Introduction
In the previous section we identified a need to develop alternative energy sources because the dwindling fossil fuel reserves may soon result in problems matching supply with demand. In this section we look at the environmental effects and global consequences of fossil fuel consumption and present this as another argument for moving towards sustainable power generation.
The Greenhouse Effect
The conventional greenhouse effect (Fig. 1) occurs because glass transmits visible light readily but is a relatively poor conductor of heat. On a sunny day, light enters the glasshouse and is absorbed by the floor. The floor warms up and re-radiates the energy as heat (infrared radiation). The heat radiation cannot easily escape through the glass, consequently the glasshouse heats up.
Something similar (but not identical) happens on the Earth where the atmosphere acts as a blanket over the surface. The sun radiates an energy spectrum or energy range with the peak output at the electromagnetic frequency corresponding to green light. Visible light passes largely unimpeded through the atmosphere and reaches the surface where the energy is absorbed by the soil, water, buildings, plants etc. As a consequence, the surface heats up after which energy is re-emitted upwards as longer wavelength infrared radiation (just as in the glasshouse).
However, certain gases in the atmosphere though transparent to light can absorb heat very effectively, notably water vapour, carbon dioxide, methane and ozone. The heat leaving the surface that would otherwise escape into space is absorbed by these molecules.
But a molecule will only retain absorbed energy for a short time (because of spontaneous emission), after which the captured energy is released. The important point is that the energy is re-radiated in every direction, including downwards—it does not just continue its journey upwards through the atmosphere. It will eventually escape into space but only after millions of absorptions and re-emission events. The energy radiated from the surface is therefore held up and warms the atmosphere.
For example - ”This is like trying to move through a crowd of people going in all directions. You are eventually going to get through (probably after many ‘collisions’) but you will be held up for some time”.
Figure 2: The atmospheric greenhouse effect [source (CC3.0)]
As a consequence of this effect, the Earth is warmer than it would be were there no water or carbon dioxide in the atmosphere. This is the atmospheric greenhouse effect (Fig. 2) and the temperature elevation is strongly dependent on the concentration of water and carbon dioxide in the atmosphere. The average temperature on the surface of the Earth is about 14oC: Without the greenhouse effect, the temperature on the surface would be –18oC or ‘snowball Earth’. With too much greenhouse gas, we could have a situation similar to that on our sister planet Venus (Fig. 3) where the surface temperature is above 450oC because of its runaway greenhouse effect. This is a vision of ‘fireball Earth’.
Figure 3: Venus — runaway greenhouse effect.
All the oceans have boiled away, the clouds rain sulphuric acid and the atmosphere at ground level is hot enough to melt lead.
Activity 1
- When a greenhouse floor absorbs light, why is the energy re-radiated, and why as heat rather than as visible light?
- Do clouds contribute to the greenhouse effect?
- Figure 2 illustrates the principle of the atmospheric greenhouse effect but we would like to associate specific energy flows to each effect. Are the numbers consistent? Describe the energy flows quantitatively. This is shown on page 96, Fig. 1 of [https://www.ipcc.ch/report/ar4/wg1/] (you can Download Report from here also).
Solution
a.
In classical terms as a model of Rayleigh and Jeans, when electromagnetic radiation is absorbed, a molecule in the absorber moves or vibrates faster. The moving molecule will then collide with another, perhaps transferring some of the acquired energy.
Through multiple collisions and interactions the energy becomes distributed within according to a relationship called the blackbody spectrum whose form is primarily a function of the average temperature of the body. We can determine this internal distribution of energies by observing the electromagnetic waves that escape from the body.
The Earth is much cooler than the sun and we see from the diagram on the right the sun will radiate with a peak energy in the middle of the visible spectrum; however the Earth will mostly radiate at a much lower energy in the infrared region of the spectrum.
We can see this temperature dependence in our day-to-day experience by putting a piece of metal in the fire.
Figure 4 [source (CC0)]
As the metal heats up, the colour goes from dull to red to yellow to white as the blackbody temperature moves steadily up the spectrum in the direction of increasing energy and decreasing wavelength. (Note: To change a temperature from Celsius (C) to Kelvin (K), add 273; 1 μm is 1 millionth of 1 metre)
b.
Clouds have a high water vapour content. Water vapour is a greenhouse gas, and will contribute to the greenhouse effect. This is apparent from our day-to-day experience: At night, more energy is leaving the Earth than is being received, hence the Earth will lose the heat gained during the day and cool by radiating energy. On clear cloudless nights, the Earth can cool so much that frost will form on the ground. However on overcast nights, the energy escaping upwards is trapped by the clouds. This heats the air up and prevents the Earth cooling as rapidly. Cloudy nights are therefore not as cold as clear nights. Clouds are not accounted for separately but are lumped into an average atmospheric water vapour composition.
c.
