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GLOBAL WARMING A guide to its origins and effects GLOBAL WARMING a guide to its origins and effects Acknowledgements: Research for this report was conducted by David Zekria under the direction of Dr Ian Mays and Stephen Balint of Renewable Energy Systems Ltd (RES) ([email protected]). With thanks to Crispin Aubrey for editorial advice. Additional editing by Anna Stanford. Design and production by Inmarc Associates. The authors would also like to express their thanks to those organisations and individuals who contributed illustrations, the sources of which are referenced in the text. Disclaimer: This Guide (the ‘Report’) has been prepared by Renewable Energy Systems Ltd (‘RES’) by reference to internal and published materials. RES has endeavoured in preparing this Report to ensure that it is accurate and objective, its purpose being to inform a wider audience of the current status of research on climate change, its origins and effects. As a company whose business is derived from wind energy and other renewable resources, RES has its own perspective on the subject matter of this Report. Nonetheless, it has tried to ensure that the Report is accurate and balanced. It is hoped that readers of this Report will find it helpful and informative, but it is not RES’s intention that it may be relied upon by others, and anyone utilising the Report for any reason does so at their own risk. Accordingly, RES shall not be deemed to make any representation regarding the accuracy, completeness, methodology, reliability or current status of any material contained in this Report, nor do RES or any of its affiliated companies or employees assume any liability with respect to any matter or information referred to or contained in the Report. This Report is subject to copyright protection. This Report may be reproduced free of charge provide that it is reproduced accurately and the source and copyright status of the material is made evident in so doing. © Renewable Energy Systems Limited 2007. GLOBAL WARMING a guide to its origins and effects CONTENTS FOREWORD ................................................................................................................................2 EXECUTIVE SUMMARY..............................................................................................................3 PART ONE: THE BACKGROUND TO GLOBAL WARMING..........................................................................5 PART TWO: WHY THE EARTH IS GETTING WARMER ................................................................................6 1 Irradiance ........................................................................................................................6 2 The Greenhouse effect ..................................................................................................6 PART THREE: THE FUTURE DEVELOPMENT OF GLOBAL WARMING .........................................................9 1 Future emissions and atmospheric levels of CO2 ......................................................9 2 Future global temperature...........................................................................................10 3 Feedback mechanisms ................................................................................................11 PART FOUR: THE CONSEQUENCES OF GLOBAL WARMING....................................................................14 1 Direct effects of heat and cold ...................................................................................14 2 Disease ..........................................................................................................................14 3 Agriculture and nutrition .............................................................................................15 4 Drought and water resources ....................................................................................15 5 Sea level rises and flooding........................................................................................16 6 El Niño ...........................................................................................................................16 7 Storms ...........................................................................................................................17 8 Ecosystems and biodiversity......................................................................................17 9 Economic consequences ............................................................................................18 PART FIVE: SOLUTIONS...............................................................................................................................19 PART SIX: CONCLUSIONS .........................................................................................................................20 REFERENCES ...........................................................................................................................21 1 GLOBAL WARMING a guide to its origins and effects GLOBAL WARMING a guide to its origins and effects Foreword Global warming has become the most prominent environmental issue of our times. Growing public awareness of the effects of elevated global temperatures has been driven by clear signs around the world that climate change is already happening. Climate change is now one of two key drivers for sustainable energy investment, the other being energy security and the availability of future fuel resources. We therefore recommend that this report is read in conjunction with ‘Plugging the Gap: A Survey of World Fuel Resources and their Impact on the Development of Wind Energy’, published by RES and the Global Wind Energy Council. We hope that together they will demonstrate that quickening our pace along the clean energy path can bring social, environmental and economic benefits to us all. Dr Ian Mays, CEO, RES Group ©Greenpeace/Beltrá/Archivo Museo Salesiano/De Agostini From the UK Stern Review in 2006 to the latest Intergovernmental Panel on Climate Change (IPCC) report published in February 2007, stark warnings are coming from scientific and economic experts that climate change is a reality and that the consequences to our society will be significant. Governments around the world are taking action in the form of legislation, such as the UK’s Climate Change Bill and the European Union’s 2007 target of a 20% reduction in emissions by 2020. Individual countries, regions and states, such as California, have ambitious plans for action. But how can these challenging obligations be achieved? Mechanisms such as emissions trading schemes have an important role to play. However, renewable energy technologies have huge potential to assist in meeting reduction targets. Making greater use of wind and solar power, geothermal energy, biomass and marine technologies such as tidal and wave power, represents one of our best strategies for meeting the climate change challenge, whilst also helping to secure the availability and security of future energy supplies. Our aim in publishing this report is to provide an accessible and up-to-date overview of current scientific thinking on global warming, its origins and effects, that will be of use to all those with an interest in the subject. The report has been written and published by Renewable Energy Systems Ltd (RES) following a comprehensive survey of scientific and technical sources including leading international and national bodies such as the IPCC, NASA, the World Health Organisation (WHO), and published papers in scientific and technical journals. A full list of references is given at the end. It is intended that this report can be used freely as a resource to help inform policy and activities in the field of climate change and sustainable energy. The decline of glaciers, such as the Upsala Glacer in Patagonia, seen here in 1928 (top) and 2004 (bottom), could be one sign of rising global temperatures. 2 GLOBAL WARMING a guide to its origins and effects Executive Summary Global mean temperatures are currently at their highest level since direct measurements were first made. Over the last 100 years, the world’s temperature increased by 0.74°C, faster than at any time in recent human history. The warmest year on record was 20051, with eleven of the last twelve years (1995 – 2006) ranking among the twelve warmest years on record. Temperatures before the mid-19th century, when worldwide measurements became widespread, can be estimated from indirect sources such as tree rings. This data suggests that temperatures are now higher than at any time over the last 2,000 years. 