water• Water vapor molecules rise, condense to form droplets in

clouds, and release their stored heat higher in the atmosphere• These combined effects means that the earth’s aveage surface

temperature is about 59o F• Two greenhouse gases with largest concentrations in air are

– H2O

– CO2 (increases can occur from forest turnover in fall and winter)

• Others present– CH4 (natural)

– N2O (natural)

– CFC, SF6 SF5 CF3 (only from human sources)

Human Sources

• Rice paddies• Burning fossil fuels• Livestock wastes• Coal production (leaks)• Air conditioners• Plastic foams• Refrigerators• Deforestation• Use of inorganic fertilizers

• Since 1860, there has been a sharp rise in concentrations of– CO2

– CH4

– N2O

• This is a strong indication of global warming• Analysis of ancient ice shows– Concentrations of CO2 in troposphere is higher that it has

been in the past 420,000 years and is rising by 0.5% a year

– 20th century was hottest in the past 1000 years– Since 1860, average global temperature near the surface

has risen by 0.6– 0.7o C (1.1 -1.3o F)

Other Observed Signs

• Increased temperatures and melting ice caps and floating ice

• Retreat of some glaciers in the Alps, Andes, Himalayas, and Cascades

• Northward migration of some warm-climate fish and trees

• Bleaching of coral reefs

• Does this data indicate that our dramatic increase in fossil fuel use, agriculture, and deforestation have had an influence on earth’s temperature?

• Maybe to probably due to limited knowledge abut how complex our earth’s systems work

• Some of the increase may be due to fluctuations in average global temperature built into the earth’s systems or by human activities

• Such warming could accelerate and last for decades to hundreds of years or could be temporary with a leveling off

• It is clear that in the past 200 years, human activities have been changing the chemical composition of the atmosphere more rapidly than it has changed at anytime during the past 10,000 years

IPCC• Intergovernmental Panel on Climate Change–2500 of world’s leading climate experts from 70

nations– Established by the UN and World Meteorological

Organization –1995 report• Discernable human influence on climate in past

50 years • Earth’s mean surface temperature is likely

increase by 1.8 -6.3o F between 2000-2100

Factors that Affect Climate Change• Explain how each of the following affect the

Earth’s climate.– Changes in solar output– Changes in the Earth’s albedo– Moderating effect of oceans– Clouds and water vapor– Air pollution– Jet contrails

Possible effects of a warmer world• We are looking at a projected global change in climate –

not swings in local weather• Describe what effects a warmer world would have in• Agriculture• Water resources• Biodiversity• Weather extremes• Human population • forests• Sea level and coastal areas• Human health

Solutions with dealing with the threat of climate change

• Describe possible options in dealing with climate change.

• Describe how prevention can occur.• Describe cleanup can occur.• Explain how we can prepare for possible

global warming.• What were the results of the 1992 Earth

Summit and the Kyoto Protocol?

Ozone Depletion in the Stratosphere• Ozone (O3) keeps 95% UV radiation which–Allows human and other life forms to exist

on Earth– Protects humans from• Sunburn•Cataracts – the clouding of th eye• Immune systems damage

–Prevents much O2 in the trophosphere to be converted to O3

• Measurements show seasonal depletion called thinning over Antarctica and Arctic

• Thomas Migley Jr. Discovered the first chlorofluorocarbons (CFCs) in 1930 and created a family of highly useful ones

• Two most widely used are CFC-11 and CFC-12 (CCl2F2) which are called freons used in refrigeration

• Characteristics of CFCs which were called dream chemicals– Stable– Odorless– Nonflammable– Nontoxic– Noncorrosive– Cheap to make

•Uses –Coolants–Propellants in aerosol sprays–Cleaners for electric parts–Sterilants in hospitals–Fumigants for graineries –Bubbles in plastic wraps

Too Good To Be True• Molina and Rowland in 1974 indicated that CFCs were thinning

the ozone in the stratosphere– Called a ban on all CFCs– Stated that large amounts were being released into the troposphere

from• Propellants in spray cans• Leaks in refrigerators and air conditioners• Producction and burning of plastic foam products

– CFCs reamin in the troposphere because they are insoluble in water and unreactive

– Over 11-20 years, they rise into the stratosphere through convection, random drift and turbulent mixing

– In stratosphere, CFC molecules break down under the influence of UV radiation and release Cl-, reactive atom which speeds up the break down of ozone

– Each CFC molecule can last in the stratosphere 65-385 years– Each Cl- can destroy 100,000 molecules of O3

• CFC industry led by Dupont attacked Molina and Rowland but they stood their ground.

• Not until 1988 did nations agree to ban them and other ozone eaters and find substitutes in the Montreal Protocol in 1987 which went into effect in 1989

• Other ozone eaters– Halons and HBFCs – used in fire extinguishers– Methyl bromide (CH3Br) – used in fumigants

– Carbon tetrachloride (CCl4) – used in Clorox

– Methylchloroform 1,1,1-trichloroethane (C2H3Cl3) - used as cleaning solvent for clothes and metals and as a propellant in dry-cleaning sprays, adhesives, and other aerosols

– Hydrogen chloride (HCl) – emitted by space shuttles

Seasonal Thinning of Ozone over the Poles

• 1984 – 40-50% of ozone over Antarctica was being destroyed during the Antarctica spring and summer when sunlight returned– Loss was significant after 1976 when large amounts

were produced in the 1960s and even more in the 1970s– The ones produced in the 1980s have still to reach the

stratosphere• Ozone thinning varies with altitude and location• In 2000, thinning in Antarctica was largest ever

covering an area 3 times the size of the U.S.

• Each sunless winter, steady winds blow in a circular pattern ove the poles creating a polar vortex isolated until the sun returns– Water enters this circling stream of frigid air and forms

ice crystals– Ice crystals collect CFCs and others and speeds up their

breakdown to release Cl atoms and ClO– ClO atoms combine with one another to form Cl2O2

molecules which cannot react with ozone and accumulate in the polar vortex

– When the sunlight returns in the spring, the light breaks up the stored ClO molecules releasing large amounts of Cl-

– Within weeks, 40-50% of the ozone is destroyed

• The returning sunlight–Gradually melts the ice crystals–Breaks up the vortex of trapped polar air–Allows it to begin mixing again– Then new ozone forms until next winter–When the vortex breaks up • Huge masses of depleted air above Antarctica

flow northward and linger for a few weeks over Australia, New Zealand, South America, and South Africa• Raises damaging UV-B levels by 3-10% and up

to 20%

• There is some thinning in Arctic and will be at its worst between 2010-2019

• More damaging UV-A and UV-B will reach the Earth and lead to– Worse sunburn– More catarcts– More skin cancers like

• Basal cell carcinoma• Melanoma – the deadliest and which develops from a mole• Squamous cell

– Immune system suppression– More acidic deposition and eye-burning smog– Lower crop yields in key crops– Decline in forest productivity– Degradation of materials like paint, plastic– Reduction in productivity of phytoplankton

• Solutions for decreasing ozone depletion– Substitutes like HC (hydrocarbons like propane, butane)

are a way to prevent ozone depletion – HCFs break down faster and HFCs do not contain

chlorine