Synthesis Report - Question 5

Climate Change 2001: Synthesis Report

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Figure 5-3: Stabilizing CO2 emissions at current levels will result in a continously rising atmospheric CO2 concentration and temperature. Stabilization of atmospheric CO2 and temperature change will eventually require the emissions to drop well below current levels. In all three panels the red curves illustrate the result of emissions held constant at the level prescribed by the WRE 550 profile for the year 2000 (which is slightly higher than the actual emissions for the year 2000), while the blue curves are the result of emissions following the WRE 550 stabilization profile. Both cases are illustrative only: Constant global emissions are unrealistic in the short term, and no preference is expressed for the WRE 550 profile over others. Other stabilization profiles are illustrated in Figure 6-1. Figure 5-3 was constructed using the models described in WGI TAR Chapters 3 & 9.

WGI TAR Sections 3.7 & 9.3

Although warming reduces the uptake of CO2 by the ocean, the oceanic net carbon uptake is projected to persist under rising atmospheric CO2 , at least for the 21st century. Movement of carbon from the surface to the deep ocean takes centuries, and its equilibration there with ocean sediments takes millennia.

WGI TAR Sections 3.2.3 & 3.7.2, & WGI TAR Figures 3.10c,d
5.8 When subjected to rapid climate change, ecological systems are likely to be disrupted as a consequence of the differences in response times within the system. The resulting loss of capacity by the ecosystem to supply services such as food, timber, and biodiversity maintenance on a sustainable basis may not be immediately apparent. Climate change may lead to conditions unsuitable for the establishment of key species, but the slow and delayed response of long-lived plants hides the importance of the change until the already established individuals die or are killed in a disturbance. For example, for climate change of the degree possible within the 21st century, it is likely, in some forests, that when a stand is disturbed by fire, wind, pests, or harvesting, instead of the community regenerating as in the past, species may be lost or replaced by different species.

WGII TAR Section 5.2
5.9 Humans have shown a capacity to adapt to long-term mean climate conditions, but there is less success in adapting to extremes and to year-to-year variations in climatic conditions. Climatic changes in the next 100 years are expected to exceed any experienced by human societies over at least the past 5 millennia. The magnitude and rate of these changes will pose a major challenge for humanity. The time needed for socio-economic adaptation varies from years to decades, depending on the sector and the resources available to assist the transition. There is inertia in decision making in the area of adaptation and mitigation, and in implementing those decisions, on the order of decades. The fact that adaptation and mitigation decisions are generally not made by the same entities compounds the difficulties inherent in the identification and implementation of the best possible combination of strategies, and hence contributes to the delays of climate change response.

WGII TAR SPM 2.7, WGII TAR Sections 4.6.4, 18.2-4, & 18.8, & WGIII TAR Section 10.4.2
Figure 5-4: The range of time scales of major processes within the global carbon cycle leads to a range of response times for perturbations of CO2 in the atmosphere, and contributes to the development of transient sinks, as when the atmospheric CO2 concentration rose above its pre-1750 equilibrium level.
5.10 There is typically a delay of years to decades between perceiving a need to respond to a major challenge, planning,researching and developing a solution, and implementing it.Thisdelaycan be shortened by anticipating need sthrough the application of foresight, and thus developing technologies in advance. The response of technological development to energy price changes has historically been relatively rapid (typically, less than 5 years elapses between a price shock and the response in terms of patenting activity and introduction of new model offerings) but its diffusion takes much longer. The diffusion rate often depends on the rate of retirement of previously installed equipment. Early deployment of rapidly improving technologies allows learning-curve cost reductions (learning by doing), without premature lock-in to existing, low-efficiency technology. The rate of technology diffusion is strongly dependent not only on economic feasibility but also on socio-economic pressures. For some technologies, such as the adoption of new crop varieties, the availability of, and information on, pre-existing adaptation options allows for rapid adaptation. In many regions, however, population pressures on limited land and water resources, government policies impeding change, or limited access to information or financial resources make adaptation difficult and slow. Optimal adaptation to climate change trends, such as more frequent droughts, may be delayed if they are perceived to be due to natural variability, while they might actually be related to climate change. Conversely, maladaptation can occur if climate variability is mistaken for a trend. WGII TAR Sections 1.4.1, 12.8.4, & 18.3.5, & WGIII TAR Sections 3.2, 5.3.1, & 10.4

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