Global Warming

Table of Contents


Introduction
8.6.1
Models of Global Warming
8.6.2
Enhanced Greenhouse Effect
8.6.3
Increased Combustion of Fossil Fuels as Major Cause of Greenhouse Effect
8.6.4
Links Between Global Warming and Increased Levels of Greenhouse Gases
8.6.5
Mechanisms Increasing the Rate of Global Warming
8.6.6
Coefficient of Volume Expansion
8.6.7
Rise in Sea Level as Effect of Enhanced Greenhouse Effect
8.6.8
Reasons for Predicted Rise in Mean Sea Level

Bibliography

Introduction

Global warming is the recent trend of an increase in the average temperature of the earth's surface, and is expected to continue escalating. The causal grounds are mo stly due to human activity and interference, but are also subjagated to natural environmental occurrences.
The effects of global warming include increased natural disasters such as hurricanes, tycoons, drought, flooding and bush fires. An increase in the Earth's albedo will result in melting ice caps which will consequently raise ocean levels. The increase in global temperature will also affect percipitation disposition, leading to stunted crop growth in agricultural areas, prevalence of diseases, famine and extinction of species of animals and plants.

To understand the basic idea of global warming and the greenhouse effect, click on the link below: (guided animation)
http://earthguide.ucsd.edu/earthguide/diagrams/greenhouse/


8.6.1 - Possible models of Global Warming

The change in the temperature of the Earth’s climate are caused by a variety of external forces, including changes in the composition of greenhouse gases in the atmosphere, increased solar flare activity, cyclical changes in the Earth’s orbit and volcanic activity. Forcing causes an inbalance in the climate, and the inability of the earth to adjust to these forces allows these factors to dramatically change the climate, leading on to drastic consequences. These are a few models of global warming.

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Components that affect climate change. Image taken from www.daviddarling.info


Changes in the composition of greenhouse gases in the atmosphere
Many components have been related to affecting a change in the Earth’s climate, either externally (extraterrestial) or internally (components of the earth). But the force that has probably been given the most credit to the increase of global warming is the changes in the composition of greenhouse gases in the Earth’s atmosphere. The increase in atmospheric greenhouse gases mainly due to human activity has been the likely cause of the warming trend of the earth’s temperature since the industrial age.




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Greenhouse effect image take from www.wikipedia.org/greenhouseeffect



This process begins by atmospheric gases absorbing the emission of infrared radiation from the Sun. The greenhouse layer just above the atmosphere consists of gases (mainly carbon dioxide) and acts as a barrier to keep heat within the Earth’s lower atmosphere. The existence of the greenhouse layer is in fact beneficial, because without it the Earth’s temperature would decrease into levels in which life would be difficult to sustain. The problem of global warming only occurs because of the increase of the intensity of the greenhouse effect due to human pollution.

The sun’s radiation enters the Earth’s atmosphere in the form of lights rays. The light waves are not reflected back because the waves can pass through the greenhouse layer. When the rays enter the atmosphere and hit’s the Earth’s surface, it warms the earth increasing its temperature. Much of the light rays hit surfaces with reflective properties (i.e clouds, water) and are reflected back out. However the light waves are now converted to infrared waves, which cannot freely pass through the greenhouse layer. Consequently, the CO2 and other atmospheric gases trap the heat within the Earth. If the gases comprising of the greenhouse layer become more concentrated, more heat will be trapped in the atmosphere thus global warming occurs. Recent trends has shown an alarming rate of an increase in carbon dioxide in the atmosphere, which would propell the global temperature.

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CO2 levels in the atmosphere in the last 50 years. Image taken from www.wikipedia.org/globalwarming

Solar Flare activity
Scientists believe that the one of the sources of climate change may be the variations in solar acitvity. Solar activity are changes in the amount of
solar radiation emitted by the Sun. Studies have shown that the climate sensitivity toward a change in solar radiation is much greater than was previously expected. It was suggested that almost half of the increase in the average global temperature in the 20th century was held responsible by the sun’s radiation pattern.

