Claim: Global warming makes frost damage worse

Guest essay by Eric Worrall

The Australian CSIRO has claimed that global warming increases both the incidence of frost, and the amount of damage frost causes to crops.

According to the CSIRO;

University of Queensland research scientist, Dr Jack Christopher, said climate modelling of 60 years’ worth of data has shown that while average temperatures have been increasing, the incidence and impact of frost has also increased during that period.

“One of the main factors causing that is the fact that the plants are actually growing a lot quicker in the warmer weather, so that when they’re planted at what we think is the correct time, they’re actually flowering too soon and are flowering during a much higher frost risk period than was intended,” he said.

Frost damage costs Australian agriculture millions of dollars each year due to reduced yield.

“On average, we’re losing around 10 per cent of the crop nationally, so that’s a huge loss in terms of yield and in terms of dollars,” Dr Christopher said.

“So if we’ve got 24 million tonnes of wheat in an average year, it may be $250 a tonne, that might be $6 billion worth of wheat, so 10 per cent of that is $600 million in an average year, so it’s a huge loss.”

Read more: http://www.abc.net.au/news/2015-08-21/qch-frost-field-trial/6715106

The abstract of the study;

Radiant spring frosts occurring during reproductive developmental stages can result in catastrophic yield loss for wheat producers. To avoid frost during susceptible heading stages, wheat crops are often sown later than is optimal for maximum yield given seasonal rainfall limitations, for example. To better understand the spatial and temporal variability of frost, occurrence and impact of frost events on rainfed wheat production was estimated across the Australian wheatbelt using 0.05° gridded weather datasets. Current genotypes are assumed to be sensitive at Stevenson-screen temperatures lower than 0°C, and simulated yield outcomes at 60 key locations were compared to those for virtual genotypes with different levels of frost tolerance for early-, mid- and late- maturity types and a wide range of sowing dates. No significant trend in frost occurrence over time was observed in most parts of the Australian wheatbelt over the last 57 years. However, more frost events, later last frost day and a significant increase in frost impact on yield was estimated in certain areas, in particular in the South-East and several parts of the West. Across Australia, we found that mean yield could be improved by between 10% and 20% on average if frost tolerant lines were available. Considering frost seasons only, the mean yield could be improved by 50 to %100 by frost tolerance. Across all seasons for the wheatbelt, yield increases resulted from (1) reduced frost damage (ca. 10% improvement) and (2) the ability to use earlier sowing dates to increase yield potential (additional 10% improvement in East). Simulations indicate that genotypes with an improved frost tolerance of 1°C lower than the 0°C reference would provide substantial benefit in most wheat production areas. Greater tolerance ((to 3°C lower temperatures) would provide further benefits in the eastern cropping regions but not in the west. Our results indicate that breeding for a level of reproductive frost tolerance that is at least 1°C lower than present should remain a priority for the Australian wheat industry, despite an average warming trend in the winter season.

Read more: https://publications.csiro.au/rpr/pub?pid=csiro:EP149710

I personally find it fascinating that “global warming” is now supposed to cause more frequent frosts, later in the growing season, in susceptible areas. Having said that, in my opinion, an estimation model built upon the kind of grossly adjusted temperature data Australia produces, is not a very compelling chain of evidence upon which to base a conclusion.