Our Changing Atmosphere – Global Warming and Climate Change

1.0 IntroductionGlobal warming is an issue that is hotly debated in modern society. The cause of the earth’s climate change, which involves the increase of global temperatures and extreme weather patterns, currently does not have a unanimously agreed-upon cause – with some parties claiming that the issue is due to human (anthropogenic) causes, while other parties claim that the current global warming is part of the Earth’s natural cycle uninfluenced by humans. Significant amounts of research in to the validity of each of these claims are occurring, with evidence strongly suggesting that global warming is, indeed, due to anthropogenic causes.

2.0 The AtmosphereThe atmosphere is comprised oflayers of gases surrounding Earth,separating the planet’s surfacefrom the edge of space. Atapproximately 100km thick (NASA - Glenn Research Centre 2010), theatmosphere protects Earth fromharmful UV radiation emitted fromthe sun and maintains itstemperature – without which Earth’saverage surface temperature wouldbe -18°C (Kowoma 2009). Earth’satmosphere is comprised of four mainlayers, listed in order from closest

Figure 1: The four main layers of Earth's atmosphereand their thicknesses

to to furthest from the crust: troposphere, stratosphere, mesosphere and thermosphere as seen in figure 1. (University of Tennessee - Knoxville 2000). In these layers, the major constituent gases are nitrogen (78%), oxygen (21%) and argon (<1%) as well as some trace gases such as carbon dioxide (CO2 ,0.1%), ozone (O3, 0.01%) and greenhouse gases (0.01%). Although these trace gases occur in relatively low percentages, they have a profound effect on the Earth’s climate (Allen, J & NASA Earth Observatory 2004).

3.0 Chemical Systems3.1 Greenhouse EffectAs illustrated in figure 2, the greenhouse effect occurs when atmospheric greenhouse gases (GHGs), such as CO2, O3 and H2O vapour trap infraredradiation, preventingit from escapingEarth’s atmosphere andin turn causing thetroposphere, where lifeis contained, to warm.This effect is naturaland a required part ofthe planet’s ecosystem.Without it, averagesurface temperatureswould be -18°C (Kowoma 2009). Although the greenhouse effect is necessary for life onEarth’s survival, it becomes a problem when it is too pronounced. When an excess of GHGs are present in the atmosphere, the effect becomes enhanced and the planet begins to warm above natural levels. As well as the naturally occurring GHGs, anthropogenic halocarbons such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) contribute significantly to the greenhouse effect(Bureau of Meteorology n.d.). CFCs were in the past very widely used worldwide as refrigerants, propellants and

Figure 2: The greenhouse effect, showing radiation being trapped in the atmosphere by greenhouse gases

solvents, however in recent years usage has declined significantly due to their negative effects on the atmosphere.

3.2 Ozone LayerOzone (O3) is found as atrace gas throughout theatmosphere. Within the stratosphere, a layer ofconcentrated ozone called the ozonosphere, or the ozone layer is found (see figure 3). This layer is vital for the survival of life on Earth as it prevents ultraviolet (UV) radiation which damages or kills cells in living

organisms as well as causing skin cancer and genetic damage (Australian Government - Department of Sustainability, Environment, Water, Population and Communities 2012).

Since 1960, the ozone layer has thinned by 9% over Australia, meaning more UV rays are passing through. CFCs, halons, methyl chloroform (CH3CCl3), carbon tetrachloride (CCl4), HCFCs, nitrous oxides and methyl bromide are all anthropogenic compounds known to cause ozone depletion(Australian Government - Department of Sustainability, Environment, Water, Population and Communities 2012).

Ozone, an unstable molecule, is formed naturally in the atmosphere via what is known as the Chapman reactions.

O2 + UV light O + OA diatomic oxygen molecule comes in to contact with UV radiation from the sun and is then decomposed into two individual oxygen atoms.

O + O2 O3

Figure 3: The ozone layer, or ozonosphere, shown within the stratosphere of the Earth's atmosphere (Comission for Environmental Cooperation n.d.)

An oxygen atom reacts with a diatomic oxygen molecule to form ozone.

O3 + UV light O2 + OOzone is exposed to UV radiation from the sun and, similarlyto diatomic oxygen, decomposes into a diatomic oxygen molecule and a free radical oxygen atom. (University of California Berkeley 2008)

Ozone is constantly formed and broken down in equilibrium naturally in the atmosphere, however the introduction of pollutants can cause a significantly increased rate of breakdown.

