addressing climate change adaptation in regional transportation plans

Addressing Climate Change Adaptation in Regional Transportation PlansA Guide for California MPOs and RTPAsWhat are Climate Scenarios and How are They Used in my Region?Different scenarios have been developed to estimate the potential level of emissionseach country will produce in the future. The emissions scenarios most commonlyused by California state agencies are A2 (medium‐high emissions) and B1 (lowemissions) scenarios. Each scenario corresponds to a projection of possible emissionslevels based on population growth, economic development, technology deploymentand other factors. Ultimately, the effect on climate change depends on the amountand the rate of accumulation of heat‐trapping gases in the atmosphere that thesescenarios suggest, along with atmospheric sensitivity to those emissions levels.Of the two scenarios extensively evaluated in climate change analyses in California,the A2 scenario is the more realistic choice for decision‐makers to use for climateadaptation planning. Generally, the B1 scenario might be most appropriately viewedas a version of a “best case” or “policy” scenario for emissions, while A2 is more of astatus quo scenario incorporating incremental improvements. Measured carbonemissions compared to the hypothetical IPCC scenarios is shown in Figure 3.5.Figure 3.5Observed Global Mean Temperature over Land and OceanSource: Flint, L. E., and A. L. Flint, 2012.3-8 Cambridge Systematics, Inc.