resolved · Unscored / disputed
Business-as-usual emissions would produce roughly 0.3°C global warming per decade, with substantial uncertainty.
Source-backed summary; not presented as a verbatim quotation.
IPCC Working Group I
International scientific assessment · Multinational
The world at the time.
The first assessment linked greenhouse-gas growth to warming under specified emissions scenarios. Its business-as-usual case was conditional, not an unconditional prediction of future policy.
What happened.
Observed warming was lower than that scenario’s central rate. Later assessment found the temperature response broadly aligned once the lower actual forcing was accounted for.
Predicted vs actual.
| Metric | Predicted | Actual | Variance / caveat |
|---|---|---|---|
| 1990–2017 forcing increase (W/m²) | 1.6 | 1.1 | Scenario forcing about 45% higher |
Forecast and observation.
1990–2017 forcing increase (W/m²): predicted 1.6, actual 1.1. These are sourced endpoint observations, not an interpolated historical trajectory.
The counter-signal.
The original assessment acknowledged natural variability and uncertain detection. It also lacked a quantitative aerosol-cooling treatment, added in later assessments.
Verdict.
Reasoning: sound · Outcome: partial
Partial for the calendar-time scenario; strong mechanism skill after forcing adjustment.
Cause of death / explanatory lens.
No cause of death assigned
The lesson.
Should a conditional model be scored against its assumed inputs or against the inputs that actually occurred?
Sources.
- Scientific Assessment of Climate Changeprimary · 1990 · forecast and contemporary uncertainty
- AR4 Technical Summary: near-term changeprimary · 2007 · aerosol omission and forecast rate
- AR6 WGI chapter 1primary · 2021 · retrospective forcing-adjusted outcome
Related predictions.
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