Cambridge University Press
9780521870283 - Climate Extremes and Society - Edited by Henry F. Diaz and Richard J. Murnane
The significance of weather and climate extremes to society: an introduction
HENRY F. DIAZ AND RICHARD J. MURNANE
Events over the past few decades have brought extreme weather and climate events to the fore of societal concerns. Ordinary citizens, individuals in the private sector, and people at the highest levels of government worry about the apparent increase in the frequency of weather and climate events causing extreme, and in some instances catastrophic, impacts. We differentiate between weather events – relatively short-term phenomena associated with, for instance, tropical cyclones (hurricanes and typhoons, for example), severe floods, and the like – and climate events – longer-lived and/or serial phenomena such as drought, season-long heat waves, record wildfire seasons, multiple occurrences of severe storms in a single season or year, etc. The differentiation is related to the distinction between weather, which can be forecast on short timescales of less than 1–2 weeks, and climate, which can be forecast on monthly, seasonal, and annual timescales. The adage “Climate is what you expect and weather is what you get” probably originates from the fact that climate is the statistical average of the weather over a specified time period. Regardless of whether an extreme event is weather- or climate-related, it could have significant and numerous implications for society.
This book summarizes our knowledge of different aspects of weather and climate extremes and then focuses on their recent and potential future consequences for different socioeconomic sectors. We also examine some actions that may enable us to better respond to and adapt to climate variability regardless of its source – for example, the development of public–private research and applications partnerships, and the development of state-supported public hurricane risk models for decision support. The book is divided into two parts: Part I, titled “Defining and modeling the nature of weather and climate extremes,” where we examine evidence for recent and projected changes in extremes of weather and climate events, and Part II, titled “Impacts of weather and climate extremes,” where we assess the impacts of these events on the insurance industry. The chapters in Part I progress through the description of extremes and an assessment of recent changes in climate through an examination of how extremes might change in the future. Those in Part II evaluate the changing socioeconomic impacts of extremes and provide examples of how public and private enterprises are attempting to understand and respond to ongoing changes in extreme events.
The likely connection between climate change and extreme event frequency on multiple timescales has been recognized for some time (see Wigley, 1985). Wigley’s paper illustrated for arbitrary climate variables the high sensitivity of low-probability occurrences to shifts in the mean. It seems likely that our experience and response to changes in weather and climate extremes will be a function of physical and temporal factors, for example: the intensity of the extreme; the temporal scale of the extreme (short-lived or persistent); the frequency of the extreme (rare or common); and the sensitivity and resiliency of our societies to a range of typical, and potentially new, extremes. Extremes in weather and climate are an inherent part of nature. Nature, and in many cases society, have a built-in resiliency to extreme events. Often, natural systems require extreme events in order for a species to reproduce or survive. Problems may arise when the frequency, intensity, distribution, or other characteristic of an extreme changes either beyond a threshold, or too rapidly. Therefore, it seems appropriate that this book opens with a chapter by Stephenson, which examines the subject from a taxonomic viewpoint, considering both statistical descriptions of extreme events and the fundamental climate patterns that give rise to them.
Increases in heat waves and intense precipitation are two of the most probable consequences of anthropogenic climate change. The increasing risk of severe heat waves (Schär et al., 2004; Stott et al., 2004) and flooding (Milly et al., 2002, 2005) as global climate change progresses is a major concern for insurers, public health managers, and policy makers. Chapter 2, by Easterling, provides an overview of recent changes in temperature and precipitation derived from observational data. Temperature and precipitation are often the focus of studies on changes in extremes, in large part because of the relatively high quality of the data record. Chapter 3, by Brooks and Dotzek, illustrates the limitations of weather and climate data and provides an example of how people deal creatively with data inhomogeneities.
The fourth chapter, by von Storch and Weisse, examines how wind and wave extremes have changed over the past decades; Gershunov and Douville’s chapter (Chapter 5) provides a unique assessment of extremes that accounts for the spatial scale of climate extreme events. Gershunov and Douville also examine how the probability distribution of seasonal extreme temperature values is changing and how it is likely to change based on projections from global climate models. Chapter 6, by Tebaldi and Meehl, provides the reader with our best estimates of how temperature and precipitation extremes are likely to change under high atmospheric concentrations of greenhouse gases.
The final chapter in Part I by Knutson and Tuleya (Chapter 7), examines how the intensities of tropical cyclones are likely to change under specific future emission scenarios of greenhouse gases. The theory relating tropical cyclone intensity to climate is well established (see Emanuel, 1987 and Holland, 1997). The likely impact of climate warming due to increased atmospheric CO2 and other so-called greenhouse gases will be to increase, on average, tropical cyclone intensity (i.e., stronger maximum winds and lower central pressures). Recent studies support the contention that greenhouse forcing is already having an effect on tropical cyclone intensity in the North Atlantic (Emanuel, 2005; Elsner, 2006) as well as in the other ocean basins (Webster et al., 2005; Hoyos et al., 2006). There are a number of issues related to data quality (Chan, 2006; Landsea et al., 2006) that raise questions about the robustness, or even existence, of recently observed changes. However, recent work (Kossin et al., 2007) suggests that recent changes in hurricane intensity observed in the Atlantic are real.
The salient messages conveyed by the chapters in Part I are that climate is not static, that the frequency and intensity of extremes have changed over the past decades, and that we can expect to see similar changes in the future due in part to anthropogenic climate change. The newsworthiness of recent extreme events naturally makes people anxious about the future and leads to questions of how recent changes in weather and climate extremes are related to increases in greenhouse gases emitted through fossil fuel burning and other societal activities, and whether these events are harbingers of the future. Of course, without a decrease in our vulnerability, the losses of life and property to extreme events will continue to increase as long as the number of people and amount of property exposed to extremes continues to increase. An increase in the intensity and frequency of an extreme will only exacerbate the situation, sometimes in very nonlinear ways. Many of these issues are examined in Part II, which considers some of the impacts that recent extreme climate events have had on society, and some implications for the future.
