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Ch 4. The three modern global change problems.

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Earth has been changing and will continue to do so. It is changing faster today than it ever has. The major reason is human activity.

1. Ozone depletion; Ozone hole in South Pole

2. deforestation;

3. Greenhouse gases and global warming

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Vertical Structure of the Atmosphere

4 distinct layersdetermined bythe change oftemperaturewith height

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Figure 1. Global lower stratospheric departure of temperature from average since 1979, as measured by satellites. The large spikes in 1982 and 1991 are due to the eruptions of El Chicon and Mt. Pinatubo, respectively. These volcanos ejected huge quantities of sulphuric acid dust into the stratosphere. This dust absorbed large quantities of solar radiation, heating the stratosphere.

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• Ozone depletion describes two distinct, but related observations:

(1) a slow, steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere (ozone layer) since the late 1970s,

(2) a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period.

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Image of the largest Antarctic ozone hole ever recorded (September 2006).

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Ozone over Antarctic during Oct.

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It shows a sharp drop beginning in the early 1970s. The graph to the left shows long-term ozone levels over Arosa, Switzerland. Although ozone levels rise and fall in natural cycles, the average level remained constant from 1926 until 1973. Beginning in 1973, however, and continuing through 2001, ozone levels have dropped at a rate of 2.3 percent / decade.

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Too much ultra-violet light can result in:

• Skin cancer • Eye damage such as cataracts • Immune system damage• Reduction in phytoplankton in the oceans that

forms the basis of all marine food chains including those in Antarctica.

• Damage to the DNA in various life-forms. So far this has been as observed in Antarctic ice-fish that lack pigments to shield them from the ultra-violet light (they've never needed them before)

• Probably other things too that we don't know about at the moment.

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Why does a ozone hole form over Antarctica?

The ozone hole is caused by the effect of pollutants in the atmosphere destroying stratospheric ozone. During the Antarctic winter something special happens to the Antarctic weather.

• Firstly, strong winds blowing around the continent form, this is known as the "polar vortex" -  this isolates the air over Antarctica from the rest of the world. • Secondly, clouds form called Polar Stratospheric Clouds. Clouds turn out to have the effect of concentrating the pollutants that break down the ozone, so speeding the process up.

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DeforestationDeforestation is the permanent removal of forest cover from anarea, and the conversion of this previously forested land to otheruses.

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Deforestation affectsCarbon balance

Hydrological cycleRadiative energy balance

Biodiversity

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Statistics

North America and Europe – already done

85% of old growth forests in US destroyed by settlers – most replanted

Parts of Pacific NW and Alaska – deforesting now as fast as Brazil

It has been estimated that about half of the earth's mature tropical forests — between 7.5 million and 8 million km2 of the original 15 million to 16 million km2 , have now been cleared since 1947.

Canada:One case of deforestation in Canada is happening in Ontario's boreal forests, near Thunder Bay, where 28.9% of a 19,000 km² of forest area had been lost in the last 5 years and is threatening woodland caribou. This is happening mostly to supply pulp for the facial tissue industry. In Canada, less than 8% of the borealforest is protected from development and more than 50% has been allocated to logging companies for cutting.

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Tropics

Rainforests 50 years ago covered 14% of the world's land surface and have been reduced to 6%, and that all tropical forests will be gone by the year 2090

Brazil – slash and burn; Amazon – 200% increase in deforested area from 1979 - 1988

Some scientists have predicted that unless significant measures (such as seeking out and protecting old growth forests that have not been disturbed) are taken on a worldwide basis, by 2030 there will only be ten percent remaining.

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The reasons

Disappearing at a rate of tens of thousands of square miles per year

Land clearing in developing countries for farming and ranching (e.g., Brazil)

Wood as a fuel (e.g., 90% of Africans use wood as primary fuel)

Ballooning populations in developing countries

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The effects

Loss of fauna associated with the forests

Loss of soil value for farming (formation of laterites) ;

Current extinction rate of 50,000 species per year Rate reflects fact that most fauna and flora in tropics are disappearing

increased soil erosion (i.e., global erosion rate of 25.4 billion tons of top soil per year)

Lowered oxygen production levels

Increased CO2

Changed climate (radiation, temperature) and hydrologic cycle

Landslides

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Dust Storm in Beijing, China on March 20, 2002. It lasted 52 hours.

