Atmospheric CO2, global annual mean · World · 1 year ahead

2026: the model assigns an 80 percent probability to 428.1 to 429.3 ppm

Point estimate 428.3 ppm from Holt (exponential smoothing with additive trend), against 425.6 ppm observed in 2025. holt beats last_value on out-of-sample MAE by 87.2 percent over 16 cutoffs (minimum 8, margin 5 percent).

ModeledMetric page

Distribution over the history

Fan chart

Solid: observed (ppm). Dashed and shaded: model point estimates and 80 percent intervals from empirical residual quantiles. Filled dot: the record on this page. Green or red dot: the realised value, inside or outside its interval.

Quantiles: p5 428.1 · p10 428.1 · p25 428.2 · p50 428.3 · p75 428.5 · p90 429.3 · p95 429.5
Source: empirical quantiles of 12 in-window 1-step residuals; no normality assumed

The record

Immutable fields

Key: co2-global-annual-mean:WLD:1
Id: 64f8c21f-8356-4fb0-9c40-a383cf0c41be
Created: 2026-09-07 22:16 UTC
Data cutoff: 2026-09-07 22:16 UTC
Origin: 2025 = 425.6 (obs 264263)
Target period: 2026 (365 days)
Point: 428.3 ppm
Interval: 428.1 to 429.3 at 80 percent
Model: holt models_v1.targets_v1
Baseline: last_value
Snapshot: 1eb45b53b7c41ceb8686bb3966ce4da2d95779829970e38f89bfe4f2c8d7482d
Data mode: ingested_at
Status: active

Drivers

Statistical association, not causal

Holt (exponential smoothing with additive trend) uses only the target's own history; there are no driver contributions.

Outcome

Not yet realised

The observation for 2026 has not been ingested. The weekly forecast.evaluate job attaches it when it arrives; the record above does not change.

Scenario assumptions

What the forecast takes for granted

No structural break in co2-global-annual-mean between the data cutoff and the target period.
The source keeps publishing the series on the same definition; a rebasing or redefinition invalidates the comparison.
The smoothed level and trend at the cutoff persist over the horizon.

Falsifiers

What would show this forecast wrong

If the first published value of co2-global-annual-mean (WLD) for 2026 is below 428.1 ppm or above 429.3 ppm, the 80 percent interval is falsified.
The model assigns a 10 percent probability to a value below 428.1 ppm and a 10 percent probability to a value above 429.3 ppm; interval misses should occur about one time in five over many forecasts, and a run of misses well above that rate falsifies the calibration.
The point forecast is above the last observed value (425.6 ppm); a realised value at or below that level falsifies the direction call.

Competing models

Scorecard for this target and horizon

Model	Status	Cutoffs	MAE	RMSE	Direction	80% coverage	Skill vs last value
Holt (exponential smoothing with additive trend) models_v1.targets_v1	champion	16	0.3139	0.4881	100%	75%	87.2%
Drift models_v1.targets_v1	challenger	16	0.6652	0.7877	100%	81%	72.8%
Last value models_v1.targets_v1	baseline	16	2.45	2.49	0%	81%	0.0%
Linear trend models_v1.targets_v1	challenger	16	0.5595	0.7006	100%	50%	77.1%

Model card

Holt (exponential smoothing with additive trend)

Purpose. Point and 80 percent interval forecasts of co2-global-annual-mean (WLD) 1, 2, 5 years ahead. Owner: Forecast Lab (HV 3.0).

Method

Simple exponential smoothing with an additive trend. Level and trend smoothing parameters (alpha 0.95, beta 0.3) are chosen by grid search on one-step-ahead squared error inside the training window.

Uncertainty

Intervals are empirical: the model is refitted at earlier origins inside the training window, the realised errors at the same horizon are collected, and the interval is the 10th to 90th percentile of those errors around the point forecast. No normality is assumed.

Training and evaluation

Training window: 47 periods, 1979-01-01 to 2025-01-01. Evaluation: rolling-origin backtest over 16 cutoffs using pseudo real-time data (the earliest ingested value per period; no vintage archive exists for this series, so revisions between the cutoff and today are not reproduced).

Known limitations

Structural breaks after the cutoff are not modelled.
Driver contributions are statistical associations, not causal effects.
Promotion to champion requires beating the last-value baseline on out-of-sample MAE by at least 5 percent over the minimum number of cutoffs; otherwise the baseline stays champion.
Retraining: every scheduled forecast.run refits on the data then available; backtests re-run from /admin/forecasts.

Version chain

Supersedes

This is the first record for its key.