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Topic 6: Global Warming The greenhouse effect and global warming In this topic we will consider: The natural greenhouse effect and greenhouse gases The recent increase in greenhouse gases and the enhanced greenhouse effect. Potential effects of global warming Feedback mechanisms associated with global warming Pollution management strategies to address global warming; global and local Arguments surrounding global warming (for and against) Conflicting perceptions about global warming/climate change Topic 6: Global Warming The greenhouse effect (6.1.1) A garden greenhouse keeps plants warmer than they would be outside. It does this because the glass traps some of the Sun’s radiation energy. The atmosphere keeps the Earth warm in a similar way. This is because the energy entering our atmosphere is mostly short wave, which includes light energy and energy leaving the planet is mostly long wave, which includes heat energy. Some long wave radiation is absorbed by greenhouse gases before it escapes from the atmosphere and is reflected back to Earth. Without the greenhouse effect the Earth would be about 33°C cooler than today’s pleasant average of 15°C. The 'greenhouse effect' is a normal and necessary condition for life on Earth. Look at the diagram on the front page. Neatly write the following labels onto the diagram in the correct places. Natural greenhouse effect: http://sciencebitz.com/?page_id=582 Simulation: http://www.sumanasinc.com/webcontent/animations/content/greenhouse.html P135 – ESS, Rutherford If there was no atmosphere and the greenhouse effect did not exist, what would the normal temperature of the Earth be? Greenhouse gases Historically, the main greenhouse gases were water vapour, carbon dioxide, nitrous oxide and methane. Evidence for the link between the concentration of carbon dioxide in the atmosphere and global mean temperatures over the last quarter of a million years is shown in the graphs. Similar data exists going back hundreds of millions of years. How was this data collected? What conclusion can you draw from the two graphs? Topic 6: Global Warming The effect of greenhouse gas increases is called the enhanced greenhouse effect or simply global warming. Recent evidence for global warming The following graph shows data collected at one of the most unpolluted places on Earth, Mauna Loa, Hawaii in the middle of the Pacific Ocean. What is the increase in mean CO2 concentration in the last 40 years? Look at the more detailed inset. Why do CO2 levels decrease between May and September every year? Why do the CO2 levels climb higher each year from October until May? Topic 6: Global Warming Global mean temperatures since the Industrial Revolution The graph below shows the Central England Temperatures, or CET data, which go back to 1660 when thermometers were first used. The 20th century has clearly had the warmest in recent history. In the last 100 years the average temperature has increased by 0.6°C, but this warming has speeded up, jumping 0.5°C in the last 25 years. The 10 hottest years since records began have been since 1990. Computer modelling is now used to predict future temperature increases, which currently are between 1.4 – 5.8°C. What evidence is there that methane, nitrous oxide and CFC-11 may also be contributing to global warming? Look at the graph on p137 of ESS Rutherford. What do we mean by the term ‘’Radiative forcing’’? What does the term albedo mean? Why is it so important? Topic 6: Global Warming Anthropogenic greenhouse gas emissions (6.1.2) The list of greenhouse gases now includes carbon dioxide, water vapour, nitrous oxide, methane and chlorofluorocarbons (CFCs). Complete the table from the information on p137 of ESS Rutherford: Greenhouse gas Pre-industrial concentration Present concentration Greenhouse effect % greenhouse effect CO2 Methane, CH4 Nitrous oxide CFC-11 Why is water vapour seldom mentioned as a greenhouse gas? Anthropogenic sources of greenhouse gases Complete the table with sources due to human activities. Greenhouse gas Sources due to human activities Carbon dioxide Methane Ozone Nitrous Oxide CFC’s (chloroflurocarbons) Water vapour Atmospheric life times / years Topic 6: Global Warming Use your Rutherford book (p133 onwards) and the information pack to complete these questions. a) Approximately what proportion of world greenhouse gas emissions come from energy? b) Which part of the energy sector emits most greenhouse gases (by volume)? c) What are the main greenhouse gases emitted? What is their relative % contribution in world emissions? d) Apart from the energy sector, what are the main sources of greenhouse gases? e) What are the main sources of (i) methane? (ii) nitrous oxides? Topic 6: Global Warming Effects of global warming (6.1.3) The potential effects of global warming will affect human societies and biodiversity. Shifting climate belts will move biomes, affecting local weather, biodiversity, agriculture and human health. Melting ice caps and glaciers combined with thermal expansion of the seas will lead to coastal inundation and loss of