GLOBAL WARMING DVD ACTIVITY SHEET
NAME: ______CLASS: ______DATE: ______
1 What were some new facts you learned about global warming from the DVD? Place your answers in the table.
What is global warming?What is causing global warming?
What is some evidence that global warming is occurring?
How are scientists investigating this problem?
What might be some possible consequences of global warming in the future?
2 What questions do you still have about global warming?
3 What is your opinion of the DVD? Did any of its contents surprise you? Do you think it would convince climate-change-sceptics to investigate the issue further and perhaps change their mind?
4 Design a concept map to show how various aspects of global warming are related to each other. Incorporate the following key words into your concept map. Can you think of any other key words? Add them into your concept map as well.
Global warming Energy from the Sun
Methane Ice cores
Greenhouse gases Thermal expansion
The greenhouse effect Temperature
The enhanced greenhouse effect The atmosphere
Extreme weather events Refugees
Rising ocean levels Flooding
Carbon dioxide Balance
9
GLOBAL WARMING ACTIVITY SHEET
NAME: ______CLASS: ______DATE: ______
Introduction
Global warming is the term we use for the gradual increase in the average temperature at the Earth’s surface that has occurred over the past century or so. Why is this happening? First, we need to understand some of the natural processes that have occurred on Earth for millions of years.
Many people mistakenly think that the greenhouse effect is a really bad thing. They say that it may cause our ocean levels to rise, which in turn will cause flooding of low-lying coastal areas, and all kinds of other problems. Certainly, if the ocean levels rise coastal flooding will occur, but the natural greenhouse effect is not the culprit! In fact, we would not exist if it wasn’t for the natural greenhouse effect. So what is it? And why does life depend on it?
The energy from the Sun
To understand the natural greenhouse effect, we first must understand what happens to all the energy from the Sun that reaches our planet. This is shown in Figure 1.
Source: http://www.junkscience.com/Greenhouse/Radiation_Budget.gif,
Accessed: 18 November 2009
Figure 1 What happens to the energy from the Sun?
The Sun’s energy travels through space in the form of electromagnetic radiation. This radiation is composed of ultraviolet (UV) light, infrared (IR) light, X-rays, radio waves, microwaves and visible light. The radiation is in the form of little packets of energy known as photons, which stream out from the Sun.
When this radiation reaches the Earth, not all of it is absorbed by the Earth’s surface. About 30% of the radiation that reaches us is reflected back into space by the particles in the atmosphere and clouds and by the Earth’s surface. Of the remaining energy from the Sun, some is absorbed by the water vapour in the atmosphere and by clouds. Some (about 3%) is absorbed by the ozone layer. (This layer is not shown in this diagram and will be discussed later.)
The energy absorbed by the Earth
The rest of the Sun’s energy is absorbed by the Earth’s surface (land and oceans). If it kept being absorbed and none was ever given back out, the Earth would get hotter and hotter. The oceans would have boiled away long ago, and all our water would have evaporated!
Fortunately for us, this does not happen, because the Earth radiates heat energy in the form of infrared radiation back into the atmosphere. And ultimately the atmosphere radiates heat energy back into space. What happens in the atmosphere is of crucial importance to life on Earth.
Greenhouse gases
The Earth’s atmosphere consists of particles that are so tiny they cannot be seen. The closer they are to the Earth’s surface, the more densely packed they are. The atmosphere largely consists of molecules of oxygen and nitrogen. Water molecules also are present, although the proportion of water vapour in the air keeps changing and depends on many factors. Present in much smaller amounts are other molecules, such as carbon dioxide molecules, which play an important role.
Carbon dioxide molecules and water molecules (shown in Figure 2) can do something that oxygen and nitrogen molecules cannot do – they can absorb infrared radiation and also radiate it out. So when the infrared radiation from the Earth reaches them, they absorb some and radiate out the rest – some of it back to the Earth. This means they ‘trap’ some of the heat energy radiated out from the Earth’s surface, thereby acting like the glass roof and walls of a greenhouse. For this reason they are termed greenhouse gases.
Figure 2 Models of molecules of carbon dioxide and water – two important greenhouse gases
A number of other gases in the atmosphere also act as greenhouse gases, although the percentage of them in the lower atmosphere is much less than that of water and carbon dioxide. These gases include methane (CH4), nitrous oxide (N2O), nitrogen trifluoride (NF3) and ozone (O3). (The ozone in the ozone layer is too high above the Earth to act in this way.)
The greenhouse effect
The greenhouse effect is the process whereby some of the infrared radiation from the Earth’s surface is trapped by greenhouse gases, which helps moderate the temperatures at the Earth’s surface. (Figure 3.)
The natural greenhouse effect has enabled life to evolve on this planet. Without it, the temperatures experienced on Earth would be like those on the Moon, which is the same distance from the Sun as we are – far too hot by day and far too cold by night for us to survive. The average ground temperature on the Moon is –17ºC. On Earth it is 16ºC. The difference arises because the Moon has no atmosphere and hence no greenhouse gases to help moderate the temperatures at its surface.
Source: maps.grida.no/go/graphic/greenhouse-effect
Accessed: 18 November 2009
Figure 3 A schematic diagram of the greenhouse effect
Global warming
Over the millions of years in which the greenhouse gases have been present in the Earth’s atmosphere, natural cycles have ensured that the proportion of these gases in the atmosphere has remained steady. There are natural processes by which they are produced and other natural processes by which they are used up. These processes balance each other out.
But now the level of human activity we have today has altered this balance. Our large-scale burning of coal, natural gas and oil, our mass production of materials such as steel, cement and aluminium, and our huge piles of rotting garbage, not to mention burning trees to clear land or cutting them down to make goods (including paper), are producing more greenhouse gases than can be used up in natural processes.