The material in Part II attempts to assess the impact of changes in weather and climate extremes on society in general and the insurance industry in particular. These chapters provide case studies of how changes in climate extremes can influence different parts of our society. However, one should not forget that the impacts of extreme weather and climate events are by no means limited to the examples presented here. More recent, larger impact events are often in the news. The 2004 and 2005 Atlantic hurricane seasons, for example, were very active, with multiple landfalls affecting the United States. Because the United States was struck repeatedly, the cumulative impact was very costly to insurers. Different parts of the world are prone to different types of weather and climate hazards. In the western United States, for example, a widespread and intense 5-year drought was punctuated in 2003 by extreme wildfires in southern California that caused losses worth billions of dollars. Three years later, in 2006, the wildfire season set a new record for acreage burned. In fact, in the past decade or two, several new records have been set for acreage burned in the United States, while in Europe the summer of 2003 saw record-breaking heat that contributed to the premature deaths of thousands of people.
The first two chapters in Part II provide examples of how weather and climate extremes can affect ecosystems and society. Beniston’s chapter (Chapter 8) examines regional-scale changes in temperature and precipitation in the European Alps, an area with sharp climatic gradients driven by changes in elevation. The author then evaluates climate change projections for the region in the context of observed climate changes over the past century. Chapter 9, by Crabbe et al., examines how temperature and wave extremes influence coral growth. Crabbe et al. show that for many coral communities, an increase in temperature of only a few degrees may result in significant reductions in growth rates and widespread mortality. In addition, an increase in tropical cyclone intensity will also have a direct effect on coral reef systems, as stronger wave action can also result in reef damage.
Loss data are one of the few benchmarks that can be used to assess the impact of weather and climate extremes over time. However, issues related to the collection and quality of loss data generally make temperature and precipitation data appear to be ideal. This is an unfortunate situation, as monetary losses provide one of the few measures of the impacts of extremes that easily conform to a typical decision-making process.
Chapter 14, by Cutter et al., discusses some of the issues related to the collection of loss data and presents an overview of a public archive of losses from extremes. This information is difficult to collect, in part because there is no formal mechanism for collecting or identifying loss data.
The insurance industry commonly collects the most complete information on losses from extreme climate and weather events. Unfortunately, this information is often proprietary. Nevertheless, a number of companies produce publicly available reports that aggregate and analyze losses on regional and global scales. The total amount of insured losses arising from the top 40 extreme weather and climate extremes worldwide from 1970 to 2004 was approximately US$142 billion (in 2004), with US hurricanes causing the lion’s share of these losses (Murnane and Diaz, 2006). In December 2005, the Munich Re Foundation reported that 2005 was the costliest year on record for economic losses due to natural disasters, with about US$200 billion in economic losses from weather-related disasters. These losses surpassed the previous record of about US$145 billion set the previous year (see also Chapter 13 by Dlugolecki, this volume).
The data on overall natural hazards and disaster losses for the past 35 years suggest a rather steady increase in the level of monetary losses adjusted for inflation (Cutter and Emrich, 2005). Inflation-adjusted economic losses from catastrophic events – those that resulted in economic losses that exceeded some arbitrary criterion – rose 8-fold in the last four decades of the twentieth century, and insured losses rose by 17-fold (Mills, 2005). But these studies do not account for changes in other factors, such as population and wealth, that also play a role in loss (Diaz and Pulwarty, 1997; Choi and Fisher, 2003; Simpson, 2003). Chapter 12, by Miller et al., analyzes loss data on national and global scales and accounts for changes in population and wealth. Miller et al. find no statistically significant trend in these normalized losses.
Although there is no definitive trend in normalized losses, available records indicate a significant increase in the size and frequency of insured losses. Dlugolecki (Chapter 13) discusses the implications of these increases from a global perspective. In particular, the author argues that recent rapid increases in insurance losses may in part reflect the rather rapid pace of global warming in the past few decades. An insurer’s rational response to the potential for large losses would be to estimate the probability of the loss and then plan appropriately. We include three chapters that offer examples of potential planning tools that could be useful as risk management tools. Chapter 10 by Jagger et al. provides a novel approach for directly forecasting annual insured losses for US landfalling hurricanes as a function of seasonal and interannual climate variability. Chapter 11, by Watson and Johnson, discusses an approach for integrating climate model simulations into catastrophe risk models commonly used by insurers for estimating losses. Chapter 15 by Muir-Wood and Grossi describes the impact that Hurricane Katrina had on the catastrophe insurance industry in general and from the perspective of one company, Risk Management Solutions (RMS).
We end our discussion of the impacts of weather and climate extremes with two examples of institutional actions to manage our response to extremes. In Chapter 15 Muir-Wood and Grossi discuss the aftermath of Hurricane Katrina from the point of view of the catastrophe modeling community. The final chapter, by Murnane and Knap (Chapter 16), discusses a science–business partnership – funded by companies active in the catastrophe risk insurance industry – that supports research on weather and climate extremes of interest to the insurance industry.
This book provides examples of the impacts of climate and weather extremes on society; how these extremes have varied in the past, and how they might change in the future; and the types of efforts that will help society adapt to future changes in climate and weather extremes. This is obviously a huge subject that is evolving rapidly. We hope that we provide the reader with a snapshot of our understanding of extremes and how our society is attempting to respond to them.
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I Defining and modeling the nature of weather and climate extremes
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