addressing climate change adaptation in regional transportation plans

Addressing Climate Change Adaptation in Regional Transportation PlansA Guide for California MPOs and RTPAsA2. Medium-high emissions resulting from continuous population growthcoupled with internationally uneven economic and technological growth.Under this scenario, emissions increase through the 21 st century and by 2100atmospheric carbon dioxide (CO 2 ) levels are approximately three-timesgreater than pre-industrial levels.B1. Lower emissions than A2, resulting from a population that peaks midcenturyand declines thereafter, with improving economic conditions andtechnological advancements leading to more efficient utilization of resources.Under this scenario, emissions peak mid-century and then decline, leading toa net atmospheric CO2 concentration approximately double that of preindustriallevels.Since the introduction of these emissions scenarios, the climate science, as well asglobal climate conditions, has rapidly evolved. Since these emissions scenarioswere introduced in 2000, actual global GHG emissions have exceeded 35 of the40 emissions scenarios considered for the SRES (Le Quéré et al., 2009). Newformulations of potential emissions scenarios are currently under developmentfor the IPCC’s 5 th assessment report (AR5). Rather than representingsocioeconomic conditions leading to different levels of GHG emissions, the newscenarios are based on alternative futures of atmospheric concentrations of GHGand aerosols referred to as Representative Concentration Pathways (RCPs). Forthe AR5, emissions scenarios informed by the RCPs will, for the first time,incorporate approaches to climate change mitigation in addition to scenariosconstructed without mitigation policy measures in place. Future analyses inclimate change projections will apply these new emissions scenarios and willreplace and update projections developed under the current scenario framework.As the science of climate change progresses and scientific understanding ofemissions pathways and climate dynamics improve, it will be important to keeppace with developments in climate projections and update planning documentsaccordingly.General Circulation Models and DownscalingAnother source of variability in projecting climate stressors is the generalcirculation model (GCM), or range of GCMs, employed. To identify the GCMsthat best suited to predicting climate phenomena in the State of California, Cayanet al. (2012) selected six models from the IPCC Fourth Assessment Report basedon data availability and on historic skill in representing climate patterns inCalifornia, including seasonal precipitation and temperature, annual variabilityof precipitation, and the El Niño/Southern Oscillation (ENSO) phenomenon.The six models selected for the assessment were:1. The NCAR Parallel Climate Model (PCM);2. The NOAA Geophysical Fluids Dynamics Laboratory (GFDL) model,Version 2.1;3. The NCAR Community Climate System Model (CCSM);10-10 Cambridge Systematics, Inc.