2007 is expected to break the global record again2. The temperature of the earth has fluctuated over the 4.65 billion years of its history. What is important for our society in the 21st century is how the current trend of rising temperatures compares to long-term patterns, what the underlying causes driving this increase might be and how we can avoid the potentially devastating impacts of a warming world. It is now accepted that the increase in the atmospheric concentration of carbon dioxide, the principal so-called ‘greenhouse gas’, caused by the combustion of fossil fuels, is a significant driver behind growing global temperatures. The most recent report from the IPCC, the Fourth Assessment Report published in 2007, is firmer than ever before in its conclusion that humankind is having a significant input into global warming: ‘Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations3. Many other factors also interplay to determine the global heat budget, and identifying the exact extent to which global warming is anthropogenic (humanrelated) is still contentious. However, measurements of past atmospheric carbon dioxide concentrations and global temperatures indicate a clear correlation between the two. Anthropogenic sources of other gases, such as methane, nitrous oxide, ozone and CFCs, as well as black carbon and sulphates, also influence global temperatures. Predicting future temperatures is complicated because it is difficult to be precise about ‘climate sensitivity’ – to what extent temperature depends on atmospheric carbon dioxide levels – and because future levels of CO2 are uncertain. This uncertainty has been dealt with by considering a number of different scenarios, outlined by the IPCC, spanning the range of the most likely courses of events. This enables us to see the boundaries within which future carbon dioxide levels are likely to fall, even if we are unable to accurately determine actual values. Climate sensitivity has been defined as an increase of 2.0 – 4.5°C, with a best estimate of 3.0°C, for a doubling of carbon dioxide concentrations, a level anticipated around the year 2100. The latest research suggests that we should therefore expect a warming of about 0.2°C per decade for the next two decades. By the final decade of the 21st century global temperatures are expected to have risen by 1.8–4.0°C compared with the end of the 20th century. This estimate, however, does not take feedback mechanisms into account, which could amplify the warming process. There are numerous examples of ‘feedback effects’ which could have a climatic influence. Melting of white polar ice, for instance, reduces the reflectivity of the land, causing more sunlight to be absorbed and thus greater heating of the environment, leading to further melting of ice. Stagnant sea-surface waters could become saturated with carbon dioxide, thereby losing their ability to absorb CO2 from the atmosphere. Carbon dioxide-absorbing phytoplankton, which depends on nutrients drawn from the ocean floor by the circulation, could also dwindle. Rising temperatures may cause greenhouse gases frozen in polar ice, permafrost and sea floors to be released, further strengthening the greenhouse effect. These, and other potentially unrecognised mechanisms, are likely to play a role in the evolution of the climate, and may even lead us beyond a point where temperatures can be restored to their original state. Global warming is important because of its many influences on our lives. The anticipated rise in sea levels threatens to flood and submerge low-lying land masses. Sea levels have already risen by 17cm during the last century. Higher temperatures will influence the transmission and range of diseases such as malaria, the quality and productivity of agriculture, the availability of fresh water and the frequency and intensity of weather events such as storms. We can expect hundreds of millions of ‘climate refugees’ and significant impacts on the global economy. Whilst global warming-related climate change may benefit some sectors, the effects will on balance be negative. If we are to limit the detrimental consequences of global warming, we must take steps to counter its root cause and do so without delay. This 3 GLOBAL WARMING a guide to its origins and effects means cutting our emissions of greenhouse gases by reducing our dependence on fossil fuels and replacing them with clean, renewable energy. The potential for low-carbon technologies such as wind, biomass, geothermal, solar and marine power is enormous and increasing investment in these as soon as possible makes economic, social and environmental sense. AT A GLANCE 4 ● Global temperatures now higher than at any time in the last 2,000 years ● Eleven of the last twelve years have been amongst the warmest twelve years on record ● Latest IPCC report (2007) concludes that global warming is ‘very likely’ caused by greenhouse gas emissions from human activity ● Measurements of past CO2 concentrations and global temperatures (eg in ice core data and tree rings) shows a correlation between the two ● Before the industrial era, atmospheric concentrations of CO2 were relatively stable for several thousand years at around 280 parts per million (ppm). Over the past 650,000 years, the range of concentration has never been above 300ppm ● In 2005 atmospheric CO2 concentration stood at 379 ppm, a 35% increase on preindustrial era levels ● Other greenhouse gas emissions, such as methane and nitrous oxide, are having an additional heating effect on the earth ● CO2 concentrations are predicted to rise by the end of the 21st century under three emissions scenarios used by the IPCC ● The last 100 years registered a warming of about 0.74°C and an increase of 17cm in sea levels ● During the last interglacial period, when temperatures were 4°C higher than at present, sea levels were 6 metres higher ● By the year 2100, it is estimated that global average temperatures will have risen by between 1.8 and 4.0°C over present values ● This may be even greater if feedback mechanisms kick in and could lead to runaway climate change ● Global warming will have significant impacts on human health, the economy and the biodiversity of the planet ● While some warming is inevitable and adaptation is important, an immediate shift to a lowcarbon economy and increased investment in sustainable energy can help avoid the most serious consequences of climate change and bring social and economic benefits GLOBAL WARMING a guide to its origins and effects PART ONE: THE BACKGROUND TO GLOBAL WARMING The mean surface temperature of the earth has been steadily rising, particularly over the last 30 years. Over the last 100 years (1906–2005), the world’s temperature increased by 0.74°C. The warming trend over the last 50 years is nearly twice that for the last 100 years4. 0.6 0.5 Temperature Anomaly /ºC 0.4 0.3 0.2 0.1 0 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 -0.1 Natural variations in mean temperature take place on a wide range of timescales, from yearly fluctuations to changes over millions of years. The world has been free of ice over much of its history, but these iceless periods have been interrupted by several major glacial epochs. The current epoch began about 3.2 million years ago. Since then we have had about 15 to 20 major advances and subsequent retreats of the ice field, the advances being known as ice ages, the retreats as inter-glacial periods. We are currently in an inter-glacial period. Climatic fluctuations may also be localised. Over the last two millennia, there have been two periods of anomalous (abnormal) temperatures across Europe, and possibly further afield. A relatively warm period, often referred to as the Medieval Climatic Optimum7, lasted from the 10th to 14th centuries, then a relatively cold period called the Little Ice Age8 from the mid-15th century to the beginning of the 19th century. -0.2 -0.3 -0.4 Year Annual mean 5-year mean Figure 1: Global mean surface temperature variation from 1951–1980 mean, from direct measurements since 1880 5. Before the middle of the nineteenth century, temperature data was not gathered widely on a global basis. Direct measurements are therefore not available. But we can still reconstruct local climatic conditions from secondary sources such as ice boreholes and cores, sediment records, tree rings and corals. From these analyses it is clear that recent temperatures are not only the highest they have been over the last century, but probably over the last two millennia. 0.6 0.5 Most of the warming that has occurred since then has been in two phases. The first lasted from around 1910 to the early 1940s, the second from around 1975 to now. Current global mean surface temperatures are the highest they have been for at least two thousand years, and are continuing to rise. It is suspected this anomalous recent trend is a result of human influences. While natural climatic variations and the many factors influencing them, underline the difficulty in establishing the exact extent to which current trends are anthropogenic (caused by human activity) in origin, the latest (2007) conclusions from the IPCC are less equivocal than previously, stating in its Working Group I report that it is extremely unlikely that the observed widespread warming of the atmosphere and ocean in the last century can be due to known natural causes alone. This report looks first at the factors which drive global temperatures, then at the likely future trends, and finally at the impact of global warming on our planet and society. Temperature Anomaly /ºC 0.4 0.3 0.2 0.1 0 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 -0.1 -0.2 -0.3 -0.4 Year Annual mean Figure 2: Global mean surface temperature anomaly from proxy data (years 200–1980) and direct measurement (1981–2005), with respect to 1951–1980 mean based on direct measurement data 6. 