By Janne Hansen
23 November 2016
(PhysOrg) – Three independent methods of modelling climate change impact on yield display the same bleak tendency: When global temperature increases, wheat yield will decline. This is demonstrated in a study carried out by an international group scientists, including Professor Joergen E. Olesen and Postdoc Mohamed Jabloun from the Department of Agroecology at Aarhus University.
The good news is that the comparison of the three very different climate models allowed the scientists to be even more precise in their projections and enabled them to put more accurate figures on the relation between global warming and declining yields. The models unanimously demonstrate that for each 1°C that the global temperature increases, the global wheat production is projected to decline by an average of 5.7 percent. […]
The scientists compared three very different crop model types: grid-based, point-based and regression-based. The two first were simulation models while the third was based on statistical data analyses. Each type included a series of different models and thus included actual implementation of the model types.
A simulation model creates a model of reality based on the existing knowledge of reality. The model makes it possible to predict what will happen if some of the conditions/parameters are changed. Examples of input include facts on how crop growth periods and productivity react to temperature, precipitation and CO2 levels, and how evapotranspiration depends on temperature and atmospheric CO2 concentration. In such models you can tweak the temperature and find an answer to the question “What will happen if the global temperature increases by 5°C?”
Regression models use a statistical process for estimating the relationship between data. For instance, observed crop yield is statistically related to temperature and precipitation during the growing season. This estimated relationship can then be used to predict crop yield when temperature increases. […]
Depending on the model in question, the expected wheat yield will decline between 4.1 and 6.4 percent with each 1°C global temperature increase. Warmer regions are most likely to experience the greatest decline in wheat yield. [more]
ABSTRACT: The potential impact of global temperature change on global crop yield has recently been assessed with different methods. Here we show that grid-based and point-based simulations and statistical regressions (from historic records), without deliberate adaptation or CO2 fertilization effects, produce similar estimates of temperature impact on wheat yields at global and national scales. With a 1 °C global temperature increase, global wheat yield is projected to decline between 4.1% and 6.4%. Projected relative temperature impacts from different methods were similar for major wheat-producing countries China, India, USA, and France, but less so for Russia. Point-based and grid-based simulations, and to some extent the statistical regressions, were consistent in projecting that warmer regions are likely to suffer more yield loss with increasing temperature than cooler regions. By forming a multi-method ensemble, it was possible to quantify ‘method uncertainty’ in addition to model uncertainty. This significantly improves confidence in estimates of climate impacts on global food security.