Convergence Year Extrapolation
Our downscaling methods track changes in country-level emissions (E) by assuming that the emissions intensity (EI=E/GDP) converges to the regional emissions intensity in that scenario's convergence year. As indicated by input/mappings/convergence_year_mapping.csv, the convergence year is always after 2100. This means we must extrapolate regional GDP and emissions.
For countries whose 2100 emissions are positive, we extrapolate emissions using the following equation:
For countries whose 2100 emissions are negative, we extrapolate emissions using the following equation:
For all countries, we extrapolate GDP using the following equation:
See equations 2 & 2a in IPAT Downscaling for how 
