Climate change may shrink wheat crop yields

Wheat is harvested in temperate zones on more than 220 million hectares, making it the most widely grown crop on Earth.

Paris: More intense heat waves due to global warming could diminish wheat crop yields around the world through premature ageing, according to a study published today in Nature Climate Change.

Current projections based on computer models underestimate the extent to which hotter weather in the future will accelerate this process, the researchers warned.

Wheat is harvested in temperate zones on more than 220 million hectares, making it the most widely grown crop on Earth.

In some nations, the grain accounts for up to 50 per cent of calorie intake and 20 per cent of protein nutrition, according to the International Maize and Wheat Improvement Center (CIMMYT), near Mexico City.

In 2010, drought and wildfires in wheat-exporting Russia pushed world prices of the grain to two-year highs, underscoring the vulnerability of global supplies to weather- and climate-related disruptions.

Greenhouse experiments have shown that unseasonably warm temperatures -- especially at the end of the growing season -- can cause senescence, the scientific term for accelerated ageing.

Excess heat beyond the plant`s tolerance zone damages photosynthetic cells.

Fluctuations in wheat yields in India have also been attributed by farmers to temperature, most recently a heat wave in 2010 blamed for stunting plant productivity.

To further test these experiments and first-hand observations, a trio of researchers led by David Lobell of Stanford University sifted through nine years of satellite data for the Indo-Ganges Plains in northern India and then used statistical methods to isolate the effects of extreme heat on wheat.

They found that a 2.0 Celsius increase above long-term averages shortened the growing season by a critical nine days, reducing total yield by up to 20 per cent.

"These results imply that warming presents an even greater challenge to wheat than implied by previous modelling studies, and that the effectiveness of adaptations will depend on how well they reduce crop sensitivity to very hot days," the researchers concluded.

The world`s nations, under the UN Framework Convention on Climate Change (UNFCCC), have said that Earth`s average temperature should not exceed the preindustrial benchmark by more than 2.0 C if dangerous warming impacts are to be avoided.