5 GLOBAL WARMING a guide to its origins and effects PART TWO: WHY THE EARTH IS GETTING WARMER 1. Irradiance The source of practically all heat at the surface of the earth, and in the atmosphere above us, is the sun. Its brightness is a critical factor determining the earth’s temperature. The temperature of the earth is normally at equilibrium – as much energy is absorbed from the sun’s rays as is radiated back into space. The energy radiated back depends fundamentally on the temperature of the earth’s surface and atmosphere system. If the energy absorbed from the sun’s rays increases or decreases, the temperature of the earth will also increase or decrease until a new equilibrium is reached. In order to understand global warming, it is therefore important to know to what extent variability in the sun’s brightness, measured by its ‘irradiance’, affects the earth’s surface temperature. The sun’s irradiance at the distance of the earth from the sun is approximately 1,367 Watts per square metre (W/m2). This quantity is often referred to as the ‘solar constant’, although it does in fact vary slightly. The largest cause of such variations is the existence of sun spots (dark patches on the surface of the sun), the number of which tends to follow an 11 year cycle. Results from satellite observation show that the variation in irradiance over the sun spot cycle is of the order of 1 W/m2. This would lead to a small temperature change at the earth’s surface. It is therefore clear that sun spots cannot account for the global temperature changes we have seen over the last 30 years. Some solar radiation is reflected by the earth and the atmosphere 2. The Greenhouse Effect The basic principle of the ‘greenhouse effect’ is that heat is trapped by the atmosphere, thereby providing a secondary heating effect on the earth in addition to that from the sun. Short-wavelength sunlight easily penetrates the earth’s atmosphere to reach the ground and warm it up, whereas the longer-wavelength light radiated by the earth is absorbed or trapped within the atmosphere, rather than escaping into space. This causes the atmosphere to warm up marginally, which itself then reradiates long-wavelength light into space, as well as back towards the ground, providing the additional warming. The greenhouse effect keeps our climate at an inhabitable temperature. It is estimated that without it the earth would be about 33°C cooler. The constituents of the atmosphere responsible for trapping this radiation are known as ‘greenhouse gases’. The most important of these is water vapour. Other significant greenhouse gases include carbon dioxide, methane, nitrous oxide, ozone and halocarbons. Greenhouse gases: Water vapour Water vapour is the most abundant greenhouse gas, and accounts for the largest proportion of the greenhouse effect, although its concentration is variable. Generally, warmer air has a greater capacity for holding water vapour, leading to a feedback mechanism. The warmer the atmosphere, the higher its average water vapour content and the higher its heating effect. However, water vapour has a short life in the atmosphere, as it is quickly removed through Some of the infrared radiation passes through the atmosphere, and some is absorbed and re-emitted in all directions by greenhouse gas molecules. The effect of this is to warm the earth’s surface and the lower atmosphere Solar radiation passes through the clear atmosphere Most radiation is absorbed by the earth’s surface and warms it Figure 3: The Greenhouse Effect mechanism 6 Infrared radiation is emitted from the earth’s surface GLOBAL WARMING a guide to its origins and effects Greenhouse gases: Carbon dioxide Carbon dioxide (CO2) is considered the most significant greenhouse gas because its concentration in the atmosphere has increased at an exceptional rate over the last half century. Before the industrial era, atmospheric concentrations of CO2 were relatively stable for several thousand years at around 280 parts per million (ppm). Between 1850 and 2000, however, a total of 1,620 billion tonnes of carbon dioxide is estimated to have been released into the atmosphere from anthropogenic sources. Of this, 560 billion tonnes originated from changes in land use, 1,030 billion tonnes from combustion of fossil fuels and 20 billion tonnes from chemical processes involved in cement manufacture. Approximately half of this has been removed by plants and the ocean, the rest remaining in the atmosphere. The 2005 value of atmospheric CO2 concentration stood at 379 ppm10, a 35% increase on pre-industrial era levels. The average rate of increase since 1980 has been 0.4%/yr11. It has been estimated that the increase of CO2 between 1750 and 2005 has caused a global average radiative forcing, or additional heating effect, of 1.66 W/m2 on the earth10. Historical atmospheric carbon dioxide levels can be measured from ice cores. These are formed in polar regions when layers of snow are gradually compressed into solid ice under the weight of successive annual layers. During this compression, samples of atmospheric air are trapped as tiny bubbles in the ice. These can be analysed to determine both the historical atmospheric gas composition and temperature. Such measurements were made from ice cores extracted at the Vostok station in the Antarctic, giving data spanning over the last 400,000 years and four glacial/interglacial periods. In November 2005, Science Magazine12 published new data from the European Project for Ice Coring in Antarctica (EPICA) which went even further back to 650,000 years ago and confirmed the Vostok records. As can be seen on the graph (Figure 4), atmospheric CO2 content and Although not completely understood, the 100,000 year periodicity of these ice ages is believed to result from small, periodic changes to the position of the Earth as it orbits around the sun. These changes influence the irradiance from the sun, increasing it where the Earth is slightly closer, and decreasing it where it is further away. The shape of the Earth’s orbit around the sun is eccentric, meaning that rather than following a perfectly circular path, it is elongated somewhat into an ellipse. The shape of this ellipse itself varies, with a principal periodicity of 413,000 years, and other periodicities varying between 95,000 and 136,000 years. These loosely combine into an approximately 100,000-year cycle, commensurate with the ice-ages. Carbon Dioxide and Temperature Records -320 400 Vostok temperature Vostok CO 2 Present CO 2 level -360 EPICA temperature EPICA CO 2 -340 350 -380 -360 -400 300 -380 -420 -400 -440 4 250 Atmospheric CO2 (ppm) Nevertheless, much uncertainty exists in defining the extent and importance of water vapour in the climatic balance. As vapour levels increase, more of it will eventually condense into clouds, which are able to reflect sunlight back into space, and thus allow less energy to reach the surface of the earth and heat it up. Greater understanding of the feedbacks related to water vapour is critical in projecting future climate change9. temperature appear to follow a very similar pattern. Over the last 650,000 years there have been seven periods of relative coolness, with a frequency of approximately 100,000 years. These correspond to ice ages. We are currently in an interglacial stage, and therefore sit at a relative peak in temperature. δ²H (permille) precipitation (rain/snow). As far as global warming is concerned, therefore, it is more important as a feedback mechanism than a driver. -420 -460 6 -440 650 200 -480 600 550 500 450 400 350 300 250 200 150 100 50 0 Thousands of Years Ago Figure 4: Historic atmospheric carbon dioxide and temperature (by proxy) data for the last 650,000 years obtained from the Vostok and EPICA ice core analyses. Source: Science Magazine It has been estimated that the rise of atmospheric CO2 concentration associated with glacial terminations, i.e. the ends of the ‘ice ages’, actually lags the local temperature profile by approximately 800 years13-16, suggesting that these periods of warming were not triggered by rises in atmospheric CO2, but rather were the initial cause of them. This does not, however, contradict the role of CO2 in global warming. Although atmospheric CO2 levels may not have been responsible for the initial rise in temperature in these periods, the subsequent increase in CO2 concentration has contributed to the continuing rise in temperatures in a feedback cycle, causing a further release of CO2 and consequently greater warming. The entire warming process, and associated temperature rise, at the end of a glacial period, takes place over about 5,000 years. The results of the ice core analyses show that preindustrial era atmospheric CO2 concentrations were much lower than present levels and have not exceeded 300ppm in any of the last eight inter-glacial 7 GLOBAL WARMING a guide to its origins and effects periods. The present day concentration is 379ppm. CO2 levels today are therefore 27% higher than their highest previous level in the last 650,000 years. Greenhouse gases: Methane Methane is a significant greenhouse gas because, although its atmospheric concentrations are much lower than CO2, it is over 20 times more effective at trapping heat in the atmosphere. The gas is produced principally through anaerobic decay of organic matter, major natural sources being wetlands, oceans, termites and methane hydrates17. Over half of all methane emissions are anthropogenic, mainly from animal husbandry, waste management, fossil fuel production, rice cultivation and biomass burning. At present, atmospheric methane concentrations stand at around 1,774 parts per billion (ppb)18, having more than doubled since the pre-industrial era. This excess methane contributes an additional heating of 0.48 W/m2, or about 18% of the greenhouse effect from all the