Radiative Forcing of Climate Change Expanding the Concept and Addressing Uncertainties (2005) / Chapter Skim
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5 Uncertainties Associated with Future Climate Forcings
5 Uncertainties Associated with Future Climate Forcings
Pages 100-116
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From page 100... ...
In this chapter, current capabilities for projecting future forcings are discussed and critical uncertainties associated with these forcings and their effect on climate are identified. To date, all model projections of future climate have included a subset of climate forcings, typically greenhouse gas emission scenarios, solar variability, and more recently, aerosol emissions.
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From page 101... ...
The available approaches for estimating future emissions to the atmosphere from human activities are described in this section. The methods used to relate emissions to atmospheric concentrations of greenhouse gases and aerosols are discussed in Chapter 6.
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From page 102... ...
Noninterventionist, the currently preferred term, also requires clarification because society is currently taking some steps, such as vehicular mileage standards and hybrid car marketing and research, that could be interpreted as climate policy. Emissions scenarios that take account of policy intervention include those in which greenhouse gas concentrations are stabilized and cost-benefit scenarios.
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From page 103... ...
These emissions, along with the ozone precursor emissions of methane, carbon monoxide, nitrogen oxides, and volatile organic compounds, were also gridded onto 1o × 1o latitude-longitude maps for use in global climate, atmospheric chemistry, and air quality models. The grids were developed using simple scaling applied to a base-year 1990 map and using the projected four to six regional changes from the SRES emissions models.
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From page 104... ...
in which environmental impact is the result of a multiplication of three driving forces: population, affluence per person, and technological impact per unit of affluence. When applied to greenhouse gas emissions, the impact is the rate of greenhouse gas emissions, while the technological factor is the rate of greenhouse gas emissions per unit of gross domestic product (GDP)
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From page 105... ...
To circumvent the relative dearth of long-term economic projections, the IPCC SRES report adopted a scenario approach in which story lines were developed that sketched in some detail the broad outline of future world development pathways. These story lines facilitated the selection of specific targets for economic growth in the year 2100.
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From page 106... ...
For example, demographic, human welfare, and economic development are often seen as linked through various factors. When the IPAT model is applied to greenhouse gas emissions, analysts have found it useful to further disaggregate the technology factor into the product of "emissions per unit of energy" (CO2/E)
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From page 107... ...
Similarly, some models are now producing scenarios that consider the competition between land uses implied by large-scale development of commercial biomass crops and the interaction between the energy system, land use, and the terrestrial carbon cycle. Emissions Scenarios for Short-Lived Compounds One category of future emissions with particularly high uncertainties is the shorter-lived compounds, including tropospheric ozone precursors (carbon monoxide [CO]
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From page 108... ...
The IPCC SRES provided estimates for emissions of methane, other ozone precursors, and sulfur dioxide (precursor for sulfate aerosols) , but not for carbonaceous aerosols, dust, or sea salt (Nakicenovic´ et al., 2000)
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From page 109... ...
. However, this does not rectify the spatially static character inherent in rescaling the 1990 EDGAR emissions grid because only the reporting region emissions results were used in the top-down gridding, rather than explicit future population distribution information.
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From page 110... ...
The projections of future decreases in dust emissions result from changes in soil moisture and surface winds in arid regions; however, future human landscape conversion and landscape degradation have not been included in these projections. Decreases could reduce cooling, thereby enhancing climate warming trends.
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From page 111... ...
Regulations targeting black carbon emissions or ozone precursors would have combined benefits for public health and climate (Hansen et al., 2000; Jacobson, 2002)
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From page 112... ...
. More recent modeling studies that have incorporated aerosols show that aerosol direct and indirect forcing may have offset as much as 50 to 75 percent of the radiative forcing due to greenhouse gas increases since preindustrial times.
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From page 113... ...
That current levels of solar activity are at overall high levels, according to both sunspot numbers and cosmogenic isotopes, suggests that future solar irradiance values may not be significantly higher than seen in the contemporary database. A projection of future solar activity based on spectral synthesis of the cosmogenic isotope record confirms that solar activity is presently peaking and in 2100 will reach levels comparable to those in 1990 (Clilverd et al., 2003)
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From page 114... ...
for the United States and globally will permit detailed data to be obtained into the future. The consequences of future land-use change on the forcing of the climate system include alterations in the surface albedo, portioning of the surface net radiation between latent and sensible turbulent fluxes, and trace
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From page 115... ...
The climate forcing of future landscape change on the surface energy and water budget, and how this effect is transmitted through the atmosphere, has been little studied. Most previous work on future landscapes has concentrated on how the landscape responds to future climate change simulated in models (e.g., NAST, 2001)
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From page 116... ...
. Knowledge of what triggers abrupt climate changes is still quite limited; more research is needed to determine whether human-caused increases in greenhouse gases or land-use changes might lead to an abrupt change.
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