Executive Summary 63219 Turn Down Heat the Why a 4°C Warmer World Must be Avoided Executive Summary Turn Down Heat the Why a 4°C Warmer World Must be Avoided November 2012 A Report for the World Bank by the Potsdam Institute for Climate Impact Research and Climate Analytics © 2012 International Bank for Reconstruction and Development / The World Bank 1818 H Street NW Washington DC 20433 Telephone: 202-473-1000 Internet: www.worldbank.org This work is a product of the staff of the World Bank with external contributions. The findings, interpretations, and conclusions expressed in this work do not necessarily reflect the views of The World Bank, its Board of Executive Directors, or the governments they represent. The World Bank does not guarantee the accuracy of the data included in this work. The boundaries, colors, denominations, and other information shown on any map in this work do not imply any judgment on the part of The World Bank concerning the legal status of any territory or the endorsement or acceptance of such boundaries. Rights and Permissions The material in this work is subject to copyright. Because the World Bank encourages dissemination of its knowledge, this work may be reproduced, in whole or in part, for noncommercial purposes as long as full attribution to this work is given. Any queries on rights and licenses, including subsidiary rights, should be addressed to the Office of the Publisher, The World Bank, 1818 H Street NW, Washington, DC 20433, USA; fax: 202-522-2422; e-mail: pubrights@worldbank.org. Acknowledgements The report Turn Down the Heat: Why a 4°C Warmer World Must be Avoided is a result of contributions from a wide range of experts from across the globe. We thank everyone who contributed to its richness and multidisciplinary outlook. The report has been written by a team from the Potsdam Institute for Climate Impact Research and Climate Analytics, including Hans Joachim Schellnhuber, William Hare, Olivia Serdeczny, Sophie Adams, Dim Coumou, Katja Frieler, Maria Martin, Ilona M. Otto, Mahé Perrette, Alexander Robinson, Marcia Rocha, Michiel Schaeffer, Jacob Schewe, Xiaoxi Wang, and Lila Warszawski. The report was commissioned by the World Bank’s Global Expert Team for Climate Change Adaptation, led by Erick C.M. Fernandes and Kanta Kumari Rigaud, who worked closely with the Potsdam Institute for Climate Impact Research and Climate Analytics. Jane Olga Ebinger coordinated the World Bank team and valuable insights were provided throughout by Rosina Bierbaum (University of Michigan) and Michael MacCracken (Climate Institute, Washington DC). The report received insightful comments from scientific peer reviewers. We would like to thank Ulisses Confalonieri, Andrew D. Friend, Dieter Gerten, Saleemul Huq, Pavel Kabat, Thomas Karl, Akio Kitoh, Reto Knutti, Anthony J. McMichael, Jonathan T. Overpeck, Martin Parry, Barrie Pittock, and John Stone. Valuable guidance and oversight was provided by Rachel Kyte, Mary Barton-Dock, Fionna Douglas and Marianne Fay. We are grateful to colleagues from the World Bank for their input: Sameer Akbar, Keiko Ashida, Ferid Belhaj, Rachid Benmessaoud, Bonizella Biagini, Anthony Bigio, Ademola Braimoh, Haleh Bridi, Penelope Brook, Ana Bucher, Julia Bucknall, Jacob Burke, Raffaello Cervigni, Laurence Clarke, Francoise Clottes, Annette Dixon, Philippe Dongier, Milen Dyoulgerov, Luis Garcia, Habiba Gitay, Susan Goldmark, Ellen Goldstein, Gloria Grandolini, Stephane Hallegatte, Valerie Hickey, Daniel Hoornweg, Stefan Koeberle, Motoo Konishi, Victoria Kwakwa, Marcus Lee, Marie Francoise Marie-Nelly, Meleesa McNaughton, Robin Mearns, Nancy Chaarani Meza, Alan Miller, Klaus Rohland, Onno Ruhl, Michal Rutkowski, Klas Sander, Hartwig Schafer, Patrick Verkooijen Dorte Verner, Deborah Wetzel, Ulrich Zachau and Johannes Zutt. We would like to thank Robert Bisset and Sonu Jain for outreach efforts to partners, the scientific community and the media. Perpetual Boateng, Tobias Baedeker and Patricia Braxton provided valuable support to the team. We acknowledge with gratitude Connect4Climate that contributed to the production of this report. iii iv Foreword It is my hope that this report shocks us into action. Even for those of us already committed to fighting climate change, I hope it causes us to work with much more urgency. This report spells out what the world would be like if it warmed by 4 degrees Celsius, which is what scientists are nearly unanimously predicting by the end of the century, without serious policy changes. The 4°C scenarios are devastating: the inundation of coastal cities; increasing risks for food produc- tion potentially leading to higher malnutrition rates; many dry regions becoming dryer, wet regions wet- ter; unprecedented heat waves in many regions, especially in the tropics; substantially exacerbated water scarcity in many regions; increased frequency of high-intensity tropical cyclones; and irreversible loss of biodiversity, including coral reef systems. And most importantly, a 4°C world is so different from the current one that it comes with high uncer- tainty and new risks that threaten our ability to anticipate and plan for future adaptation needs. The lack of action on climate change not only risks putting