potential yields is further complicated by the presence of numerous other вЂњyield gapвЂќ factors, including variations in cultivars and farmer management, as well as soil characteristics, pests, diseases, and weeds ( 38). All four of these models explicitly represent nitrogen stress. GEPIC, PEGASUS, and pDSSAT used historical patterns of fertilizer application rates, while EPIC used standardized low-, moderate-, and high-input management systems with thresholds that trigger fertilizer and irrigation automatically. LPJmL is similar to LPJ-GUESS in that nitrogen stress is not explicitly represented however, growth parameters in the model are calibrated so that simulations over the historical period reproduce realistic average yield patterns (see SI Appendix for details). They are best suited to studies that are designed to advance scientific understanding of the plant-atmosphere processes being represented and their sensitivity to climatic stresses, rather than for economic forecasts or sensitivity to soil edaphic conditions. The GAEZ-IMAGE and LPJ-GUESS results represent potential yields, unlimited by nutrient or management constraints and without calibration of growth parameters to reproduce historical yields. GGCM Structural DifferencesДЄn important disparity in GGCM outputs is whether the models calculate actual or potential yields as the primary output. The GGCM results generally display a wider range of uncertainty compared to the AR4 results, reflecting the much broader geographical coverage, projected temperature, and diversity of crop models represented in the current study. There is considerable variation in response within these broader latitudinal bands, with mid- and high-latitude crop yields spanning both positive and negative responses, especially at high levels of temperature change (which are also associated with higher ). The 15вЂ“85% range of all GGCM results (indicated by the shaded envelope) suggests that climate impacts on tropical croplands are generally more negative than the mid- and high-latitude impacts. GGCMs without nitrogen stress tend to be more optimistic in yield response (green line in Fig. We find that general patterns of the GGCM results are similar, especially among those models that simulate nitrogen stress on crops and include fertilizer application rates based on observational databases (red line in Fig. Furthermore, increases in tropical temperatures can lead to greater evaporative demand and thus water stress on crops. In low-latitude regions, even moderate temperature increases (1 to 2 вЊ) were found to have negative yield impacts for major cereals, because the climate of many tropical agricultural regions is already quite close to the high-temperature thresholds for suitable production of these cereals ( 33, 34). 32 reproduced as orange dots and quadratic fit in Fig. Crop modeling results in the IPCC AR4 showed that small beneficial impacts on rainfed crop yields may be found in mid- and high-latitude regions with moderate-to-medium local increases in temperature (1вЂ“3 вЊ) along with associated increase and rainfall changes (figure 5.2 in ref. Uncertainties related to the representation of carbon dioxide, nitrogen, and high temperature effects demonstrated here show that further research is urgently needed to better understand effects of climate change on agricultural production and to devise targeted adaptation strategies.ДЄ relevant question is to what extent findings of this substantial effort of coordinated GGCM modeling are different from what was reported in the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4 32) ( Fig. Across seven GGCMs, five global climate models, and four representative concentration pathways, model agreement on direction of yield changes is found in many major agricultural regions at both low and high latitudes however, reducing uncertainty in sign of response in mid-latitude regions remains a challenge. Results indicate strong negative effects of climate change, especially at higher levels of warming and at low latitudes models that include explicit nitrogen stress project more severe impacts.

Here we present the results from an intercomparison of multiple global gridded crop models (GGCMs) within the framework of the Agricultural Model Intercomparison and Improvement Project and the Inter-Sectoral Impacts Model Intercomparison Project.

Gridded journal