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Climate Target (C module)

Status: Not yet implemented in TargetEcon 2026. Present in other model versions.

var_C = 0 in the current model — the scalar exists but no constraints or equations activate when set to 1.

What it would do

A climate target would add a constraint requiring a minimum reduction in agricultural greenhouse gas (GHG) emissions — primarily CO₂ equivalents from soil carbon stock changes and N₂O from reduced fertilization.

The commented-out code in the main .gms hints at the structure: 

*CO2_per_j_eq(j).. CO2_per_j(j) =e=
*   Sum(i, PotV(i,j)$(notforest(j)) * ag_co2(i) * x(i,j)) +
*   Sum(i, (PotV(i,j)$(forest(j)) * ag_FO_co2(i) + PotV(i,j)$(forest(j)) * ag_co2(i)) * x(i,j))
This suggests field-specific CO₂ parameters: ag_co2(i) (general) and ag_FO_co2(i) (forest-specific).

Relevant measures

Measure Climate relevance
FO Afforestation — large C sequestration in biomass + soil
LRl Rewetting peatlands — very large GHG reduction (stops peat oxidation)
WL Rewetting — large GHG reduction
LRh Soil carbon accumulation under permanent vegetation
SA Some soil C accumulation under fallow
EC Perennial crops — some soil C benefit
N10/N20 Reduced N₂O from lower N application

LRl on peat soils (lavbund) is likely the most powerful climate measure — stopping peat oxidation on drained peatlands can deliver several tons of CO₂eq/ha/yr. This makes LRl potentially triple-counted: N reduction, biodiversity, and climate.

Data needed to activate

  • ag_co2(i) — field-level CO₂ equivalent emissions per ha under business-as-usual
  • ag_FO_co2(i) — CO₂ sequestration under afforestation, field-specific
  • Climate targets (tons CO₂eq/yr? national or regional?)
  • var_C target level

Interaction with N and P targets

The climate target is expected to strongly reinforce the N target for LRl and WL: - LRl on peat delivers both high N reduction (NR, 40 kg N/ha) and large climate benefit - FO delivers moderate N reduction and large climate benefit - This means the climate module should reduce the total cost of the N+C combined scenario relative to N + C separately — genuine synergy

Open questions / to document when ready

  1. Which model version has the C module implemented?
  2. What GHG parameters are used — are they from SEGES/DCE data?
  3. Is the climate target defined in tons CO₂eq/yr, or as a % reduction?
  4. How are peat soils identified within the existing lav(i) parameter? Is there a separate peat classification?