prosperity out of reach of millions of people in the developing world, it threatens to roll back decades of sustainable development. It is clear that we already know a great deal about the threat before us. The science is unequivocal that humans are the cause of global warming, and major changes are already being observed: global mean warming is 0.8°C above pre industrial levels; oceans have warmed by 0.09°C since the 1950s and are acidi- fying; sea levels rose by about 20 cm since pre-industrial times and are now rising at 3.2 cm per decade; an exceptional number of extreme heat waves occurred in the last decade; major food crop growing areas are increasingly affected by drought. Despite the global community’s best intentions to keep global warming below a 2°C increase above pre-industrial climate, higher levels of warming are increasingly likely. Scientists agree that countries’ cur- rent United Nations Framework Convention on Climate Change emission pledges and commitments would most likely result in 3.5 to 4°C warming. And the longer those pledges remain unmet, the more likely a 4°C world becomes. Data and evidence drive the work of the World Bank Group. Science reports, including those produced by the Intergovernmental Panel on Climate Change, informed our decision to ramp up work on these issues, leading to: a World Development Report on climate change designed to improve our understanding of the implications of a warming planet; a Strategic Framework on Development and Climate Change, and a report on Inclusive Green Growth. The World Bank is a leading advocate for ambitious action on climate change, not only because it is a moral imperative, but because it makes good economic sense. But what if we fail to ramp up efforts on mitigation? What are the implications of a 4°C world? We commissioned this report from the Potsdam Institute for Climate Impact Research and Climate Analytics to help us understand the state of the science and the potential impact on development in such a world. v It would be so dramatically different from today’s world that it is hard to describe accurately; much relies on complex projections and interpretations. We are well aware of the uncertainty that surrounds these scenarios and we know that different scholars and studies sometimes disagree on the degree of risk. But the fact that such scenarios cannot be discarded is sufficient to justify strengthening current climate change policies. Finding ways to avoid that scenario is vital for the health and welfare of communities around the world. While every region of the world will be affected, the poor and most vulnerable would be hit hardest. A 4°C world can, and must, be avoided. The World Bank Group will continue to be a strong advocate for international and regional agreements and increasing climate financing. We will redouble our efforts to support fast growing national initiatives to mitigate carbon emissions and build adaptive capacity as well as support inclusive green growth and climate smart development. Our work on inclusive green growth has shown that—through more efficiency and smarter use of energy and natural resources—many opportunities exist to drastically reduce the climate impact of development, without slowing down poverty alleviation and economic growth. This report is a stark reminder that climate change affects everything. The solutions don’t lie only in climate finance or climate projects. The solutions lie in effective risk management and ensuring all our work, all our thinking, is designed with the threat of a 4°C world in mind. The World Bank Group will step up to the challenge. Dr. Jim Yong Kim President, World Bank Group vi vii Executive Summary Executive Summary This report provides a snapshot of recent scientific literature and new analyses of likely impacts and risks that would be asso- ciated with a 4° Celsius warming within this century. It is a rigorous attempt to outline a range of risks, focusing on developing countries and especially the poor. A 4°C world would be one of unprecedented heat waves, severe drought, and major floods in many regions, with serious impacts on ecosystems and associated services. But with action, a 4°C world can be avoided and we can likely hold warming below 2°C. Without further commitments and action to reduce greenhouse Uncertainties remain in projecting the extent of both climate gas emissions, the world is likely to warm by more than 3°C change and its impacts. We take a risk-based approach in which above the preindustrial climate. Even with the current mitigation risk is defined as impact multiplied by probability: an event with commitments and pledges fully implemented, there is roughly a low probability can still pose a high risk if it implies serious 20 percent likelihood of exceeding 4°C by 2100. If they are not consequences. met, a warming of 4°C could occur as early as the 2060s. Such a No nation will be immune to the impacts of climate change. warming level and associated sea-level rise of 0.5 to 1 meter, or However, the distribution of impacts is likely to be inherently more, by 2100 would not be the end point: a further warming to unequal and tilted against many of the world’s poorest regions, levels over 6°C, with several meters of sea-level rise, would likely which have the least economic, institutional, scientific, and tech- occur over the following centuries. nical capacity to cope and adapt. For example: Thus, while the global community has committed itself to • Even though absolute warming will be largest in high latitudes, holding warming below 2°C to prevent “dangerous� climate the warming that will occur in the tropics is larger when com- change, and Small Island Developing states (SIDS) and Least pared to the historical range of temperature and extremes to Developed Countries (LDCs) have identified global warming of which human and natural ecosystems have adapted and coped. 