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?"
Globally, average air temperature has warmed by more than 1°C since records began in 1850, with the land warming faster than the oceans. Each of the past four decades has been warmer than the previous one.
Such warming is driven by increasing concentrations of all the major long-lived greenhouse gases in the atmosphere, with carbon dioxide (CO2) concentrations rising above 415 parts per million and the CO2 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 more than 1°C since 1910.
The current acceleration of global warming is expected to continue based on future greenhouse gas (GHG) emissions trajectories.
The warming of global temperatures has changed seasonal patterns of rainfall variability and resulted in changes in rainfall extremes.
April to October rainfall has decreased in the south-west of Australia, with May to July rainfall experiencing the largest declines - about 20 per cent since 1970.
Over much of the country's south-east there has been a decline in April to October rainfall of about 11 per cent since the late 1990s.
In addition, changes in rainfall patterns, sea levels, rates of glacial retreat and biological responses have also been detected consistent with expected climate change projections.
This mounting evidence has led to scientific consensus that:
- emissions of GHGs and aerosols due to human activities continue to alter the atmosphere in ways that affect the climate system and these changes and resultant trends will continue for the foreseeable future;
- there is at least 95 per cent confidence that humans are the main cause of global warming since 1950, and most likely responsible for 100 per cent of that temperature rise with a less than one in 100,000 chance that human activities are not responsible for the observed increase in global temperatures; and
- these changes are already likely to have negatively impacted on Australian agriculture, acting as a major drag on yield growth with similar impacts on yield growth globally for the major crops.
A major unknown about historical and future climate change is how much the various human-induced activities (greenhouse gas emissions, stratospheric ozone depletion, Asian aerosols and landcover change) interact with the components of natural variability such as El Nino systems.
Future impacts
Scientists estimate that global average temperatures could increase by up to 4.8°C by the end of the present century if we continue to follow the current emissions trajectory.
Recent research has shown that the synoptic features (large-scale weather systems) responsible for prolonged heatwaves are on average 50 per cent more prevalent under a business-as-usual GHG emissions trajectory, highlighting an increase in the number and severity of these events in the future.
To put this in context, the difference between our historical temperatures and those of the last ice age was only about 5°C, and so the 4.8°C of warming possible by 2100 signals a huge change in how the climate-ocean-land systems of the earth function and, as a consequence, how agriculture will operate.
In Australia, national projections suggest up to 1.3°C of additional warming could be experienced by 2030 and up to 5.1°C of warming could be experienced by 2090, with the greatest warming being in inland Australia.
While changes in rainfall are more uncertain, projections suggest drier conditions in the southern half of Australia - particularly in the south-west and during the cool season months of May to October - with as much as 20 per cent less by 2030 and up to 50 per cent less rainfall by 2090.
In response to global changes in rainfall and temperature, agricultural productivity is likely to alter further with some regions improving and others declining.
On average, global potential crop production may drop by six per cent for every degree of warming the globe experiences. In Australia, the reductions are likely to be larger.
Additional issues include reductions in water availability for irrigation coupled with increased demand due to temperature rises, and a change in frequency of climatic extremes such as heatwaves, droughts and floods.
Adapting to climate change
Australian farmers will respond to these climate change impacts. This is called adaptation.
Many actions required for adapting to modest changes in climate are extensions of those currently used for managing seasonal variability.
For this reason, efforts to improve current levels of adaptation to climate variability will have positive benefits in addressing likely climate change impacts.
Examples of adaptation options include:
- enhancing the current implementation of zero tillage and other minimum-disturbance techniques, retaining crop residues, extending fallows, changing row spacing, changing planting density, staggering planting times, traffic and erosion controls;
- altering planting decisions to be more opportunistic by more effectively considering environmental conditions (soil moisture), climate (seasonal climate forecasting) and market conditions;
- expanding routine record-keeping of weather, production, degradation, pest and diseases, and weed invasion;
- incorporating seasonal climate forecasts and climate change into farm enterprise plans;
- improving the efficiency of water distribution systems (to reduce leakage and evaporation), irrigation practices and moisture monitoring;
- learning from growers in more marginal areas;
- the selection of varieties with appropriate thermal time and vernalisation requirements, heat shock resistance, drought tolerance, high protein levels, resistance to new pests and diseases and perhaps that set flowers in hot or windy conditions; and
- enhanced use of decision-support tools or training to access or interpret climate data and analyse alternative management options.
There are also longer-term decisions at a family farm level that may include weighing up whether to sell, buy more land or invest off-farm.
These decisions, along with industry infrastructure (for example, grain silos and transport infrastructure) and industry support (such as drought policy) require a full understanding of likely future risks.
The value of adaptation
David, left, and Michael Mailler have set up a family run solar farm across 120 hectares at Boggabilla in north-west New South Wales. Photo: Nick Cubbin, The Farmer, courtesy NSW Farmers Association
There is a growing international body of research examining the benefits of adaptation to climate variability and change, showing a number of adaptation options are available to reduce the possible impacts of climate change.
In Australia a number of studies have examined the economic benefits of adaptation in the wheat industry at both national and regional scales under a range of likely future climate conditions.
The adoption of new technology and management systems has held yields steady over the past couple of decades. Without these advances, water-limited yield would have dropped by 27 per cent due to climate changes such as drought, heat shock and frost.
It was estimated that rainfall declines should have accounted for about three-quarters of the fall in simulated yield potential, while observed warming should have accounted for about one-quarter of the fall in yield potential.
Continued adaptation to climate change has been estimated to add an additional $500 million to Australia's annual income every year from wheat exports via the introduction of improved water-use efficiency options, and may mitigate potential yield losses by up to 18 per cent through broader scale adaptation.
Under conditions of substantial climate change, tactical adaptation will likely only have limited effectiveness and more extensive adaptation options, often termed transformation adaptation, may be required.
Transformational adaptation may include changing a proportion of existing land use to non-agricultural production (for example solar power production) to diversify income.
Adding electricity to the farm production portfolio where the infrastructure and regulations allow could not only diversify income but also provide a stable income stream, which is likely to be increasingly valuable as the volatility of traditional commodity farming increases.
More information: Dr Steven Crimp, 02 6125 7265, steven.crimp@anu.edu.au; Professor Mark Howden, 02 6125 7266, mark.howden@anu.edu.au