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Solar cycle variation in the last 30 years. image taken from http://www.science.org.au/nova/016/016glo.htm

The increase in solar activity warms the stratosphere, the major layer of the Earth’s atmoshpere which supports bacterial life, causing the average global temperature to rise. However recent trends show that the sun’s radiation have not been reaching to high levels. In the last 30 years, solar cycles has only experienced an increase of 0.07 percent in brightness. Crticisms of this theory began to emerge, but some argue that the combination of solar and volcanic activity could produce a warming effect on the earth.

Cyclical changes in the Earth’s orbit
There are three orbital characteristics in which the Earth undergo normal cyclical variations. According to the Milankovitch Theory, these cyclical changes are held responsible for some of the past climate changes. The culmination of all three cycles can cause a deep impact in the warming or cooling of the Earth’s climate.

The first cyclical variation, also known as eccentricity, deals with the shape of the Earth’s orbit around the sun. The Earth orbits around the sun in an elliptical motion, then changes to a nearly perfect circular motion and then back to an elliptical motion. This process is predicted to be about 100,000 years, and the theory suggests that the greater the eccentricity, the greater the solar variation the Earth recieves. When the Earth orbits in an elliptical motion, the eccentricity will be greater because the difference in the distance between the farthest and closest point from the Earth to the sun is higher. Currently though, the Earth is experiencing a low eccentricity, as the Earth’s orbital motion is fairly equidistant to the sun at all points in its path.

The second cyclical variation results from the Earth rotating on its polar axis causing it to wobble. This process is known as the precession of the equinox, which has a cycle of about 26,000 years. As of now, the Earth seems to be close to the sun in January and the farthest in July, but in theory because of precession the reverse effect will take place in 13,000 years. The Earth will be farthest in January instead of July and vice versa. This would induce climate change in both the Northern and Southern hemispheres and the seasonal patterns would be altered.

The third and final cyclical variation depends on the change of tilt (obliquity) of the Earth’s axis. The obliquity of the Earth’s axis may vary between 22.50 to 24.50 approximately over a 41,000 year cycle. Currently, the obliquity is 23.50 but when the tilt is large the climatic changes in the seasons would be more rigorous. It would cause a colder climate in winter and a hotter summer.

Volcanic Activity
Volcanic eruptions can also potentially lead to change in climate. Large-scale eruptions cause a vast amount of different chemicals and particles injected into the stratosphere to kilometers above the Earth’s surface. Water vapor (H2O), carbon dioxide (CO2), hydrogen flouride (HF), sulfur dioxide (SO2) and ash are pumped into the atmosphere. When the sulfur dioxide becomes converted into sulfuric acid, it transforms into sulfate aerosols through rapid condensation in the stratosphere. These aerosols increases the Earth’s albedo by acting as a secondary barrier to the greenhouse layer and shields much of the sun’s rays back out to space. However it also can absorb heat radiated from the Earth’s surface. Each year it is approximated that 145 to 255 million short tons of carbon dioxide enter the stratoshphere from volcanic activity, and these large injections may cause a varaition in the climate, mainly by cooling it.
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Volcanic ash and sulfur dioxide emmitted from Halema’uma’u vent. image taken from www.wikipedia.org/volcanicactivity



8.6.2 - The Enhanced Greenhouse Effect


This occurs when there is a rise in the cycle of the greenhouse effect; an increase in the amount of 'greenhouse gasses' reflecting infrared radiation back to Earth that causes a larger greenhouse effect. Carbon dioxide, methane, and water are the three main greenhouse gasses. These greenhouses absorb infrared radiation reflected back into atmosphere from the Earth's absorption of the Sun's radiation, and reflects the infrared radiation back into Earth; therefore heating it up. This is why the Earth stays at a constant temperature, because the greenhouse effect regulates the amount of heat the Earth receives from the Sun's radiation.