1.5°C as warming above which there would be serious threats to The projected emergence of unprecedented high-temperature their own development and, in some cases, survival, the sum total extremes in the tropics will consequently lead to significantly of current policies—in place and pledged—will very likely lead to larger impacts on agriculture and ecosystems. warming far in excess of these levels. Indeed, present emission trends put the world plausibly on a path toward 4°C warming • Sea-level rise is likely to be 15 to 20 percent larger in the trop- within the century. ics than the global mean. This report is not a comprehensive scientific assessment, as • Increases in tropical cyclone intensity are likely to be felt will be forthcoming from the Intergovernmental Panel on Climate disproportionately in low-latitude regions. Change (IPCC) in 2013–14 in its Fifth Assessment Report. It is • Increasing aridity and drought are likely to increase substan- focused on developing countries, while recognizing that developed tially in many developing country regions located in tropical countries are also vulnerable and at serious risk of major damages and subtropical areas. from climate change. A series of recent extreme events worldwide continue to highlight the vulnerability of not only the developing A world in which warming reaches 4°C above preindustrial world but even wealthy industrialized countries. levels (hereafter referred to as a 4°C world), would be one of 1 Turn Do wn t he H e at: W h y a 4 ° C War m e r Wor ld Mu st B e Avoided Figure 1: Median estimates (lines) from probabilistic temperature projections for two non-mitigation emission scenarios (SRES A1FI and a reference scenario close to SRESA1B), both of which come close to, or exceed by a substantial margin, 4°C warming by 2100. The results for these emission scenarios are compared to scenarios in which current pledges are met and to mitigation scenarios holding warming below 2°C with a 50% chance or more. A hypothetical scenario is also plotted for which global emissions stop in 2016, as an illustrative comparison against pathways that are technically and economically feasible. The spike in warming after emissions are cut to zero is due to the removal of the shading effect of sulfate aerosols. The 95% uncertainty range (shaded area) is provided for one scenario only to enhance readability. See (Rogelj et al., 2010; Hare et al., 2011; Schaeffer et al., 2012) for scenarios and modeling methods. 5 Global average surface temperature increase IPCC SRES A1FI very likely to exceed 4°C Reference (close to SRES A1B) 4 above pre-industrial levels (°C) likely to exceed 3°C Current Pledges Effect of current virtually certain to exceed 2°C; 50% chance above 3°C pledges 3 Stabilization at 50% chance to exceed 2°C RCP3PD likely below 2°C; medium chance to exceed 1.5°C 2°C 1.5°C Global sudden stop to emissions in 2016 1 likely below 1.5°C Geophysical intertia 0 Illustrative low-emission scenario with negative CO2 emissions from upper half of literature range Historical observations in 2nd half of 21st Century 1900 1950 2000 2050 2100 unprecedented heat waves, severe drought, and major floods in concentration of approximately 278 parts per million (ppm) many regions, with serious impacts on human systems, ecosystems, to over 391 ppm in September 2012, with the rate of rise now and associated services. at 1.8 ppm per year. Warming of 4°C can still be avoided: numerous studies show • The present CO2 concentration is higher than paleoclimatic that there are technically and economically feasible emissions and geologic evidence indicates has occurred at any time in pathways to hold warming likely below 2°C (Figure 1). Thus the the last 15 million years. level of impacts that developing countries and the rest of the world • Emissions of CO2 are, at present, about 35,000 million metric experience will be a result of government, private sector, and civil tons per year (including land-use change) and, absent further society decisions and choices, including, unfortunately, inaction. policies, are projected to rise to 41,000 million metric tons of CO2 per year in 2020. Observed Impacts and Changes to the • Global mean temperature has continued to increase and is Climate System now about 0.8°C above preindustrial levels. A global warming of 0.8°C may not seem large, but many The unequivocal effects of greenhouse gas emission–induced climate change impacts have already started to emerge, and the change on the climate system, reported by the IPCC’s Fourth shift from 0.8°C