Openlearn - Global Warming

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Overview

Introduction This unit provides an introduction to global warming. We will be considering the history of global warming by looking at the pattern of ice ages and analyisis of recorded temperatures. We will aim to gather meaningful information from this data. We will briefly assess the impact and influence of humans on global warming and, finally, we will examine climate models and how to predict future changes.

Learning Outcomes

The learning outcomes for this unit are to: Develop an understanding of the current evidence for global warming. Model and apply the techniques of ?measuring? the Earth's temperature. Understand the current warming in relation to climate changes throughout the Earth's history. Explain factors forcing climate change, and the extent of anthropogenic influence. Assess the ?best predictions? of current climate models.

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1. Natural climate change? The chart below shows a record of the global mean surface temperature of the Earth compiled for the past 140 years. Clearly there is an upward trend, but what does a chart like this really show?

To understand what the chart shows, it is necessary to take the ?long view?, looking back through the whole history of the Earth.

How can we know the temperature of the planet over time-scales of billions of years?

Is this current warming part of the Earth's natural temperature variation?

What factors affect and force changes to the global temperature, and to what extent are these being affected by human activity?

What are the best predictions for change over the next 100 years?

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2. A 4.6 billion-year history Climate change is a natural process of warming and cooling that has occurred all through the Earth's history. Throughout geological time there have been ?hot-house? periods and ice ages. In

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order to understand the current situation, it is necessary to have some sense of context and perspective, from historical and geological time-scales. The document below shows a chart showing a generalised temperature history of the Earth. Click on 'View document' to see the chart View document

We are currently enjoying an interglacial period of an ice age that began approximately two million years ago. (Ice ages are composed of colder ?glacial? and warmer ?interglacial? periods.) This is at least the seventh ice age in the Earth's 4.6 billion-year history. During the Cretaceous (65?147 Ma) the whole Earth was up to +15 (C warmer than at present, with tropical forests covering Antarctica, whereas during the Quaternary (?2 Ma) ice sheets spread across much of Europe and the mean surface temperature was up to (5 (C colder than at present. The range of these changes is much greater than the observed increase in temperature over the past century (+0.6 ±0.2 (C) and predictions for the next hundred years (+3 ±1.5 (C). Click on 'View document' to read ?Glaciers past and present? View document

Click on 'View document' to read ?Pollen diagrams and ancient climates? View document

Activity 1 Past temperatures: before measurement, before people Measuring temperature is a relatively recent affair. Galileo Galilei invented his thermometer in 1597, but the longest running record of surface temperature to the present day only dates from 1815. For periods prior to these measurements, our understanding of the history of climate change is inferred from geological evidence, primarily:

Glaciation (showing that much of the northern hemisphere was covered in ice, some 18 000 years BP).

Fossilised pollen (showing that over the past 140 000 years, the mean temperature has varied by almost 15 °C). Prepare a brief (no more than five minutes) presentation on the information concerning climate change provided by either glaciation or the pollen record. The presentation should close with 3?7 key ideas to explore. Two resources are provided to help you do this: ?Glaciers past and present? and ?Pollen diagrams and ancient climates?. To access these resources, click on the "view document" links above.

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3. Recorded temperatures Analyses of over 400 proxy climate series (from trees, corals, ice cores and historical records) show that the 1990s was the warmest decade of the millennium and the 20th century the warmest century. The warmest year of the millennium was 1998, and the coldest was probably 1601. (Climatic Research Unit, 2003) Throughout historical times, fluctuations in the Earth's mean temperature have been recorded. During the seventeenth century, the Thames periodically froze over during winter and mini-glaciers were present in the North West Highlands of Scotland. More recently, the 1990s included some of the hottest years ever recorded in the British Isles, and 10 August 2003 was the hottest day ever on record. An annual temperature record for central England has been constructed, beginning in 1659. Click on 'View document' to open a chart of central England temperatures from 1659 to 1995 View document

Look at the chart in the aboce document. How do the readings for 1660?1700 compare to 1960?2000? You have probably noticed that in the first period most points were below the mean, but in the latter period, most were above it. Because the data are so scattered, some method is required for seeing the overall trend more clearly. A single ?line of best fit? (regression analysis) is not appropriate, as it hides small-scale variations that may be significant. Such changes in the recorded temperatures are manifest throughout the British Isles, resulting in changes to natural fauna and flora. These changes are also having local economic impact, such as the northwards spread of vineyards in the UK. (At the time of writing I believe the most northerly vineyard in the UK is in Swillington, near Leeds.)

