The idea of sustainability is pretty simple: Manage our resources such that they can continue to support us indefinitely. And, for an individual resource, sustainability is simple. Avoiding something like depleting our groundwater means that future generations have access to as much water as we do and don't face the consequences of sinking soil.

But sustainability gets complicated when you start considering multiple, competing uses. Cutting back on water usage may influence things like agriculture, energy production, and more, making them less sustainable.

Just how complicated does all of this get? Lei Gao and Brett Bryan of Australia's CSIRO research organization decided to use their home country as a test of sustainability goals, and the results are disheartening. While moving any aspect of land use into the "sustainable" column is possible, the more aspects you try to push into that column, the harder it gets.

Setting priorities

To look into sustainability in a concrete manner, the authors started with the UN's Sustainable Development Goals. There are 17 of those, but Gao and Bryan focused on land use, which determined their priorities: sustainable food production, clean water, clean energy, limiting climate change, and maintaining biodiversity. The authors translated these into specific targets for 2030 and 2050 Australia at three levels of what they call "ambition."

(A weak target might be "slow the rate of groundwater depletion," a moderate target could be "stop groundwater depletion," while getting ambitious might be "restore groundwater levels to those prior to European arrival.")

The authors have a computerized modeling system, called Land-Use Trade-Offs (LUTO), that can project where things will be in response to a combination of economics, environmental constraints, and policy decisions. Given the constraints of policy and the environment, LUTO allocated land use based on what will provide the owners with the greatest return. Gao and Bryan also considered a variety of potential future scenarios, including different levels of climate change (and attempts to address it), as well as changes in Australia's population growth.

All these scenarios and considerations led to a dizzying array of potential results. So the authors analyzed them in terms of pathways—if you prioritize food production and start down that pathway, does it preclude anything else?

The answer is yes. "Simultaneous achievement of multiple targets is rare," the authors conclude, "owing to the complexity of sustainability target implementation and the pervasive trade-offs in resource-constrained land systems." It's possible to achieve more only by lowering your standards and accepting some of the weaker sustainability goals.

Competing interests

To give a sense of the trade-offs, we can start by looking at the scenarios in which addressing climate change is a priority. This leads to policies that promote reforestation, which can offset carbon emissions. New forests can also help with biodiversity, although complex ecologies takes a while to develop, so some of the benefits would be outside the time period being studied. Unfortunately, reforestation would also make water use less sustainable and, not surprisingly, displace agriculture. In fact, any serious attempts to address climate change involved reforestation and tipped water use into unsustainable territory.

Agriculture was also problematic in many pathways. To meet food production targets, there needed to be continued productivity improvements; without them, food started competing with other types of land-use priorities. Only eight percent of the pathways achieved biodiversity goals, typically when government policy prioritized it.

As a result of all these competing priorities, only a quarter of the pathways managed to hit two targets when the ambition was set to moderate. Ten percent hit three of them, and another 3.5 percent hit three. A full 18 percent of the pathways achieved none of the goals.

The easiest combo to hit together involved food, water, and biofuels. That's in part because the unused portions of food crop plants can be shunted into biofuel productions, assuming government policies prioritize the creation of the facilities to process them. But you'd only be prioritizing biofuels if you cared about climate change, and these pathways don't end up addressing that effectively.

None of this means that meeting goals is ultimately impossible. Solar and wind power prices have plunged so much that we have blown past a variety of goals that once seemed optimistic. But the CSIRO study does highlight that real sustainability requires solving multiple problems at once while balancing competing priorities. It may be a wicked problem, and no two countries are likely to end up with the exact same solutions. But that doesn't mean sustainability isn't a problem worth tackling.

Nature, 2017. DOI: 10.1038/nature21694 (About DOIs).