AN international report has made a sobering finding, with computer models showing global wheat production could fall six per cent for every one degree of temperature rise.
The study, published online in Nature Climate Change, found that not only would production fall, but volatility would increase.
The rate of decreases in productivity is a massive concern for Australian producers, given a joint release from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the Bureau of Meteorology (BoM) last week showed temperatures could rise up to 1.2 degrees on average in southern Australia from the average from 1986-2005.
The BoM/CSIRO study showed temperatures could rise a whopping 4.2 degrees on average by 2090 under a high emissions scenario and also forecast lower rainfall in key cropping zones in southern and eastern Australia, especially in winter and spring, the critical seasons for winter crop production.
However, contributor to the Nature Climate Change study on wheat production, Garry O’Leary of the Victorian Department of Economic Development, Jobs, Transport and Resources (DEDJTR) said the study was based on no adaptation to a changing climate.
"This study is concerned solely with rising temperatures, we have just used standard varieties and have not factored in the impact of rising carbon dioxide levels," Dr O’Leary said.
The work involved comparing 30 simulation crop models against field experiments where crops were grown at mean temperatures ranging from 15 to 32 degrees.
CSIRO and BoM researchers say their study, which makes use of 40 different global models, shows warming patterns will continue after an increase in average temperatures of 0.9 degrees since 1910.
"There is very high confidence that hot days will become more frequent and hotter", CSIRO principal research scientist, Kevin Hennessy said.
Rainfall declines will be first felt in southern mainland Australia before the area with lower rainfall increase across subtropical regions after 2030.
Mr Hennessy said the agriculture sector would need to prepare for the changes predicted in the report.
"This research has been strongly aligned with the needs of Australia's natural resources sector", Mr Hennessy said.
"Other researchers are using this information to assess potential impacts and management options."
And in worrying news for growers, Dr O’Leary said many crop production modelling products had not adequately factored in the damage done by high temperatures.
"The wheat yield declines due to temperature increases were likely to be larger than previously thought and are likely to begin taking effect earlier than expected with only small temperature increases having an impact," he said.
Tim McClelland, the co-ordinator for forecasting tool Yield Prophet with Birchip Cropping Group (BCG) said there were a number of ongoing challenges with forecasting tools.
"We’ve factored in increased temperatures and the impact it has on the crop in terms of earlier flowering, but modelling systems inherently overestimate the yield slightly."
Mr McClelland said the tool could also make allowances for different cultivars and maturity dates.
"We have eight different categories in terms of variety choice and that is factored into our modelling."
He said with Yield Prophet, challenges now included creating a system for new crops and better accounting for mineralised fertiliser.
Dr O’Leary said Australia, with large tracts of near-arid cropland, could be especially hard hit by rising temperatures.
However, he said adaptation of new practices could help.
"Drought and heat tolerant varieties will be the holy grail for breeders, and there is also a lot of work to be done to extreme events at sensitive stages of a crop’s development, such as heat or frost at flowering."
In terms of in-crop yield monitoring, Dr O’Leary said that the Australian models performed well but not in all tests and no single model of all the 30 was shown to be superior.
Australian models used included the Agricultural Production Systems Simulator (APSIM) and other experimental forms of that system.