some island states. Explain the above effects with examples and data where possible. Shifting climatic belts and biomes What are the possible trends? Complete the diagrams. Effect 1: Biodiversity Effect 2: Agriculture Effect 3: Human health Melting ice caps and glaciers combined with thermal expansion of the seas Read Annex B ‘The big melt’. Highlight examples of these two issues. Topic 6: Global Warming Coastal inundation Loss of nation states Topic 6: Global Warming Feedback mechanisms and global warming (1.1.6 & 6.1.4) Review of feedback The changes associated with global warming are long-term and are most easily understood in terms of feedback. Feedback is the return of part of the output from a system as input, so as to affect succeeding outputs. There are two kinds of feedback: Negative feedback is feedback that tends to reduce or counteract any deviation from an equilibrium, and promotes stability. For example, increased evaporation in tropical latitudes leads to increased snowfall on the polar ice caps, which reduces the mean global temperature. Positive feedback is feedback that amplifies or increases change; it leads to exponential deviation away from an equilibrium. For example, increased thawing of permafrost leading to an increase in methane levels, which increases the mean global temperature. Read the following article and highlight instances of positive feedback. Draw a diagram to summarise the links. Feedbacks that could be paybacks Particularly alarming are the possibilities of indirect effects of global warming that could further accelerate climatic changes. These are known as ‘positive feedbacks’ and so far they have not been adequately accounted for in the climate models. With the warming of the oceans and the surface air above them, evaporation would increase, increasing the amount of water vapour in the air. Water vapour is in fact the most potent natural greenhouse gas, and any increase, caused indirectly by warming due to increases in other greenhouse gas concentrations, would further trap heat. Frank Wentz, a physicist at Remote Sensing Systems of Santa Rosa, California, analysed data from three NASA satellites to come up with the alarming conclusion that this feedback has already begun. During the 1990s he found the amount of water vapour in the atmosphere had gone up by two per cent. Once positive feedbacks are triggered, they could go on to trigger others, leading to runaway warming — the models may not predict it but that it is possible cannot be denied. Here is a hypothetical but not entirely improbable doomsday scenario. As greenhouse gases build up in the atmosphere, temperatures rise. Forests begin to dry and die back or burn. Felling continues apace, diminishing forests’ ability to fix atmospheric carbon dioxide. Areas under ice melt to expose the Earth below, which begins to soak up the sun’s heat instead of reflecting it. Long-frozen dead tundra vegetation begins to decompose releasing more carbon dioxide and methane. The seas, swollen by rising temperatures and melting polar ice, swallow densely populated coastal regions. With warming seas also begin to lose their ability to absorb carbon dioxide and could start releasing the gas already dissolved in them — estimated at 50 times the amount contained in the atmosphere... and so on. As vicious circles go this one is hard to beat. As the 20th century closed, the warming speeded up, with average global temperatures jumping 0.5°C in the last 25 years. This would be the equivalent of 2°C per century. However the amount of change to which ecosystems can adapt is estimated at a maximum of 1°C over a century. And that is if no further changes are expected. But as Thomas Karl, director of the National Climate Data Centre put it, ‘We are already experiencing the rate of warming predicted right through this coming century. And there could be worse to come, as today’s effects are believed to be mainly the work of carbon dioxide emitted half a century ago. The much higher levels of emissions today are damage we are storing up for the future. Also to be factored into the equation are the effects of sulphate aerosols, by-products of industrial pollution which have masked the greenhouse effect by their cooling properties. But they have a short atmospheric lifetime and as cleaner production processes become more desirable in our increasingly polluted world, their role could well decline, revealing the true extent of warming. Topic 6: Global Warming For more examples of positive feedback read the rest of this article, Annex B The big melt and Annex C Carbon store. Draw a Diagram of the potential feedback processes that you have highlighted. Topic 6: Global Warming Pollution management strategies (6.1.5) Creating international commitments stimulate local action and to change personal lifestyles are three ways to tackle global warming. International action: a timeline of agreements and commitments for action 1979 1988 1990 1992 1995 1997 2001 2004 First World Climate Conference. Climate change officially recognized as a serious problem needing an international response when evidence of