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Severe frosts will be more frequent due to man-made greenhouse gas: scientists

Steven Schubert, Wednesday October 15, 2014 - 16:13 EDT
Audience submitted image
Severe frosts could happen in different times of the year due to greenhouse gas in the atmosphere, say scientists. - Audience submitted

Frosts like the ones that caused so much damage to crops this season could be more common for the next 20 years, according to scientists.

They say greenhouse gases in the atmosphere were changing the way high pressure systems formed and moved, causing severe frost problems for farmers.

Frosts in August this year devastated grain, legume and oilseed crops across Australia's cropping regions.

Final crop losses would not be known until what was left was harvested, but anecdotal reports suggest some farmers have lost up to 80 per cent of their crop, while others had hardly been affected at all.

But frosts like these may be something farmers would have to adjust to in the future.

Melissa Rebbeck, an agricultural researcher at the University of Adelaide and who also runs her own consulting business, said the weather system that produced the frosts was unusual.

"This high pressure system slipped through the system and it went across the Australian Bight. It took 10 days to cross the continent," she said.

"It was very, very large as well, so that's why it took so long to cross the continent and it basically just dragged very cold, dry, stable air in from the Antarctic and dumped it onto the regions affected.

"Basically what that meant was we had five days in a row of temperatures that were sub-zero in major cropping regions for 12 hours.

"It's the duration of those events that caused the devastating damage that producers are seeing."

Ms Rebbeck said the synoptic changes were coming as a result of greenhouse gases.

"Certainly the research we're seeing is that the high pressure systems are becoming larger than normal and that is definitely from the hole in the ozone layer and the impact of the gasses in the atmosphere, which basically expand the size of these high pressure systems."

Steven Crimp, the senior research scientist from the CSIRO's agriculture flagship, agreed there had been a change in the way high pressure systems behaved during crucial growing periods when crops were susceptible to frosts.

"The period over which frosts occur has changed," he said.

"On the eastern portion of Australia, we find that the frost window has broadened. So that means there are earlier starts to the season, or the period over which frosts would occur, and much later finishes."

Mr Crimp said the reason behind the change was manmade.

"We believe that there's an anthropogenic or human reason for why those high pressures have actually moved further south. We see that movement south is well-correlated with the increase in greenhouse gases in the atmosphere."

But he was less certain that the effect would be reversed if the amount of greenhouse gas in the atmosphere was reduced.

"That's the next step for our research. So what we're trying to see is - is this a permanent feature going forward in the future, or is there some sort of point in which the number of frosts actually starts to decline?

"The preliminary results at the moment would suggest that the sort of frost risk that we're currently experiencing will be a feature probably out until around 2030, 2035 and then in association with sort of mean warming that we're seeing then that frost risk will start to decline and become less of a risk in the production system.

"But certainly it will still be there but will be reduced, and the scale of reduction really depends on the emissions pathways that we follow going forward."


© ABC 2014

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