Allow input inventory years within range of base inventory years

[liammegill]

Type of issue

• Feature request

Description

As noted in #23, the emission inventories (inv_dict) and base emission inventories (base_inv_dict) must align at least in the years defined by inv_dict. The problem with this is that a user may want to calculate the climate impact of a single flight or yearly emission inventory in say 2024, but global emission inventories are only available in say 2020 and 2050. We should find some way to interpolate between base emission inventories so that any year within the range defined by the base inventories can be considered.