increasing carbon dioxide levels established. Intergovernmental Panel on Climate Change, IPCC established by United Nations Environment Programme (UNEP) and the World Meteorological Organization. The IPCC is a collaborative activity comprising over 2000 climate scientists worldwide. Its main activity to provide in regular intervals an assessment of the state of knowledge on climate change First IPCC Report on Climate Change. The Report confirmed that climate change was a reality and was supported by scientific data. Rio Earth Summit (United Nations Conference on Environment and Development). United Nations Framework Convention on Climate Change (UNFCCC) signed by 154 governments. The objective of the Convention is to stabilize greenhouse gas concentrations. The governments of developed or annex I nations were voluntarily committed to developing national strategies for reducing greenhouse gas emissions to 1990 levels by the year 2000. First UNFCCC conference. Governments recognized that voluntary commitments were inadequate and work started to draft a protocol for adoption at the third Conference of Parties in 1997. Second IPCC report concludes that the balance of evidence suggests a discernible human influence on the global climate. The Kyoto Protocol signed by some 160 nations at third UNFCCC conference. The Protocol calls for the first ever legally binding commitments to reduce carbon dioxide and five other greenhouse gas emissions to 5.2 per cent below 1990 levels before 2012. Third IPCC Report states that anthropogenic emissions will raise global mean temperature by 5.8°C by 2050. The fourth IPCC Report is due in 2007. The Kyoto protocol is still ineffective! For the Kyoto Protocol to be effective at least 55 countries have to ratify (fully adopt the commitments) and there must be enough annex I (developed) countries who together are accountable for ore than 55% of the emissions according to the 1990 levels. However the percentage of annex I countries is only 37.5%. Why is the protocol not on track? What three ways can Annex I countries have to meet their Protocol commitments Local action: Agenda 21, the blueprint for sustainable development (6.1.5) As adopted at the 1992 Rio Earth summit urges countries to promote national energy efficiency and emissions standards tax industries in ways that encourage, clean, safe technologies transfer clean technologies to developing countries integrate energy, environment and economic policies in a sustainable manner develop efficient, cost-effective, less polluting and safe rural and urban mass transport systems. Topic 6: Global Warming National policies List as many ways as possible that countries could reduce greenhouse gas emissions What alternative energy sources could be developed? What is meant by a carbon tax? What would it be used for? Personal lifestyles List as many ways as you can that you could help reduce local greenhouse emissions: Evaluation of management strategies Which of the above strategies would be the most effective in reducing greenhouse gases? Consider whether people would cooperate, technology availability, etc. Which potential solutions are ecocentric or technocentric? Topic 6: Global Warming Arguments surrounding global warming (6.1.6) Read the article Annex A Reaping the whirlwind. Do you need any more evidence that climate is changing? Contrasting human perceptions of the issue of global warming Individual and group perceptions (6.1.7) Topic 6: Global Warming Global warming review questions 1. Explain what is meant by the green house effect. 2. Why is the greenhouse effect normally of benefit to the Earth and its organisms? 3. List 4 greenhouse gases in order of importance. 4. Explain the sources of these four greenhouse gases. 5. Describe the increase in the levels of carbon dioxide i.e. how much has it increased, when did the increase begin and what are the main causes of the increase in carbon dioxide level? 6. What are the main sources of methane, CFC’s and water vapour, the other greenhouse gases? 7. Have their levels been increasing and if so, why? 8. Explain how at least four human activities such as deforestation, burning fossil fuels, rice and cattle farming and use of CFC’s add to greenhouse gases. 9. Discuss four ways in which global emission of greenhouse gases can be reduced (include conservation of energy (including carbon tax) and use of alternative energy sources). 10. What is global warming and how is it related to the greenhouse effect? 11. Why might the following processes occur due to global warming: (j) thermal expansion of the oceans, (ii) melting of the polar ice caps, (iii) increased evaporation in tropical latitudes leading to increased snow fall on the polar ice caps, triggering a new ice age, (iv) the effect of air pollutants (aerosols) in reflecting radiation, thus offsetting the warming trends. 12. How may global warming affect the planetary distribution of biomes? 13. If the distribution of biomes changes what impacts might this have on global agriculture. 