CH18: Mitigation: Reducing Greenhouse Gas Emissions, Sinks, and Solutions

FIGURE 18.1 Stabilization triangles and wedges. Stabilizing greenhouse gas concentrations in the atmosphere requires the leveling of emissions by 2050 and reductions thereafter. To offset new demand, a “stabilization triangle” (green) is required. One way to satisfy the energy demand in such a triangle is through existing technologies, each contributing a wedge of approximately one-seventh of the triangle (solid lines within green). More than 15 existing technologies have been identified that can supply one of 12 needed wedges, meaning that choices can still be made in energy supply (e.g., foregoing nuclear power) and still achieve the steps toward stabilization needed in the first half of the twenty-first century. Source: Pacala and Socolow (2004). Reproduced with permission from AAAS.

FIGURE 18.2 End of oil. Oil production will peak and decline, with the shape of declining production roughly mirroring the upward curve of increasing production. Abundant other fossil fuels, including oil sands, oil shale, and coal, will ensure that the fossil fuel era will continue, regardless of when oil supply is exhausted (unless climate policy intervenes). Source: From Wikimedia Commons.

FIGURE 18.3 Solar and wind co-location (Top). Photovoltaic panels can be co-located with other land uses, such as residential roofs or open space, reducing the impact on natural habitats. Source: From Wikimedia Commons. (Bottom) Co-location of solar and wind with agriculture. From Juwi.

FIGURE 18.4 Alternative energy footprint. The land area required to supply all transportation needs in the United States from different renewable energy sources is shown relative to the overall land area of the United States. Battery Electric Vehicles (BEV) assumed for wind and solar options. Percentages refer to the proportion of total US land area. Source: Figure based on data from Mark Jacobson.

FIGURE 18.5 Energy pathways and extinction risk.Global area use of energy technologies by latitude. Average land use by latitude associated with global energy development to 2100. Land use is shown rather than biodiversity loss, because at 200 times greater impact on biodiversity for biofuels, no other technology shows on a graph of the same scale. The high-area losses for biofuels shown here combine with a high concentration of biofuel potential in the species-rich tropics to make species extinction risk from biofuels the highest of all sources by orders of magnitude. Source: N. Snider and L. Hannah.

Photovoltaic (PV) cells use the electromagnetic properties of sunlight to generate electricity. Light falling on a PV array releases electrons, which are captured and channeled by the silicon structure of the PV cells. This stream of flowing electrons is electricity, which can be used to power any conventional electrical appliance or motor. Rooftop PV has the potential to provide as much as half of all of the world’s energy demand, if all available rooftop space were employed. A major fraction of electricity needs could be met by rooftop PV with no land use demands that might reduce wildlife habitat.

Wind turbines come in all sizes, from units the size of a bread box used to provide electricity on small boats, to giant multimegawatt turbines used in central electricity generation. Visual impacts are a major concern with large wind farms. Although the turbine towers have a small footprint, associated roads and support infrastructure may result in significant habitat loss where wind is sited in natural areas.

Nuclear power has major potential for generation without GHG emissions, but it faces major safety and environmental concerns. Among the safety concerns are potentially devastating radiation damage to humans and wildlife in the event of a major accident, and the possibility of the use of by-products to build nuclear arms. Environmental concerns include the safe disposal of very long-lived radioactive waste from nuclear reactors. Climate change provides reason to reexamine nuclear power possibilities, but social concerns seem likely to limit its overall importance as a CO2-free energy source.