by Judith Curry
On the politics of climate expertise thread, we discussed Kevin Trenberth’s statement:
Given that global warming is “unequivocal”, to quote the 2007 IPCC report, the null hypothesis should now be reversed, thereby placing the burden of proof on showing that there is no human influence.
About two months ago, both Kevin Trenberth and I received the following invitation from Mike Hulme, editor of WIRES Climate Change:
Using Kevin Trenberth’s speech to the 2011 AMS Joint Presidential Session as the framing for these proposed essays, the journal WIREs Climate Change would like to invite you to develop a reasoned and lightly referenced argument for and against the proposition highlighted in the extract below – “the null hypothesis should now be reversed, thereby placing the burden of proof on showing that there is no human influence”. . . Both essays would be written ‘blind’ – i.e., without seeing the others’ essay – but the two essays would be peer-reviewed by the same three experts.
Both Trenberth and I accepted the invitation. Trenberth has apparently already submitted his essay, which was given a suggested submission deadline of 30 June 2011. I probably won’t be able to start working on my essay until May 28. So I am throwing this topic open for discussion. I have an idea of how I want to frame my essay, but really haven’t had time yet to work on it. I would be most interested in your thoughts and ideas on this topic.
Selected previous comments on the null hypothesis
Here are some “editors choice” comments on the topic of the null hypothesis from previous threads:
David L. Hagen | October 25, 2010 at 11:28 pm
Whatever happened to the “null hypothesis”? Assuming nature will continue on as before unless proven otherwise? Then again, it is important to recognize that an inherent difficulty of testing null hypotheses is that one cannot confirm (statistically) the hypothesis of no effect.While robustness checks (reported in the appendix), as well as p values that never approach standard levels of statistical significance, provide some confidence that the results do not depend on model specification or overly strict requirements for statistical significance, one cannot entirely dismiss the possibility of a Type II error. Jana von Stein (2008)
TomFP | October 26, 2010 at 8:16 am | Finally, another null hypothesis nut! I was beginning to think it was just me. Judith the misgivings I have about your Italian flag, and the whole calculus of uncertainty, include the question David asks. It seems that to view every hypothesis solely through the prism of uncertainty allows the null hypothesis to fade from view like the Cheshire cat. I’ve seen plenty of evidence that climate scientists may not even properly understand (or at least share my understanding of) the term, in that they confuse it with the consensus. One see talk by climate scientists of x “becoming the new null hypothesis”, where what is meant is that x has attained the status of “the consensus view” and thus deserves to thought of as the default position. Elsewhere one sees the null hypothesis (on the rare occasions when it makes its unwelcome appearance) adduced as a sort of box to be ticked only at certain milestone junctures in the experimental process, rather than as an ever-present, if often irksome, companion the scientist, to be consulted at every step. So in climate science it seems to me that the null hypothesis is poorly understood, and honoured more in the breach than in the observance. This underlies my earlier plea for a post on The Scientific Method.
Experimental science basically advances by demonstrating that “on the odds” theories don’t fit the evidence. Hypotheses get falsified, and by doing so their alternates gain credence.
My point is that scientists are absolutely free to choose what they are going to try and disprove. A scientist setting out can choose to try and falsify “AGW false” or falsify “AGW true”. In either case if they are successful they add weight to the alternate hypothesis and thereby have added to the sum total of our knowledge.
But this means there are as many null hypotheses as there are things scientists want to speculate about.
I should add that if a scientist is unsuccessful in knocking the null off its perch they haven’t proved anything. There are lots of reasons unrelated to what is really going on that might make it impossible to disprove something (e.g. all the things that happen in climate science – poor data, lots of confounding influences etc).
So Dr T is free to choose his null hypothesis as he sees fit, but that will determine what he has shown if he disproves it.
One of the supreme ironies of Dr T saying we should adopt “AGW true” as the null means that climate science should then be focused on disproving this. This is of course the skeptics’ position and it’s the failure of the believers to do this that leads to much of the angst.