14. What international measures have been taken to combat global warming. How successful have these measures been’ 15. List five ways in which emissions of greenhouse gases can be reduced in your local community. 16. Discuss the complexities and uncertainties surrounding the issue of climate change. Topic 6: Global Warming Syllabus 6.1.1 Describe the role of greenhouse gases in maintaining mean global temperature. 2 The greenhouse effect is a normal and necessary condition for life on Earth. Consider carbon dioxide (CO2) levels in geological times. 6.1.2 Describe how human activities add to greenhouse gases. 2 Water, CO2, methane and CFCs are the main greenhouse gases. Human activities are increasing levels of CO2, methane and CFCs in the atmosphere which may lead to global warming. 6.1.3 Discuss qualitatively the potential effects of increased mean global temperature. 3 Consider the potential effects on the distribution of biomes, global agriculture and human societies. Students should appreciate that effects might be adverse or beneficial, e.g. biomes shifting change in location of crop growing areas changed weather patterns coastal inundation (due to thermal expansion of the oceans and melting of the polar ice caps) human health (spread of tropical diseases). 6.1.4 Discuss the feedback mechanisms that would be associated with an increase in mean global temperature. 3 6.1.5 Describe and evaluate pollution management strategies to address the issue of global warming. 2, 3 Include: global—intergovernmental and international agreements, carbon tax, alternative energy sources local—allow students to explore their own lifestyle in the context of local greenhouse gas emissions preventive and reactive. 6.1.6 Outline the arguments that are surrounding global warming. 2 Students should appreciate the variety of sometimes conflicting arguments surrounding this issue. Note the complexity of the problem and the uncertainty of global climate models (see 1.1.10). 6.1.7 Evaluate contrasting human perceptions of the issue of global warming. 3 Students should explore individual and group perceptions. 1.1.6 Define and explain the principles of positive feedback and negative feedback. 1, 3 The self-regulation of natural systems is achieved by the attainment of equilibrium through feedback systems. Negative feedback is a self-regulating method of control leading to the maintenance of a steady-state equilibrium—it counteracts deviation, eg El Niño and La Niña. Positive feedback leads to increasing change in a system—it accelerates deviation. Feedback links involve time lags. 1.1.10 Evaluate the strengths and limitations of models. 3 A model is a simplified description designed to show the structure or workings of an object, system or concept. In practice, some models require approximation techniques to be used. For example, predictive models of climate change may give very different results. In contrast, an aquarium may be a relatively simple ecosystem but demonstrates many ecological concepts. Topic 6: Global Warming Annex A Reaping the whirlwind Extreme weather prompts unprecedented global warming alert The Independent 03 July, 2003 In an astonishing announcement on global warming and extreme weather, the World Meteorological Organisation signaled last night that the world's weather is going haywire. In a startling report, the WMO, which normally produces detailed scientific reports and staid statistics at the year's end, highlighted record extremes in weather and climate occurring all over the world in recent weeks, from Switzerland's hottest-ever June to a record month for tornadoes in the United States - and linked them to climate change. The unprecedented warning takes its force and significance from the fact that it is not coming from Greenpeace or Friends of the Earth, but from an impeccably respected UN organisation that is not given to hyperbole (though environmentalists will seize on it to claim that the direst warnings of climate change are being borne out). The Genevabased body, to which the weather services of 185 countries contribute, takes the view that events this year in Europe, America and Asia are so remarkable that the world needs to be made aware of it immediately. The extreme weather it documents, such as record high and low temperatures, record rainfall and record storms in different parts of the world, is consistent with predictions of global warming. Supercomputer models show that, as the atmosphere warms, the climate not only becomes hotter but much more unstable. "Recent scientific assessments indicate that, as the global temperatures continue to warm due to climate change, the number and intensity of extreme events might increase," the WMO said, giving a striking series of examples. In southern France, record temperatures were recorded in June, rising above 40C in places - temperatures of 5C to 7C above the average. In Switzerland, it was the hottest June in at least 250 years, environmental historians said. In Geneva, since 29 May, daytime temperatures have not fallen below 25C, making it the hottest June recorded. In the United States, there were 562 May tornadoes, which caused 41 deaths. This set a record for any month. The previous record was 