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1 Introduction
Pages 15-28

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From page 15...
... Globally, greenhouse gas emissions have been increasing as the growing demand for energy has more than offset what progress there has been from improved efficiency and deployment of new energy sources with lower GHG emissions (Le Quéré et al., 2013)
From page 16...
... Unlike many other air pollutants -- such as nitrogen oxides and sulfur oxides, which are removed by natural physical and chemical processes in just hours to days after they are emitted -- the GHGs most responsible for causing climate change remain in the atmosphere for decades to centuries.1 In order to stabilize or reduce atmospheric concentrations, and thus avoid the worst impacts of warming, global emissions of GHGs must be reduced by at least an order of magnitude (NRC, 2011a)
From page 17...
... . A sea level rise of up to 1 m is possible by the end of the century if current emission trends continue.
From page 18...
... path toward reducing the threats associated with anthropogenic climate change. Even if an aggressive global mitigation program is undertaken, substantial reductions in greenhouse gas levels would not be realized for several decades, and the halting or reversing of some of the detrimental effects already built into the climate system (e.g., ocean warming, ocean acidification, polar ice melting, sea level rise)
From page 19...
... as "climate intervention." Climate intervention includes actions designed to remove carbon dioxide or other greenhouse gases from the atmosphere or to mask some of the climate effects of these gases by changing Earth's radiation balance. This report examines approaches that actively increase the amount of short-wavelength radiation that is reflected to space, referred to as "albedo modification." The terms "climate engineering" and " ­ geoengineering" have been used to refer to highly heterogeneous and poorly defined collections of activities.
From page 20...
... .a Some carbon dioxide removal techniques such as reforestation have already been considered in the public policy process as a form of mitigation -- the effort to reduce net greenhouse gas emissions resulting from human activity. Linking direct air capture of carbon with carbon sequestration (DACS)
From page 21...
... , so the above numbers can be thought of as the amount of electricity produced by 2,300 large power plants globally or 460 large power plants for the United States alone. If society is to decarbon­ze the electricity system, it will be necessary to replace much of that i infrastructure with carbon-free energy sources or to modify existing power plants to be carbon free.
From page 22...
... Note that roughly 88 percent of the energy that presently enters the U.S. economy involves combustion of a fuel, which releases carbon dioxide to the atmosphere (1 quad is 1012 BTUs or 293 TWh)
From page 23...
... Note, however, that all cases involve a greater diversity of energy sources than exist today, with a smaller role for freely emitting fossil fuels and a greater role for energy efficiency, renewable energy, fossil fuels with CCS, and nuclear power. The vir tual elimination by 2050 of coal without CCS -- presently the mainstay of U.S.
From page 24...
... The left-hand panels show the energy supply for each scenario by year, which, in absence of new policies to reduce GHG emissions, would continue to be dominated by fossil fuels. Right-hand panels show alternative scenarios that limit GHG concentration to low levels through rapid and pervasive replacement of fossil fuels.
From page 25...
... . Globally, communities are already experiencing changing conditions directly linked to climate change -- including rising seas that threaten low-lying island nations, loss of glaciers and sea ice and melting permafrost that expose Arctic communities to increased shoreline erosion, and consecutive record years of heat and drought stress (IPCC, 2013a,b, 2014a; NCA, 2014)
From page 26...
... . With sufficient planning, the possibility of moving infrastructure to higher ground is a cost-effective mitigation strategy for many localities, but there is little history of abandoning commercial use of coastal land in anticipation of sea level rise and there are many social and societal factors involved in potentially relocating communities (NRC, 2010a)
From page 27...
... With the exception of trying to increase uptake of carbon dioxide by fertilizing the ocean, most strategies for CDR, such as directly scrubbing carbon dioxide from the atmosphere, are local in scale. CDR technologies for removing carbon dioxide directly from the atmosphere at scale are unlikely to be energetically or financially advantageous over using carbon capture and sequestration technologies to remove carbon dioxide from stack gases associated with combusting fossil fuels or biomass (see discussion in Chapter 3 below)
From page 28...
... . The companion volume to this report, Climate Intervention: Reflecting Sunlight to Cool Earth, considers strategies to increase the fraction of incoming solar radiation that is directly reflected back to space (increase the albedo)


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