The Ricardian method also does not measure the effect of carbon fertilization. Controlled laboratory experiments consistently report that higher carbon dioxide levels increase yields in most crops (Kimball 1983, 2007). The research reveals that yields go up with the log of the CO2 concentration. The average response to a doubling of CO2 for C3 plants (95% of crops) is for yields to increase by 30% (Kimball 1983, 2007). Only FACE experiments yield lower results (Long et al. 2006). The FACE experiments suggest
that perhaps the carbon fertilization rate will be lower if crops are not adequately fertilized. However, it is expected that by 2100, all commercial farms will be using sufficient fertilizer to get the full carbon dioxide fertilization effect. This effect can be calculated by multiplying the future net revenues predicted with warming by 0.30×log[CO2 (2100)/CO2 (2000)]. In this analysis, we assume that CO2 (2100) will reach
650 ppm whereas CO2 (2000) is 395 ppm.