The diagram of energy fluxes is reproduced below. In units of Watts per square metre, 342, on average, reaches the outer atmosphere of the Earth. Of this 107 is immediately reflected off the surface (particularly snow and ice) and the atmosphere. Of the remaining 235, 168 is absorbed by the surface and 67 by the atmosphere. The surface radiates 390, of which 40 escapes directly to space. The atmosphere and clouds gain 350 from the surface, 67 initially absorbed from the sun is radiated back to the surface along with 24 carried upwards by rising air and 78 carried upwards by evaporating water returning, a total of 519. Of this 195 is radiated into space and 324 is radiated back to the surface. All the numbers therefore tally, but this is merely an aggregation of what are a number of very complex processes, but it does illustrate equilibrium and conservation of energy.
Figure 5 from [source (public domain)]
Carbon Dioxide
Carbon dioxide (CO2) is a molecule formed when two oxygen atoms bond to one carbon atom. It is produced by heating carbon or its compounds to a high temperature in the presence of oxygen. The reaction releases energy and the CO2 gas normally escapes into the atmosphere .
Plants extract CO2 from the air and combine it with water to form organic compounds. Energy is required to fix CO2 and this is supplied by sunlight in the photosynthesis process. If the plant material is consumed (by animals or bacteria for example) the CO2 is released back into the air as a by-product of respiration. Dead plant material may instead sink into the soil and eventually (through pressure and over time) form rock such as coal. Burning these fossil fuels releases the CO2 back into the atmosphere. The constant recycling of carbon through the biosphere is referred to as the carbon cycle (Fig. 6).
Natural processes maintain the level of CO2 in the atmosphere at about 280 parts per million (ppm). You should appreciate there is very little CO2 in the air; there are about 600 oxygen molecules for every single carbon dioxide molecule.
Figure 6: The carbon cycle. From [source (Public domain)]
Since the Industrial Revolution began in the 1700s, people have added a substantial amount of greenhouse gases into the atmosphere by burning fossil fuels, cutting down forests, and conducting other activities. When greenhouse gases are emitted into the atmosphere, many remain there for long time periods ranging from a decade to many millennia. Over time, these gases are removed from the atmosphere by chemical reactions or by emissions sinks, such as the oceans and vegetation, which absorb greenhouse gases from the atmosphere. As a result of human activities, however, these gases are entering the atmosphere more quickly than they are being removed, and thus their concentrations are increasing. The present concentration of CO2 has now passed above 400 ppm.
Figure 7: The historic concentration of greenhouse gases. [source (public domain)]
Figure 7 shows concentrations of carbon dioxide in the atmosphere from hundreds of thousands of years ago through 2019, measured in parts per million (ppm). The data comes from a variety of historical ice core studies and recent air monitoring sites around the world. Each line represents a different data source.
For carbon dioxide, methane, nitrous oxide, and halogenated gases, recent measurements come from monitoring stations around the world, while measurements of older air come from air bubbles trapped in layers of ice from Antarctica and Greenland. By determining the age of the ice layers and the concentrations of gases trapped inside, scientists can learn what the atmosphere was like thousands of years ago.
This indicator also shows data from satellite instruments that measure ozone density in the troposphere, the stratosphere, and the “total column,” or all layers of the atmosphere. These satellite data are routinely compared with ground-based instruments to confirm their accuracy. Ozone data have been averaged worldwide for each year to smooth out the regional and seasonal variations.
If we were to globally stop burning fossil fuels and allow forests and vegetation to regenerate, natural processes will bring the concentration back to the equilibrium pre-industrial levels of 280 ppm. However one should be aware there may exist a ‘tipping point’ beyond which recovery is impossible.
An analogy is stretching a rubber band—when the force is removed, the band will return to its original length. But if too great a force is applied the band will break. This is the transition from a reversible to an irreversible process.
Activity 2
- What does 400 ppm really mean as a quantity?
- What is the mass of Carbon Dioxide (CO2) in the atmosphere? Use the following information; CO2 Concentration is 400ppm.
Solution
a.
400 parts per million is less than one part in one thousand:
Parts per million (ppm) is the number of units of mass of a contaminant per million units of total mass. This is a way of expressing very dilute concentrations of substances. Just as per cent means out of a hundred, so parts per million or ppm means out of a million.
b.
To find the mass of CO2 in the atmosphere in kg, multiply the concentration (in ppm) by .