Since the 18th century, emissions of greenhouse gases have enhanced the natural greenhouse effect. Carbon dioxide has had the greatest influence.
external image enhanced_greenhouse_effect.jpg



The Industrial Revolution has caused this increase in the level of carbon dioxide and the other greenhouse gasses. Large amounts of factories that produce these gasses (especially carbon dioxide) were erected and are still expanding since the 1850's. Most of these factories rely on fossil fuels, which produces huge amounts of carbon dioxide when burned, to provide energy to manufacture goods and also electricity to provide power for our daily needs. As civilization develops, the demand for energy could not have been greater. This increase in greenhouse gasses results in more infrared radiation (also known as heat), to be reflected back towards Earth. As more heat radiates back towards Earth, the temperature of the Earth rises.

For more information, go to The Greenhouse Gasses


8.6.3 - The increased combustion of fossil fuels as the likely major cause of the enhanced greenhouse effect?


As we know the biggest cause of global warming is because of the increase in the greenhouse gas CO2. The world’s biggest CO2 emission is from the combustion of fossil fuel used in power plants, cars, and etc. As seen in the graph below:


h1_08.gif



It clearly shows that 85% of the energy users in the world are using fossil fuel as their source of energy such as 23% natural gas, 40% petroleum and coal 23%. Before we know the reason why global warming would almost be impossible to stop and is it getting worse or not we need to know what a fuel is first.

What is fuel?
Any material that can give off energy when it’s chemical or physical properties can be altered and it would only work if it’s combusted. For a material to be combusted it need 3 things and those 3 things are: oxygen, heat and fuel.
From this there’s already a couple of things that causes it increase the CO2 emission just from the process of making a fuel. Firstly when any material is combusted it would release CO2 into the air. Secondly that to create a fuel we need heat and fuel where basically the final product are used to create the same thing and it is wasting energy and emitting more CO2 to create a fuel than to use it for others.

The sources of the greenhouse gas emission or the combustion of fossil fuel or fuel can be seen below:



ghg.png



http://3.bp.blogspot.com/_jK8dknziNRM/SAyampVqpJI/AAAAAAAAADk/AA8JtE4k0j8/s400/ghg.gif


The global warming all around the world (from the Kyoto Protocol) were predicted that it would get worse and worse as the time goes on if people all around the world don’t change the way they are living such as fuel consumption, electrical, water and etc. Because it was predicted that the whole world would be worse and the fossil fuel would be depleted the countries are trying to cut down the fuel consumption. To see if they have succeeded or not we need to see the statistics from the past and comparing it to the present, as we can see below:


Fossil_Fuels_in_2004.gif



http://earthtrends.wri.org/images/Fossil_Fuels_in_2004.gif

V.S.


BPStatReview2007WorldConsumptionEnergy.gif



http://tececo.com/images/graphics/sustainability/BPStatReview2007WorldConsumptionEnergy.gif

To see more consumption for energy and some facts check out this website:
http://www.nationmaster.com/graph/ene_oil_con-energy-oil-consumption
http://www.pbl.nl/en/publications/2008/GlobalCO2emissionsthrough2007.html

Where it shows the increase in fossil fuel consumption all around the world and especially the big countries such as the US and China. The rise in fossil fuel consumption in these 2 countries are because of the transportation used for cars and every other things and also that the country (for china) are developing into a developed country and striving to increase their economy to the top as shown below also:



mn_china.jpg



http://www.sfgate.com/c/pictures/2007/03/05/mn_china.jpg
Because of the need for transportation around the world this is a fact to know about emission of cars:

  • For every liter of gasoline used, 2.4 kg of CO2 are emitted

As because of the increased consumption of Fossil Fuel around the world and the burning of Fossil Fuel releases carbon dioxide and increasing the greenhouse gasses the greenhouse effect would be increased, this is called ‘Enhanced Greenhouse effect’ (look at section 8.6.2).