to 2°C warming or beyond will pose even greater Assessment Report (AR4) in 2007, have continued to intensify, challenges. It is also useful to recall that a global mean temperature more or less unabated: increase of 4°C approaches the difference between temperatures today and those of the last ice age, when much of central Europe • The concentration of the main greenhouse gas, carbon diox- and the northern United States were covered with kilometers of ice ide (CO2), has continued to increase from its preindustrial 2 Execu ti ve Sum m ary and global mean temperatures were about 4.5°C to 7°C lower. And The effects of global warming are also leading to observed this magnitude of climate change—human induced­ —is occurring changes in many other climate and environmental aspects of the over a century, not millennia. Earth system. The last decade has seen an exceptional number of The global oceans have continued to warm, with about 90 extreme heat waves around the world with consequential severe percent of the excess heat energy trapped by the increased green- impacts. Human-induced climate change since the 1960s has house gas concentrations since 1955 stored in the oceans as heat. increased the frequency and intensity of heat waves and thus also The average increase in sea levels around the world over the 20th likely exacerbated their societal impacts. In some climatic regions, century has been about 15 to 20 centimeters. Over the last decade extreme precipitation and drought have increased in intensity and/ the average rate of sea-level rise has increased to about 3.2 cm per or frequency with a likely human influence. An example of a recent decade. Should this rate remain unchanged, this would mean over extreme heat wave is the Russian heat wave of 2010, which had 30 cm of additional sea-level rise in the 21st century. very significant adverse consequences. Preliminary estimates for The warming of the atmosphere and oceans is leading to an the 2010 heat wave in Russia put the death toll at 55,000, annual accelerating loss of ice from the Greenland and Antarctic ice sheets, crop failure at about 25 percent, burned areas at more than 1 and this melting could add substantially to sea-level rise in the million hectares, and economic losses at about US$15 billion (1 future. Overall, the rate of loss of ice has more than tripled since percent gross domestic product (GDP)). the 1993–2003 period as reported in the IPCC AR4, reaching 1.3 In the absence of climate change, extreme heat waves in Europe, cm per decade over 2004–08; the 2009 loss rate is equivalent to Russia, and the United States, for example, would be expected to about 1.7 cm per decade. If ice sheet loss continues at these rates, occur only once every several hundred years. Observations indicate without acceleration, the increase in global average sea level due to a tenfold increase in the surface area of the planet experiencing this source would be about 15 cm by the end of the 21st century. extreme heat since the 1950s. A clear illustration of the Greenland ice sheet’s increasing vulner- The area of the Earth’s land surface affected by drought has ability to warming is the rapid growth in melt area observed since also likely increased substantially over the last 50 years, somewhat the 1970s. As for Arctic sea ice, it reached a record minimum in faster than projected by climate models. The 2012 drought in the September 2012, halving the area of ice covering the Arctic Ocean United States impacted about 80 percent of agricultural land, in summers over the last 30 years. making it the most severe drought since the 1950s. 3 Turn Do wn t he H e at: W h y a 4 ° C War m e r Wor ld Mu st B e Avoided Figure 2: Multi-model mean compilation of the most extreme warm monthly temperature experienced at each location in the period 2080-2100 for the months of July (left) and January (right) in absolute temperatures (top) and anomalies compared to the most extreme monthly temperature simulated during present day (bottom). The intensity of the color scale has been reduced over the oceans for distinction. °C °C Negative effects of higher temperatures have been observed on Projected Climate Change Impacts in a agricultural production, with recent studies indicating that since 4°C World the 1980s global maize and wheat production may have been reduced significantly compared to a case without climate change. The effects of 4°C warming will not be evenly distributed around Effects of higher temperatures on the economic growth of poor the world, nor would the consequences be simply an extension of countries have also been observed over recent decades, suggesting those felt at 2°C warming. The largest warming will occur over a significant risk of further reductions in the economic growth land and range from 4°C to 10°C. Increases of 6°C or more in in poor countries in the future due to global warming. An MIT average monthly summer temperatures would be expected in large study1 used historical fluctuations in temperature within countries regions of the world, including the Mediterranean, North Africa, to identify its effects on aggregate economic outcomes. It reported the Middle East, and the contiguous United States (Figure 2). that higher