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Rebuilding the EU ETS1 Calculator with River

How Climact replaced a legacy Excel model with a structured, auditable engine, ready for EU legislative negotiations in 2026.

CLIENT

Climact SA

SECTOR

Climate Policy & Regulatory Analysis

DELIVERABLE

EU ETS1 scenario calculator, 2020–2040

30+

policy levers modeled

20yr

model horizon

15

model users

River Case Study – Climact ETS1 Calculator
Background

A high-stakes model on a robust foundation

The EU Emissions Trading System (ETS1) is one of Europe's most consequential climate policy instruments. In 2025, Climact, a Brussels-based climate consultancy, was engaged to build a calculator that lets policymakers, NGOs, and analysts test how different design choices affect the EU's ability to meet its 2030 and 2040 climate targets.

The model had to cover 20 years of allowance supply and demand, simulate over 30 interlocking policy levers simultaneously, and survive multiple revisions, shareable in both Excel and a public web tool. Climact's prior version, built in standard Excel formulas, was not robust enough to handle this. Climact decided to use River and its innovative modeling technology and build a new visual, robust and documented model in Excel.

The challenge

Iterative logic, interdependencies and complex scenarios

The EU ETS works by capping total greenhouse gas emissions across power and heat generation, industry, aviation, and maritime transport. Each allowance gives the right to emit one tonne of CO₂ equivalent. The cap declines each year according to a linear reduction factor (currently 4.3% per year), and is further adjusted by scheduled rebasings, sector scope changes, and set-asides for funds like the Innovation Fund. On top of this annual cap trajectory sits the Market Stability Reserve, which absorbs or releases allowances based on the total volume in circulation, creating feedback loops that ripple through supply year after year.

Before River

Formula chains spread across a dozen sheets. Complex cell-specific formulas. Adding a scenario meant duplicating entire sheets. Auditing the model took days and still left gaps.

With River

The full model, from raw emissions to per-member-state auction revenues, is a visual Model Map any team member can read immediately. Scenarios are configurable. The iterative logic is transparent and robust.

What River made possible

Four capabilities that weren't viable before

Complex stock modeling made transparent The Market Stability Reserve involves a running cumulative surplus that feeds back each year into intake and release rules: genuinely iterative. River simplifies this and makes it visible: each step is a sequenced operation you can inspect.
True scenario switching Three predefined scenarios are driven by parameter tables, not sheet copies. Switching between them is instant and error-free.
Multi-table merges without formula nesting Matching sector emissions to benchmark tables, allocation factors, and member-state splits required joining tables on multiple keys. River's auditable visual merge operations replaced nested INDEX-MATCH formulas.
Automatic data quality checks Each merge and aggregation step validates that no allowances are silently lost or double-counted. When inputs are refreshed, breaks surface immediately rather than propagating undetected through the model.
Team enablement

Two modelers, 15 users

Climact brought two climate policy consultants to build the new ETS1 model, to be used in total by 15 users. Neither had used River before. Because River's operations map directly to how analysts think about data, both were productive within their first week, no new programming language or database concepts required.

"River had everything I needed: a tool easy to get to grips with, agile modeling, and a model logic you can read directly."

Simon Lalieu, Senior Consultant, Climact

The Model Map also serves as living documentation, always in sync with the model itself, no separate diagram to maintain.

Results

A model the whole coalition can rely on

The rebuilt ETS1 calculator was delivered ahead of the Commission's Q3 2026 legislative proposal. It serves multiple audiences simultaneously: Carbon Market Watch analysts running the full Excel model, stakeholders accessing predefined scenarios via a public web tool, and Climact's team updating it as new positions emerge from the Commission, Parliament, and Council.

20 yr Full model horizon with annual granularity, 2020–2040
< 1 day To integrate a new institutional scenario
Zero Silent errors on data refresh

 Published as a dynamic website.

This website is published at https://my.climact.com/tools/ets-simulator (requires registration) using the River Publisher Feature.


Get started with River

Install the trial version and test it for 14 days or let us walk you through a demo.

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