8.6.4 - Evidence that links global warming to increased levels of greenhouse gases


There is a direct relationship between the global temperature levels and the levels of greenhouse gasses. There are many ways to measure this relationship, as there are many factors that contribute to the rise in global temperatures. But the main cause of this rise in temperature is the increase in carbon dioxide levels in the atmosphere, a greenhouse gas that traps heat from the Sun. Carbon dioxide levels can be measured by investigating carbon dioxide footprint in ice cores. The graph below shows the level of carbon dioxide in the ice core for a century.

external image fig10.gif
Graph showing rise of CO2, from measurements in ice cores (Siple, Antarctica) and measurements from Mauna Loa, Hawaii (Keeling curve) since James Watt, inventor of the steam engine. (Pre-1990 data in: B. Moore & D. Schimel, 1992. Trace Gases and the Biosphere. UCAR, Boulder CO)
From the 1800's to the present, there's a significant increase in the concentration of carbon dioxide, and the 19th century was known for the Industrial Revolution. The Industrial Revolution saw the development of industries as the powerhouse of the economy, and these factories release a huge amount of carbon dioxide into the atmosphere. The graph below shows the significant increase in carbon dioxide emissions.
external image CO2atm.gif
Carbon dioxide levels have increased drastically, especially with the continous increase in the number of factors around the world to provide the energy needed for daily needs and activities. These high carbon dioxide levels are increasing the amount of heat trapped in the Earth's atmosphere, as seen in the rise in global temperatures. The graph below shows the global temperature increasing along with the carbon dioxide levels.

external image fig11.gif
Graph showing that the observed temperature rise can easily result from the observed rise of CO2 , based on simple numerical experiment. (Smoothed temperature data in Jones et al., 1998; CO2 forcing data from CO2 history, and calculated expected rise in temperature assuming 2 degree Celsius rise for CO2 doubling; sunspot abundance from J.Lean, NASA)
The fluctuations of the sun spots on the graph could be a cause for the rise in global temperature, but research has not proven the relationship between them so far. As you can see, the higher the carbon dioxide level, the global temperature increases. The balance of the greenhouse gasses in the atmosphere is disrupted by human development, especially industrial development. The graph below shows a more detailed data of the increase in global temperature.

external image Temp.gif
Global temperatures have risen by about 1 degress Celcius. This may not seem significant, but the effects are apparent as the weather fluctuates more often and natural disaster (except earthquakes) occur more frequently. Below is the graph that shows the rising costs to repair the damage done by natural disasters such as hurricanes, floods, etc.
external image image5RP.JPG

The occurence of natural disaster has dramatically increased, as the global temperatures rise. There's a definite direct relationship between the global temperature and the weather. The enhanced greenhouse effect certainly has humungous effects on the weather and environment. Human development for the last century has drastically changed our planet Earth, as we continue to pump carbon dioxide into the atmosphere through industries to supply our great demand for energy.


8.6.5 - Some mechanisms that may increase the rate of global warming


Enhanced Greenhouse Effect –

The greenhouse effect “is the process by which absorption and emission of infrared radiation by atmospheric gases warm a planet's lower atmosphere and surface” (wikipedia.org). Greenhouse gases in the atmosphere trap heat that would otherwise escape to space, raising the Earth’s temperature. The natural greenhouse effect allows Earth to be warm enough to be inhabitable. However, human activities such as the burning of fossil fuels, industrial operations and forest clearing release carbon dioxide, methane, nitrous oxide and CFC’s (among other gases), increasing the concentration of greenhouse gases, raising the amount of heat trapped in the atmosphere thus increasing the rate of global warming. This process is called enhanced greenhouse effect.