Even growing more and more rice and increasing the number of sheep and cattle to feed our increasing populations contribute to the problem. Rotting garbage, rice paddies and animals that eat grass (known as ruminant animals) produce huge amounts of methane gas, which is a far more potent greenhouse gas than carbon dioxide. (The animals burp the gas out, on average, more than 300litres each per day.)
In addition, new very potent greenhouse gases such as nitrogen trifluoride are being produced as new technologies are developed.
The enhanced greenhouse effect is the trapping of additional infrared radiation by the excessive amounts of greenhouse gases in the atmosphere that have been produced as a result of human activity. It is this process that many scientists are concerned about.
Scientific modelling by atmospheric scientists and meteorologists, using data they have collected from ice core studies and measurements of atmospheric temperatures and gas concentrations in the atmosphere, indicates that this is causing a gradual increase in the average temperature at many locations around the Earth’s surface. This phenomenon is commonly known as global warming, or climate change.
What might be the consequences of global warming?
Source: www.rushprnews.com/press/wp-content/2008/08/polar_ice_caps_melting1.jpg
Accessed: 18 November 2009
Figure 4 The polar ice caps are already melting at an increased rate
Based on their models, many scientists believe that unless we dramatically reduce our production of greenhouse gases, and reduce our destruction of forests, which help use up carbon dioxide, the temperature of the Earth’s surface could increase by as much as 2ºC by 2030.
If this is true, then one consequence would be the warming of our oceans. Some of the possible consequences of this would be as follows.
▪ Rising sea levels, mostly from expansion of the upper layers of the sea water, would result in the flooding of low-lying coastal areas. A large number of people would lose their homes and livelihoods.
▪ There would be damage to marine ecosystems due to the loss of species that cannot survive in the warmer water.
▪ Much of the polar ice caps would melt, resulting in the loss of specie and contributing to rising sea levels.
▪ There would be significant changes to climate around the world, including an increase in the frequency and severity of cyclones, typhoons and other extreme weather events. This may also lead to a wider spread of tropical diseases such as malaria.
The enhanced greenhouse effect is not the only factor contributing to global warming. The vast amount of heat radiated out by our big cities and big industrial complexes also contributes to the problem.
The ozone layer
Many people mistakenly think the ‘holes’ in the ozone layer are the cause of global warming. This is not so. They are entirely separate problems.
The ozone layer is a layer within the stratosphere, about 16 km above the Earth’s surface, in which ozone is present.
Ozone is a form of oxygen. ‘Normal’ oxygen exists naturally as molecules that contain two oxygen atoms. This has the chemical formula O2. Ozone molecules contain an additional oxygen atom and so have the chemical formula O3.
Both gases are present in the ozone layer. But they are constantly reacting. The ozone molecules keep reacting with one another, forming ‘normal’ oxygen molecules, and ‘normal’ oxygen molecules keep reacting with each other, forming ozone molecules. This is depicted in Figure 5.
Figure 5 In the ozone layer, ozone molecules are constantly broken down to normal oxygen and reformed
The balanced equations for these chemical reactions are:
2O3(g) → 3O2(g)
3O2(g) → 2O3(g)
Each of these reactions uses some of the energy the Earth receives from the Sun. Fortunately this is high-energy ultraviolet (UV) radiation. Thus the ozone layer absorbs a significant proportion of the UV radiation the Earth receives from the Sun, which means we are exposed to much less UV radiation. While our skin needs some exposure to UV radiation, in order to manufacture Vitamin D, too much exposure can cause problems such as skin cancers and cataracts. (A cataract is the clouding of the lens of the eye, as shown in Figure 6.) Most animals as well as humans are at risk.
Source: http://www.sightsurgeryinternational.com/uploads/cataract_complete_cataract.jpg
Accessed: 18 November, 2009
Figure 6 Untreated cataracts lead to blindness
Note: Ozone also is produced in other processes that occur at the Earth’s surface, such as the action of sunlight on the exhaust gases emitted by motor vehicles. The energy from the Sun enables the molecules to react and form other substances, including ozone. The ozone close to the ground is classified as a pollutant. When breathed in, it can cause many health problems.
The ‘holes’ in the ozone layer
Normally the reactions in which ozone is broken down and reformed, shown on page 6, are in balance. Sometimes this balance is disturbed, however. As a result, in some parts of the ozone layer, especially in the region over the South Pole, the concentration of ozone (amount of ozone present in each litre of the air) has decreased. It has not disappeared altogether! Those areas in which the concentration of ozone has decreased are called ‘holes’. The result of this reduction of ozone concentration is that more UV radiation reaches the parts of Earth’s surface located under the ‘holes’. This means the incidence of skin cancer and cataracts will increase in those regions, so the holes are of concern.
What causes the ‘holes’?
The loss of ozone is caused by chemical processes by which ozone molecules are broken down into normal oxygen.
This is not only caused by chemicals produced through human activity. However, a family of chemicals called chlorofluorocarbons (commonly known as CFCs) have been a major cause. These chemicals were once widely used as propellants for aerosol sprays and as refrigerant gases because they are chemically stable. The problem with these is that each CFC molecule can last for more than100 years in the ozone layer and during that time ‘destroy’ billions of ozone molecules!
Once scientists realised this, many countries agreed to ban the use of CFCs. Their action has already made a significant difference to the extent and frequency of ozone hole formation. This is an excellent example of collaborative international action to reduce a global problem caused by human activity.
Questions
1 Which of the following gases are greenhouse gases?
A Oxygen