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Effects

deforestation soil erosion and loss of wood materials lowered productivity of soil and loss of wood source increased human needs enhanced deforestation

Cycle (vicious circle):

e.g., 40-50 million trees removed in Haiti each year

– correlates with 7x increase in food aid over last 20 years

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Global warming

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The balance of evidence The balance of evidence suggestssuggests that there is that there is a discernible human influence on global a discernible human influence on global climateclimate

Intergovernmental Panel on Climate Change (United Nations), Second Assessment Report, 1996

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There is new and There is new and stronger evidence stronger evidence that most of that most of the warming observed over the last 50 years is the warming observed over the last 50 years is attributable to human activity'attributable to human activity'

Intergovernmental Panel on Climate Change (United Nations), Third Assessment Report, 2001

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`̀Most of the observed increase in globally Most of the observed increase in globally averaged temperatures since the mid-20th averaged temperatures since the mid-20th century is century is very likely very likely due to the observed increase due to the observed increase in anthropogenic greenhouse gas concentrations’in anthropogenic greenhouse gas concentrations’

Intergovernmental Panel on Climate Change (United Nations), Fourth Assessment Report, 2007

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Intergovernmental Panel on Climate Change (United Nations), Fifth Assessment Report, 2013

Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes. This evidence for human influence has grown since AR4. It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.

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Svante Arrhenius (1896)Performed numerical calculations that suggested that doubling the amount of carbon dioxide in the atmosphere could raise global mean surface temperatures by 5-6°C.

Joseph Fourier (1827)Recognized that gases in the atmosphere might trap the heat received from the Sun.

John Tyndall (1859)Careful laboratory experiments demonstrated that several gases could trap infrared radiation. The most important was simple water vapor. Also effective was carbon dioxide, although in the atmosphere the gas is only a few parts in ten thousand.

Argued that rising levels of carbon dioxide were responsible for measurable increases in Earth surface temperatures. Estimated that doubling the amount of CO2 in the atmosphere could raise global mean surface temperatures by 2°C.

Guy Callender (1939)

Discovery of the Greenhouse Effect

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GREENHOUSE EFFECT?

Glass allows visible radiation to pass through the glass which absorbs thermal radiation and re-emits some of it back intothe greenhouse --- like a radiation blanket.

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Radiation is emitted out to space by these gases from level somewhere near the top of the atmos. – typically from between 5 and 10km high. Here, temperature is much colder -30 – 50C or so colder than at the surface. => emitting less radiation to space. So: absorb radiation emitted from the earth surface but then to emit much less radiation out to space.

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The enhanced greenhouse effect

average levels from which thermal radiation leaving the atmosphere originates

F = T4

= 5.67 x 10-8 W/m2/K4

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Component of the radiation (in watts per square meter) which on average enter and leave the earth’s atmos. and

make up the radiation budget for the atmosphere.

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Planetary energy balance•Earth is at steady state: Energy emitted by Earth = Energy absorbed ..(1)

•E emitted = (area of Earth) Te4

= 4 Re2 Te

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(Te= Earth’s effective rad. temp., Re= Earth’s radius)

•E absorbed = E intercepted - E reflected

•Solar E intercepted = S Re2 (solar flux S)

•Solar E reflected = AS Re2 (albedo A)

•E absorbed = (1-A) S Re2

•(1) => 4 Re2 Te

4 = (1-A) S Re2

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Magnitude of greenhouse effect• Te

4 = (1-A) S/4

•Te = [(1-A) S/(4 )]1/4 (i.e. fourth root)

•Te = 255K = -18°C, very cold!

•Observ. mean surf. temp. Ts = 288K = 15°C

•Earth’s atm. acts as greenhouse, trapping outgoing rad.

•Ts - Te = Tg, the greenhouse effect

•Tg = 33°C

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Greenhouse effect of a 1-layer atm.

EarthTs

Atm.Te

S/4AS/4

(1-A)S/4 Ts4

Te4

Te4

•Energy balance at Earth’s surface: Ts

4 = (1-A)S/4 + Te4 ..(1)

•Energy balance for atm.: Ts

4 = 2 Te4 .. (2)

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Subst. (2) into (1):

Te4 = (1-A)S/4 ..(3) (same eq. as in last lec.)