Albedo -
Albedo is the “percentage of solar radiatio
The Albedo Effect. Image taken from www.esr.org/outreach/glossary/albedo.html
The Albedo Effect. Image taken from www.esr.org/outreach/glossary/albedo.html
n reflected back into space” (Teacher’s Domain). Darker objects such as the ocean and land have low albedos and absorb more energy than they reflect while bright objects such as snow, ice and clouds have high albedos and reflect more energy than they absorb. Earth-atmosphere’s combined albedo is 30%, a low albedo (Budikova), and is dependent mainly on surface make-up (the orientation of objects such as land, ice, ocean on the Earth’s surface).
Global warming, the warming of the Earth’s surface temperature (zfacts.com) results in melted snow and ice, decreasing the amount of ‘whiteness’ covering the surface of the Earth, and therefore decreasing the Earth’s albedo. A lower albedo indicates that Earth is absorbing more heat and therefore increasing Earth’s surface temperature. This will then lead to further warming and melting, continuing the positive feedback (when a warming trend results in further warming) cycle that will increase the rate of global warming.
Activities such as burning coal, oil, and wood among others can also lead to an increase in the rate of global warming. When burning these materials, the carbon by-product (soot) is released into the atmosphere and will fall and settle on the Earth’s surface, darkening the Earth’s surface and decreasing the Earth’s albedo.

For an animation regarding the ice-albedo effect, click the link below:
http://www.teachersdomain.org/assets/wgbh/ipy07/ipy07_int_albedo/ipy07_int_albedo.html


The link to a clip from the BBC Documentary, "Can We Save Planet Earth?" further explains the effect of albedo
http://www.youtube.com/watch?v=q3ikWdckxSQ

CO2 concentration -
Due to the enhanced greenhouse effect, the concentration of carbon dioxide has increased rapidly. The ocean acts as an enormous carbon sink, “[absorbing]…one-third of all human-generated CO2 emissions (wikipedia.org). Gas solubility is the measure of how much gas will dissolve in the solvent (Martin). As water temperature increases, gas solubility decreases. Thus global warming, which increases the Earth’s surface temperature including water temperature, reduces the amount of CO2 the oceans can dissolve and therefore releases CO2 from the ocean into the atmosphere, increasing the concentration of greenhouse gases. The positive feedback cycle will then repeat itself gradually increasing the rate of global warming.

The Carbon Cycle - oceans absorb carbon dioxide
The Carbon Cycle - oceans absorb carbon dioxide

Water Vapor –
Water vapor is the gas phase of water and is produced from evaporation or boiling of water. It also “accounts for the largest percentage of the greenhouse effect” (wikipedia, the free encyclopedia). When the earth’s temperature increases due to global warming, the air becomes warmer. As warm air can hold more water vapor than cold air, the concentration of greenhouse gases, including water vapor, increases and thus positive feedback occurs a
nd the rate of global warming increases.


Carbon Fixation –

I_LOVE_MR_LAMB.jpg
Example of deforestation, increasing carbon dioxide concentration in the atmosphere. Image taken from www.martinfrost.ws/.../deforestation.html
Plants need carbon dioxide in order to produce carbohydrates and sugars to grow.
Trees and plants reduce the amount of carbon dioxide in the atmosphere during the process of photosynthesis because this is required for carbon fixation. Due to deforestation, the number of trees and plants will reduce; hence the process of carbon fixation will decline as well. As carbon fixation decreases, the number of carbon dioxide absorbed will fall as well, causing more carbon dioxide to remain in the atmosphere. Since carbon dioxide is a green house gas, this will increase the rate of global warming.
Additionally, when a tree or plant decays or burns down, the stored carbon will be released to the atmosphere. The process of deforestation will also allow carbons stored in the soil to expose to the atmosphere.


The link to the clip from BBC's "Are We Changing Planet Earth?" further explains the carbon cycle:

http://www.youtube.com/watch?v=gSx30bhnxBY


8.6.6 Coefficient of volume expansion

The coefficient of volume expansion is the fractional change in volume per degree change in temperature


8.6.7 State that one possible effect of the enhanced greenhouse effect is a rise in mean sea-level


One possible effect of the enhanced greenhouse effect is a rise in mean sea-level.

