Table 2.

Comparison of model-simulated climate responses to the physiological effect of doubling CO₂

	This study*	Sellers et al. (1996)	Betts et al. (1997)	Cox et al. (1999)	Betts et al. (2007)	Boucher et al. (2009)†
Evapotranspiration over land (mm day-1)	−0.054 ± 0.004	−0.045		−0.07		−0.04
Surface air temperature over land (K)	0.47 ± 0.04	0.3	0.2	0.39		0.52
Fractional contribution of surface warming over land from CO2-physiological forcing‡	16.4 ± 0.7%	10.7%		11.3%		12.9%
Runoff (mm day-1)	0.082 ± 0.005			0.04	0.04	0.03
Fractional contribution of runoff increase from CO2-physiological forcing‡	65.2 ± 11%			57.1%	37.2%	27.3%
Precipitation over land (mm day-1)	0.028 ± 0.01	−0.01	−0.02	−0.03	0.01	−0.01

^*To be consistent with the method used in other studies, the CO₂-physiological effect shown here is calculated from the difference between the results of RAD + PHYS - CTR and RAD - CTR listed in Table 1.

^†The CO₂-physiological effect reported by Boucher et al. (10) was calculated from the transient simulations under the IS92a emission scenario, which have a CO₂ increase somewhat more than a doubling.

^‡The fractional contribution of changes in temperature and runoff due to CO₂-physiological forcing is calculated as the ratio between changes in temperature and runoff in response to CO₂-physiological forcing and their changes in response to the combined effect of CO₂-radiative and physiological forcing.