Table 1.
Climate responses to CO2-radiative forcing, CO2-physiological forcing, and the combined effect of CO2-radiative and physiological forcing, as a result of CO2 doubling.
| RAD - CTR | PHYS - CTR | RAD + PHYS - CTR | |
| Change in surface energy balance (Wm-2)* | |||
| Latent heat flux over globe | 4.26 ± 0.05 | −0.29 ± 0.04 | 4.12 ± 0.05 |
| Latent heat flux over land | 2.85 ± 0.09 | −1.54 ± 0.08 | 1.59 ± 0.09 |
| Sensible heat flux over globe | −1.17 ± 0.02 | 0.58 ± 0.02 | −0.62 ± 0.02 |
| Sensible heat flux over land | −0.30 ± 0.05 | 2.11 ± 0.04 | 1.75 ± 0.05 |
| Surface net shortwave flux over globe | −0.65 ± 0.04 | 0.54 ± 0.04 | −0.09 ± 0.04 |
| Surface net shortwave flux over land | −0.85 ± 0.08 | 1.62 ± 0.08 | 0.82 ± 0.08 |
| Surface net longwave flux over globe | −3.68 ± 0.04 | 0.25 ± 0.03 | −3.53 ± 0.03 |
| Surface net longwave flux over land | −3.36 ± 0.09 | 1.06 ± 0.07 | −2.46 ± 0.08 |
| Change in key climate variables | |||
| Surface air temperature (K) | 2.50 ± 0.02 | 0.22 ± 0.02 | 2.78 ± 0.02 |
| Surface air temperature over ocean (K) | 2.36 ± 0.02 | 0.15 ± 0.02 | 2.55 ± 0.02 |
| Surface air temperature over land (K) | 2.86 ± 0.02 | 0.42 ± 0.02 | 3.33 ± 0.03 |
| Precipitation (%) | 5.21 ± 0.06 | −0.32 ± 0.05 | 4.96 ± 0.06 |
| Precipitation over land (%) | 6.13 ± 0.26 | 0.38 ± 0.24 | 7.35 ± 0.29 |
| Precipitable water (%) | 16.80 ± 0.18 | 0.87 ± 0.12 | 18.17 ± 0.16 |
| Runoff (%) | 5.16 ± 0.60 | 8.38 ± 0.61 | 14.87 ± 0.70 |
| Low cloudiness (fraction) | 0.0060 ± 0.0003 | −0.0022 ± 0.0003 | 0.0037 ± 0.0003 |
| Low cloudiness over land (fraction) | 0.0105 ± 0.0004 | −0.0102 ± 0.0003 | 0.0003 ± 0.0003 |
RAD - CTR represents the effect of CO2-radiative forcing; PHYS - CTR represents the effect of CO2-physiological forcing; RAD + PHYS - CTR represents the combined effect of CO2-radiative and CO2-physiological forcing from a doubling of CO2. All results are annual mean values averaged from the last 70-yr results of 100-yr simulations. Percent changes represent values in the experiment minus the control cases, divided by the value in the control case. Fractional changes represent the fraction in the experiment minus the fraction in the control. Uncertainties are represented by ± 1 standard error calculated from the last 70-yr results of 100-yr simulations. Also refer to Table S1 for a list of changes in other fields.
The effect of CO2-physiological forcing can also be obtained by subtracting the results of RAD - CTR from the results of RAD + PHYS - CTR, which gives the effect of CO2-physiological forcing under 2 × CO2 background climate. The effect of CO2-physiological forcing diagnosed this way is in broad agreement with the results of PHYS - CTR. However, there is some nonlinearity in the system. For example, the effect of CO2-physiological forcing on surface temperature diagnosed from the difference between RAD + PHYS - CTR and RAD - CTR is 0.28 K, which is somewhat higher than the value of 0.22 K diagnosed from the results of PHYS - CTR.
*Shortwave fluxes are positive downward (from the atmosphere to the surface). Other fluxes are positive upward (from the surface to the atmosphere).