long-lived greenhouse gases18. Such concentrations exceed by far the natural range of the past 650 000 years, as determined by ice cores18. However, as methane has a relatively short lifetime in the atmosphere of about 12 years, any reduction in emissions will be promptly followed by a corresponding reduction in atmospheric concentration. Greenhouse gases: Nitrous oxide Current atmospheric levels of nitrous oxide (N2O) stand at approximately 319ppb, up about 18% on preindustrial levels18. Approximately one third of current emissions are estimated to have anthropogenic origins, principally from the use of fertilisers in agriculture, nylon and nitric acid production, cars with catalytic converters and the burning of organic matter. The oceans, forests and soil are the main natural sources. Nitrous oxide is a strong absorber of infrared radiation. Therefore, in spite of its relatively low atmospheric concentration, the radiative forcing of increased nitrous oxide since 1750 is estimated18 at 0.16 W/m2. This is about 6% of the total from all the long-lived greenhouse gases18. Other greenhouse gases There are a number of other greenhouse gases present in the atmosphere in low concentrations. These include man-made halocarbons such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs), as well as other gases like trichloroethane (CH3CCl3), carbon tetrachloride (CCl4), 8 and carbon monoxide (CO). The atmospheric concentrations of some CFCs, trichloroethane and carbon tetrachloride have been decreasing in response to reduced emissions, but HCFC and HFC concentrations are on the increase as they have been adopted as CFC substitutes. Halocarbons contribute a radiative forcing of 0.34 W/m2, which equates to 13% of the total from all greenhouse gases18. However, CFCs have been responsible for destroying stratospheric ozone, resulting in a cooling effect. Ozone Ozone is an important greenhouse gas, although its influence on the greenhouse effect is dependent on its altitude. Some ozone exists in the troposphere, the lower part of the atmosphere – from ground level up to about 12km. This gas originates primarily from photochemical reactions with hydrocarbons and nitrogen oxides emitted by motor vehicles, fossil fuel refineries, power plants and other industries. The global average radiative forcing due to increases in tropospheric ozone since pre-industrial times is estimated to have enhanced the anthropogenic gas forcing by approximately 0.35 W/m2 18. This makes tropospheric ozone the third most important greenhouse gas after CO2 and methane. Other factors affecting temperature Apart from greenhouse gases, there are other atmospheric constituents, some natural, some manmade, which play a role in the global temperature balance. Most of these are in the form of microscopic solid particles called aerosols. Natural aerosols include dust, sea salt, spores and volcanic particles. Their influence on the climate is complex, as they have various absorptive and reflective properties, and also take part in secondary effects related to cloud formation and cloud quality. The most significant aerosols of anthropogenic origin are black carbon and sulphates. Black carbon is soot produced by incomplete combustion of carbonaceous material, mainly fossil fuels and biomass, each of which are estimated to contribute about half of the total. As soot particles absorb sunlight, they have the effect of both heating the air and reducing the sunlight reaching the ground. Black carbon is also believed to play a significant role in the loss of ice and permafrost. As black carbon infiltrates ice and snow, its dark colour acts to reduce the albedo, or reflectivity. More radiation is thus absorbed, warming the ice and promoting its melting19. The total anthropogenic radiative forcing by black carbon18, including the indirect effects on snow and ice albedo, is 0.1W/m2. GLOBAL WARMING a guide to its origins and effects Sulphate aerosols have their origins in sulphur dioxide (SO2) released into the atmosphere primarily from unscrubbed power plants and large scale agricultural burning, but also from volcanic eruptions. Sulphur dioxide is transformed in the atmosphere into sulphate aerosols. These particles largely reflect the sun’s radiation, and are therefore believed to have a net cooling effect. However, it has been suggested that sulphur dioxide leads to the formation of more ice crystals in the upper atmosphere, some of which move upwards into the stratosphere, where they increase the amount of water vapour. This extra humidity enhances the greenhouse effect, but water vapour also destroys ozone20, reducing the concentration of one of the other greenhouse gases. The overall influence of these various effects is complex, A number of studies have suggested that atmospheric pollution, especially aerosol particles, is responsible for blocking sunlight from reaching the surface of the earth, sometimes referred to as ‘global dimming’. However, there is evidence that the effects of global dimming have declined since 1990 in response to reduced atmospheric aerosol pollution following tighter controls on particulate and sulphurous emissions21,22. The IPCC estimates21 that anthropogenic contributions to aerosols (including sulphate, organic carbon, black carbon, nitrate and dust) produce a cooling effect, with a total direct radiative forcing of –0.5W/m2. Concentrations and their changes Species CO2 CH4 N2O 2005 379 ± 0.65ppm 1,774 ± 1.8ppb 319 ± 0.12ppb ppt CFC-11 251 ± 0.36 CFC-12 538 ± 0.18 CFC-113 79 ± 0.064 HCFC-22 169 ± 1.0 HCFC-141b 18 ± 0.068 HCFC-142b 15 ± 0.13 19 ± 0.477 CH3CCI3 CCI4 93 ± 0.17 3.7 ± 0.10 HFC-125 HFC-134a 35 ± 0.73 3.9 ± 0.11 HFC-152a HFC-23 18 ± 0.12 5.6 ± 0.038 SF6 74 ± 1.6 CF4(PFC-14) C2F6(PFC-116) 2.9 ± 0.025 CFCs Total HCFCs Total Montreal Gases Other Kyoto Gases (HFCs + PFCs + SF6) Halocarbons Total LLGHGs Radiative Forcing Change Change since since 1998 2005(Wm-2) 1998(%) +13ppm +11ppb +5ppb ppt –13 +4 –4 +38 +9 +6 –47 –7 +2.6 +27 +2.4 +4 +1.5 – +0.5 1.66 0.48 0.16 +13 – +11 0.063 0.17 0.024 0.033 0.0025 0.0031 0.0011 0.012 0.0009 0.0055 0.0004 0.0033 0.0029 0.0034 0.0008 –5 +1 –5 +29 +93 +57 –72 –7 +234 +349 +151 +29 +36 – +22 0.268 0.039 0.320 –1 +33 –1 0.017 0.337 2.63 +69 +1 +9 Source IPCC2007 PART THREE: THE FUTURE DEVELOPMENT OF GLOBAL WARMING 1. Future emissions and atmospheric levels of CO2 Forecasting the future pattern of CO2 emissions is difficult because it depends on a multitude of factors. For short timescales, past trends can be extrapolated. For timescales of several decades, however – more relevant to the long term development of global warming – unpredictable factors come into play. Future world population, economics, the availability of different energy sources, improvements in efficiency, changes in land use and government regulations on emissions are some of the human factors which may influence CO2 production. On the other hand, natural feedback mechanisms will potentially have a much greater effect on future atmospheric levels. As our ability to foresee the effect of human influences is limited, and our current understanding of feedback mechanisms is poor, any firm prediction of future CO2 emissions would be unreliable. Instead, the common practice is to use a set of scenarios which cover a range of possible courses of events. On the basis of these, it is possible to run climatic simulations to give us an idea of the outer boundaries of future global warming. The principal scenarios of future CO2 emissions on which climatologists base their models are those produced by the IPCC and the World Meteorological Organisation. The future is considered in terms of global economic development and three different energy scenarios given: fossil fuel intensive, a mixture of fossil and non-fossil fuels, and making an eventual transition to non-fossil fuels. The projected annual CO2 emissions from each of these have been used to make estimates of future atmospheric CO2 concentrations. Other emissions As with CO2, similar uncertainties exist over future emissions of other climate influencing gases. Growth rates of methane emissions have declined since the early 1990’s, consistent with total emissions being nearly constant during this period24. The growth rate of global atmospheric nitrous oxide concentration has been fairly constant since 198024. Whilst the growth rates may not be increasing, this nevertheless means that, in all cases, the atmospheric concentration is expected to rise25. Sulphur dioxide is projected to decrease under all scenarios after about 203026. Figure 5: Long-lived greenhouse gases, their present-day concentrations and radiative forcing, with changes since 198823 9 GLOBAL WARMING a guide to its origins and effects 2. Future global temperature Establishing the exact effect of these increasing atmospheric greenhouse gas and aerosol concentrations on future global temperatures is still a matter of controversy. Some argue that the warming observed so far is unrelated to changes in atmospheric greenhouse gas levels, whilst others believe it is the result of anthropogenic emissions. Quantifying future warming is difficult because firstly, we are unsure of the primary temperature response in relation to changes in atmospheric greenhouse gas levels, and secondly, the potentially greater influence of feedback effects is not well understood. However, the most recent report from the IPCC provides increased confidence in the