Divide (2) by ; take 4th root:

Ts = 21/4 Te = 1.19 Te

For Te = 255K, Ts = 303K. (Observ. Ts = 288K)

Tg = Ts - Te = 48K,

15K higher than actual value.

•Overestimation: atm. is not perfectly absorbing all IR rad. from Earth’s surface.

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•Weather forecasting also uses atm. GCMs. Assimilate observ. data into model. Advance model into future => forecasts.

•Simpler: 1-D (vertical direction) radiative-convective model (RCM):

Doubling atm. CO2 => +1.2°C in ave.sfc.T

•Need to incorporate climate feedbacks:

•water vapour feedback

•snow & ice albedo feedback

•IR flux/Temp. feedback

•cloud feedback

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Water vapour feedback• If Ts incr., more evap. => more water vapour

=> more greenhouse gas => Ts incr.

• If Ts decr., water vap. condenses out => less greenhouse gas => Ts decr.

•Feedback factor f = 2.

•From RCM: T0 = 1.2°C (without feedback)

=> Teq = f T0 = 2.4°C.

Ts

Greenhouse effect

Atm. H2O(+)

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Snow & ice albedo feedback•If Ts incr. => less snow & ice => decr.

planetary albedo => Ts incr.

Ts

planetary albedo

snow & ice cover

(+)

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IR flux/Temp. feedback•So far only +ve feedbacks => unstable.

•Neg. feedback: If Ts incr. => more IR rad. from Earth’s sfc. => decr. Ts

Ts Outgoing IR flux(-)

•But this feedback loop can be overwhelmed if Ts is high & lots of water vap. around => water vap. blocks outgoing IR => runaway greenhouse (e.g. Venus)

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Climatic effects of clouds•Without clouds, Earths’ albedo drops from

0.3 to 0.1. By reflecting solar rad., clouds cool Earth.

•But clouds absorb IR radiation from Earth’s surface (greenhouse effect) => warms Earth.

•Cirrus clouds: ice crystals let solar rad. thru, but absorbs IR rad. from Earth’s sfc.

=> warm Earth•Low level clouds (e.g. stratus): reflects

solar rad. & absorbs IR => net cooling of Earth

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•IR rad. from clouds at T4

•High clouds has much lower T than low clouds

=> high clouds radiate much less to space than low clouds.

=> high clouds much stronger greenhouse effect.

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Uncertainties in cloud feedback•Incr. Ts => more evap. => more clouds

•But clouds occur when air is ascending, not when air is descending. If area of ascending/descending air stays const.

=> area of cloud cover const.•High clouds or low clouds? High clouds

warm while low clouds cool the Earth.

•GCM’s resolution too coarse to resolve clouds => need to “parameterize” (ie. approx.) clouds.

•GCM => incr. Ts => more cirrus clouds => warming => positive feedback.

=> Teq = 2 -5°C for CO2 doubling

Greenhouse GasesGreenhouse Gases

Water Vapor: Carbon Dioxide (CO2)CH4 methane, N2O = nitrous oxide...

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NATURAL GREENHOUSE EFFECT

Evaporation = > water vapor

Common name: marsh gas that can be seen bubbling up from marsh area where organic material is decomposing.

plant and animal respiration, the decay of organic materials.

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ENHANCED GREENHOUSE EFFECT

The increase in carbon dioxide (CO2) has contributed about 72% of the enhanced greenhouse effect to date, methane (CH4) about 21% and nitrous oxide (N2O) about 7%.

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• Water Vapor: Water Vapor: source: evaporation from Earth’s surfacesource: evaporation from Earth’s surface location: the lowest 5 km of the atmospherelocation: the lowest 5 km of the atmosphere residence time: 10 daysresidence time: 10 days variation range: 0.1% - 4% variation range: 0.1% - 4% roles in atmosphere: source of moisture for roles in atmosphere: source of moisture for

cloud; absorber of energy emitted by cloud; absorber of energy emitted by

Earth’s surface: greenhouse gas. Earth’s surface: greenhouse gas.

