Each of the three towers is a separate emissions-trading system (ETS) with its own cap and its own unconstrained demand for permits. Left alone, a market's price drifts toward basePrice × (demand/cap)^1.2 — tightening the cap or growing demand pushes its own price up, nothing else moves. Linking two markets (Article 6 "corresponding adjustments" in real climate policy) lets allowances physically cross the border: sellers in the cheaper market ship permits to buyers in the pricier one until the gap narrows. That flow is what the travelling spheres on the arcs show — they always run from the cheaper tower to the pricier one, because that is the direction real money and real allowances move.
autarky_price = base · (demand/cap)^1.2
price += (autarky_price − price) · ownSpeed · dt
if linked(a,b): flow = (price_b − price_a) · linkRate · dt
price_a += flow ; price_b −= flow ; traded += |flow|
- Market links — toggle which pairs of regions can trade allowances across borders. No links = three isolated caps, each free to drift to its own price.
- EU cap tightening — how fast the EU ETS cap shrinks each simulated year; a tighter cap raises the EU's own price faster.
- Global demand growth — economic activity driving unconstrained emissions demand in all three markets at once (China's demand is most sensitive to it, reflecting faster industrial growth).
- Simulation speed — how many simulated years pass per real second.
Real-world relevance: EU allowances have traded anywhere from about €5 to over €100/tonne across ETS phases, while unlinked systems like California's or China's national scheme sit at very different price levels for the same tonne of CO₂ — linking is the mechanism proposed to close that gap without forcing every country onto an identical domestic policy.