understanding of the climate system’s response to radiative forcing27. The fact that observed changes are consistent with their climate models and that the rise in temperatures has only been reproduced in models that include anthropogenic emissions, provides a stronger link between human activities and global warming. The extent to which the global mean surface temperature responds to changes in atmospheric greenhouse gas concentrations is called the ‘climate sensitivity’. The more accurately we know the climate sensitivity, the better we can estimate climate change based on projected atmospheric greenhouse gas levels. The IPCC, in its 2007 report, stated that the climate sensitivity in relation to a doubling of equivalent CO2 concentration is likely to be in the range of 2.0 to 4.5°C, with a best estimate of 3.0°C, based primarily on climate models28. The range of the estimate arises from uncertainties in the models and their internal feedbacks, particularly those involving cloud feedback and related processes. Future temperature projections from the IPCC report are shown in Figure 6 for a range of scenarios identified by the IPCC and as discussed above. Figure 6: Projected future increase in global mean temperature, based on the IPCC scenarios Figure 7 (left) shows how observed continental and global surface temperatures have changed from 1906–2005. The average temperature changes that have been observed (black line) more closely match the predictions from climate models that include both natural and anthropogenic forcings (red shaded band), than the predictions made from models which only include natural forcings from solar activity and volcanoes (blue shaded band). Figure 7: Global and Continental Temperature Change. Decadal averages of observations are shown for the period 1906–2005 (black line) plotted against the centre of the decade and relative to the corresponding average for 1901–1950. Lines are dashed where spatial coverage is less than 50%. Blue shaded bands show the 5–95% range for 19 simulations from 5 climate models using only the natural forcings due to solar activity and volcanoes. Red shaded bands show the 5–95% range for 58 simulations from 14 climate models using both natural and anthropogenic forcings29. 10 GLOBAL WARMING a guide to its origins and effects In 2006 a channel large enough to allow a ship to sail to the North Pole briefly opened up in the Arctic, according to the European Space Agency, who said that this could become more common within the next two decades31. The Greenland ice sheet is also showing signs of recession and thinning. This sheet currently covers about 80% of Greenland’s 2.16 million square kilometres, is over 2km thick on average and is the second largest body of ice in the world after the Antarctic. Though some areas are actually gaining in thickness as a result of increased precipitation32, the ice sheet as a whole lost a volume of approximately 220 cubic kilometres through increased ice melt and glacier flow in 2005 alone33. Scenario B1 Scenario A1B Scenario A2 Source: IPCC, 2007 Figure 8: Surface Temperature Projections for 2020–2029 and 2090–2099 under a range of IPCC scenarios. 3. Feedback mechanisms The path that global warming actually takes in the future may be largely determined by climatic feedback mechanisms. These include phenomena related to ice and snow cover, oceanic circulation patterns, natural greenhouse gas emissions and cloud formation. They are important because their behaviour is non-linear. In other words, the magnitude of their effect will depend on the stage reached in the warming process. As global temperatures increase, those that give rise to an ever greater warming effect constitute positive feedback mechanisms, and those that cause a greater cooling effect are negative feedback mechanisms. Negative feedbacks have a tendency towards stability in the system, whereas positive feedbacks force the system to diverge from its steady state. These possibilities contribute the greatest uncertainty to our projections of future global temperatures. Polar ice caps Evidence shows that climatic warming has already had an effect on the Arctic ice sheet. This has been receding over at least the last three decades. Satellite observations have been used to create a graphic representation of the northern polar region, revealing a clear difference in the extent of arctic sea ice cover between 1979 and 2003 (see Figure 9). 1979 There are numerous consequences of diminishing polar ice. The most obvious is the resulting increase in sea levels from the melting of land-based ice sheets (ie not floating sea ice), such as the Greenland ice sheet. Such sea level rise threatens to inundate coastal areas of some low-lying countries, and even submerge others completely. A feedback mechanism associated with receding ice cover could also accelerate its melting. This is related to the albedo of the earth’s surface – its reflectivity. Fresh snow can have an albedo of up to 0.9, meaning that 90% of incident sunlight is reflected back into space. With a decreasing coverage of ice and snow, the albedo decreases, resulting in a locally greater absorption of sunlight. This acts to warm the region up further, causing greater recession of the ice, and yet further warming. Moreover, evaporating melt water could also increase the water vapour content in the lower atmosphere. As water vapour is a greenhouse gas, this would contribute further to the overall feedback mechanism. Because of this feedback, continued warming could push the recession across a threshold beyond which complete melting of the Greenland ice sheet is inevitable, an event that could contribute to global sea level rise by up to 7 metres. It has been suggested that a regional warming of 2.7°C above present levels may be enough to trigger the melting of the Greenland ice sheet. As the local response to global warming is greater at high latitudes, this corresponds to a global average temperature rise of about 1.5°C34. As the IPCC’s 2007 report gives a range for global temperature rises of 1.8–4 degrees by 2100, it can reasonably be expected that the initiation of long-term complete melting of the ice sheet will occur by the end of this century. The melting would occur over a period of time ranging from centuries to millennia. 2003 Figure 9: Arctic sea ice in 1979 and 200330. The first image shows the minimum sea ice concentration for 1979 and the second image shows the minimum sea ice concentration in 2003. Source: NASA. 11 GLOBAL WARMING a guide to its origins and effects Thermohaline circulation Arctic melt water could also influence global sea currents, or ‘thermohaline circulation’. At present, evaporation from the sea in the north Atlantic region leads to cooling and greater salinity of the water. This has the effect of increasing the density of the water, whereupon it sinks to the bottom of the ocean, causing warm equatorial waters to flow in and replace it. The cold salty water slowly migrates down the Atlantic and eastwards into the Indian and Pacific Oceans. By the time it reaches these areas, the salinity has decreased, and the water rises again to the surface. It then begins its journey back towards the Atlantic, picking up heat along the way. The overall effect of this circulation is to transport heat from equatorial regions towards the north. These currents warm North Atlantic regions by an average of 5°C, significantly tempering the winter season in Europe and North America35. The sinking of the cold salty water in the north Atlantic serves as the engine driving this thermohaline circulation. However, an influx of fresh water into the surface of the North Atlantic could form a layer inhibiting heat loss and evaporation of the sea water below, preventing it from increasing in density. The fresh water would also dilute the salinity of the North Atlantic, further reducing the density of these waters. The force driving the ocean conveyor would weaken and disappear, and the ensuing cessation of the thermohaline circulation would quickly impact on the world’s climate. Ironically, this consequence of global warming would plunge Northern Europe into a mini-ice age, since it would no longer be receiving the heat brought from the tropics via the circulation. Ocean currents also govern the rate at which deep sea waters are brought to the surface. Should such currents weaken, the replacement of surface water will be hampered, increasing the acidity of the water due to saturation with carbon dioxide and reducing the ocean’s ability to further absorb atmospheric CO2. This constitutes a potential global warming feedback mechanism. The ocean’s pH has decreased by 0.1 units since 1750 due to the uptake of anthropogenic carbon. The latest research from the IPCC says that it is very unlikely that there will be a sudden transition this century. Although the circulation is slowing, temperatures over the Atlantic and Europe are still expected to increase due to global warming. The slowing of the circulation will cause changes to CO2 uptake described above and affect marine ecosystems36. 