NO + O3 NO2 + O2

A nitric oxide molecule reacts with an ozone molecule to form nitrogen dioxide and dioxygen – breaking down the ozonein the process.

NO2 + O NO + O2

Nitrogen dioxide reacts with a monatomic oxygen to form nitric oxide and diatomic oxygen. This cycle of nitric oxiderepeats itself causing catastrophic breakdown of ozone.

NET:2O3 3O2

Through one cycle of nitric oxide reactions, two ozone molecules are broken down to three dioxygen molecules. With the resulting NO molecule from previously explained reactions, increasing amounts of ozone are broken down in repetitive reactions (University of Wisconsin 2008).

4.0 Anthropogenic or Natural

It is near unanimously agreed upon by the scientific communitythat the globe is warming (United States Environmental Protection Agency 2013). What is not universally accepted, however, is whether the extent to which it is happening is as a result of human (anthropogenic) influences or natural causes.

4.1 Argument for Natural CausesSome climate scientists are of the belief that the current warming of the globe is solely due to natural causes and that humans are not influencing the course of nature.(United States Environmental Protection Agency 2013). As seen in figure 4, global CO2 levels have fluctuated greatly over time,

increasing and decreasing,even prior to the industrial

revolution.The CO2 levels

correlate strongly

with the average

temperature, indicating that the current warming is merely apart of a natural cycle.

4.2 Argument for Anthropogenic CausesIt can also be argued that the current climate change is due to human development. CO2 is universally agreed upon to be related to the Earth’s temperatures, and many climate scientists believe that the increasing levels of carbon dioxide in the atmosphere are due to anthropogenic causes (United States Environmental Protection Agency 2013). As

Figure 5 illustrates, the concentrations of CO2, CH4 and N2O have all increased dramatically since the industrial revolution in the late 1700’s.

This indicates significant human impact on levels of greenhouse gases in the atmosphere. As previously discussed, CO2 levels are very strongly correlated with the temperature on Earth – suggesting that humans are indeed to blame for the warming globe.

Furthermore, as a result of human activities, increasing amounts of carbon are stored in carbon ‘sinks’ such as the ocean and to a lesser extent the land. (Netting 2010). Rather than it entering the atmosphere, significant masses of carbon are stored in sinks such as the ocean – containing up to 50 times the amount of carbon in the atmosphere. As the sinks are

Figure 5: The concentrations of greenhouse gases and their exponential increase since theindustrial revolution, showing a very strong correlation between human activity and greenhouse gases

temperature sensitive, the warmer the climate the more carbon released in to the atmosphere by the ocean sink – perpetuatingthe warming by adding to the greenhouse effect.

On balance, it is clear that the warming of the globe and the current climate change is due to anthropogenic causes.

5.0 ThreatsGlobal warming, should it be allowed to continue at a similar rate, would have many wide reaching negative effects on Earth.With temperature increasing rapidly, the Earth may soon becometoo hot for many species – severely disrupting natural food webs and ecosystems worldwide.

Furthermore, increasing temperatures are very likely to cause polar ice caps to melt – resulting in fast-rising sea levels. This would cause significant flooding of coastal areas across the globe.

In addition, the continued depletion of ozone in the stratosphere will have severe negative impacts on the world’s population, including increased risk of skin cancer and other radiation related diseases.

Moreover, smog is a result of climate change. Smog is formed when NO2 reacts with sunlight.

NO2 + sunlight NO + OWhen exposed to sunlight, nitrogen dioxide decomposes in to nitric oxide.

O + O2 O3

The free radical monatomic oxygen reacts with dioxygen formingtropospheric ozone.

O3 + NO NO2 + O2

Nitric oxide and oxygen react to form nitrogen dioxide and oxygen.

The nitrogen dioxide formed in this reaction causes the set ofreactions to repeat upon being exposed to sunlight (Environment Protection Agency South Australia 2004).

Smog, in the form of tropospheric ozone, has numerous negativeeffects on the lungs including aggravated asthma; reduction oflung function and is suspected to be linked to bronchitis(United States Environmental Protection Agency 2012).

