Fig. 3. Ensemble estimates of climate–carbon cycle feedback parameters from observations and models.

a Histogram of the β estimates (error bars for mean ± 1σ) derived from four instrumental temperature and CO₂ datasets for 1880–2017 (in gray), β^BGC derived from 11 C⁴MIP models⁷ for 1880–2017 (in dodger blue) and for 2018–2100 (in navy blue), and β^BGC derived from nine CMIP5 models¹¹ for the 140-year 1pctCO₂ experiment (in deep pink). b Boxplot of the γ* derived from four instrumental temperature and CO₂ for 1880–2017 (in gray), and γ_100yr estimates derived from an ensemble of 15 members (3 ice-core CO₂ records × 5 reconstructed temperature, in black) and from the EnOBS for 1000–1850 (in green), and γ^COU-BGC derived from 11 C⁴MIP models for 1880–2017 (in dodger blue) and for 2018–2100 (in navy blue), and γ^COU-BGC derived from nine CMIP5 models (in deep pink). In b, the large ensemble estimates of the γ_100yr from the EnOBS also provides probability distributions (right panel) of the cooler period of Little Ice Age (LIA, 1400–1700) and the warmer period of Medieval Climate Anomaly (MCA, 1000–1300), compared to those of the full preindustrial last millennium (PILM, 1000–1850). c Same as (a), but for the feedback gain factor (g) derived from the β and AF estimates.