12 Figure 10: Illustration of the thermohaline circulation35. Phytoplankton Global warming could also affect phytoplankton, the agent which removes CO2 from water. The oceans serve as a sink of atmospheric carbon dioxide, absorbing about 2 billion tons of carbon annually37. This amounts to about half the total absorption of carbon dioxide. Phytoplankton absorb carbon dioxide during the process of photosynthesis, fixing the carbon and transferring it to the ocean floor as waste. The plankton, however, rely on nutrients from the bottom of the ocean being stirred up and brought to the surface. An increase in global sea surface temperatures creates more distinct ocean layers, however, and prevents mixing of deeper nutrient-rich cooler water with warmer surface water. The lack of rising nutrients limits growth of phytoplankton, thus reducing the ocean’s capacity to absorb carbon dioxide38. Methane hydrates Gas hydrates are a kind of crystalline compound most commonly formed by water molecules frozen into a cubic structure, trapping gas molecules inside them. Methane occurs most abundantly as a trapped gas in natural hydrates. If each pocket in the structure is occupied by a molecule of methane, then the total volume of methane gas contained within the hydrate can be up to 170 times that of the hydrate itself39. Such methane hydrates exist in abundance in nature, and are therefore a huge potential source of greenhouse gas emissions. Methane hydrates are stable only under a range of low temperature or high pressure conditions, and are found mainly at high latitudes and along the continental margins in the oceans40. A temperature increase of a few degrees could cause these gases to volatise and be released into the atmosphere. This would have the knock-on effect of raising global temperatures further, causing even more release of hydrate methane, and so on in a feedback cycle. Once triggered, this cycle could result in catastrophic runaway global warming, which would continue until all of the methane has been volatised. Geological evidence suggests that similar events have taken GLOBAL WARMING a guide to its origins and effects place before, one about 55 million years ago and another 251 million years ago. This came close to wiping out all life on earth. Detrital organic matter 60 Peat 500 Land biota 830 Atmosphere 3.6 Marine biota 3 Gas Hydrates 2900 Dissolved organic matter 980 Global temperatures would not continue to rise indefinitely, but would be restricted by the limits of the system driving them. For example, the decreasing polar albedo effect would be capped when all ice cover disappears, or the intensifying greenhouse effect caused by the release of methane from hydrates would cease when all of the hydrates have completely volatised. The climate may be able to return to its preindustrial state, but this is likely to be on a timescale of many thousands of years, just as the climate of the earth flipped in the past between glacial and interglacial periods. Soil 1400 Fossil fuels 5000 Figure 11: Carbon content of the various carbon stores on earth (in gigatonnes of carbon). Gas hydrates constitute a significant proportion. ‘Adaptive Infrared Iris’ effect All of the feedback mechanisms described so far have been of the positive variety, threatening to exacerbate global warming and destabilise the climate. However, negative feedbacks would have the opposite effect. It has been suggested that in cloudy regions, a higher sea surface temperature is strongly linked to fewer clouds41. A one degree Celsius increase seems to reduce upper level clouds by 22%. As clouds are effective at trapping infrared radiation, this reduction in cloud cover would give rise to an increased cooling potential, thereby providing a stabilising influence on sea surface temperatures. This effect is known as the adaptive iris effect and enables more infra-red cooling. The magnitude of this effect has not been firmly established, but some researchers claim that the widely accepted climate sensitivity of 2.0–4.5 °C would be diminished to the much lower range of 0.6–1.6 °C if this feedback mechanism is taken into account. Runaway global warming The magnitude of the response to a given increase in greenhouse gases may be dependent on the state of the climate at the time, and could be much larger in the future than it would be now. This means that the more advanced the stage of global warming, the more sensitive the climate may be to a further forcing. Of most significance to the long term development of global warming is the possibility of ‘tipping points’, beyond which positive feedbacks become selfperpetuating, causing ‘runaway’ warming regardless of the quantity of further anthropogenic greenhouse gas emissions. In this situation, the global climate system would enter an irreversible state. 13 GLOBAL WARMING a guide to its origins and effects PART 4: THE CONSEQUENCES OF GLOBAL WARMING Global warming is expected to affect all our lives. For some of us, the net effects may be beneficial; for others they could spell disaster. This will depend on where in the world we live, our ability to respond and adapt to climatic warming, and its effect on our environment and livelihood. In recent years the quantity and quality of studies of observed trends in the environment and their relationship to regional climate change has increased greatly. The IPCC has concluded that many natural systems are being affected42. Figure 13: The northern section of the Larsen B ice shelf breaking away from the Antarctic Peninsular in February and March 2002. Satellite single and multi-view images. Source: NASA. This chapter outlines some of the consequences already identified. Figure 12 shows the changes which have already been measured in global temperature, sea level and Northern Hemisphere snow cover, relative to corresponding averages for the period 1961–1990. There is a correlation between daily mortality and weather, in particular extreme temperature events such as heat waves and cold spells. High temperatures can lead to heat exhaustion, heat stroke with possible permanent neurological damage, heart attacks and death44,45. 1. Direct effects of heat and cold Hot days, hot nights and heat waves have become more frequent, and will be both hotter and more frequent in future46. The expected rise in mean temperature will result in an increase in the frequency of extreme warm temperature events. Even a small warming can cause a relatively large increase. For example, a rise of 2 to 3°C in average summer temperatures in temperate climates would approximately double the number of very hot days47. August 2003 was the hottest August on record in the northern hemisphere and caused a large number of fatalities. France suffered worst, with 14,802 people dying from causes attributable to the blistering heat48. 7,000 people died in Germany, nearly 4,200 in both Spain and Italy and over 2,000 in the UK. The World Meteorological Organisation estimates that the number of heat-related deaths could double in less than 20 years48. Figure 12: Observed changes in (a) global mean surface temperature; (b) global average sea level rise from tide gauge (blue) and satellite (red) data; and (c) Northern Hemisphere snow cover for March – April. All changes are relative to corresponding averages for the period 1961–1990. Smoothed curves represent decadal averaged values while circles show yearly values. The shaded areas are the uncertainty intervals estimated from a comprehensive analysis of known uncertainties (a and b) and from the time series (c)43 Cold days, cold nights and frost have become less frequent, and will be both less frequent and less cold in future46. Exposure to low temperatures can have direct health effects such as hypothermia, and indirect effects such as increased rates of pneumonia, influenza and other respiratory illnesses49. Including the indirect effects, the overall number of deaths related to cold exceeds the number related to heat. As the relationship of mortality to cold is complex, it is unclear whether the reduction in cold-related deaths due to environmental warming will exceed50 or be less than49,51 the expected increase in heat-related deaths45. 2. Disease Diseases which rely on carriers for transmission, such as malaria, borne by mosquitoes, also depend on climatic conditions for their geographical distribution. 14 GLOBAL WARMING a guide to its origins and effects Malaria has a massive impact on human health; it is the world’s second most prolific killer after tuberculosis. Up to 500 million clinical episodes of malaria occur each year, resulting in over a million deaths52. The IPCC concludes that climate change is likely to expand the geographical distribution of several carrier-borne diseases, including malaria, to higher altitudes and higher latitudes, as well as extending the transmission seasons in some locations. For some carrier-borne diseases, such as tick-borne encephalitis in Europe, climate change may decrease transmission through reductions in rainfall or temperatures too high for transmission53. Temperature variance can also have an indirect influence on health. Diarrhoeal disease, for example, has a strong correspondence with temperature, particularly in developing countries with poor sanitation. This is because the bacteria responsible are encouraged by high temperatures. It is estimated that in such countries there is a 5% increase in diarrhoea incidence per degree centigrade increase in temperature54. Deaths from diarrhoeal disease associated with floods and droughts are expected to rise in East, South and Southeast Asia55. 