Marohasy vs the Murray
Following up on my previous posts, I thought it might be useful to summarise my objections to the claims put forward by Jennifer Marohasy of the IPA, supporting the conclusion that scientists have “greatly exaggerated their claims that the Murray River’s health was declining.” You can read her full paper here (1.5 Mb PDF).
As I read it, Marohasy has three main claims. The first and most important relates to salinity trends. There appears to be agreement between Marohasy and the scientists working for the Murray-Darling Basin Commission (among other scientists working in the field) that salinity was generally getting worse until the 1980s, and that the Salinity and Drainage Strategy adopted by the MDBC at least partially reversed this increase. The disagreement comes with respect to projections for the future. As shown below the MDBC regards the Salinity and Drainage Strategy as providing breathing room rather than a permanent fix.
Marohasy says that the scientists have got all this wrong. She doesn’t appear to offer any real scientific basis for this claim. Rather she asserts (in comments on this blog) that the scientists working for MDBC, CSIRO, ABS and other key research institutions are “environmental activists masquerading as scientists” and (in her report) that they are committed to “promoting the myth of an ecological disaster” or are lying in order to improve their chances of getting research funding (p5). Similar points have been made, even more strongly, in The Land for which Marohasy writes. Reader David Nash has sent me this reply to one of Marohasy’s pieces attacking scientists.
Unless you’re prepared to redo thirty years of scientific research yourself, the debate on this point comes down to a pure question of comparative credibility. I don’t think scientists or government agencies are perfect by any means, but the kind of large-scale conspiracy theory required to explain the absence of any significant scientific support for the IPA position is implausible. On the other side of the ledger, I’ve already stated my reasons not to give any credence to anything said by the IPA.
Marohasy’s second point relates to the use of median rather than mean measures of river flows. As she correctly observes, the use of means rather than medians would make things look better in many cases. As she does not inform her readers, any elementary statistical text will tell you that, where means and medians differ, the median is generally more representative. I think this is clearly true in relation to river flows.
The final set of points made by Marohasy are a set of isolated pieces of information supportive of a favorable assessment. There is no serious attempt at a general assessment of trends, This kind of pointscoring is essentially useless, except as an answer the kind of caricature opponent who believes that everything in the system is getting uniformly worse. No serious scientist or policymaker working on the Murray-Darling believes this, though some popular discussion tends that way.
As I’ve mentioned, I’ve done a good deal of work on this topic myself. You can read a fairly recent (2001) survey article here (PDF). It’s mainly concerned with economic theory and policy, but it naturally draws on the scientific evidence. I think anyone who reads it will search in vain for the kind of doomsday mentality that Marohasy suggests is driving the policy debate. Nevertheless, there’s pretty good evidence that the system, like other irrigation systems in the mature phase, is overstressed and needs, among other things a reduction in irrigation diversions.