8.6.8 Outline possible reasons for a predicted rise in mean sea-level

Sea water level changes due to atmospheric pressure, plate tectonic movements, wind, tides, flow of larger rivers into sea, changes in water salinity, etc. the change in sea level is natural and occurs normally. However, a new cause to the change in sea level has developed, which is the enhanced greenhouse effect. This cause has made the sea level to change in an unnatural rate, which might harm earth.
Enhanced greenhouse will cause mean-sea level to rise in two different ways. Firstly, it will cause more ice on the earth’s surface to melt into water, thus increasing the sea-level. Secondly the warmer water will expand, causing it to require more volume.

However, making precise predictions are difficult due to factors such as:

1. The anomalous expansion of water
water_expansion_graph.jpg
the relationship between the temperature and volume of water

The expansion of water follows the graph on the left. Normally, when a substance is heated up, its volume will expand. This theory applies for water only after the temperature of 4 degrees C. However, from 0 degrees C to 4 degrees C, then volume will contract.
Thus, sea level will only rise when water is being heated at temperature of 4 degrees C and above. However. If water is heated from between 0 degrees C to 4 degrees C, the sea level will decrease.
This makes predictions difficult because it will be complex to know which areas of the earth is above or below 4 degrees C.







2. Different effects of ice melting on sea water compared to ice melting on land

We need to distinguish between land ice and sea ice. Land ice is ice supported on land while sea ice is ice floating on sea water. When sea ice is melted, it will not result in a change in sea level. This is because the weight of the ice is equal to the displaced water, so when ice melts; it will fill up an equal volume of the weight of the displaced water. Conversely, when land ice melts, it will increase the mean sea level.
This makes predictions for the rise in sea-level difficult because it is hard to determine whether the melted ice is a land ice or a sea ice.
Below is a link to a video explaining land and sea ice:
http://www.teachersdomain.org/resource/ess05.sci.ess.watcyc.sealevel/


8.6.9
Climate Change- An Outcome of the Enhanced Greenhouse Effect

  • Climate change refers to any change in the state of the climate that can be identified by changes in the average and/or the variability of its properties (e.g., temperature, precipitation), and that persists for an extended period, typically decades or longer.

  • One of the external changes of factors of climate change may involve a variation in the sun's output which would externally vary the amount of solar radiation received by the Earth's atmosphere and surface.
  • Many chemical compounds found in the Earth’s atmosphere act as “greenhouse gases” like carbon dioxide, water vapor and methane. These gases allow sunlight to enter the atmosphere freely.

  • When sunlight strikes the Earth’s surface, some of it is re-radiated back towards space as infrared radiation (heat). Greenhouse gases are able to alter the energy balance of the Earth by being able to absorb longwave radiation emitted from the Earth's surface and trap the heat in the atmosphere.

  • The net result of this process and the re-emission of longwave back to the Earth's surface increases the quantity of heat energy in the Earth's climatic system.

  • Moreover, in computer-based models, rising concentrations of greenhouse gases produce an increase in the average surface temperature of the Earth over time. Initial changes in global temperature were triggered by changes in received solar radiation by the Earth. The increase in greenhouse gases then amplified the global warming by enhancing the greenhouse effect.

  • Where global warming is the combined result of anthropogenic (human-caused) emissions of greenhouse gases and changes in solar irradiance.

  • Thus, rising temperatures may, in turn, produce changes in precipitation patterns, storm severity, and sea level commonly referred to as “climate change.”

  • The IPCC’s Fourth Assessment Report (Summary for Policymakers) states, “Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.” It goes on to state, “The observed widespread warming of the atmosphere and ocean, together with ice mass loss, support the conclusion that it is extremely unlikely that global climate change of the past 50 years can be explained without external forcing, and very likely that it is not due to known natural causes alone.”




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