Water VaporWater Vapor

• Naturally Naturally occurring occurring greenhouse greenhouse gas, gas, generally generally unaffected unaffected by humans.by humans.

Importance: Importance: The Clausius-Clapeyron relationship (shown below) suggests that warmer air can hold more water vapor. As the planet warms due to the greenhouse effect, more

water vapor will change global climate conditions.

By solving for water vapor (e), we can see that temperature (T) increases the amount of water vapor.

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•Carbon Dioxide (CO2)Carbon Dioxide (CO2) sourcesource: plant and animal respiration, the : plant and animal respiration, the

decay of organic materials, and natural decay of organic materials, and natural and anthropogenic (human-produced). and anthropogenic (human-produced).

Current concentrationCurrent concentration: 380ppm (parts : 380ppm (parts per million, i.e., 0.038%); a global per million, i.e., 0.038%); a global increase in recent decades.increase in recent decades.

The increase in carbon dioxide (CO2) has The increase in carbon dioxide (CO2) has contributed about 72% of the enhanced contributed about 72% of the enhanced greenhouse effect to date, methane greenhouse effect to date, methane (CH4) about 21% and nitrous oxide (CH4) about 21% and nitrous oxide (N2O) about 7%. (N2O) about 7%.

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• Carbon is exchanged between the biosphere, Carbon is exchanged between the biosphere, lithosphere, hydrosphere, and atmosphere of the Earth.lithosphere, hydrosphere, and atmosphere of the Earth.

• Four reservoirs of CO2: atmosphere, ocean, biosphere Four reservoirs of CO2: atmosphere, ocean, biosphere and sediments. and sediments.

• Carbon cycle modeling. Models of the carbon cycle Carbon cycle modeling. Models of the carbon cycle can be incorporated into can be incorporated into global climate models, so that , so that the interactive response of the oceans and biosphere on the interactive response of the oceans and biosphere on future CO2 levels can be modeled. Such models future CO2 levels can be modeled. Such models typically show that there is a positive feedback typically show that there is a positive feedback between temperature and CO2. between temperature and CO2.

The “Carbon Cycle” The “Carbon Cycle” There is a natural process by which carbon dioxide is cycled through the Earth's ecosystems and atmosphere.

The blue arrows represent the natural processes by which living organisms emit and absorb carbon throughout their life and death (e.g. Respiration, photosynthesis, decomposition)

The red arrows represent the “anthropogenic flux” which is a scientific term for the human effect on the carbon cycle, including industrialization and fossil fuel burning.

"GtC" stands for GigaTons of Carbon

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• The land and ocean are large reservoirs to The land and ocean are large reservoirs to stock carbon than atmos. For example, the stock carbon than atmos. For example, the release of just 2% of the carbon stored in the release of just 2% of the carbon stored in the oceans would double the amount of atmos. oceans would double the amount of atmos. CO2. CO2.

• At the time scales which we concern, CO2 is At the time scales which we concern, CO2 is not destroyed but redistributed among the not destroyed but redistributed among the various carbon reservoirs. E.g., about 50% of various carbon reservoirs. E.g., about 50% of an increase in atmos. CO2 will be removed an increase in atmos. CO2 will be removed within 30 years, a further 30% within a few within 30 years, a further 30% within a few centuries, and the remaining 20% may remain centuries, and the remaining 20% may remain in the atmos. for many thousands of years.in the atmos. for many thousands of years.

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The Human FootprintThe Human Footprint• 5% of the world's population resides in the United States, creating ¼ of the total 5% of the world's population resides in the United States, creating ¼ of the total

greenhouse gas emissions.greenhouse gas emissions.

• For most people, their car is the main source of emissions. 22Lbs of COFor most people, their car is the main source of emissions. 22Lbs of CO22 is is produced from every gallon of gas. Do the math: produced from every gallon of gas. Do the math:

• Number of miles traveled by car each year _10000_ , divide by average miles per gallon = Number of miles traveled by car each year _10000_ , divide by average miles per gallon = 15__ gallons of gas, multiplied by 22 lbs 15__ gallons of gas, multiplied by 22 lbs COCO22/gallon of gas = _14667_ pounds of /gallon of gas = _14667_ pounds of COCO22

• The 1997 Kyoto protocol called for all people to limit their carbon emissions to 5.4 The 1997 Kyoto protocol called for all people to limit their carbon emissions to 5.4 tons, or about 11,000 lbs, per year.tons, or about 11,000 lbs, per year.

