ARS | Publication request: Crop Models, CO2, and Climate Change

Submitted to: Science
Publication Type: Other
Publication Acceptance Date: January 10, 2007
Publication Date: January 26, 2007
Publisher's URL: http://www.science.org
Reprint URL: http://www.sciencemag.org/cgi/content/summary/315/5811/459a?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=ainsworth+and+long&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT
Citation: Long, S.P., Ainsworth, E.A., Leakey, A., Ort, D.R., Nosberger, J. 2007. Crop Models, CO2, and Climate Change - Response. Science. 26(315):459.

Technical Abstract: Our research article did not criticize the design of models used to predict global change impacts on future food supply. We argued that reliable model projections require accurate model parameterization. Data from the fully open-air field treatments with elevated CO2 (FACE) indicate that the commonly used parameterization for the CO2-fertilization effect is overoptimistic. We recognized that rising CO2 is only one of many factors affecting future food supply, but CO2 has been shown to be pivotal in projecting an increase versus a decrease in future food supply under global change (1¿4). Ewert et al. suggest that rising CO2 has had, and will have, little impact, attributing only 4% of wheat yield improvement over the past 30 years to rising CO2. This 4% is consistent with FACE, but not non-FACE results (extrapolating from Fig. 2A). We agree that the 50 ppm increase in CO2 may have played a relatively minor role in the past 30 years. But it is projected to increase to 180 ppm over the next 50 years and thus has the potential to be far more important. Ewert et al. note the tripling of wheat yield since 1960, due to technology development, and imply that this will continue. Large increases in cereal crop yields have been achieved by improved harvest index and nitrogen fertilization, but returns on these strategies are diminishing (5, 6). Although we hope that the improvements of past decades can be maintained, it will not happen without innovative new approaches and a perceived need for crop adaptation. In our judgment, urgent action is needed given the long times required to develop new cultivars adapted to change and able to realize in farmers¿ fields the higher CO2 fertilization effect observed in protected environments. Equally, fieldscale manipulations of CO2, including, for example, tropical locations, interactions with rising ozone, and genetic variation, are needed. Without this more secure parameterization, projections of future global food security may have feet of clay. If we fail in taking these practical measures, then might history say, were they modeling while the world¿s grain supply burned?