The mass of CO2 in the atmosphere is;
Climate Change: Global Temperature
We have seen that burning fossil fuel (and to an extent deforestation) has increased atmospheric CO2 concentration. Because CO2 is a greenhouse gas, the rising concentration will enhance the greenhouse effect and cause a global temperature increase. The effect is magnified because there will be more water vapour in the atmosphere of a warmer Earth from increased evaporation, and water vapour is itself a greenhouse gas and can cause further warming. Burning fossil fuel therefore has the potential to change the environment. To understand the global consequences of fossil fuel consumption there are two critical questions to answer: What is the exact relationship between CO2 concentration and temperature; what is the effect of an overall temperature rise on climate?
Given the size and tremendous heat capacity of the global oceans, it takes a massive amount of heat energy to raise Earth’s average yearly surface temperature even a small amount. Figure 6 illustrates that the Earth's temperature had already warmed by 1°C compared to industrial levels and 2°C since the pre-industrial era (1880-1900). This temperature rise may appear small, but small rises in temperature translate into big changes for the world’s climate. This is because the amount of extra energy needed to increase the world’s temperature, even by a little, is vast. This extra energy is like force-feeding the global climate system. That extra heat is driving regional and seasonal temperature extremes, reducing snow cover and sea ice, intensifying heavy rainfall, and changing habitat ranges for plants and animals—expanding some and shrinking others.
Figure 8: History of global temperatures since 1880. The zero line represents the long-term average temperature for the whole planet; blue and red bars show the difference above or below average for each year. [Image: https://www.ncdc.noaa.gov/sotc/global/202013 (public domain)
Figure 9 shows the trend of how temperature has changed over time. Though warming has not been uniform across the planet, the upward trend in the globally averaged temperature shows that more areas are warming than cooling. According to NOAA's 2020 Annual Climate Report the combined land and ocean temperature has increased at an average rate of 0.08°C (0.13°F ) per decade since 1880; however, the average rate of increase since 1981 (0.18°C / 0.32°F) has been more than twice that rate.
Figure 9: Changes in global average surface temperature from 1990-2019. Places that warmed by up to 1° Fahrenheit over the past 30 years are red, places that have cooled by up to 1° F are blue, and places with inadequate observations to calculate a trend are light grey.(Image: NOAA Climate.gov map based on NCEI data)(public domain)
NOAA’s 2020 Annual Climate Report can be viewed at (https://www.ncdc.noaa.gov/sotc/global/202013) for further information.
Figure 10 shows a table consisting the ranks and records recorded for temperature over land, ocean, and land and ocean combined. The year 2020 was characterized by warmer-than-average temperatures across much of the globe. Record high annual temperatures over land and ocean surfaces were measured across parts of Europe, Asia, southern North America, South America, and across parts of the Atlantic, Indian, and Pacific oceans. However, no land or ocean areas were record cold for the year.
Figure 10: Global rankings of temperature between 1901 and 2020.
[Table: https://www.ncdc.noaa.gov/sotc/global/202013] (public domain)
Activity 3
- Make a list and provide an explanation of how climate change is affecting the world?
Solution
a.
- Melting ice and rising seas
- When water warms up it expands. At the same time global warming causes polar ice sheets and glaciers to melt.
- The combination of these changes is causing sea levels to rise, resulting in flooding and erosion of coastal and low lying areas.
- Extreme weather, shifting rainfall
- Heavy rain and other extreme weather events are becoming more frequent. This can lead to floods and decreasing water quality, but also decreasing availability of water resources in some regions.
- Consequences for Europe
- Southern and central Europe are seeing more frequent heat waves, forest fires and droughts.
- The Mediterranean area is becoming drier, making it even more vulnerable to drought and wildfires.
- Northern Europe is getting significantly wetter, and winter floods could become common.Urban areas, where 4 out of 5 Europeans now live, are exposed to heat waves, flooding or rising sea levels, but are often ill-equipped for adapting to climate change.
- Consequences for developing countries
- Many poor developing countries are among the most affected. People living there often depend heavily on their natural environment and they have the least resources to cope with the changing climate.
- Risks for human health
- There has been an increase in the number of heat-related deaths in some regions and a decrease in cold-related deaths in others.
- Noticing changes in the distribution of some water-borne illnesses and disease vectors.
- Costs for society and economy
- Damage to property and infrastructure and to human health imposes heavy costs on society and the economy.
- Sectors that rely strongly on certain temperatures and precipitation levels such as agriculture, forestry, energy and tourism are particularly affected.
- Risks for wildlife
- Climate change is happening so fast that many plants and animal species are struggling to cope.
- Many terrestrial, freshwater and marine species have already moved to new locations. Some plant and animal species will be at increased risk of extinction if global average temperatures continue to rise unchecked.
Mitigation and Adaptation
Climate change is one of the most complex issues facing us today. It involves many dimensions – science, economics, society, politics and moral and ethical questions – and is a global problem, felt on local scales, that will be around for decades and centuries to come. Carbon dioxide, the heat-trapping greenhouse gas that has driven recent global warming, lingers in the atmosphere for hundreds of years, and the planet (especially the oceans) takes a while to respond to warming. So even if we stopped emitting all greenhouse gases today, global warming and climate change will continue to affect future generations. In this way, humanity is “committed” to some level of climate change.
