ACCORDING to long-term climate forecasts, temperatures in Australia could rise by 4.5 degrees by 2090 and for every degree of warming, Western Australian rainfall may decline anywhere from four to seven per cent.
The frightening statistics were delivered at The University of Western Australia's Institute of Agriculture Industry Forum 2020 last week which delved into the topic of climate change and agriculture.
In the keynote address, Australian National University Climate Change Institute research fellow Steven Crimp explained that rising temperatures and declining rainfall will undoubtedly make agricultural production globally and in Australia far more challenging.
Since 1880 the planet has been warming and monthly temperature anomalies - departures from the long-term mean - have been changing.
At the earlier part of the record there was a balance of both warm and cold temperature anomalies.
However moving through the historical record, toward the present day, the frequency of the cold month anomalies starts to decline and the size of those anomalies starts to shrink, while the size and frequency of the warm anomalies starts to increase.
In the most recent decades, the average temperature anomalies are in excess of 1o-2oC warmer than the longer term average.
Dr Crimp said there had been significant change in global temperatures and Australia had seen changes in the same vein.
"2019 was the hottest year on record in Australia - 1.5oC warmer than the long-term mean - and it had several months with heat waves, plus several records of consecutive days with temperatures up to 41o C and 42oC," Dr Crimp said.
"Both the west and east coast have experienced significant decline in annual rainfall, with much of those declines have been driven by decline in winter and spring rain.
"Plus we've also had a fivefold increase in extreme heat events since the 1950s."
In terms of temperature extremes, almost the entire continent has experienced an increase in the frequency in the number of days above 37oC.
In some instances those increases have resulted in anywhere between 15 and 20 more days over the most recent part of the historical record.
However, it's not just the extreme hot temperatures that have been changing, but also the extreme cold temperatures, with more temperatures below 2oC, which is defined as the starting point for when frost can start to occur.
Despite the warming that has occurred, temperatures below 2oC were occurring later in the year and in some instances the frequency of those events had also increased.
While the first extreme hot days, above 32oC, are occurring early in the calendar year.
Dr Crimp said a situation had arisen where frosts were occurring later in the year and these extreme heat events were occurring earlier, causing the optimal flowering window for broadacre crops to shrink.
"There are very significant trends occurring across much of the southern parts of Australia, particularly in WA, that trend is almost a shortening of the optimal flowering window by a day a year since 1970," he said.
"Potential yields have declined by about 27pc since 1990, so on average 4.4 tonnes per hectare to 3.2t/ha.
"Most of that has been driven by rainfall decline, 83pc of those yield declines are attributed to the changes in rainfall that we have seen historically, while 17pc are in response to both the increase in frequency of the minimum and maximum temperature extremes."
When looking at the impact of climatic conditions on broadacre agriculture, not just an individual crop, a very similar pattern of decline has presented.
Over the period of 2000 to 2015 the production of broadacre agriculture in WA declined, in some instances, by as much as 20pc due to changes in historical climate.
Geological shifts have also occurred in the areas in which cropping is undertaken, with cropping density increasing in the wetter southern fringe of the cropping belt in WA and declining in some inland areas.
There have been some very significant changes to the historical climate and that has resulted in a significant impact of Australian agricultural productivity.
When it comes to greenhouse gas emissions, Dr Crimp said at the world's current trajectory, the representative concentration pathway (RCP) commits Australia to being anywhere from 3oC to almost 6oC warmer by 2100.
"If we think about the Paris Agreement commitment, if every country was to adhere to those voluntary commitments, which they're not, then that might bring temperature down to anywhere between 2.5oC and 4oC of warming," he said.
"But the threshold that most scientists talk about is trying to cap warming at 2oC, in order to do that emissions would need to drop considerably over the next few years to keep us below that target.
"At the moment we're on the very top end of emission trajectories but if there is collective action taken then we may be able to bring those emissions down, but where we get to depends on the extent of action."
Global climate models provide different rates of warming and rainfall change, plus other different climate variables for the future.
According to the short-term forecast from those models, the temperatures by 2025 in Australia could rise by 0.5oC-1.5oC, while by 2090 it could be 4.5oC warmer.
For every degree of global warming, WA rainfall may decline anywhere from 4pc to 7pc, meaning agricultural production in the southern hemisphere will become a more challenging prospect.
In response to the southern hemisphere rainfall declines, agricultural productivity is likely to be lower - about 3pc to 7pc - for the mid part of the century.
"A detailed analysis by ABARES (Australian Bureau of Agricultural and Resource Economics and Sciences) shows the impact of future changes to rainfall and temperature on wheat, sheep, beef and wool production," Dr Crimp said.
"Without significant adaptation or change, the agricultural production in the context of Australia will be more challenging in the future.
"At the moment, our focus has been on trying to ascertain what the future changes in rainfall and temperature and crop suitability would be, but when we think about adaptation it needs to be looked at as a hierarchy of options."
At the lowest tier there are incremental or tactical adaptation and change - these are really small modifications including changing varieties for planting times and looking at stubble retention.
They're small changes to existing practice and are lower risk with lower cost, but the problem is that they're successful for only very small changes to temperature and rainfall.
To cope with the more extreme changes to rainfall and temperature, systemic or transformational adaptation options are necessary, these are more risky but they are likely to give better resilience to the more extreme predictions.
"We have a linear relationship between the emission scenarios, the rates of accumulation of greenhouse gases and global temperatures," Dr Crimp said.
"If we want to have a 50pc chance of keeping temperatures below 1.5oC degrees until the end of the century, we can only omit a further 480 gigatonnes of carbon dioxide and that's from 2018.
"Based on the current rates of emissions, that really only gives us nine years until we have to take some very significant and decisive action."
The climate is already changing and more change is certain, meaning agricultural production globally and in Australia will be far more challenging.
These are challenges that need to be addressed both through managing emissions and through adaptation.
