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Predicted climate change impacts on northern farming systems By Steven Crimp and Mark Howden, ANU
AT A GLANCE… An increasing body of scientific evidence regarding the impact of human activity on the earth’s climate has shifted the debate from “Is climate change real?” to “What can we do about it?” Adapting current management activities must include considerations of both climate variability and change. Advisers have a vital role in helping to develop information-rich farming systems that will improve responses to current climate variability and that can enhance adaptation to climate changes.
FIGURE 1: Probability distributions of mean daily maximum temperature (left) and mean daily minimum temperatures (right) for Dubbo for two periods, 1960 to 1985 and 1986 to 2018
FIGURE 2: Mean annual dry spell length (left) and seasonal dry spell length for December to January (DJF), March to May (MAM), June to August (JJA) and September to November (SON)
Dry spell lengths are expressed in days
28 — COTTON YEARBOOK 2019
Historical changes in climate? Globally averaged air temperature has warmed by over 1°C since records began in 1850, and each of the last four decades has been warmer than the previous one. This warming is driven by increasing concentrations of all the major long-lived greenhouse gases in the atmosphere, with carbon dioxide (CO2) concentrations rising above 400ppm and the CO equivalent (CO2-e) of all gases reaching 500ppm for the first time in at least 800,000 years. In Australia, the pattern of warming (average temperature) has been largely similar to that experienced globally, with warming of just over 1°C since 1910. Examining the shift in the distributions of monthly day and night-time temperature shows that very high monthly maximum temperatures that occurred around 2 per cent of the time in the past (1951–80) now occur around 12 per cent of the time (2003–17). Very warm monthly minimum, or night-time, temperatures have shown a similar change from 2 per cent of the time in the past (1951–80) to 12 per cent more recently. This shift in the distributions towards hotter temperatures and more extreme high temperature conditions has occurred across all seasons, with the largest change being in spring. In the Dubbo region over the period 1950 to 2018 (the length of the temperature record), warming has occurred in both minimum and maximum temperatures, with mean temperatures now approximately 1.2°C warmer than in 1950. For the period 1950 to 1985 a maximum daily temperature of 25°C occurred, on average, 18 per cent of the year i.e. 66 times. More recently (1986 to 2018), this temperature now occurs on average 31 per cent of the time i.e. 113 times. Similarly, mean minimum temperatures have warmed with the frequency of a minimum temperature of 19°C increasing from 11 to 29 times each year on average (Figure 1). The Dubbo rainfall record exhibits a declining trend, with declines during the December to February period most pronounced. Mean dry spell lengths have also increased, with the average time between rainfall events now four days
