Climate change and the Murray-Darling Basin plan are two of the most divisive environmental issues in Australia. They are also two of the most important. But what does the Murray-Darling Basin Authority (MDBA) plan to do about climate change in its Murray-Darling Basin plan?

Not enough, says John Williams, of the Wentworth Group of Concerned Scientists. “The estimate of the sustainable diversion limit, which is the amount of water we need to have in the system to maintain a healthy river, doesn’t have any provision for climate change at the moment,” he told Crikey.

Williams served as the NSW Natural Resources Commissioner from 2006-11 and is a former chief of land and water at the CSIRO.

“They haven’t looked at what the river needs to be healthy,” said Williams. “Society may choose to have unhealthy rivers, but we need the science to say how we have a healthy river, and they haven’t provided that.”

Williams’ concerns were backed up by a recent report from the Goyder Institute for Water Research, which criticised the Murray-Darling Basin Authority for not taking sufficient account of the future effects of climate change in its controversial plan.

According to the report: “The possible impacts of climate change and increased groundwater allocations on future water availability are not evaluated in the flow recovery scenarios provided by the MDBA.”

But the MDBA’s chief executive Rhondda Dickson claims that this is not the case, arguing that the plan must be flexible enough to respond to unanticipated changes to climate.

Dickson recently told a climate change conference that “we believe that our adaptive and pragmatic approach is a critical step in adapting to climate change: allowing enough flexibility in the planning process. Our ability to predict future climate trends is improving all the time, as is our understanding of how climate will affect stream inflows.”

Given the high degree of environmental diversity within the Murray-Darling catchment area — which takes in four states and the ACT across several climate zones — the basin’s climate will continue to be highly variable, Dickson argues. Not only must residents contend with global climate change, but cyclical effects — droughts, floods and everything in between — will continue to cause short and mid-term inconsistencies in weather around the catchment.

The MDBA’s general manager of water planning Tony McLeod agrees with his colleague, citing Australia’s experience with an already variable climate as giving the MDBA an advantage in anticipating future climate changes. “We’re setting out a framework that deals with extreme wets and extreme drys,” he told Crikey. “We’ve got a lot of lived experience with those extremes. It doesn’t mean we can’t learn more and do more, and we’re certainly doing this. But extremes aren’t a new thing.”

The plan will be reviewed at least every 10 years, and there is the capacity for reviews as frequently as every five. The first is to take place in 2015, before the plan’s proposed enforcement date in 2019.

But Williams thinks the MDBA shouldn’t wait until 2015 to decide what its targets will be. “I think that the science is more than sufficient to build that into where the sustainable diversion limit is, and they haven’t provided the science to establish this SDL. It puts awful uncertainty onto the community,” he told Crikey.

Williams thinks that the MDBA’s well-publicised backing-down from its scientifically based proposed sustainable diversion limit of 3000 to 4000 gigalitres was a political move.

“They’ve decided to base the recommendation on a political judgment rather than what the science, so they can instead through what society wants to do,” he said. “They’ve mixed up politics and science, and that’s a murky thing to do.”

The most important thing Australia needs to do, according to McLeod, is decide what environmental objectives the MDBA should aim for. Last Friday the MDBA announced the creation of a new advisory committee on social, economic and environmental sciences, which will examine science and socio-economic knowledge to help the basin plan adapt in coming years.

“We are keen to establish this independent advisory committee to help us focus our future science and knowledge priorities over the next few years,” said MDBA head Craig Knowles in a press release. “We are looking for the best and brightest minds in the fields of hydrology, ecology, social sciences and economics.”