temperatures substantially reduce economic growth in Projections for a 4°C world show a dramatic increase in the poor countries and have wide-ranging effects, reducing agricultural intensity and frequency of high-temperature extremes. Recent output, industrial output, and political stability. These findings extreme heat waves such as in Russia in 2010 are likely to become inform debates over the climate’s role in economic development the new normal summer in a 4°C world. Tropical South America, and suggest the possibility of substantial negative impacts of central Africa, and all tropical islands in the Pacific are likely to higher temperatures on poor countries. regularly experience heat waves of unprecedented magnitude and duration. In this new high-temperature climate regime, the coolest months are likely to be substantially warmer than the warmest months at the end of the 20th century. In regions such as the 1 Dell, Melissa, Benjamin F. Jones, and Benjamin A. Olken. 2012. “Temperature Mediterranean, North Africa, the Middle East, and the Tibetan Shocks and Economic Growth: Evidence from the Last Half Century.� American plateau, almost all summer months are likely to be warmer than Economic Journal: Macroeconomics, 4(3): 66-95. 4 Execu ti ve Sum m ary Figure 3: Median estimates (lines) from probabilistic projections of ocean-surface pH. Lower pH indicates more severe ocean acidification, which inhibits the growth of calcifying organisms, including shellfish, calcareous phytoplankton and coral reefs. The SRES A1FI scenario shows increasing ocean acidification is likely to be associated with over 4°C warming relative to pre-industrial levels. The 95% uncertainty range (shaded area) is provided for one scenario only to enhance readability and is driven mainly by carbon-cycle uncertainty. See (Bernie et al. 2010; Rogelj et al., 2010; Hare et al., 2011; Schaeffer et al., 2012) for scenarios and modeling methods. Illustrative low-emission scenario with 8.1 strong negative CO2 emissions Global sudden stop to emissions in 2016 RCP3PD 8 Ocean Acidity (pH) 50% chance to exceed 2°C 7.9 Current Pledges Reference (close to SRES A1B) 7.8 7.7 IPCC SRES A1FI 1900 1950 2000 2050 2100 Year the most extreme heat waves presently experienced. For example, Coral reefs in particular are acutely sensitive to changes in the warmest July in the Mediterranean region could be 9°C warmer water temperatures, ocean pH, and intensity and frequency of than today’s warmest July. tropical cyclones. Reefs provide protection against coastal floods, Extreme heat waves in recent years have had severe impacts, storm surges, and wave damage as well as nursery grounds and causing heat-related deaths, forest fires, and harvest losses. The habitat for many fish species. Coral reef growth may stop as CO2 impacts of the extreme heat waves projected for a 4°C world have concentration approaches 450 ppm over the coming decades (cor- not been evaluated, but they could be expected to vastly exceed responding to a warming of about 1.4°C in the 2030s). By the the consequences experienced to date and potentially exceed the time the concentration reaches around 550 ppm (corresponding adaptive capacities of many societies and natural systems. to a warming of about 2.4°C in the 2060s), it is likely that coral reefs in many areas would start to dissolve. The combination of thermally induced bleaching events, ocean acidification, and Rising CO2 Concentration and Ocean sea-level rise threatens large fractions of coral reefs even at 1.5°C Acidification global warming. The regional extinction of entire coral reef eco- systems, which could occur well before 4°C is reached, would Apart from a warming of the climate system, one of the most have profound consequences for their dependent species and for serious consequences of rising carbon dioxide concentration in the people who depend on them for food, income, tourism, and the atmosphere occurs when it dissolves in the ocean and results shoreline protection. in acidification. A substantial increase in ocean acidity has been observed since preindustrial times. A warming of 4°C or more by 2100 would correspond to a CO2 concentration above 800 ppm Rising Sea Levels, Coastal Inundation and an increase of about 150 percent in acidity of the ocean. The and Loss observed and projected rates of change in ocean acidity over the next century appear to be unparalleled in Earth’s history. Evidence Warming of 4°C will likely lead to a sea-level rise of 0.5 to 1 is already emerging of the adverse consequences of acidification meter, and possibly more, by 2100, with several meters more to be for marine organisms and ecosystems, combined with the effects realized in the coming centuries. Limiting warming to 2°C would of warming, overfishing, and habitat destruction (Figure 3). likely reduce sea-level rise by about 20 cm by 2100 compared to 5 Turn Do wn t he H e at: W h y a 4 ° C War m e r Wor ld Mu st B e Avoided a 4°C world. However, even if global warming is limited to 2°C, example, loss of protective reefs due to temperature increases and global mean sea level could continue to rise, with some estimates ocean acidification). ranging between 1.5 and 4 meters above present-day levels by the year 