3. Agriculture and nutrition Increased atmospheric carbon dioxide concentrations, global warming and associated climate change are expected to have an influence on agriculture. Higher temperatures will increase crop yields at high and midlatitudes, as the growing season becomes longer, but decrease them at lower latitudes. More carbon dioxide will benefit crops, as it is an essential ingredient in the photosynthesis process. The IPCC reports that with moderate temperatures, a long-term doubling of current ambient CO2 will lead to a 30% enhancement in the seed yield of rice. However, the grain yield will fall by about 10% for each 1°C rise above 26°C as a result of a shortening of the growing period and increased sterility. Similar scenarios have been reported for soybean and wheat56. Taking Australia and New Zealand as an example, the IPCC estimates that by 2030 more drought and wildfire will cause agriculture and forestry production to decline over much of southern and eastern Australia and over parts of eastern New Zealand. However, a longer growing season, less frost and increased rainfall will bring initial benefits to western and southern parts of New Zealand and areas close to major rivers55. Developed countries are expected to suffer least from these changes. Most of the developed world lies at latitudes at which temperature increases are expected to be of most benefit. With their greater economic resources and better infrastructure, developed countries should also find it easier to make the necessary modifications in agricultural methods57. Activities at the margin of climatic suitability stand to lose (or gain) the most from climate change. A decrease in rainfall or longer droughts could tip the balance from a meagre livelihood to no livelihood at all for subsistence farmers under severe water stress in semi-arid regions of Africa or south Asia. It will also exacerbate malnutrition in these regions. An increase in rainfall, on the other hand, could reduce pressure on marginal areas58,55. Fisheries could suffer from regional changes in the distribution and production of particular fish species due to continued warming. The rising water temperatures of large lakes is likely to decrease their fisheries resources59. The world food trade system may be able to alleviate the effect of changes in agricultural production on a global scale, though isolated regions may still face hardship. Malnutrition will also make people more susceptible to other risks such as diarrhoea and malaria. 4. Drought and water resources Changes in rainfall patterns will undoubtedly affect water resources. Current global climate models vary widely in their predictions of the effect of global warming on precipitation60. It is likely that precipitation will increase globally, though some regions are likely to see a reduction in rainfall due to changes in local meteorological patterns. The area affected by droughts has increased since the 1970’s and is likely to increase in future61. Figure 14: Projected Patterns of Precipitation Changes Source: IPCC 2007 Climatic and human influences can have a major impact on the availability of water. Lake Chad in Africa, for example, covered an area of 25,000 square kilometres in 1960. As a result of reduced rainfall, and greatly increased amounts of irrigation water being drawn from the lake and rivers feeding it, its area has dropped to less than 1,500 square kilometres. This in turn has forced people to concentrate around the shrinking lake edge, leading to conflict or migration, and adding to social pressures in other areas62. The dramatic decrease in the size of the lake is evident from satellite images (see Figure 15). 15 Photo: Getty Images GLOBAL WARMING a guide to its origins and effects 1973 1987 Figure 15: Lake Chad in 1973 and 1987 (NASA63) Warmer and drier conditions in the Sahelian region of Africa has shortened the growing season and in southern Africa growers are adapting to longer dry seasons and changes to rainfall patterns64. In Central, South, East and Southeast Asia, freshwater availability is expected to decrease65. Regions that obtain their water as meltwater from mountain ranges will suffer as water supplies stored in glaciers and snow cover decline over the course of the century. More than one-sixth of the world population lives in such regions66. 5. Sea level rises and flooding Temperature affects the volume of sea water because of thermal expansion. The warmer a given mass of water, the greater its volume. Based on a range of models, the combined effects of thermal expansion and melting ice, already described, are expected to result in a global average sea level rise of between 18 and 59 cm by the last decade of the 21st century, compared to the last decade of the 20th century67. However, as the response to climatic change is slow, sea levels are likely to continue to rise long after that, even if global warming were to be limited. 16 Higher sea levels threaten to submerge low-lying lands and coastal areas. Island nations, such as Tuvalu in the south Pacific, with its highest elevation of 5 metres, and the Maldives, with a highest natural ground level of 2.3 metres, are at particular risk. Most parts of Bangladesh are less than 10 metres above sea level; about 10% of its land would be flooded if sea levels rose by 1 metre. Apart from outright submersion, many low-lying coastal areas will be at risk of increased flood frequency and severity from storm surges. Coastal areas will be more susceptible to erosion, causing retreat of the shore-line. There will also be intrusion of salt water further inland, affecting fresh water sources. The consequences of global warming could be more serious in the longer term if the melting of the Greenland and West Antarctic ice sheets is initiated. As mentioned previously, the complete melting of the Greenland ice sheet would produce a sea level rise of 7 metres68. Many of the world’s cities would be under threat of flooding, including London, New York and Shanghai. Rising sea levels could result in a large number of environmental refugees and millions permanently displaced. Historic records support the link between higher temperatures and sea level rise. During the last interglacial period (about 125,000 years ago) temperatures were 3–5°C higher than now and sea level was likely 4–6m higher than during the 20th century69. 6. El Niño Strong ‘trade’ winds normally blow towards the west over the Pacific Ocean, driving the surface waters westwards with them. As a result, cold water from the ocean depths rises to the surface off the coasts of North and South America, causing the mean sea surface temperature in the western Pacific to be as much as 8°C warmer than in the east. However, occasionally these winds weaken, causing warm water to accumulate in the eastern Pacific. This leads to increased rainfall, storm activity and flooding in the Americas, and drought in the western Pacific region covering Australia, Indonesia and the Philippines, increasing the risk of forest fires. Such events, known as El Niño, have historically occurred at intervals of GLOBAL WARMING a guide to its origins and effects 2 to 7 years, with a typical duration of 1 or 2 years. 50 45 40 Percent total hurricanes/category The strongest El Niño on record was in 1982–83, and the period from 1990 to 1995 unusually had three consecutive events, with no real recovery between them70. Although no conclusive connection between global warming and the El Niño phenomenon has been established, it has been suggested that their apparent increasing frequency will continue until a permanent El Niño state is established71. 35 30 25 20 15 10 5 7. Storms 0 70/74 Damage caused by storms accounts for almost three quarters of financial losses from weather-related catastrophes, amounting to $10–40 billion each year72 and rising sharply. This upward trend can mainly be attributed to growing, wealthier populations, with greater assets at risk, but there is evidence to suggest that the frequency of powerful storms is also on the rise. A tropical cyclone is a storm system with a closed circulation around a central column of rising low pressure air. Tropical cyclones derive their power from the latent heat of water vapour. The vapour condenses in the updrafts, releasing the stored heat and causing intense precipitation. The source of the storm’s energy is heat drawn from the warm sea surface and returned to the cold upper atmosphere73. Climate change scenarios predict that more intense cyclones will occur because more energy is available to the storms from higher sea surface temperatures74. Although the frequency of cyclones is not anticipated to change, the frequency of highly destructive storms is expected to rise75. A look at the number and intensity of past hurricanes suggests that this effect is already manifesting itself (see Figure 16). 75/79 1 80/84 85/89 Pentad 90/94 2+3 95/99 00/0 4 4+5 Figure 16: Plot showing frequency of storms categorized by windspeed per five year period over the last 35 years75. Coastal communities and habitats around the world, in the developed and developing world, are likely to suffer from an increase in the intensity of tropical storms. 8. Ecosystems and biodiversity Ecosystems are vulnerable to a range of climate change impacts, compounded by land use change, increased development, pollution and over-exploitation of resources. A global increase in temperature of 1.5–2.5°C could increase the risk of extinction of approximately 20–30% of plant and animal species76. In some areas of Europe, species loss could be as much as 60% by 2080 under high emission scenarios77. Impacts on ecosystems and biodiversity and habitat loss are likely to occur at polar regions, as a consequence of loss of tropical forest in Latin America and through increased pests, disease and wildfire in North American forests. Acidification and warming of oceans can have negative impacts on coral reefs and significant loss of biodiversity is projected at the Great Barrier Reef in Australia by 2020. 