# Carbon and environmental valuation

    library(greenbook)

## Carbon values for appraisal

DESNZ publishes a single consolidated carbon value series with low / central / high scenarios. The November 2023 publication superseded the historical traded / non-traded split. `gb_carbon_value()` looks the values up directly:

    gb_carbon_value(2024)
    #> [1] 268.97
    gb_carbon_value(2024, scenario = "high")
    #> [1] 403.45
    gb_carbon_value(2030)
    #> [1] 294.5

The values are published in 2022 prices. Rebase to a different year via `base_year`:

    gb_carbon_value(2030, base_year = 2024)
    #> [1] 325.4126

## Net present value of an emissions path

A greenhouse-gas-emitting project has its environmental externality monetised at the published carbon value, then discounted under the standard STPR.

    # 100 tCO2e per year for 2024 to 2030, treated as a cost
    emissions <- rep(100, 7)
    years <- 2024:2030
    gb_carbon_npv(emissions, years, base_year = 2024)
    #>
    #> ── Green Book appraisal ────────────────────────────────────────────────────────
    #> NPV (real, standard schedule): "GBP -196.5k"
    #> Horizon: 7 years (year 0 to 6)
    #> Base year: 2024
    #> Vintage: Green Book "2022"

For an abatement project (avoided emissions), use `sign = "benefit"`:

    gb_carbon_npv(emissions, years, base_year = 2024, sign = "benefit")
    #>
    #> ── Green Book appraisal ────────────────────────────────────────────────────────
    #> NPV (real, standard schedule): "GBP 196.5k"
    #> Horizon: 7 years (year 0 to 6)
    #> Base year: 2024
    #> Vintage: Green Book "2022"

## Wellbeing valuation

Life-satisfaction changes can be monetised via WELLBYs (HMT Wellbeing Guidance for Appraisal, July 2021). Default unit value: GBP 13,000 per WELLBY in 2019 prices.

    # 1-point lift in life satisfaction, 100 people, 5 years
    gb_wellby(1, persons = 100, years = 5)
    #> [1] 6500000

    # In 2024 prices
    gb_wellby(1, persons = 100, years = 5, base_year = 2024)
    #> [1] 8013957

    # Sensitivity range
    gb_wellby(1, persons = 100, years = 5, scenario = "low")
    #> [1] 5e+06
    gb_wellby(1, persons = 100, years = 5, scenario = "high")
    #> [1] 8e+06

## Risk to life and health

Value of Preventing a Fatality (VPF) and Quality-Adjusted Life Year (QALY) per DfT TAG and DHSC supplementary guidance.

    gb_vpf()        # 2024 published value: GBP 2.153m
    #> [1] 2523828
    gb_vpf(2018)    # 2018 baseline
    #> [1] 2241087

    gb_qaly(1)                          # DHSC: GBP 70k per QALY
    #> [1] 70000
    gb_qaly(1, scenario = "nice_upper") # NICE upper threshold: GBP 30k
    #> [1] 30000

## Provenance

    gb_data_versions()
    #>         dataset
    #> 1 stpr_schedule
    #> 2  gdp_deflator
    #> 3 optimism_bias
    #> 4          metb
    #> 5        wellby
    #> 6           vpf
    #> 7          qaly
    #> 8 carbon_values
    #>                                                                                                                              source
    #> 1                                                         HM Treasury Green Book 2022 Annex A6 / supplementary discounting guidance
    #> 2 HM Treasury, GDP deflators at market prices (December 2025 Quarterly National Accounts release, calendar-year series, 2024 = 100)
    #> 3                                                HM Treasury Supplementary Green Book Guidance: Optimism Bias (Mott MacDonald 2002)
    #> 4                                                  HM Treasury Green Book 2022 chapter on real terms and Marginal Excess Tax Burden
    #> 5                                                                                  HMT Wellbeing Guidance for Appraisal (July 2021)
    #> 6           DfT Transport Analysis Guidance (TAG) data book v2.03FC (December 2025), Table A4.1.1, WTP element for fatal casualties
    #> 7                                                                      DHSC Supplementary Green Book Guidance + NICE HTA thresholds
    #> 8                          DESNZ Valuation of Energy Use and GHG Emissions for Appraisal (November 2023), Data Tables 1-19, Table 3
    #>   last_updated
    #> 1   2026-04-26
    #> 2   2026-04-26
    #> 3   2026-04-26
    #> 4   2026-04-26
    #> 5   2026-04-26
    #> 6   2026-04-26
    #> 7   2026-04-26
    #> 8   2026-04-26
    #>                                                                                                                                                                              notes
    #> 1                          Kinked STPR: 3.5/3.0/2.5/2.0/1.5/1.0 percent across bands at 30/75/125/200/300 years. Health and catastrophic-risk variants per supplementary guidance.
    #> 2 Outturn 1990-2024 from CGDP_Deflators_Qtrly_National_Accounts_December_2025_update.xlsx. Forecast years can be added via inflateR or the Spring Statement supplementary release.
    #> 3                                                                Indicative upper bounds for capex and duration uplift across six project categories. Values unchanged since 2003.
    #> 4                                                               Uplift on revenue raised through distortionary taxation. 20 percent in 2018 onwards (was 30 percent historically).
    #> 5                                                           WELLBY central value GBP 13000 in 2019 prices (low/central/high range). Convert to other base years via gb_deflator().
    #> 6                                               Anchor 2023 = GBP 2,474,341 (WTP component). Other years derived by 2 percent annual real GDP per head growth per TAG methodology.
    #> 7                                                            GBP 70k per QALY in 2024 prices for cross-government appraisal. NICE thresholds GBP 20k-30k retained for HTA context.
    #> 8                                     Single consolidated series (replacing historical traded / non-traded split). Low / central / high paths 2020-2050 in 2022 prices, GBP/tCO2e.

## Provenance

The bundled DESNZ carbon path is the November 2023 publication (Data Tables 1-19, Table 3), 2020 to 2050. A future refresh will extend through to 2100.

The VPF series anchors on the DfT TAG data book v2.03 (December 2025) Table A4.1.1 WTP element of GBP 2,474,341 in 2023 prices, uplifted at 2 percent annual real GDP per head growth per TAG methodology.