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Further reading For information on changes to flora, click on Science magazine. For changes to fauna, and economic effects, go to Information Sheet 4, or for the paper quoted at the top of the screen, Information Sheet 1, both at Climatic Research Unit. Click on 'View document' to open the data-smoothing information View document

Click on 'View document' to read about >working with global mean surface temperature View document

Activity 2 There are two key ways of getting meaningful information out of climatic data sets:

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data-smoothing;

working with global mean surface temperature ? GMST. Click on the "view document" links above to read explanations of these techniques. Consider how you might model these two processes with students. You may want to consider:

using a maximum/minimum thermometer over 24-hour periods;

data-logging temperature over a longer period;

using a rain gauge;

comparing your own data with data from the Meteorological Office. (The Meteorological Office provides monthly rainfall and mean monthly temperature data from 1961 to the present. Click on the link Meteorological Office to access their site: scroll down to ?Past? and click on ?Monthly information? to look at the statistical details. Sketch out an outline of a teaching sequence that explores data-smoothing and the concept of GMST.

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4. Human influence? Evidence suggests that global temperature is beginning to rise. There are several factors that could cause this. Only one is affected by human activity. Click on 'View document' to view a chart showing the rates of energy gain and loss by the Earth's surface and atmosphere View document

Up to this point we have been primarily concerned with evidence and trends, with ?what has happened?. This sort of analysis does not tell you ?why? something happened. To understand ?why?, we need some sort of explanatory model that works on a global scale. The starting point of ?why? for climate change, is to consider energy flows in the climatic system. Click on the 'View document' link above to see a chart showing the rates of energy gain and loss by the Earth's surface and atmosphere. Note that even though the arrows starting and stopping in the atmosphere do so in small region in the centre, the atmospheric energy gains and losses that they represent take place throughout the atmosphere. 100

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units represent the rate at which solar radiation is intercepted by the Earth. The width of each arrow is proportional to the rate of energy transfer. If you would like a full explanation of the energy flows in the diagram, click on 'View document' below to read more. View document

Activity 3 explores the possible causes that may be disturbing the equilibrium of such a model, and the evidence of human influence.

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Further reading The models being used in research take such simple energy flows and increase the ?granularity? of the components used, to build complex time sequences. You may like to see Information Sheet 8 at the website of the Climatic Research Unit for a summary of how these have developed. Click on 'View document' to see charts mentioned in the activity below View document

Activity 3 Click here to read Information Sheet 2, ?Causes of climate change?, from the website of the Climatic Research Unit. Which of the potential causes are influenced by human activity? Click on the "view document" link above and compare the charts for greenhouse gases (carbon dioxide, nitrous oxide and methane) and temperature over the last 1000 years.

Discuss the key features and implications of these two sets of information.

Compare the radiative forcing for the human influences ? what does this suggest?

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Climate models To understand climate change it is necessary to construct climate models, to explore and predict

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interactions between different factors. Models are tested for accuracy against known sets of data, before being run forward to predict future changes.

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Comparing modelled and observed temperature The IPCC comparison between modelled and observed temperatures since the year 1860 is shown in the three charts below

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It is clear from these charts that both natural influences and anthropogenic forcing are required to explain the recent rises in temperature.

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Running the models forward What happens when the models are run forward? It depends upon the models used and the scenarios they are asked to run. It seems almost certain, however, that there will be increases in the global mean surface temperature, to the order of +1.5 to +4.5 (C ? possibly more, according to some models and scenarios. These changes are predicted to be associated with increases in sea level, changes to weather conditions (e.g. more regular and violent winter storms in the UK) and changes to the distribution of habitats and their associated organisms. The current predictions for the global climate in the twenty-first century are shown for a range of scenarios and models in the charts below. (Chart (a) shows the range of scenarios for CO2 emissions; charts (b) and (c) show the corresponding predictions for temperature change and rise in sea level.