17 GLOBAL WARMING a guide to its origins and effects 2–3°C, all regions will experience either declines in net benefits or increases in net costs and that the reduction in GDP would be 1–5% for 4°C of warming. It estimates that projected sea-level rise could cost at least 5–10% of GDP in adaptation for low-lying coastal areas with large populations81. Both conclude that impacts will vary regionally and that the poorest countries, with high exposure, high sensitivity and/or low adaptive capacity, will suffer considerably, losing more than 10% of their output according to the Stern Review. The IPCC concludes that their net costs from climate change will be significantly larger than the global aggregate. The Stern Review concluded that it would cost just 1% of GDP each year to stabilise emissions (at 500–550 ppm, a level which he suggests would avoid the worst impacts of climate change) in the next 20 years and to reduce them by between 1% and 3% of GDP per year thereafter. Sir Nicholas Stern’s recommendations for achieving this include generating 60% of energy from non-fossil fuel sources by 2050. He also foresees a continued role for coal but carbon capture and storage are needed. The most recent report on mitigation measures from the IPCC says keeping greenhouse gas concentrations to levels equivalent to between 445 and 535 ppm of CO2 could costs up to 3% of GDP over two decades82. Recent anthropogenic warming has already affected physical and biological systems. Observed changes include, for example, the earlier arrival of spring and upward shifts in the range of plant and animal species. Rising water temperatures also appear to be changing marine and freshwater biological systems, including changes to the range and abundance of algae, plankton and fish and changes to fish migration patterns78. The IPCC predicts that by the middle of the 21st Century, net carbon uptake by terrestrial ecosystems is likely to peak and could then weaken or even reverse, causing more climate change79. 9. Economic consequences The economic impacts of climate change will be significant and will hit the poorest hardest. Though varying regionally, rising temperatures and their impacts are likely to impose additional annual costs.80 In 2006, Sir Nicholas Stern, a former Chief Economist of the World Bank, compiled a report for the UK Government on the economic consequences of climate change80. He reported that a 2–3°C rise in global average temperatures could reduce global economic output by 3%. A 5°C rise could reduce global output by 10%. Extreme weather could reduce global GDP by up to 1%. The overall cost of not acting could be as much as 20% of global GDP. The IPCC estimates that for increases greater than about 18 GLOBAL WARMING a guide to its origins and effects PART FIVE: SOLUTIONS The latest IPCC research82 has concluded that there is substantial economic potential for reducing greenhouse gas emissions by 2030 and beyond. This reduction would require measures across a range of sectors (including the transport, industry, energy supply, agriculture and forestry, industry and waste sectors). The IPCC recommends greater energy efficiency, use of renewable energy, biofuels and nuclear power, more use of Carbon Capture and Storage (CCS) technology, along with protection of the world’s forests and changes in lifestyle patterns. This is considered technically feasible but incentives are needed for more investment. Leading international environmental organisations support investment in renewable energy, energy efficiency and cleaner fossil fuel burning technologies in order to bring about significant cuts in global emissions. In 2007, WWF83 called on the G8+5 nations to adopt a technology package that included binding global energy efficiency standards, a global target of 25% for new renewable sources by 2025, plans for the development of newer renewable and CCS technologies, and the fitting of CCS to fossil fuel plants. Research by Greenpeace and the Global Wind Energy Council84 has shown that wind power alone has the potential to supply 34% of the world’s electricity by 2050 and in so doing save 113 billion tonnes of CO2 emissions. Wind power is one of the world’s fastest-growing energy sources and a vital part of mankind’s response to the challenge of climate change. It has a leading role to play in the transition to a low carbon economy. The installed capacity for wind continues to increase at a staggering rate of 30% per annum. 2006 saw the installation of 15,000MW, bringing global wind energy capacity to over 74GW85. Decision-makers and investors are recognising the myriad benefits of a range of renewable heat and power technologies. The commercial, industrial and public sectors are increasingly looking to wind, biomass, ground source heat pumps and solar collectors as ways to reduce their carbon footprint in a cost-effective way, whilst having on-site secure and reliable heat and power generation. Marine renewable technologies such as tidal and wave energy also have the potential to make significant contributions to the provision of secure, renewable and low carbon energy in meeting the challenge of global warming. 19 GLOBAL WARMING a guide to its origins and effects PART SIX: CONCLUSIONS Global mean temperatures have been steadily increasing over the last 30 years. The 20th century as a whole registered a warming of 0.74°C. We are currently experiencing the highest temperatures since direct measurements began. At the same time, atmospheric concentrations of the main greenhouse gases carbon dioxide and methane have risen sharply since the industrial revolution, and particularly over the last five or six decades. This is primarily as a result of anthropogenic emissions originating from the use of fossil fuels. Climatic models indicate that global temperatures are linked to atmospheric greenhouse gas levels. Whilst other factors influence climate, historical data drawn from ice cores show that mean temperatures generally increase with atmospheric carbon dioxide concentrations. It is thus fairly certain that greenhouse gases emitted by human activities are contributing to global warming. Increased temperatures will have a wide impact on the climate, influencing such phenomena as precipitation and cloud cover, affecting industries, economies and the general welfare of the population. Whilst some areas may benefit from the effects of global warming, it is expected that the overall consequences will be negative. Mechanisms which threaten to exacerbate global warming include the effect of positive feedbacks, such as the warming-melting-warming cycle in polar 20 regions. The more established such cycles become, the more difficult they are to moderate. There are believed to be critical points beyond which the effects are irreversible by human intervention. Existence of such feedbacks leads to the possibility of ‘runaway’ global warming, which could have catastrophic consequences. By the year 2100, it is estimated that global mean temperatures will have risen by between 1.8 and 4.0°C over present values. The consequences of such warming include the direct effects of heat on human health, on the spread of diseases, agriculture and nutrition, on drought and water resources, on sea level rises and flooding, and on storms and other extreme weather phenomena. In view of the generally detrimental consequences of climate change, it is in our best interests to avoid global warming as far as possible. While adaptation strategies are essential in order to address the unavoidable impacts of climate change that we face in the next few decades, making serious cuts to our greenhouse gas emissions is the most effective course of action, however difficult this may seem in a world of ever-increasing energy demand. Making greater use of renewable energy sources, such as wind, solar power, biomass, geothermal and marine technologies, represents one of our best strategies for meeting this challenge. We have the technological know-how – what is needed now is political will, and the earlier we act, the less we risk damaging our earth. GLOBAL WARMING a guide to its origins and effects References 1. 2005 Warmest Year in Over a Century (2006) National Aeronautics and Space Administration [http://www.nasa.gov/vision/earth/environment/2005_warm est.html] 2. Meterological Office, reported in The Guardian ‘El Niño means 2007 likely to be hottest year on record’, 4.1.07 3. 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International Wind Energy Development: Status by end of 2006 and Forecast 2007–2011 (2007) BTM Consult ApS.[http://www.btm.dk/world-index.htm] GLOBAL WARMING a guide to its origins and effects Renewable Energy Systems Ltd (RES) Beaufort Court Egg Farm Lane Kings Langley Herts WD4 8LR United Kingdom Tel: +44 (0)1923 299200 Fax: +44 (0)1923 299299 Web: www.res-group.com Email: [email protected] Date of publication: May 2007 Printed on environmentally friendly paper comprising 25% post-consumer waste, 30% pre-consumer waste and 45% virgin elemental chlorine free fibre