• Some scientists believe that in order to reverse the damage caused by greenhouse Some scientists believe that in order to reverse the damage caused by greenhouse gas emissions, we would need to reduce our individual emissions down to 5,000 lbs gas emissions, we would need to reduce our individual emissions down to 5,000 lbs per year. per year.

Solving the Carbon Solving the Carbon Dilemma:Dilemma:

What are some things that you can do to reduce your What are some things that you can do to reduce your carbon emissions? carbon emissions?

Energy-efficient, energy-conserving electronics, lightbulbs, hardware and other devices are available for almost anything. You can expect that energy-efficient products are meant to last longer and will save you money.

Reduce your dependency on cars!

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Greenhouse gases•Greenhouse gases (CH4 = methane, N2O =

nitrous oxide): trap outgoing radiation from Earth’s surface

•Coal burning Sulfur dioxide (SO2) acid rain.

•SO2 Sulfate aerosol, reflects sunlight => cooling.

•1940-1970 cooling may be due to coal burning.

•Coal burning incr. CO2 (long-term warming) and incr. sulfate aerosol (short-term cooling) [aerosol washed out by precip.]

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CO2 (ppm)

CH4 (ppb)

1000 2000

N2O (ppb)CO2 (ppm)

CH4 (ppb)

1000 2000

N2O (ppb)

From IPCC Report

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Atmospheric CO2 concentrations--past 1000 years.

From “The earth system”

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Anthropogenic greenhouse warmingAtm. CO2:• Keeling started measuring atm.CO2 in 1958 on Mauna Loa,

Hawaii

• Seasonal cycle (forests absorb CO2 in summer & release CO2 in winter) + rising trend

From “The earth system”

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From “Global Warming”

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* The most important of the aerosols from anthropogenic forcing are sulphate particles. * Cooling effect; * Life time: 5 days. So their effect is mainly confined to regions

near the sources of the particles.

From “Global Warming”

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Red: removing sulphate aerosols in 2000;Blue: maintaining sulphate aerosols at the 2000 level.

From “Global Warming”

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Global mean surface temperatures have increased 0.5-1.0 F since the late 19th century; The 20th century's 10 warmest years all occurred in the last 15 years of the century. Of these, 1998 was the warmest year on record. The snow cover in the Northern Hemisphere and floating ice in the Arctic Ocean have decreased, sea level has risen 4-8 inches over the past century.

• Some facts of global changes:

(1) Global warming:

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LOSU: assessed level of scientific understanding

Figure SPM.2

From IPCC report

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The three serious problems

The three modern global change problems discussed in this chapter-- global warming, ozone depletion, or loss of biodiversity

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The ozone depletion is the serious problem because:

•It causes the most immediate damage to our planet and its inhabitants

•It can cause skin cancer

•It occurs faster than global warming, because global temperatures only rise 1 degree in 100 years so this is an insignificant amount compared to the decline in the total amount of ozone

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• Low-level ozone damages plants, reducing their capacity to take up carbon dioxide and accelerating global warming. The study suggests that projected increases of ozone concentration from industrial sources will markedly reduce plant productivity. This indirect effect could contribute significantly to global warming.

(Nature, 16, August 2007, by S. Sitch, P. M. Cox, W. J. Collins & C. Huntingford)

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The loss of biodiversity is the serious problem because:

• There is potential for recovery for the other problems: the ozone layer could recover within a few generations and greenhouse gas concentrations should return to “normal” within a few million years.

• The recovery rate for species following extinction is tens of millions of years.

• Once a species is gone, it is gone for good.

• It could cause an imbalance in the Earth’s ecosystem and economy.

• Deforestation also contributes to global warming.

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Global warming is the serious problem because:

•It affects the greatest number of people

•Migration of marine animals could result

•Rising sea level could result

•Cold climate species might die

•Ozone depletion and deforestation are both confined to particular areas whereas global warming is truly global