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Closing thoughts Of course, doing anything about this needs scientific evidence and understanding, but it also requires social, economic and technological changes, which can only be achieved through political will. If you want to explore some of the broader context, a good place to start would be the New Internationalist issue 357, ?The Big Switch: Climate Change Solutions? at New Internationalist. Faced with the sort of predictions climatologists are making, is it sufficient for science teachers to stop at the ?science?, or should we be tackling some of these broader issues in schools? If you want to find out more, the Hadley Centre is the UK's foremost climate research centre and provides a lot of useful information, as does the Intergovernmental Panel On Climate Change at IPCC. If you wish to view tis simulation in a new window click on 'Launch in separate player' Launch in separate player

Activity 4 To help you understand some of the key factors in climate modelling, click on the link above to work through a simplified simulation. In reality, climate modelling is extremely complex, because all the variables are not known. The ability to develop mathematical models of climate change is constantly improving, but there are still many competing models, each making different predictions of how the climate will change. All models, currently, show a significant increase in the global mean surface temperature attributable to human influences.

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References and Acknowledgements

References Climatic Research Unit (2003) Information Sheets at http://www.cru.uea.ac.uk New Internationalist (2003) ?The Big Switch: Climate Change Solutions?, June, issue number 357. The Open University (1998) S103 Discovering Science, Block 2 ?A Temperate Earth??, Milton Keynes, The Open University.

Acknowledgements

The content acknowledged below is Proprietary (see terms and conditions) and is used under licence.

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Acknowledgements

Author

This unit was prepared by Tom Power with guidance from Dr Arlene Hunter. Tom Power is a lecturer in science education at The Open University. His research interests include teacher education in the global south (www.open.ac.uk/deep) and the CASE intervention. He has been a teacher and an advisory teacher in East Sussex and a specialist adviser to the TTA teacher research panel. Dr Arlëne Hunter, Staff Tutor in Science in Ireland, The Open University, is responsible for the management of the science programme across Ireland and contributes to various undergraduate earth and environmental science courses. Her research is divided between geochemistry and enhancing the learning and teaching experience for students and staff. This unit draws upon many sources, but has been developed primarily from the Open University Science short course (1998) S103 Discovering Science: 2 A Temperate Earth, Milton Keynes, The Open University.

Further acknowledgements

Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: Charts of: variation of the Earth’s surface temperature, carbon dioxide, nitrous oxide, methane, natural forcing, anthropogenic forcing, natural and anthropogenic forcing, carbon dioxide emissions, temperature change, rise in sea level: copyright © IPCC. Extracts from the Open University course S103 Block 2 ‘A temperate Earth?’ Figures 3.3 and 3.5: courtesy of Tony Waltham; Figure 3.4: Landform Slides; Figure 3.6a: The British Geological Survey, copyright © NERC, all rights reserved Figure 3.7: John, B. S. (1977) The Ice Age, HarperCollins Publishers Ltd Figure 3.10: courtesy of C. Turner Figure 3.11: courtesy of C. J. Hawksworth Figures 3.12 and 3.13: West, R. G. (1977) Pleistocene Geology and Biology, 2nd edition, p. 362, reprinted by permission of Addison Wesley Longman Ltd Figure 3.14: reprinted with permission from Nature, 281, 18 October 1979, p. 559, Woillard, G. (1979) ‘Abrupt end of the last interglacial S.S. in North-East France’, copyright © 1979 Macmillan Magazines Limited Figure 3.15: reprinted with permission from Nature, 338, 23 March 1989, p. 312, Guiot, J., Pons, A., de Beaulieu, J. L. and Reille, M. (1989) ‘A 140,000-year continental climate reconstruction from two European

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pollen records’, copyright © 1989 Macmillan Magazines Limited Figure 3.16: Brown, G. C, Hawkesworth, C .J. and Wilson, R. C. L. (1992) Understanding the Earth, 2nd edition Cambridge University Press. Figure 2.10: Parker, D. E. et. al. (1966) ‘A new daily Central England temperature series, 1772–1991’, International Journal of Climatology, 12, Royal Meteorological Society. www.meto.gov.uk/climate/uk/2003/june.html video model of changes in the temperature of the Earth: © Crown Copyright. Reproduced with the permission of the Controller of Her Majesty’s Stationery Office. Unit image: Courtesy of kenyai / Tunde Pecsvari at Flickr Every effort has been made to trace all the copyright owners, but if any has been inadvertently overlooked, the publishers will be pleased to make the necessary arrangements at the first opportunity.

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