Climate and Social Stress Implications for Security Analysis (2013) / Chapter Skim
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3 Potentially Disruptive Climate Events
3 Potentially Disruptive Climate Events
Pages 53-74
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From page 53... ...
. When climate is changing, potentially disruptive climate events occur at different rates, with different intensities, and perhaps in different places from what people would expect from past experience.
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From page 54... ...
Climate models are based on the same basic set of equations that predict shorter-term weather variations, but they also include terms that represent a coupling of the atmosphere with the ocean and land surfaces, which inherently have memories of climate longer than the atmosphere does. Climate models have a coarser resolution than weather prediction models, which limits the level of accuracy in their simulations of atmospheric and ocean dynamics and their interactions with climate.
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From page 55... ...
An increased understanding of the physical mechanisms that govern climate variability is also critical. In sum, although physical climate science is able to project climate trends based on scenarios for increases in greenhouse gases (GHGs)
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From page 56... ...
It will also be important to improve understanding of how the GHG-forced changes in climate might change the characteristics of climate variability, such as ENSO. Despite their inability to predict specific events for the coming decade, climate models can still provide useful information about the range of plausible climate outcomes that could result from the combination of external forcing and variability of the climate system due to internal processes over the next decade.
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From page 57... ...
, each region has a reasonable chance of overall cooling for the coming decade. Each region also has a reasonable chance of warming by more than 1.8°F (1°C)
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From page 58... ...
In such situations, it may be wise for security analysts to consider what-if scenarios involving increased frequencies of occurrence for such events. ABRUPT CLIMATE CHANGE Climate models currently used to project climate change over the 21st century generally indicate that there will be a gradual response to increased greenhouse gases and other climate forcing, suggesting quite a low likelihood that major changes will occur within the coming decade.
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From page 59... ...
On a much larger geographic scale, the climatic effects of the abrupt shift in 1976–1977, mainly in sea surface temperatures in the Pacific Ocean, have been documented in a number of global and hemispheric analyses (Alley et al., 2003)
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From page 60... ...
The likelihood of any of these events occurring by the mid-2020s is difficult to estimate for a number of reasons, including the fact that global climate models do not simulate abrupt climate shifts well, which makes it hard to project when a change in some part of the climate system that might induce a broader abrupt change (e.g., regional or hemispheric temperature or precipitation) will reach a critical value.
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From page 61... ...
SINGLE EXTREME EVENTS The fundamental science of climate change suggests that continued global warming will increase the frequency or intensity (or both) of a great variety of events that could disrupt societies, including heat waves, extreme precipitation events, floods, droughts, sea level rise, wildfires, and the spread of infectious disease.
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From page 62... ...
Climate Change and Extreme Climate Events in the Coming Decade Effects of Climate Change on Extreme Events The frequency and intensity of extreme events are particularly hard to project because, among other things, there are by definition few of them, which makes it hard to validate predictive models against experience (see Appendix D for more detailed discussion of statistical issues and methods for assessing the probabilities of occurrence of extreme events)
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From page 63... ...
A subsequent IPCC special report on extreme events (Intergovernmental Panel on Climate Change, 2012) summarized available evidence on observed and projected extremes of a variety of important types of climate events globally and at the regional level.
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From page 64... ...
TABLE 3-1 Observed Changes in Extreme Weather and Climate Events Since 1950 64 Event Global Change Confidence Regional Changes Confidence Cold days and nights Decrease Very likely Decrease at the continental scale Likely in North America, Europe, and Australia Warm days and nights Increase Very likely Increase at the continental scale Likely in North America, Europe, and Australia Warming trend in daily Medium temperature extremes in Asia Warming trend in daily Low to medium, due to temperature extremes in insufficient evidence Africa and South America Length or number of heat Increase in many regions with Medium waves sufficient data Heavy precipitation events More regions have experienced Likely increases than decreases, although there are strong regional and subregional variations Tropical cyclone activity Unclear Low confidence after (intensity, frequency, accounting for past changes duration) in observing capabilities Drought Intense and longer droughts in Medium southern Europe, west Africa Extreme coastal high water Increase related to an Likely, at global scale increase in mean sea level SOURCE: Adapted from Tables 3-1 and 3-2 in Intergovernmental Panel on Climate Change (2012)
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From page 65... ...
is characterized by a weakening of the Pacific trade winds, a warming of the ocean's surface in the central and eastern Pacific, and smaller differences in tropical sea level pressures between the eastern and western tropical Pacific Ocean. Opposite conditions occur in the cold phase, or La Niña.
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From page 66... ...
The fact that ENSO drives unusual weather patterns on several continents at the same time demonstrates that extreme weather patterns in different regions may not be independent in a statistical sense, suggesting the possibility that extreme climate events may cluster in time, a topic discussed more fully in the next section. The question of whether and how anthropogenic climate change may be altering the ENSO cycle is being actively examined by climate scientists (Intergovernmental Panel on Climate Change, 2012)
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From page 67... ...
In addition to these events, there remains the possibility of unprecedented extreme events that might occur as a result of abrupt climate change or other climatic phenomena discussed later in the chapter.
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From page 68... ...
. The fact that these two extreme events corresponded in time with each other and with a single larger meteorological pattern was unusual but not totally unexpected.
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From page 69... ...
But as the above example makes clear, extreme events in different parts of the world can be driven by common underlying forces and thus have an intrinsic relationship such that when one such event occurs, the likelihood increases that other extreme events linked to them by common causes will also occur. In statistical language, such events are called dependent.
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From page 70... ...
Moreover, shifts in precipitation patterns and associated drought can promote bark beetle outbreaks by weakening trees and making them more susceptible to beetle attacks. Droughts, combined with forest die-off from beetle outbreaks, in turn increase the amount of fuel in forests, increasing the susceptibility of forests to fire, especially during heat waves, which are likely to be longer and more intense with climate change.
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From page 71... ...
Nevertheless, the example suggests that there may be a very large number of plausible ways by which climate change could set in motion a sequence of events in ecological, hydrological, or other deterministic physical and biological systems that could become seriously disruptive and that might create security concerns. GLOBAL SYSTEM SHOCKS Climate events occurring in one part of the world have the potential to affect other parts of the world through important, globally integrated systems other than climate itself.
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From page 72... ...
Hence the behavior of extreme events in a non-stationary climate cannot be fully described and projected until climate change models are run with the spatial resolution and physical processes of numerical weather prediction models. Until that time, extreme climate surprises should be expected to be more the rule than the exception.
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From page 73... ...
In addition, there remains the possibility of unprecedented extreme events or conjunctions of events that might occur as a result of abrupt climate change or other climatic phenomena (for example, a more rapid rise in sea level if the melting of ice sheets were to accelerate)
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From page 74... ...
Recommendation 3.1: The intelligence community should participate in a whole-of-government effort to inform choices about adapting to and reducing vulnerability to climate change. It should, along with appropriate federal science agencies, support research to improve the ability to quantify the likelihoods of potentially disruptive climate events, that is, single extreme climate events, event clusters, and event sequences.
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