399 in June 1992. In India, this year's pre-monsoon heatwave brought peak temperatures of 45C - 2C to 5C above the norm. At least 1,400 people died in India due to the hot weather. In Sri Lanka, heavy rainfall from Tropical Cyclone 01B exacerbated wet conditions, resulting in flooding and landslides and killing at least 300 people. The infrastructure and economy of southwest Sri Lanka was heavily damaged. A reduction of 20-30 per cent is expected in the output of lowgrown tea in the next three months. Last month was also the hottest in England and Wales since 1976, with average temperatures of 16C. The WMO said: "These record extreme events (high temperatures, low temperatures and high rainfall amounts and droughts) all go into calculating the monthly and annual averages, which, for temperatures, have been gradually increasing over the past 100 years. "New record extreme events occur every year somewhere in the globe, but in recent years the number of such extremes have been increasing. "According to recent climate-change scientific assessment reports of the joint WMO/United Nations Environmental Programme Intergovernmental Panel on Climate Change, the global average surface temperature has increased since 1861. Over the 20th century the increase has been around 0.6C. "New analyses of proxy data for the northern hemisphere indicate that the increase in temperature in the 20th century is likely to have been the largest in any century during the past 1,000 years." While the trend towards warmer temperatures has been uneven over the past century, the trend since 1976 is roughly three times that for the whole period. Global average land and sea surface temperatures in May 2003 were the second highest since records began in 1880. Considering land temperatures only, last May was the warmest on record. It is possible that 2003 will be the hottest year ever recorded. The 10 hottest years in the 143year-old global temperature record have now all been since 1990, with the three hottest being 1998, 2002 and 2001. The unstable world of climate change has long been a prediction. Now, the WMO says, it is a reality. Topic 6: Global Warming Annex B The big melt In March 2000 the World Watch Institute in Washington sent out an urgent message that the Earth’s ice cover was melting at a far speedier rate than previously predicted: a clear signal that greenhouse gases were heating up the planet. As this big melt becomes a reality, thoughts turn to the fears of rising sea levels that have beset many small island nations and low-lying coastal regions. The British Meteorological Office’s Hadley Centre for Climate Prediction and Research, a leading establishment in the field of climate modelling, forecasts an almost 16-inch (40 centimetres) rise in sea waters by 2080 if nothing is done about greenhouse gas emissions. This would mean that annual floods could threaten an estimated 94 million people — up from the 13 million at present. The coastal regions of southern and Southeast Asia would be the worst affected, as storm surges could push sea water deep inland. For about 40 low-lying island nations worldwide the combination of fiercer storms and sea-level rise could spell complete disaster. Already the United Nations Environment Program (UNEP) has recommended the evacuation of Tarawa atoll, part of the Pacific island nation of Kiribati. Some small islands fringing Kiribati have disappeared under the waters. Roads have had to be moved inland on the main island as the ocean gnaws into the shore. In June 2000 New Zealand (Aotearoa) made a promise of sanctuary to inhabitants of Tuvalu if their coral-atoll sank under the sea. These are the canaries in global warming’s coalmine. Yet the sea-level rise that threatens them and which figures in the Hadley Center’s predictions is due by and large to the thermal expansion of the warmer sea-waters. Now account also needs to be taken of the vast volumes of water that could be released from the world’s large ice masses. The Antarctic Peninsula has reported a sustained warming as high as 2.5° C. In places scientists have observed that rocks that have been covered by ice for millennia have begun to poke through. In the mid 1990s a roughly 8,000 square kilometre ice-shelf, Larsen A, broke away into the sea, looking — as an observing scientist put it - ‘like bits of polystyrene foam smashed by a child.’ According to the World Watch Institute report, the ice sheet that covers the Arctic Ocean has lost 40 per cent of its volume over the last 30 years and could be completely gone in a matter of decades. This wouldn’t make sea levels rise as the ice lies upon water to begin with. But the loss of land-based ice is another story. The Arctic’s Greenland ice sheet has had more than 1 metre shaved off it each year since 1993 along its southern and eastern edge. In Antarctica, three great ice sheets have gone completely, but whether land ice is also melting as rapidly is a matter of dispute. Some studies have suggested that the smaller of the continent’s two land ice sheets (with a mass the size of Mexico) is melting faster than normal. If the West Antarctic ice sheet were to collapse, the seas would surge by a catastrophic 6 meters.’ To put this into perspective, it is estimated that a 1metre rise in sea level could flood many of the world’s major coastal cities, such as New York, London and Bangkok and swallow up three per cent of total land area. Significantly, 30 per cent of the world’s croplands could be lost.” In the Netherlands, the famous sea defences would no longer be able to protect large areas that are under sea level. In April 2000 the inhabitants of the coastal village of Bergen on See were told that the authorities could no longer guarantee their safety due to rises in sea levels. The village, whose name in English can read as ‘Bergen on Sea’, could become ‘Bergen in Sea’. Cities like Amsterdam and Rotterdam could follow suit in the event of larger rises. And it’s not just sea ice that is melting — all over the world glaciers are in retreat as well, because the summer melt is more than can be replenished. The Quelccaya glacier in Peru is retreating 10 times faster than a decade ago, threatening water supplies for Lima’s 10 million people. Himalayan glaciers are, according to a UN study, ‘receding faster than in any part of the world’. If the Worldwatch report’s prediction of shrinkage by a fifth in this region in the next 35 years appears alarmist to some, the UN study is even starker, threatening the complete disappearance of these glaciers in the same time frame. As environmental journalist Fred Pearce put it ‘Their eventual disappearance is a potential catastrophe for the hundreds of millions of people in southern Asia, who depend on the summer melt even more than the monsoon rains to irrigate their crops and provide drinking water. For the 6,000 people whose lives are at risk from the brimming Tsho Rolpa glacial lake in Nepal, the situation is more urgent. Dozens of such lakes have formed high in the Himalayas in recent history, with only the debris left behind by retreating glaciers damming them in. About every three years, one bursts sending a wall of water rushing down the valleys. Topic 6: Global Warming Annex C Carbon store With temperatures in the high latitudes rising the most rapidly not only is the temperature record of the various layers of ice being lost as newly fallen snow often melts completely in the spring thaw, but there is the possibility that vegetation covered by permafrost in the northern hemisphere since the time when dinosaurs roamed the much warmer Earth could be laid bare. This decomposing matter forms a carbon store estimated at as much as 450 billion metric tonnes, which could release enormous quantities of carbon dioxide and methane into the atmosphere. The attack on the world’s forests has left us with just a third of the land functioning as an intact forest ecosystem than was once under forest cover. Trees store carbon and draw it down to produce food, but dead, burnt or cleared forests turn from being carbon sinks to carbon sources. One hectare of tropical rainforest contains between 100 and 250 tonnes of carbon in the form of organic matter (a figure which is much higher if one includes the carbon stored in the soil), three-quarters of which could be liberated by burning or decomposition. With such forests disappearing at the rate of one per cent a year throughout the 1990s and countries often being forced to exploit the economic potential of their timber to service their international debts the outlook is less than bright. The feedback mechanism from rainforest destruction would not only directly impact on warming but could also result in a decline in rainfall in these areas. Another potential feedback is the release of methane from methane hydrates. These resemble ice in that they are solid, but they are actually an unstable mixture of water and methane forming at low temperatures under considerable water pressure in the oceans. An essential factor for their formation is the presence of a thick enough layer of sediments to generate the methane in the first place. In the Arctic with its colder water temperatures, less pressure is required for the hydrates to form and as a result they occur in much shallower waters and could conceivably be destabilised if the water warms enough. It is not known for sure but there may be many tens of if not hundreds of billions of tonnes. And since there is a mere five billion tonnes of carbon in today’s stock of atmospheric methane, only a little methane hydrate would need to be melted to boost the greenhouse effect significantly. It is just such considerations that don’t figure in climate models, but the potential they have to start a chain of runaway feedbacks, however distant it may appear, needs to be acknowledged. And as long as that potential remains we need to act, because once the juggernaut starts rolling it is too late to stop it. This is known as the ‘precautionary principle’ in the climate debate and the time to apply it is now. For with each bit of corroborative evidence to support global warming, the outline becomes clearer. Waiting for the picture to be complete would be waiting helplessly for catastrophe.