The connecting thread of the nexus — emissions tie the energy, land and water subsystems to BC's decarbonization targets.
In CLEWs, climate is not a separate physical sub-model but the accounting layer that couples every subsystem to greenhouse-gas emissions. Any technology — a power plant, a tractor in agriculture, a fertiliser process, a water pump — can carry an emission factor, so its operation contributes to annual and cumulative emissions. The model's decarbonization question (how to meet BC targets cost-effectively) is therefore answered across energy, land and water simultaneously.
EmissionActivityRatio (emissions per unit activity), EmissionsPenalty (a carbon price added to the objective), and the caps AnnualEmissionLimit / ModelPeriodEmissionLimit.| From | Climate linkage |
|---|---|
| Energy | CO₂ from fossil combustion (NGS, DSL, COA, CRU); avoided by electrification & hydrogen |
| Land / Food | CH₄ & N₂O from agriculture, CO₂ from land-use change; bioenergy crops as a carbon sink/source |
| Water | Energy used to pump/treat water carries its own emissions (an indirect climate cost) |
The base model focuses on CO₂ emissions; the same machinery generalises to any pollutant in the EMISSION set.
Without a shared climate metric, the three subsystems would optimise independently. By pricing and capping emissions everywhere, climate forces trade-offs to surface — e.g. whether to irrigate a bioenergy crop (land + water + energy cost) versus deploy wind (energy + land cost) to cut the same tonne of CO₂. That cross-cutting tension is the entire point of a nexus model.
The tracked pollutant is CO₂-equivalent, entering through EmissionActivityRatio for every activity
across the energy, land and water systems. Emission factors are from the US EPA (2018) and BC carbon-intensity records.
EmissionsPenalty) follows BC's tax: ~$45/t (2020) → $170/t (2030+).