Abrupt Impacts of Climate Change Anticipating Surprises (2013) / Chapter Skim
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1 Introduction
1 Introduction
Pages 19-38
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From page 19... ...
This report offers an updated look at the issue of abrupt climate change and its potential impacts, and takes the added step of considering not only abrupt changes to the climate system itself, but also abrupt impacts and tipping points that can be triggered by gradual changes in climate. This examination of the impacts of abrupt change brings the discussion into the human realm, raising questions such as: Are there potential thresholds in society's ability to grow sufficient food?
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From page 20... ...
The continuous record of column ozone abundances measured at Halley Bay, Antarctica, showed Antarctic Column Ozone, October Halley Bay 60 - 90 S 350 300 Ozone total column (DU) 250 200 150 Onset Montr eal P hase Out 100 1960 1970 1980 1990 2000 2010 Year FIGURE A Total column ozone in Antarctica, at the Halley Bay station of the British Antarctic Survey (black)
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From page 21... ...
Thus, it exemplifies the scope and magnitude of the types of impacts that abrupt changes from human activities can have on the planet. Bark Beetle Outbreaks Bark beetles are a natural part of forested ecosystems, and infestations are a regular force of natural change.
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From page 22... ...
abrupt impacts of climate chang E BOX 1.1 CONTINUED FIGURE B Photographs of a pine bark beetle and of a beetle-killed forest in the Colorado Rocky Mountains. Source: Top: Photo by Dion Manastyrski; Bottom: Photo from Anthony Barnosky.
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From page 23... ...
For this reason, previous reviews of abrupt change have tended to focus on the physical climate system, and the potential for abrupt changes and threshold behavior has been expressed primarily in climatic terms (key references listed in Box 1.2)
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Abrupt changes in climate are most likely to be significant, from a human perspective, if they persist over years or longer, are larger than typical climate variability, and affect sub-continental or larger regions. Change in any measure of climate or its variability can be abrupt, including change in the intensity, duration, or frequency of extreme events." This expanded definition raised the issues of persistence, of changes being so large that they stand out above typical variability, and that changes in extremes, not just baselines, were considered to be abrupt climate changes.
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From page 25... ...
for at least a few decades, and causes substantial disruptions in human and natural systems." This simple definition directly focuses attention on the impacts of change on natural and human systems and is important in that it directly combines the physical climate system with human impacts. As an increasingly interdisciplinary approach was taken to studying abrupt climate change, there was an accompanying evolution in thinking, expanding from abrupt changes in the physical climate system to include abrupt impacts from climate change.
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From page 26... ...
Thus, the committee begins by defining that, for this report, the term "abrupt climate change" as being abrupt changes in the physical climate system, and the related term, "abrupt climate impacts," as being abrupt impacts resulting from climate change, even if the climate change itself is gradual (but reaches a threshold value that triggers an abrupt impact in a related system) This definition of abrupt climate change also helps to set a time frame for what kinds of phenomena are considered in this report.
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These abrupt changes can affect natural or human systems, or both. The primary timescale of concern is years to decades.
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. More generally, however, a key characteristic required for abrupt changes to occur is the property of state dependence (aka nonlinearity or nonseperability)
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The abrupt changes of the past are not fully explained yet, and climate models typically underestimate the size, speed, and extent of those changes. Hence, future abrupt changes cannot be predicted with confidence, and climate surprises are to be expected." The report made five recommendations in two general categories: implementation of targeted areas of research to expand observations of the present and the past, and implementation of focused modeling efforts.
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From page 30... ...
The inclusion of isotopes into some models (e.g., Sturm et al., 2010; Tindall et al., 2010) is also allowing for a more direct comparison with paleoclimate proxies of relevance to past abrupt change, and a more comprehensive evaluation of the sources and sinks of the atmospheric water cycle that is critical in assessing the risk of future abrupt change and its impacts (e.g., Risi et al., 2010)
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From page 31... ...
. However, although scientists clearly have an improved understanding of past abrupt climate changes today compared with a decade ago, in many cases the data still remain too sparse spatially to test mechanisms of change using models.
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, acknowledged that our understanding of abrupt climate change was notably incomplete and that this limited the ability to model abrupt change, stating that "Mechanisms of onset and evolution of past abrupt climate change and associated climate thresholds are not well understood. This limits confidence in the ability of climate models to simulate realistic abrupt change." However, the Working Group I report did specifically address the issue of a shutdown of the formation of North Atlantic Deep Water and concluded from modeling studies that although it was very likely (>90 percent chance)
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From page 33... ...
The AR4 WG2 report repeatedly calls for more research to be done on the impacts of abrupt change, particularly a collapse of the North Atlantic Deep Water formation (which was not considered likely) and a relatively rapid sea level rise of many meters due to rapid (century-scale)
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From page 34... ...
Physical understanding suggests that mega-droughts are more likely to be triggered by interior reorganization of the ocean-atmosphere system rather than by overall warming of Earth's surface, although overall warming can cause interior reorganization and thus can be responsible indirectly. The SAP 3.4 report states that it is unclear whether current climate models are capable of predicting the onset of mega-droughts: "… systematic biases within current coupled atmosphere-ocean models raise concerns as to whether they correctly represent the response of the tropical climate system to radiative forcing and whether greenhouse forcing will actually induce El Niño/Southern Oscillation-like patterns of tropical SST change that will create impacts on global hydroclimate…" .
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It dedicates a section to a general discussion of abrupt climate change, with an additional section allocated to the topic of extreme events. The report focuses on the coming decade, and as such they conclude that there is little expectation in the scientific community for an abrupt change on that timescale.
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Chapter 3 discusses abrupt climate impacts from the perspective of how they affect humans, building on many of the same processes discussed in Chapter 2. Examples include abrupt changes in food availability, water availability, and ecosystem services.
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What is known about the likelihood and timing of abrupt changes in the climate sys tem over decadal timescales? Are any of the phenomena considered by the committee currently embodied in computational climate models?
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