National Highway Traffic Safety Administration's 2100 Climate Scenario

In this Draft Environmental Impact Statement, the National Highway Traffic Safety Administration outlines why freezing fuel-efficiency rules for cars and light trucks for six years will do little to avert a global temperature rise of roughly 7 degrees Fahrenheit or 4 degrees Celsius by 2100.

Chapter 5 Greenhouse Gas Emissions and Ciimate Change

of underlying uncertainties and assumptions, no one number for the remaining global carbon budget
can be considered definite.

Using the IPCC estimated carbon budget, as of 2011, approximately 51 percent, or 515 Gt (1,890 Gt
C02), of this budget had already been emitted, leaving a remaining budget of 485 Gt (1,780 Gt C02)
2013b). From 2011 to 2015, C02 emissions from fossil fuels, cement production, and land-use
change totaled approximately 50 Gt [183 Gt C02), leaving a remaining budget from 2016 onwards of
435 Gt (1595 Gt C02) 2016). Under the No Action Alternative, U.S. passenger cars and trucks
are projected to emit 23 Gt (83 Gt C02) from 2016 to 2100, or 5.2 percent of the remaining global
carbon budget. Under Alternative 1, this projection increases to 25 Gt (91 Gt C02) or 5.7 percent of the
remaining budget.

The emissions reductions necessary to keep global emissions within this carbon budget could not be
achieved solely with drastic reductions in emissions from the U.S. passenger car and light truck vehicle
fleet but would also require drastic reductions in all U.S. sectors and from the rest of the devel0ped and
developing world. in addition, achieving GHG reductions from the passenger car and light truck vehicle
fleet to the same degree that emissions reductions will be needed globally to avoid using all of the
carbon budget would require substantial increases in technology innovation and adoption compared to
today?s levels and would require the economy and the vehicle fleet to substantially move away from the
use of fossil fuels, which is not currently technologically feasible or economically practicable.

5.4.2 Direct and Indirect Impacts on Climate Change Indicators

The direct and indirect impacts of the Proposed Action and alternatives on five relevant climate change
indicators are described in Section 5.4.2.1, Atmospheric Carbon Dioxide Concentrations; Section 5.4.2.2,
Temperature; Section 5.4.2.3, Precipitation; Section 5.4.2.4, Sea-Level Rise; and Section 5.4.2.5, Ocean
pH. Section 5.4.2.6, Climate Sensitivity Variations, presents the sensitivity analysis. The impacts of the
Proposed Action and alternatives on global mean surface temperature, atmospheric C02 concentrations,
precipitation, sea level, and ocean pH would be small compared to the expected changes associated
with the emissions trajectories in the GCAM Reference scenario. This is due primarily to the global and
multi-sectoral nature of climate change. Although these effects are small, they occur on a global scale
and are long-lasting. The combined impact of these emissions increases with emissions increases from
other sources could have health, societal, and environmental impacts.

MAGICC6 is a reduced?complexity climate model well calibrated to the mean of the multi-model
ensemble results for four of the most commonly used emissions scenarios?RCP2.6 (low), RCP4.5
(medium), RCP6.0 (medium-high), and RCP8.5 (high) from the IPCC RCP series?as shown in

5-30

Chapter 5 Greenhouse Gas Emissions and Climate Change

Table 5.4.2-1.29 As the table shows, the results of the model runs developed for this analysis agree
relatively well with IPCC estimates for both C02 concentrations and surface temperature.

Table 5.4.2?1. Comparison of MAGICC Modeling Results and Reported IPCC Results"

C02 Concentration (ppm) Global Mean Increase in Surface Temperature
Scenario IPCC we] (2100) MAGICC (2100) IPCC we] (2031?2100) MAGICC (2100)
RCP2.6 421 426 1.0 1.1
RCP4.5 538 544 1.8 2.1
RCP6.0 670 574 2.2 2.6
RCP8.5 935 938 3.7 4.2

Notes:

a The IPCC values represent the average of the 5 to 95 percent range of global mean surface air temperature.

parts per million; degrees Celsius; MAGICC Model for the Assessment of Greenhouse-gas Induced Climate
Change; IPCC Intergovernmental Panel on Climate Change; RCP Representative Concentration Pathways; WGI Working
Group 1

Source: IPCC 2013a

As discussed in Section 5.3.1, Methods for Modeling Greenhouse Gas Emissions, NHTSA used the GCAM
Reference scenario to represent the No Action Alternative in the MAGICC modeling runs. C02
concentrations under the No Action Alternative are 789.11 and range from 789.27 under
Alternative 7 to 789.76 under Alternative 1 in 2100 (Table For 2040 and 2060, the
corresponding range of differences across alternatives is even smaller. Because CO2 concentrations
are the key determinant of other climate effects (which in turn drive the resource impacts discussed in
Section 8.6, Cumulative impacts?Greenhouse Gas Emissions and Ciimate Change), this leads to very
small differences in these effects.

Table 5.4. 2-2. Carbon Dioxide Concentrations, Global Mean Surface Temperature Increase, Sea- Level
Rise, and Ocean pH (GCAM Reference) by Alternative

C02 Concentration Global Mean Surface .
(ppm) Temperature Sea-Level Rise [cm)b' Ocean pH?
Increase

2040 2060 2100 2040 2060 2100 2040 2060 2100 2040 2060 2100
Totals by Alternative
Alt.
Action 479.04 565.44 789.11 1.287 2.008 3.484 22.87 35.56 76.28 8.4099 8.3476 8.2176
Alt. 1 479.15 565.73 789.75 1.288 2.010 3.487 22.87 35.58 76.34 8.4098 8.3474 8.2173
Alt. 2 479.14 565.71 789.72 1.288 2.010 3.487 22.87 35.57 76.33 8.4098 8.3474 8.2173
Alt. 3 479.14 565.70 789.68 1.288 2.009 3.486 22.87 36.57 76.33 8.4098 8.3474 8.2173
Alt. 4 479.12 565.56 789.60 1.287 2.009 3.485 22.87 36.57 76.32 8.4098 8.3474 8.2173
Alt. 5 479.10 565.61 789.48 1.287 2.009 3.486 22.87 36.57 76.31 8.4099 8.3475 8.2174
A112. 5 479.09 565.57 789.40 1.287 2.009 3.485 22.87 36-57 76.31 8.4099 8.3475 8.2174
Alt. 7 479.07 565.52 789.27 1.287 2.009 3.485 22.87 36.57 76.30 8.4099 8.3475 8.2175
Alt. 8 479.08 565.54 789.32 1.287 2.009 3.485 22.87 36.57 76.30 8.4099 8.3475 8.2175

29 NHTSA used the MAGICC default climate sensitivity of 3.0 (5.4

5?3 1