Simplifying City Carbon Budgets

Budget trajectories 

With each budget comes four scenarios for how the municipality could spend this budget. Key figures about the budget are given for each scenario (e.g. when zero emissions is reached, how much CO2 will be spent etc.). A series of yearly emissions (starting at the first year of the budget) are also given to indicate the CO2 emissions each year of consuming the remaining budget.

Linear Emission Reduction Scenario.

The budget is spent using a linear cut-down from current emissions level, reducing the amount of emitted CO2 by the same absolute amount each year. This linear cut-down reaches zero emission at the same moment in time that the budget is spent.

Exponential Emission Reduction Scenario.

The budget is spent using a cut-down of emissions, from the current emission level, by the same percent each year. The actual yearly cut-down in percentage needed to stay within budget can be calculated (a mathematical integral). However, as exponential cut-down will not ever reach zero emissions, a cut off level is used, so that the series of yearly emission becomes finite. The cut off is given as a fraction of the last known historic emission and is part of the data returned from the API. Currently a fraction of 0.01 is used.

Trend Based Emissions Scenario Limited by Budget.

The budget is spent according to the trend of the historic emissions. The series of yearly emissions are ended when the budget is spent or when zero emissions are reached (whichever happens first). For a municipality where the trend is not to clearly cut down on emissions, this would mean the series of yearly emissions would end abruptly without being anywhere near zero emissions.

Trend Based Emissions Scenario Limited by Zero Emissions or End Year.

This series of yearly emission is showing the future trend of the municipality regardless of budget. The series of emissions will end at a given end year (currently 2050) if zero emissions are not reached by then.