Non-CO2 gases
Because non-CO2 gases come from much more heterogeneous sources than CO2, it is not straightforward to talk about the non-CO2 “intensity” of an economy as a whole. For this reason, we do not base our non-CO2 GHG projections on intensity change and GDP growth as we do fossil CO2; rather we take projected economy-wide rates of change out to 2030 for total non-CO2 gases, and then calibrate them to the most recent historical non-CO2 emission data. Our source of long-term projections is the US EPA [11] which covers nearly all countries (although for many smaller countries the data is derived from “rest-of-region” aggregates). For recent historical data we use data reported to the UNFCCC for Annex I countries, and take the median of growth rates between 2000-2010 as the 2010 “starting point,” for projections out to 2030; for non-Annex I countries, we use data through 2005 from the USEPA and combine them with growth rates reported in the EDGAR [12] database for the years 2006-2009. In both cases (A1 and NA1), the rate of change converges to the estimated 2030 growth rate projected by the EPA; in particular, we use a smoothing algorithm to estimate the rate of change in 2030 from the time series for 2005-2030 reported in USEPA (2012)