5.1 RecommendationIn order to prevent the Earth’s climate from further change, asignificant portion of industry and the population must begin utilising renewable energy sources, such as wind or solar, rather than fossil fuels (which are a major cause of CO2 in the atmosphere). Furthermore, it is feasible to charge companies producing pollution with a price on carbon, as currently seen in Australia. This would encourage said organisations to reduce current carbon pollution, invest in cleaner, more sustainable energy as well as providing incentive for greater research into renewable energy. These actions would contribute significantly to the reduction of carbon in Earth’s atmosphere, preventing global warming from progressing any further due to anthropogenic means.

6.0 ConclusionAlthough the cause isn’t agreed upon universally, on balance it is evident that the globe is indeed warming and that it is primarily due to anthropogenic effects. As the average temperature on Earth rises and the ozone layer decomposes, ecosystems are affected increasingly and human health begins deteriorating. Governments must aim to encourage their citizens and corporations to use renewable energy sources over pollutants such as carbon-based fossil fuels. The longer this issue is ignored, the more pronounced the effects.

7.0 Reference ListAllen, J & NASA Earth Observatory 2004, Ozone and Climate Change, viewed 5 May 2011, <http://theozonehole.com/climate.htm>.

Australian Government - Department of Sustainability, Environment, Water, Population and Communities 2012, Ozone and the ozone layer Australia, viewed 10 May 2013, <http://www.environment.gov.au/atmosphere/ozone/ozone.html>.

Bureau of Meteorology n.d., Greenhouse Effect and Climate Change, viewed 9 May 2013, <http://www.bom.gov.au/info/GreenhouseEffectAndClimateChange.pdf>.

Comission for Environmental Cooperation n.d., The Ozone Layer, Comission for Environmental Cooperation, Montreal, Quebec, Canada, viewed 12 May 2013, <http://www.cec.org/ods/EN/module01/cec_odspolicy_m01t01p01_e.asp>.

EasyChem 2013, CFC and Ozone Equations, viewed 5 May 2013, <http://www.easychem.com.au/monitoring-and-management/the-atmosphere/cfc-and-ozone-equations>.

Environment Protection Agency South Australia 2004, Photochemical smog, viewed 23 May 2013, <http://www.epa.sa.gov.au/xstd_files/Air/Information%20sheet/info_photosmog.pdf>.

Exploring the Environment 2011, Global Climate Change: Human Influences-- The Chemistry, viewed 28 April 2013, <http://www.cotf.edu/ete/modules/climate/gcclimate2e.html>.

Kowoma 2009, Earth's Atmosphere, viewed 25 April 2013, <www.kowoma.de/en/gps/additional/atmosphere.htm>.

NASA - Glenn Research Centre 2010, The Atmosphere, viewed 1 May 2013, <http://www.grc.nasa.gov/WWW/k-12/airplane/atmosphere.html>.

National Geographic 2004, Causes of Global Warming, viewed 8 May 2013, <http://environment.nationalgeographic.com/environment/global-warming/gw-causes/>.

Netting, R 2010, Carbon Cycle, viewed 23 May 2013, <http://science.nasa.gov/earth-science/oceanography/ocean-earth-system/ocean-carbon-cycle/>.

Seager, SL & Slabaugh, MR 2008, Chemistry for Today: General, Organic, and Biochemistry, 7th edn, Brooks/Cole, Cengage Learning, San Francisco, California, United States of America.

United States Environmental Protection Agency 2013, Causes of Climate Change, viewed 11 May 2013, <http://www.epa.gov/climatechange/science/causes.html>.United States Environmental Protection Agency 2013, Climate Change: Basic Information, viewed 11 May 2013, <http://www.epa.gov/climatechange/basics/>.

University of California Berkeley 2008, Chapman Reactions, viewed 22 May 2013, <http://www.cchem.berkeley.edu/molsim/teaching/fall2008/ozone/Ozone%20website_files/Page603.htm>.

University of Tennessee - Knoxville 2000, The Earth's Atmosphere, viewed 2 May 2013, <csep10.phys.utk.edu/astr161/lect/earth/atmosphere.html>.

University of Wisconsin 2008, Chemical of the Week -- Ozone, viewed 12 May 2013, <http://scifun.chem.wisc.edu/chemweek/ozone/ozone.html>.