Though a higher amount of CO2 in the atmosphere may benefit some plants, heat waves and unpredictable weather are more likely to cause significant reductions in crop yields and threaten global food supply if climate change is not tackled and reversed.

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Researchers at the University of East Anglia have said heat waves could have a marked effect on the production of major arable crops. In a new study, published on Thursday (20 March), the researchers estimated the global effects of extreme temperatures and elevated levels of carbon dioxide on the production of maize, wheat and soybean.

Earlier studies have found that climate change is projected to reduce maize yields globally by the end of the century under a 'business as usual' scenario for future emissions of greenhouse gases; however, this new study shows that the inclusion of the effects of heat waves, which have not been accounted for in previous modelling calculations, could double the losses of the crop.

Lead author Delphine Deryng, from the Tyndall Centre for Climate Change Research, said, "Instances of extreme temperatures, brought about by a large increase in global mean temperature, can be detrimental to crops at any stage of their development, but in particular around anthesis—the flowering period of the plant.

"At this stage, extreme temperatures can lead to reduced pollen sterility and reduced seed set, greatly reducing the crop yield."

CO2 fertilisation

The impacts on wheat and soybean are likely to be less profound, primarily because elevated levels of CO2 could have a fertilising effect on these crops. As CO2 is central to the photosynthesis process, more CO2 in the atmosphere could mean that, for certain plants, leaves can capture more of it, resulting in an overall increase in plant growth. Theoretically, this may mean plants are better able to manage water use more efficiently, potentially increasing their resilience to drought.

However, on Thursday the Tyndall researchers said there is no way of knowing whether 'CO2 fertilisation effects' would actually occur in the field, as climate change would bring other factors into play. They said that, though wheat and soy yields could potentially increase as a result of these effects towards the end of the century, the effects of heat waves would probably offset any increase, as these plants would still be vulnerable to the effects of extreme temperatures.

The positive impacts on soybean yield will be offset by 25 per cent and the positive impacts on wheat will be offset by 52 per cent, according to the Tyndall researchers' estimates.

What is more, they found that heat waves would be likely to affect different parts of the world in different ways. Heat waves are expected to have the largest negative effects on crop yields in key areas of production around the world, including the North American corn-belt.

They added that, should CO2 fertilisation effects fail to occur, yields of all three crops major crops studied are expected to fall in the top-five producing countries of each crop, with losses intensified by extreme heat stress.

"Our results show that maize yields are expected to be negatively affected by climate change, while the impacts on wheat and soybean are generally positive, unless CO2 fertilisation effects have been overestimated," said Deryng, expanding on the team's findings. "However, extreme heat stress reinforced by 'business-as-usual' [emissions] reduces the beneficial effects considerably in these two crops."

The Tyndall researcher recommended that "Climate mitigation policy would help reduce risks of serious negative impacts on maize worldwide and reduce risks of extreme heat stress that threaten global crop production."