2300. Sea-level rise would likely be limited to below 2 meters only if warming were kept to well below 1.5°C. Risks to Human Support Systems: Food, Sea-level rise will vary regionally: for a number of geophysically Water, Ecosystems, and Human Health determined reasons, it is projected to be up to 20 percent higher in the tropics and below average at higher latitudes. In particular, Although impact projections for a 4°C world are still preliminary the melting of the ice sheets will reduce the gravitational pull on and it is often difficult to make comparisons across individual the ocean toward the ice sheets and, as a consequence, ocean assessments, this report identifies a number of extremely severe water will tend to gravitate toward the Equator. Changes in wind risks for vital human support systems. With extremes of tempera- and ocean currents due to global warming and other factors will ture, heat waves, rainfall, and drought are projected to increase also affect regional sea-level rise, as will patterns of ocean heat with warming; risks will be much higher in a 4°C world compared uptake and warming. to a 2°C world. Sea-level rise impacts are projected to be asymmetrical even In a world rapidly warming toward 4°C, the most adverse within regions and countries. Of the impacts projected for 31 impacts on water availability are likely to occur in association developing countries, only 10 cities account for two-thirds of the with growing water demand as the world population increases. total exposure to extreme floods. Highly vulnerable cities are to Some estimates indicate that a 4°C warming would significantly be found in Mozambique, Madagascar, Mexico, Venezuela, India, exacerbate existing water scarcity in many regions, particularly Bangladesh, Indonesia, the Philippines, and Vietnam. northern and eastern Africa, the Middle East, and South Asia, For small island states and river delta regions, rising sea levels while additional countries in Africa would be newly confronted are likely to have far ranging adverse consequences, especially with water scarcity on a national scale due to population growth. when combined with the projected increased intensity of tropical • Drier conditions are projected for southern Europe, Africa (except cyclones in many tropical regions, other extreme weather events, some areas in the northeast), large parts of North America and climate change–induced effects on oceanic ecosystems (for and South America, and southern Australia, among others. 6 Execu ti ve Sum m ary • Wetter conditions are projected in particular for the northern for local average temperature rise in the range of 1°C to 3°C, but high latitudes—that is, northern North America, northern may decrease beyond these temperatures. Europe, and Siberia—and in some monsoon regions. Some New results published since 2007, however, are much less regions may experience reduced water stress compared to a optimistic. These results suggest instead a rapidly rising risk of case without climate change. crop yield reductions as the world warms. Large negative effects • Subseasonal and subregional changes to the hydrological have been observed at high and extreme temperatures in several cycle are associated with severe risks, such as flooding and regions including India, Africa, the United States, and Australia. drought, which may increase significantly even if annual For example, significant nonlinear effects have been observed in averages change little. the United States for local daily temperatures increasing to 29°C for maize and 30°C for soybeans. These new results and obser- With extremes of rainfall and drought projected to increase vations indicate a significant risk of high-temperature thresholds with warming, these risks are expected to be much higher in a being crossed that could substantially undermine food security 4°C world as compared to the 2°C world. In a 2°C world: globally in a 4°C world. Compounding these risks is the adverse effect of projected sea- • River basins dominated by a monsoon regime, such as the level rise on agriculture in important low-lying delta areas, such Ganges and Nile, are particularly vulnerable to changes in as in Bangladesh, Egypt, Vietnam, and parts of the African coast. the seasonality of runoff, which may have large and adverse Sea-level rise would likely impact many mid-latitude coastal areas effects on water availability. and increase seawater penetration into coastal aquifers used for • Mean annual runoff is projected to decrease by 20 to 40 percent irrigation of coastal plains. Further risks are posed by the likeli- in the Danube, Mississippi, Amazon, and Murray Darling river hood of increased drought in mid-latitude regions and increased basins, but increase by roughly 20 percent in both the Nile flooding at higher latitudes. and the Ganges basins. The projected increase in intensity of extreme events in the All these changes approximately double in magnitude in a future would likely have adverse implications for efforts to reduce 4°C world. poverty, particularly in developing countries. Recent projections The risk for disruptions to ecosystems as a result of ecosystem suggest that the poor are especially sensitive to increases in