Mitigation and adaptation are two different strategies for addressing climate change; Figure 11 illustrates a simple yet effective flow diagram.
Mitigation – reducing climate change
Involves reducing the flow of heat-trapping greenhouse gases into the atmosphere, either by reducing sources of these gases (for example, the burning of fossil fuels for electricity, heat or transport) or enhancing the “sinks” that accumulate and store these gases (such as the oceans, forests and soil).
Mitigation refers to “actions taken to reduce the severity”.
“Mitigation is about avoiding the unmanageable”
In the context of climate change, mitigation is an intervention to reduce the magnitude of climate change by lowering the concentration of heat-trapping greenhouse gasses in the atmosphere.
Mitigation measures can be divided into two categories:
- Steps taken reduce or eliminate emissions at the source, such as switching to renewable energy sources and improving the energy efficiency of buildings and transport.
- Steps taken to sequester greenhouse gases out of the atmosphere, either by enhancing the “sinks” of greenhouse gases through carbon capture processes and storage facilities at factories and power plants, or planting more trees to absorb carbon.
Figure 11: Climate change adaptation vs mitigation. Drawn by Owen Inger-Gray of Lews Castle College
The goal of mitigation is to avoid significant human interference with the climate system, and “stabilize greenhouse gas levels in a time frame sufficient to allow ecosystems to adapt naturally to climate change, ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner”; from the 2014 report on Mitigation of Climate Change from the United Nations Intergovernmental Panel on Climate Change. [http://www.ipcc.ch/pdf/assessment-report/ar5/wg3/ipcc_wg3_ar5_summary-for-policymakers.pdf]
Adaptation – adapting to life in a changing climate
Involves adjusting to actual or expected future climate.
Adaptation refers to a “responsive adjustment to an environmental condition”.
“Adaptation is about managing the unavoidable”
In the context of climate change, adaptation is an adjustment in natural or human systems in response to actual or expected climatic stimuli or their effects, which moderates harm or exploits beneficial opportunities.
Adaptation measures can be divided into two categories:
- Steps taken in reaction to real-life scenarios, such a response to a disaster, such as increased cyclone frequency in coastal areas.
- Steps taken based on assumptions or simulations, such as building taller dykes in anticipation that sea level will rise in the near future.
The goal is to reduce our vulnerability to the harmful effects of climate change (like sea-level encroachment, more intense extreme weather events or food insecurity). It also encompasses making the most of any potential beneficial opportunities associated with climate change (for example, longer growing seasons or increased yields in some regions).
Activity 4
- Make a list of what actions could be taken to reduce energy use on a personal level. These may have an adverse impact on your standard of living and or quality of life.
Solution
a.
There are many actions that could be taken to reduce energy use on a personal level, but many of these will impact on our standard of living, though quality of life may be improved. Standard of living is a measure of the access to commodities and services, and to an extent, the choices available to the individual. Fewer people now live in the average home, and though newer homes are more heat efficient, the cost of space heating and cooling, cooking, illumination, water heating and appliances will be greater overall as a result of less people in each home. The desire for a greater amount of personal space is therefore environmentally costly. Another need that is often satisfied with increasing wealth is the freedom to travel, either over great distances through air travel or just by owning a car. This has a huge environmental impact because a car is drastically inefficient as far as moving the payload is concerned.
It might be argued that working from home is better because travel miles are reduced, but it may be that the additional effect of heating many homes rather than one central location may result in more energy use. In general, when making changes, the indirect impact of these changes must also be considered. There is a general acceptance that modern lifestyle consumes more energy, and to return to some aspects of the lifestyle of the past would improve both quality of life and reduce energy use.
A list of some examples;
⇒ Power home with renewable energy; solar, air source heat pump, wind turbine, etc.
⇒ Get a home energy audit; this will help indicate how much energy your home consumes
⇒ Weatherise; reduce use of heating and air-conditioning
⇒ Invest in energy-efficient appliances; reduce energy consumption
⇒ Reduce water waste; reduction in pumping, heating, and treating supply
⇒ Reduce food waste; less production costs, recycling
⇒ Use public transport instead of personal vehicle
⇒ Purchase recyclable materials where possible; reduce costs and energy for machinery
⇒ Reduce electricity usage; use natural light, switch off electronic devices
⇒ Downsize the liveable area; less area to heat etc.
⇒ Hang-dry washing rather that using the dryer
If you have enjoyed this topic and wish to read further, more notes can be found by following the link below. You will require Microsoft Publisher to open the file: