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The Science of Climate Change: Informing your decision making Version: March 2012 Carbon Dioxide Now 389ppm 400 2 CO Concentration (PPM) 350 300 250 200 150 100 Variation in last 400,000 years 50 0 1700 1750 1800 1850 1900 1950 2000 Year Air Temperature A document prepared by the Australian Institute of Physics (Victorian Branch) Education Committee The Science of Climate Change: Informing your decision making 1. 2. 3. 4. 5. 6. 7. 8. 9. The Earth’s atmosphere Electromagnetic radiation Greenhouse Effect Climate Models What do climate models predict? Interpreting data Climate change impacts Cause for concern Expressing concern Overview The Earth's climate is remarkably suited to the development and sustenance of life. Neither of our neighbours in space has produced life. Venus is too hot. It has a runaway greenhouse effect which keeps it at around 4600 C. Mars has a very thin atmosphere which hardly traps any heat and so its temperature ranges between a frozen -1400 and +20°C. While their distance from the Sun is significant, it is the atmospheres of these three planets that make all the difference. It is our atmosphere, along with the moderating effect of the oceans, that have provided the Earth with the stable climate which has enabled life to develop and thrive. The 'greenhouse effect' is a crucial part of this climate system, but it is this which we are modifying by our use of fossil fuels. The essential ingredient of coal, oil and gas is carbon. When burnt, this combines with air to produce carbon dioxide, a key 'greenhouse gas'. We have already increased the amount of carbon dioxide in the air by 35% and it is still rising. To imagine that this will have no effect on our climate would seem foolish in the extreme. For this reason, over the last few decades, climate scientists have been working to understand the role of carbon dioxide and other human produced greenhouse gases in the complex climate system upon which we are so dependent. What they have discovered has given cause for alarm. Action to reduce the amount of greenhouse gas we are putting into the atmosphere will require global cooperation on a scale never before seen in human history. Despite widespread agreement in the scientific community that strong action is needed, so far little action of any real significance has come from the political sphere and global emissions continue to increase. Only when there is widespread understanding of the real nature of the issue are politicians likely to find the will needed to take the steps necessary to produce the global cooperation required to avoid what is probably the 1 greatest threat that human civilisation has ever faced. Hence this attempt to increase public understanding of the issue. The earth's temperature is determined by the balance between the incoming energy radiated from the Sun and that re-radiated back into space from the Earth's surface. The atmosphere plays a crucial role in this process. In order to appreciate the effect of human added greenhouse gases we need to understand the nature of the radiation from the Sun and that re-emitted by the Earth, and the interaction between that radiation and the atmosphere. Our brief journey of understanding starts with a description of the evolution of the Earth's climate and the factors that have affected it in the past. We then look at the nature of the incoming and outgoing energy radiation and the way the Earth's temperature is determined by the interaction between these factors. While the serious physics and chemistry of the climate is very complex, it is quite possible for all of us to appreciate the way in which climate scientists have been able to come to grips with it and then to use this understanding to determine the probable consequences of the 35% increase in carbon dioxide since humans began using fossil fuels. This document was prepared by a group of current and former science teachers. They are also parents and grandparents who believe by building greater understanding of the science of climate change that this will empower the community to force governments to take stronger and more urgent action. Useful Resources Internet: The page, www.vicphysics.org/teachingclimate.html , on the Education Committee’s website contains an annotated list of links to resources from Intergovernmental Panel on Climate Change (IPCC), The Australian Academy of Sciences, the Bureau of Meteorology, The Royal Society, the Joint Science Academies of the G8 nations, etc. The page also lists links to teaching resources and to Ideas on ‘What I can do to help’. Texts: The Hot Topic: How to tackle global warming and still keep the lights on, by Gabrielle Walker and Sir David King, Bloomsbury Publishing. 2008. Australian Institute of Physics (Victorian Branch) Education Committee PO Box 304, Glen Waverley, VIC 3150. www.vicphysics.org 2 1. The earth’s atmosphere For many thousands of years the earth has been surrounded by a finely balanced atmosphere that protects it from high-energy radiation and also absorbs enough heat to provide a moderate climate to support life. If we upset this balance, then our life support system will be at risk. However the early atmosphere was not always so. The Formation of the Earth’s Atmosphere At the beginning of the solar system when the earth was being formed 4.5 billion years ago, the leftover atmosphere of Hydrogen and Helium quickly escaped the earth’s gravitational field or was ‘blown way’ by the Sun’s radiation. The earth was initially without an atmosphere. With volcanic activity, an atmosphere formed of nearly all water with about 2% sulfur dioxide (SO2), 1% carbon dioxide (CO2) and traces of hydrogen sulfide (H2S), hydrochloric acid (HCl) and ammonia (NH3). The water in the atmosphere condensed to form the oceans. Simple life forms, such as algae, began to appear. Through the process of photosynthesis, the algae began to use sunlight to convert water and CO2 into carbohydrates and oxygen (O2), which bubbled into the atmosphere. (Our fossil fuels are the compacted bodies of these algae). Initially most of this oxygen reacted with the metals on the surface to produce the various oxides, e.g. iron ore, that we mine today. As the oxygen accumulated, ultra violet light from the sun split the oxygen molecules in the upper reaches of the atmosphere, producing an ozone shield that blocked the ultraviolet radiation (UV), which damages DNA. Previously the UV had prevented life from forming on the land or in the shallows. By about two billion years ago, the oxygen concentration was sufficient (0.2%) life begin to move out of the oceans. The development of plants continued to reduce the amount of CO2 and increased the amount of oxygen. It took until about one billion years ago for the oxygen concentration to level out. In recent millennia human activity has modified the amounts of carbon dioxide, methane and nitrous oxide in the atmosphere Today’s Atmosphere The atmosphere is now made up of a mixture of over 16 gases, the main ones and their proportion are in the table to the right. Table 1. Composition of dry atmosphere, by volume Gas nitrogen (N2) oxygen (O2) argon (Ar) carbon dioxide (CO2) neon (Ne) helium (He) methane (CH4) hydrogen (H2) nitrous oxide (N2O) water vapour (H2O) 3 Dry Volume 78.08% 20.95% 0.93% 0.038% 0.002% 0.0005% 0.0002% 0.00005% 0.00003% 1% - 4% Climate change in the past: Hothouse Earth Snowball Earth In the last few hundred million years the Earth's climate has swung between a 'hothouse Earth' with global average temperatures well over 20°C and a 'snowball Earth' with average temperatures below 10°C. Hothouse conditions were associated with sea levels over 100 metres higher than today's and no polar ice, while in snowball times polar icecaps extended down into Europe and ocean levels were much lower because so much water was locked up as ice. For most of the last few hundred million years the Earth was much hotter than today, but about two million years ago it cooled and entered an 'Ice Age'. This current ice age has, however, been characterised by swings between the very cold periods and relatively warmer 'interglacials' such as we are currently in. Interglacials are roughly half way between the hothouse and snowball Earth conditions, with average temperatures around 15°C Human civilization has developed in the relatively stable conditions of the current interglacial, which has so far lasted around 10,000 years. Although there have been small changes during this time - the 'medieval warm period' and 'little ice age' for example - these changes have been very much smaller than the hothouse - snowball swings. Clearly the concern at present is that if we upset the climate energy balance we could trigger a return toward the hothouse conditions with much higher sea levels and very different patterns of rainfall and arable regions. The problem is not so much whether life could survive in those conditions, it is the havoc that would be caused by the changing conditions - not to mention that most of the world's major cities would be drowned. For this reason, scientists have studied past climate change carefully and now understand many of the factors that have caused climate swings. Some of these are outlined below. Over the longer time scale, factors such as the changing composition of the atmosphere, variations in the Sun's output, massive volcanic activity, meteor impacts, shifting continents and uplifting land masses have been important in triggering changes in the climate. What is more relevant to our present task, however, is to understand the changes that have occurred in the last tens of millions of years. Why, for example, did the Earth suddenly (geologically speaking) plunge into the current ice age? And why, over the last million years has it cycled between a full ice age and the milder interglacials? There are several factors contribute to these climate cycles. The Milankovitch cycles: Variation in the Earth’s motion. In the 1930's Ivan Milankovitch found that there appeared to be a relationship between subtle variations in the Earth's orbit around the Sun and the interglacial climate cycles. 4 The earth spins on its axis giving us day and night. This axis is tilted at about 23 degrees which produces the seasons, however this angle of tilt varies between 22 and 24 degrees over a time span of 41,000 years, the larger the angle the greater the difference between summer and winter. Because the earth is like a spinning top or a gyroscope, the axis itself also goes around in a circle, this is called precession. The earth’s axis wobbles like a spinning top once every 22,000 years. It increases the seasonal difference in one hemisphere and decreases it in the other. See Figure 1. The earth orbits around the sun. This path is an ellipse. The other planets slowly stretch the ellipse, then ‘relax’ it over a cycle of 100,000 years. The interaction of these cycles is currently thought to be the principal cause of ice ages. They determine how much of the sun’s energy reaches the earth, and also how it is distributed across the earth. Figure 1. The earth’s orbit is an ellipse with the sun at one focus. The earth moves around its orbit in the direction of the solid arrow, while spinning about its axis in the direction shown by the thin curved arrows at the North pole. The earth’s spin axis also ‘wobbles’ or precesses, shown by the thicker curved arrow, about 22,000 years for one rotation. Changes in greenhouse gases Greenhouse gases have not been an initiating factor in the emergence from an ice age, but they have been an amplifying factor. When the cycles described above cause the earth to begin to warm, the warming oceans release the gases into the atmosphere. They ‘insulate’ the earth making it warmer. The oceans get warmer, releasing more gas, etc. This process is called positive feedback. The temperature continues to rise until the other factors listed here have a negative impact. The same process is beginning to happen now, but this time the trigger is human activity. The greenhouse effect is described later. 5 Movement of continents The oceans are the principal means by which the earth evens out its temperature. The warm seas at the equator flow towards the cold poles. The continents move very slowly across the surface of the earth, colliding and creating mountain ranges. If they block off this movement of the oceans, then the climate would be affected. Uplift of Tibetan plateau The formation of the Himalayas when the continents began colliding several million years ago produced a large ice sheet located near the equator. The white ice reflected much of the intense sunlight cooling the earth. Variation in Sun’s output The energy from the sun varies slightly with an 11 year cycle which is related to the variation in the number of sunspots. This cycle is too short to be a factor in causing ice ages, but may contribute to minor variations, such as the coldest part of the Little Ice Age in the 1800’s. Volcanoes Volcanic eruptions on land could have a significant, but temporary cooling effect. While undersea eruptions could release methane, a greenhouse gas, which could also have a temporary effect, but this time a warming effect. As with variations in the Sun’s output, the impact of volcanoes would be limited to decades. Figure 2: Ice Ages: Temperature and Carbon Dioxide concentration in the atmosphere over the past 400,000 years (from Vostok ice core) http://www.global-greenhouse-warming.com/images/VostokTempC02.jpg 6 2. Electromagnetic Radiation It is radiation from the Sun that is our ultimate energy source, it underpins life on the planet. It warms the earth. This warmth radiates into the air. The atmosphere determines how much energy the earth retains and how warm it gets. Visible light, infra red radiation, ultraviolet radiation, microwaves, radio waves and xrays are different forms of the same thing: electromagnetic radiation. They differ from each other in the same way as the signal from one radio station differs from that of another, that is, they differ only in the frequency, and because they are all waves, also in their wavelength. It is the ultraviolet that gives us sunburn. It is the infrared from a fevered face that is detected at an airport terminal as evidence of a raised temperature. Figure 3: The Electromagnetic Spectrum Note: This radiation differs from nuclear radiation which is mostly high speed charged particles from inside atoms. The earth’s atmosphere protects life from the more dangerous forms of radiation from the sun, but fortunately has a window that allows through the long wavelength radiation emitted by the earth. As we shall see, this emitted radiation keeps the Earth’s energy balance even and its temperature relatively steady. Black body radiation Hot objects, such as a stove element, give off electromagnetic radiation, which we can feel. This is infrared radiation. In fact there is a spread of wavelengths from longer than 10,000 nanometres (nm) to around 1,000 nm. One nm is one billionth (10-9) of a metre. As the object gets hotter the peak of the spread both gets higher and moves towards higher frequencies and shorter wavelengths. Eventually the object will get so hot that 7 the spread will include the red part of the visible spectrum and the object will begin to glow. In Figure 4, the graph for the cooler object is flat with a peak near the red. For the hotter objects, the graph is much larger and the peak has shifted to the left to the yellow section. The Sun is so hot that it looks yellow and its spectrum goes from infra red to deep ultra violet. Hotter stars in the sky will look white or even blue. 72000C 57000C 42000C Figure 4: The spread of radiation from various hot objects Figure 5: The radiation from the Sun at the top and bottom of the atmosphere org.ntnu.no/.../pics/chap2/Solar_Spectrum.png. wikicompany.org/wiki/images/thumb/Solar_Spect... The light colour in Figure 5 shows the spread of light from the sun when it reaches the top of the atmosphere. On the way through the atmosphere, different wavelengths are absorbed. . The dark colour shows the radiation that reaches the surface. The ultra violet radiation on the left is absorbed by the ozone in the upper atmosphere. Some parts of the incoming infrared on the right are absorbed by CO2 and water vapour (H2O). 8 Some of the visible light in the middle is scattered by the air; that is why the sky is blue. The spectrum at ground level is therefore uneven with occasional gaps. The strength of the solar radiation reaching the Earth is 1360 Watts per square metre, but averaged out over the whole surface, it is 340 Watts per square metre. 30% of this radiation is reflected back into space, mostly by ice and light coloured surfaces such as deserts. The amount of radiation reflected from a surface is termed its “albedo”, and so the Earth has an albedo of 30% or 0.3. The remaining 70% is absorbed by the earth’s surface, heating it up. Like all hot objects, regardless of their temperature, the Earth’s surface will re-radiate this energy, but because its temperature is low, this energy will be mainly as long wavelength infrared radiation. The radiation absorbed from the Sun will raise the temperature of the Earth’s surface to the point where the amount of incoming radiation is balanced by the amount of outgoing radiation. The top part of Figure 8 compares the radiation received from the Sun with that emitted from the Earth. The graphs may looks similar in shape, but notice that the scales are very different. If the atmosphere contained no greenhouse gases, the average surface temperature needed to balance the incoming and outgoing radiation would be frozen 18 0 C below zero. With greenhouse gases in the atmosphere, however, some of the outgoing radiation is ‘reflected’ back down to the surface, warming the earth. As a result, the surface temperature needs to rise to an average +15°C in order to achieve a balance. So the natural greenhouse effect is responsible for a 33 degree rise in the Earth’s temperature. Our concern now is that we are increasing this figure by adding more greenhouse gases into the atmosphere. 9 Figure 6. The global radiation balance at the top of the atmosphere and at the earth's surface. Part of the total incoming solar energy (340 Watts per square metre) is absorbed by clouds and atmospheric gases and part is reflected by clouds, atmospheric gases and the ground (land and water surfaces). Approximately half (170 Watts per square metre) is absorbed by the ground. Some of this energy is re-radiated upward and some transferred to the atmosphere by turbulence and convection. The atmosphere radiates infrared radiation in all directions. When balance is achieved in the atmosphere, the total (short wave and long wave) upward radiation from the top of the atmosphere equals the 340 Watts per square metre received from the sun. Notice that if you add together the numbers on the in-coming arrows at the top, then add together the numbers on the arrows going out at the top the totals are the same? Other maths questions: 1. How much of the incoming 340 Watts per square metre of solar energy is reflected? Express this as a percentage. 2. The amount of energy radiated out into space ( three up arrows on the right) should balance the energy absorbed by the clouds, the atmosphere and the land and sea. Show that it does. Answers 1. 20+68+14 = 102 W/m2, 30%. 2. 10 20+88+130 = 238 = 14+54+170 3. Greenhouse gases Greenhouse gases are like a blanket keeping you warm on a cold night - too thick and you overheat. How do these gases keep energy in? Because of its temperature, the surface of the earth emits radiation mainly in the long infra red. This particular radiation can interact with molecules containing three or more atoms. All types of electromagnetic radiation can affect substances, but they do it in different ways. X-rays and ultraviolet can break up the bonds joining atoms and create new chemical species that can damage living tissue. Visible light has less energy and can only move electrons around within the atom producing colour. Infrared with even less energy can make molecules bend and vibrate, but only the flexible molecules with three or more atoms. X-ray of hand: https://reich-chemistry.wikispaces.com/file/view/xray.jpg Prism spectrum: http://www.faculty.virginia.edu/consciousness/images/prism.gif Figure 7. Infrared radiation can jiggle carbon dioxide and water molecules in many ways. This means these molecules can absorb many different wavelengths of infrared radiation. The two atom molecules such as nitrogen and oxygen which make up most of the atmosphere are too tightly bound to be affected by infra red radiation. The molecules of water, CO2 and CH4 have three or more atoms and so are jiggled by infrared radiation. Figure 7 shows the different ways the molecules can be jiggled. Once they absorb the infrared radiation coming up from the earth, they then emit it, but in all directions; some upwards out into space, but some back down to earth to heat up the surface. The diagrams below show the different wavelengths of infrared radiation that carbon dioxide and water molecules absorb. These diagrams are called their spectrum. 11 ultraviolet vis infrared Figure 8: The absorption characteristics of water and CO2. The upper portion of the chart shows the spreads of radiation emitted by the Sun and the Earth. Note the different scales, the left ranges from 0 to 2000, while the right goes from 0 to 8. The lower panels show the absorption of water (H2O) and (CO2) . The black sections in the graphs in Figure 8 are the wavelengths that H2O and CO2 absorb. However as these two gases make up such a small percentage (See table 1) of the atmosphere, much infrared radiation across the full range of wavelengths goes out into space. The graphs indicates that water is the most effective of the greenhouse gases, however the concern about CO2 and methane, CH4, the other strong greenhouse gas, is that, while water molecules only stay in the atmosphere until the next rain, CO2 and CH4 stay in the atmosphere for over 100 years, so any increase is around for some time, their emission is almost irreversible. What should happen if we add more CO2 and CH4 to the atmosphere? The extra gas ‘reflects’ back more infrared radiation. This will make the surface even hotter. 12 4. Climate Models How does science explain climate? The patterns of climate on earth can be explained with two sets of information: Principles: Science of the atmosphere the Laws of motion for moving gases and liquids, the Gas Laws on temperature and pressure, the response of gases in the atmosphere, in particular the greenhouse gases, to radiation, and the various physical, chemical and biological processes that take place, in particular: - the global energy balance, - the global water cycle, and - the global carbon cycle Data: Initial conditions the strength of the radiation from the sun; the spherical shape of the earth and the tilt of its axis; the composition of the atmosphere; the rotation of the earth, and the distribution of continents and oceans. A climate model expresses the principles underlying the science of the atmosphere, as listed above, in their mathematical form. They are then put in a computer program. This program uses as its starting point the data from the initial conditions above. Figure 10 illustrates the extraordinary number of processes that must be included in a climate model to make it realistic and match observations. To analyse the climate, the model divides the earth’s atmosphere and oceans into cells. See Figure 9. Each cell at ground level is about 100km by 100km and 100metres tall. Cells higher in the atmosphere are taller as the air is thinner. Cells deep in the ocean are also longer. Most climate models have in excess of 10,000 cells. Figure 9. The cell structure for a typical climate model. The east-west cross-section in the left panel is to the grid on the right. 13 Figure 10: The components of the global climate system consisting of the atmosphere, the geosphere (which includes the solid earth, the oceans, rivers and inland water masses (hydrosphere) and the snow, ice and permafrost (cryosphere)) and the biosphere (the transition zone between them within which most plant and animal life exists and most living and dead organic matter (biomass) is to be found). The figure also shows the physical processes that take place within the climate system and exert an influence on climate. The initial conditions are first entered for each cell. The climate model program then uses the scientific principles and their equations to calculate for each cell its new temperature, pressure, windspeed, rainfall, humidity, etc for an hour later. These values become the starting data for the next calculation for the next hour, and so on for many years! With high speed computers these calculations can be done within several hours. Climate models must be validated against observations. Often the models begin with a year for which there is comprehensive data, such as 1950. The model is then run and its ‘predicted’ climate is compared with the actual climate for the following decades. If there is strong agreement then the model can be used to investigate the effect of possible scenarios into the future. 14 Rainfall observations: 1980 - 1999 Average of model predictions: 1980-99 Figure 12: Comparison of observations with climate model predictions How good are the climate models? The models produce graphs showing the variation with time of the various measures of climate, such as rainfall distribution, temperature variation, formation of poles and deserts, location and frequency of extreme events, and so on, as well as maps showing the geographical distribution of these aspects and how they change with time. The models show such details as seasonal monsoon rains in equatorial regions and the formation of cyclones off the coast of Queensland. These calculated measures of climate can be compared to actual climate data. The climate models show strong agreement and the accuracy of the models is confirmed. Figure 12 is an example of this, showing model predictions of rainfall compared to actual observations. The models can also be used to investigate the impact of the consumption of fossil fuels since the industrial revolution. The models are run twice, once with the CO2 produced from fossil fuels and second without the CO2. The two scenarios are compared again actual observations. This analysis confirms that the greenhouse gases (CO2 and CH4) generated by humans are having a significant impact on our climate. 15 The jagged line in the two graphs in Figure 13 is the variation in global surface temperature since 1900. The smoother curve in the top graph is the average prediction of all the climate models taking into account natural climate change factors and human related factors. The smoother curve in the bottom graph is the average prediction taking into account only natural climate change factors. The close fit in the top graph and the increasing gap in the bottom graph is convincing evidence of the human impact on the climate. The climate models can now be used to investigate various future emission scenarios, that is, what might happen to global surface temperature, sea level, rainfall, etc under different energy strategies. Figur Figure 13: ‘Most of the observed increase in global average temperatures since the mid-20th century is very likely (more than 90% certain) due to the observed increase in anthropogenic greenhouse gas concentrations.’ IPCC (2007) 16 5. Emission Scenarios or What do the climate models predict? Once climate models have been verified against historical data, they can be used to investigate the likely consequences of various strategies designed to reduce CO2. The figure below lists the four driving forces and how they combine to generate the four types of scenarios, for example in A1 there is a more global and technological approach to solving the problem. The 4 scenarios are: Figure 14 Categories of Emission Scenarios proposed by the Intergovernmental Panel on Climate Change (IPCC) A1 storyline: a future world of very rapid economic growth and rapid introduction of new and more efficient technologies. Ways of life between regions converge with extensive social and cultural interactions worldwide. There are subsets to the A1 family based on their technological emphasis: A1FI - An emphasis on fossil-fuels. A1B - A balanced emphasis on all energy sources. A1T - Emphasis on non-fossil energy sources. A2 storyline: a very diverse world with economic growth varying across regions. Technological change and improvements to per capita income also vary across regions and are slower than in other storylines. B1 storyline: as in the A1 storyline but with rapid changes toward a service and information economy, and the introduction of clean and resource-efficient technologies and an emphasis on global solutions to economic, social and environmental stability. B2 storyline: a world in which the emphasis is on local solutions to economic, social, and environmental sustainability. The economic development will be less rapid and there will be more fragmented technological change than in A1 and B1. 