shifts, wildfires, ecosystem transformation, and forest dieback would drought intensity in a 4°C world, especially across Africa, South be significantly higher for 4°C warming as compared to reduced Asia, and other regions. amounts of warming. Increasing vulnerability to heat and drought Large-scale extreme events, such as major floods that interfere stress will likely lead to increased mortality and species extinction. with food production, could also induce nutritional deficits and Ecosystems will be affected by more frequent extreme weather the increased incidence of epidemic diseases. Flooding can intro- events, such as forest loss due to droughts and wildfire exacerbated duce contaminants and diseases into healthy water supplies and by land use and agricultural expansion. In Amazonia, forest fires increase the incidence of diarrheal and respiratory illnesses. The could as much as double by 2050 with warming of approximately effects of climate change on agricultural production may exacerbate 1.5°C to 2°C above preindustrial levels. Changes would be expected under-nutrition and malnutrition in many regions—already major to be even more severe in a 4°C world. contributors to child mortality in developing countries. Whilst eco- In fact, in a 4°C world climate change seems likely to become nomic growth is projected to significantly reduce childhood stunt- the dominant driver of ecosystem shifts, surpassing habitat ing, climate change is projected to reverse these gains in a number destruction as the greatest threat to biodiversity. Recent research of regions: substantial increases in stunting due to malnutrition suggests that large-scale loss of biodiversity is likely to occur in a are projected to occur with warming of 2°C to 2.5°C, especially 4°C world, with climate change and high CO2 concentration driv- in Sub-Saharan Africa and South Asia, and this is likely to get ing a transition of the Earth´s ecosystems into a state unknown worse at 4°C. Despite significant efforts to improve health services in human experience. Ecosystem damage would be expected to (for example, improved medical care, vaccination development, dramatically reduce the provision of ecosystem services on which surveillance programs), significant additional impacts on poverty society depends (for example, fisheries and protection of coast- levels and human health are expected. Changes in temperature, line—afforded by coral reefs and mangroves). precipitation rates, and humidity influence vector-borne diseases Maintaining adequate food and agricultural output in the (for example, malaria and dengue fever) as well as hantaviruses, face of increasing population and rising levels of income will be leishmaniasis, Lyme disease, and schistosomiasis. a challenge irrespective of human-induced climate change. The IPCC AR4 projected that global food production would increase 7 Turn Do wn t he H e at: W h y a 4 ° C War m e r Wor ld Mu st B e Avoided Further health impacts of climate change could include injuries that experiences further specialization in production systems, and and deaths due to extreme weather events. Heat-amplified levels of thus higher dependency on infrastructure to deliver produced smog could exacerbate respiratory disorders and heart and blood goods, damages to infrastructure systems can lead to substantial vessel diseases, while in some regions climate change–induced indirect impacts. Seaports are an example of an initial point where increases in concentrations of aeroallergens (pollens, spores) could a breakdown or substantial disruption in infrastructure facilities amplify rates of allergic respiratory disorders. could trigger impacts that reach far beyond the particular loca- tion of the loss. The cumulative and interacting effects of such wide-ranging Risks of Disruptions and Displacements impacts, many of which are likely to be felt well before 4°C warm- in a 4°C World ing, are not well understood. For instance, there has not been a study published in the scientific literature on the full ecological, Climate change will not occur in a vacuum. Economic growth human, and economic consequences of a collapse of coral reef and population increases over the 21st century will likely add ecosystems, much less when combined with the likely concomitant to human welfare and increase adaptive capacity in many, if loss of marine production due to rising ocean temperatures and not most, regions. At the same time, however, there will also be increasing acidification, and the large-scale impacts on human increasing stresses and demands on a planetary ecosystem already settlements and infrastructure in low-lying fringe coastal zones approaching critical limits and boundaries. The resilience of many that would result from sea-level rise of a meter or more this cen- natural and managed ecosystems is likely to be undermined by tury and beyond. these pressures and the projected consequences of climate change. As the scale and number of impacts grow with increasing global The projected impacts on water availability, ecosystems, agri- mean temperature, interactions between them might increasingly culture, and human health could lead to large-scale displacement occur, compounding overall impact. For example, a large