FIGURE 3.8 Idealized CO2 concentration scenarios reaching between 350 and 1,000 ppm at the year 2100. At the year 2100, the atmospheric CO2 concentration and global mean temperature change is dependent on cumulative carbon emissions to date, with variation in the rate of emissions over time affecting only the rate of increase of forcing and consequent rate of temperature change. Stabilization of CO2 concentrations after the year 2100 would require continued low-level CO2 emissions (leading to increasing cumulative carbon emitted), whereas zero emission after 2100 would result in slowly declining CO2 concentrations and approximately stable global temperature. Cumulative emissions for each scenario shown here are based on simulations with the UVic ESCM, with uncertainty ranges of 70-140% of the central value based on Matthews et al. (2009) and Zickfeld et al. (2009). Temperature changes are calculated using 1.75ºC per 1,000 GtC emitted, with a 1-2.5ºC/1,000 GtC uncertainty range based on Matthews et al. (2009) and Allen et al. (2009). These uncertainty ranges reflect both uncertainty in the response of carbon sinks to elevated CO2 and climate changes, as well as uncertainty in the physical climate system response to change in CO2 forcing.

FIGURE 3.8 Idealized CO2 concentration scenarios reaching between 350 and 1,000 ppm at the year 2100. At the year 2100, the atmospheric CO2 concentration and global mean temperature change is dependent on cumulative carbon emissions to date, with variation in the rate of emissions over time affecting only the rate of increase of forcing and consequent rate of temperature change. Stabilization of CO2 concentrations after the year 2100 would require continued low-level CO2 emissions (leading to increasing cumulative carbon emitted), whereas zero emission after 2100 would result in slowly declining CO2 concentrations and approximately stable global temperature. Cumulative emissions for each scenario shown here are based on simulations with the UVic ESCM, with uncertainty ranges of 70-140% of the central value based on Matthews et al. (2009) and Zickfeld et al. (2009). Temperature changes are calculated using 1.75ºC per 1,000 GtC emitted, with a 1-2.5ºC/1,000 GtC uncertainty range based on Matthews et al. (2009) and Allen et al. (2009). These uncertainty ranges reflect both uncertainty in the response of carbon sinks to elevated CO2 and climate changes, as well as uncertainty in the physical climate system response to change in CO2 forcing.

centuries. Similarly, should emissions continue at a low level (resulting in increasing cumulative carbon emissions), atmospheric concentrations may remain stable, but global mean temperature would continue to increase over time. Atmospheric CO2 stabilization is consistent with a small amount of continued CO2 emissions at a rate equal to the level of persistent natural carbon sinks, whereas atmospheric temperature stabilization is only consistent with near-zero CO2 emissions (Matthews and Caldeira, 2008; Solomon et al., 2009).



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