17 Figure 15. Multi-model averages of surface warming (relative to 1980–1999) for the scenarios A2, A1B and B1. The shading denotes the range of individual model annual averages. ‘Constant composition commitment’ means CO2 is fixed at 2000 level. Figure 15 shows the models predict a minimum of about 1.5 degrees of warming this century on a best case scenario, and at least 3 degrees if international agreement is not reached on alternative energy sources. Figure 16: Annual warming for 2080-2099. A1B scenario. Figure 16 show that the models predict that the warming will not be uniform across the earth, that even with a ‘balanced emphasis on all energy sources’ the northern latitudes will experience a massive increase in temperature over 7 degrees. This will have a significant impact on the frozen tundra. 18 6. Interpreting Data One of the common statements by climate change deniers is that ‘the global surface temperature has cooled in recent years’. The earth’s atmosphere is a large and complex system with many diverse and varying factors. The global surface temperature fluctuates substantially from year to year, however the overall trend is apparent in Figure 17 below. A quick glance at the figure reveals numerous time during the last 160 years when the global surface temperature has declined for several years in a row. Taking the longer perspective, it is clear that there has been an underlying steady increase in the temperature since 1900. 1 Temperature Anomaly (Celsius) 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 1850 1870 1890 1910 1930 1950 1970 1990 2010 Year Figure 17: Global Air Temperature difference since 1850 The other consideration in interpreting this graph is that the Sun not only heats up the atmosphere, but also the land, but more particularly the oceans as the atmosphere and the seas easily exchange energy. In fact the massive amount of energy stored in the oceans means that the variation in temperature due to climate change is smoothed out. However while satellites enable currently allow the average global sea temperature to be measured, there is little historical data to provide a view over time. 7. Climate change impacts Already climate change has had an environmental impact. Three examples are: i) The retreat of glaciers means that there is less water held in the ice and a reduced flow from the summer melt to feed rivers downstream. Currently the mountain regions of South America are being affected, however of more concern is the Tibetan ice sheet. Significant retreat here would greatly impact on the livelihood of both China and India. Of course the water from the melting glaciers will ultimately lead to sea level rise. 19 ii) The decrease of Summer Arctic Sea ice The graph below shows a steady reduction in the amount of Arctic sea ice during the Arctic summer. Of particular concern is that the decline is significantly greater than what the climate models were predicting. The melting of this sea ice will not of itself lead to a rise in the sea level as the ice is floating, and so, the melted ice will take up the same volume as the amount of ice under the surface. Figure 19: Extent of summer arctic sea ice: Graphs of observations and model predictions However what is of concern is that a surface that was previously white and highly reflective will be replaced by one that is dark and absorbing. This is an example of positive feedback, where the melting ice results in warmer water, which leads to more ice melting. iii) Changes in acidity and salinity of the oceans. CO2 is absorbed by the oceans, making them more acidic. This weakens the skeletons of marine animals. Acidity is measured using the pH scale. A decrease in the pH of 0.1 is equivalent to a 25% increase in the acid concentration. 8.3 8.2 8.1 pH 8 7.9 7.8 10 million 1 million years ago years ago 1850 Time 1950 1900 2000 Figure 20: pH of the oceans over time Future predictions are based on the average of IPCC scenarios. 2050 2100 Figure 21: Salinity in the North Atlantic This is the largest ocean change measured. (measured in parts per thousand). This could impact of the flow of the Gulf Stream. 20 8. Causes for concern i) Temperature change Because of the CO2 already in the atmosphere, a two degree rise in temperature above 1990 values by mid century is unavoidable. The temperature rise by 2100 depends on the energy decisions to be made in the next five - 10 years. A fossil fuel dependent scenario is expected to result a temperature rise of at least four degrees above 1990 values and possibly more than six degrees. A switch to almost exclusive non-fossil fuel energy sources would still see the temperature rise, but likely to be only to 2.5 degrees. It is very likely that heat waves will be more intense, more frequent and longer lasting in a future warmer climate. Cold episodes are projected to decrease significantly in a future warmer climate. Almost everywhere, daily minimum temperatures are projected to increase faster than daily maximum temperatures. ii) Sea level rise When materials get hotter they expand, oceans are no different. The warming of the oceans alone is expected to increase the sea levels. Regardless of the scenario the sea level is expected to rise by about 3mm per year, which is about 30cm over the century on average across the globe. The models currently suggest that the Arctic area will experience the largest increase and the southern hemisphere should experience marginal sea rise. However there is much ice that is on land in Greenland, Antarctica and in many glaciers around the world. If this ice were to reduce in size and the water to flow to the sea, then the sea level rise takes on another dimension. The ice in Greenland and the Antarctic is thick and would take centuries to fully melt, but the various models suggest that a reliance on fossil fuels would produce a sea level rise by at least double that caused by thermal expansion of the oceans. Much of this effect would occur after 2100. The Arctic ice that makes up the North Pole is floating on water. When it melts, the sea level does not rise because ice is less dense than water, which why it floats. However the melting of sea ice can have a severe impact. The ice, being white, reflects much of the sun’s visible radiation back into the atmosphere and out into space. When it melts to water, it reflects much less, absorbs much more and the water warms, which warms the atmosphere, which melts more sea ice … . This reinforcing and accelerating process is called positive feedback. As mentioned in section 2, the capacity of a substance to reflect light is called its albedo. Ice has an albedo of 35%, while sea water has a value of 8%. A black surface has a value of 0. More CO2 in the atmosphere not only increases the temperature of the oceans, it will also lower their pH, making them more acidic as well as altering their carbon chemistry. This will weaken the shells and skeletons of sea creatures, affecting their survival and ultimately ocean ecology. 21 i) Best estimate projected rainfall ii) Observed trend in annual rainfall change for 2070, 1970-2007 Figure 22: Observed and projected Australian rainfall iii) Changes in rainfall patterns For a warmer climate, the models indicate that rainfall will increase in monsoon areas and the tropical Pacific and decrease in the subtropical and mid-latitude regions. Across the globe on average there will be more water vapour in the air, (higher humidity), more evaporation and more rain. Figure 22 ii) shows for Australia that over the last 37 years there has been a significant increase in rainfall in the west and while the east has suffered a major decrease. Figure 22 i) indicates that the long term trend is significantly less rainfall across the country. In mid-latitude regions such as Australia, there would also be longer periods between larger rainfall events. There is expected to be a tendency for drying of the midcontinental areas during summer, leading to a greater risk of drought. iv) Changes in crop viability and distribution of pests and diseases IPCC said in its fourth report that approximately 20-30% of plant and animal species assessed so far are likely to be at increased risk of extinction if increases in global average temperature exceed 1.5-2.5oC. With changing weather patterns, the ecosystems, within which tropical diseases such as malaria occur, are likely to move north and south away from the equator. There is some evidence that this beginning to occur. It is also likely that crops will need to planted in other parts of the Earth as rainfall and temperature change. Climate change significantly affects plant and animal species. 22 9. Expressing concern At home: • Retrofit double glazing, • Lower temperature setting for heating, • Turn off appliances at the wall, • Use throw rugs, • Put up pelmets, • Install compact fluorescents, • Use public transport, • Install solar panels and a solar water heater With Government: Write and phone and fax and email and talk to your local representatives (Council, State and Federal, upper and lower house). Advocate one or more of the following: • A maximum global CO2 level by 2020 (2050), e.g. 350 parts per million. • Zero emissions by Australia by, for example, 2050. • Carbon emissions tax combined with a tax rebate for low income earners. • Subsidy of alternative fuels, including Geothermal, Solar Thermal, Wind, Photovoltaic, Nuclear and Biomass, from a carbon emissions tax. • Feed in tariffs for solar panels. To find your electorate and federal member go to http://apps.aec.gov.au/esearch/ and enter your suburb or postcode. To find your federal member’s contact details go to http://www.aph.gov.au/house/members/memlist.pdf for an alphabetical list of members with contact details for both their electorate office and the Parliament House office. A list of senators by state can be found at http://www.aph.gov.au/Senate/Senators/homepages/index.asp?sort=state Each of their contact details can be obtained by clicking on their name. To find the contact details of both your representatives in the Victorian parliament go to http://www.parliament.vic.gov.au/handbook/menupage.cfm?menuId=2 and enter your street name and suburb. To contact your council representative, ring the council. 23