External trends packs
An external trend is a market or grid change outside the organisation. Viable publishes activity trends and emission-factor trends together as one immutable pack. A saved calculation pins that pack so a later publication does not change the plus-trends pathway unless you upgrade.
Two kinds of external trend
An activity trend changes how much of an activity occurs. Example: electric vehicles take a larger share of kilometres.
An emission-factor trend changes emissions per unit of the same activity. Example: grid electricity emits less CO₂e per kilowatt-hour.
Both sit on the plus-external-trends pathway. Internal actions sit on top of that pathway. See what are different pathways.
Viable outputs are projections, not forecasts. A pack is one published view of those trends.
Pin and upgrade
A pack id names the published set, for example 2026Q3. Activity trends and emission-factor trends share that id. There is one selector, not two.
A saved organisation pins the pack that ran at save time. A new pack does not change that calculation. You must choose to upgrade.
If a calculate request omits a pack id, the engine uses the latest published pack. New templates pin the latest id at create time.
Retired rows stay in the pack as inactive. Disable-list ids stay stable after a source is withdrawn.
Quality-weighted mid
Each source is written as cumulative change versus a 2024 baseline. Zero in 2024. A later year of −0.30 means a 30% decrease versus 2024.
Viable scores authority, transparency, confidence, and recency. Smaller pedigree scores mean higher quality. Blend weight is one divided by that score.
The mid series is the year-by-year weighted average of sources that have a value in that year. That mid is the curve the engine uses on the plus-trends pathway.
Min and max series bound the other published views. They do not replace the mid in the main projection.
Example: pin versus upgrade
Toggle activity versus emission factor. Then keep pack 2026Q3 or upgrade to 2026Q4. Bars show 2025, 2030, 2040, and 2050.
Related: pathways, emission factor trends, and API access.