shock to of populations and have adverse consequences for human security agricultural production due to extreme temperatures across many and economic and trade systems. The full scope of damages in a regions, along with substantial pressure on water resources and 4°C world has not been assessed to date. changes in the hydrological cycle, would likely impact both human Large-scale and disruptive changes in the Earth system are health and livelihoods. This could, in turn, cascade into effects on generally not included in modeling exercises, and rarely in impact economic development by reducing a population´s work capacity, assessments. As global warming approaches and exceeds 2°C, the which would then hinder growth in GDP. risk of crossing thresholds of nonlinear tipping elements in the With pressures increasing as warming progresses toward Earth system, with abrupt climate change impacts and unprec- 4°C and combining with nonclimate–related social, economic, edented high-temperature climate regimes, increases. Examples and population stresses, the risk of crossing critical social system include the disintegration of the West Antarctic ice sheet leading thresholds will grow. At such thresholds existing institutions that to more rapid sea-level rise than projected in this analysis or would have supported adaptation actions would likely become large-scale Amazon dieback drastically affecting ecosystems, riv- much less effective or even collapse. One example is a risk that ers, agriculture, energy production, and livelihoods in an almost sea-level rise in atoll countries exceeds the capabilities of con- continental scale region and potentially adding substantially to trolled, adaptive migration, resulting in the need for complete 21st-century global warming. abandonment of an island or region. Similarly, stresses on human There might also be nonlinear responses within particular health, such as heat waves, malnutrition, and decreasing quality economic sectors to high levels of global warming. For example, of drinking water due to seawater intrusion, have the potential nonlinear temperature effects on crops are likely to be extremely to overburden health-care systems to a point where adaptation is relevant as the world warms to 2°C and above. However, most of no longer possible, and dislocation is forced. our current crop models do not yet fully account for this effect, Thus, given that uncertainty remains about the full nature or for the potential increased ranges of variability (for example, and scale of impacts, there is also no certainty that adaptation to extreme temperatures, new invading pests and diseases, abrupt a 4°C world is possible. A 4°C world is likely to be one in which shifts in critical climate factors that have large impacts on yields communities, cities and countries would experience severe disrup- and/or quality of grains). tions, damage, and dislocation, with many of these risks spread Projections of damage costs for climate change impacts typi- unequally. It is likely that the poor will suffer most and the global cally assess the costs of local damages, including infrastructure, community could become more fractured, and unequal than and do not provide an adequate consideration of cascade effects today. The projected 4°C warming simply must not be allowed (for example, value-added chains and supply networks) at national to occur—the heat must be turned down. Only early, cooperative, and regional scales. However, in an increasingly globalized world international actions can make that happen. 8 9 10 List of Abbreviations °C degrees Celsius AIS Antarctic Ice Sheet AOGCM Atmosphere-Ocean General Circulation Model AOSIS Alliance of Small Island States AR4 Fourth Assessment Report of the Intergovernmental Panel on Climate Change AR5 Fifth Assessment Report of the Intergovernmental Panel on Climate Change BAU Business As Usual CaCO3 Calcium carbonate cm centimeter CMIP5 Coupled Model Intercomparison Project Phase 5 CO2 Carbon dioxide CO2e Carbon dioxide equivalent DIVA Dynamic Interactive Vulnerability Assessment DJF December January February GCM General Circulation Model GDP Gross Domestic Product GIS Greenland Ice Sheet GtCO2e Gigatonnes—billion metric tons­ —of carbon dioxide equivalent IAM Integrated Assessment Model IBAU “IMAGE (Model) Business As Usual� Scenario (Hinkel et al. 2011) ISI-MIP Inter-Sectoral Model Inter-comparison Project IPCC Intergovernmental Panel on Climate Change JJA June July August LDC Least Developed Country MGIC Mountain Glaciers and Ice Caps NH Northern Hemisphere NOAA National Oceanic and Atmospheric Administration (USA) OECD Organisation for Economic Cooperation and Development PG Population growth PGD Population growth distribution ppm parts per million RBAU “Rahmstorf Business As Usual� Scenario (Hinkel et al. 2011) RCP Representative Concentration Pathway SH Southern Hemisphere SLR Sea-Level Rise SRES IPCC Special Report on Emissions Scenarios SREX IPCC Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation SSA Sub-Saharan Africa UNFCCC United Nations Framework Convention on Climate Change WBG World Bank Group WBGT Wet-Bulb Global Temperature WDR World Bank Group’s World Development Report WHO World Health Organization 11