Via Eurekalert and Wiley-Blackwell
The human cause of climate change: Where does the burden of proof lie?
Dr. Kevin Trenberth advocates reversing the ‘null hypothesis’
The debate may largely be drawn along political lines, but the human role in climate change remains one of the most controversial questions in 21st century science. Writing in WIREs Climate Change Dr Kevin Trenberth, from the National Center for Atmospheric Research, argues that the evidence for anthropogenic climate change is now so clear that the burden of proof should lie with research which seeks to disprove the human role.
In response to Trenberth’s argument a second review, by Dr Judith Curry, focuses on the concept of a ‘null hypothesis’ the default position which is taken when research is carried out. Currently the null hypothesis for climate change attribution research is that humans have no influence.
“Humans are changing our climate. There is no doubt whatsoever,” said Trenberth. “Questions remain as to the extent of our collective contribution, but it is clear that the effects are not small and have emerged from the noise of natural variability. So why does the science community continue to do attribution studies and assume that humans have no influence as a null hypothesis?”
To show precedent for his position Trenberth cites the 2007 report by the Intergovernmental Panel on Climate Change which states that global warming is “unequivocal”, and is “very likely” due to human activities.
Trenberth also focused on climate attribution studies which claim the lack of a human component, and suggested that the assumptions distort results in the direction of finding no human influence, resulting in misleading statements about the causes of climate change that can serve to grossly underestimate the role of humans in climate events.
“Scientists must challenge misconceptions in the difference between weather and climate while attribution studies must include a human component,” concluded Trenberth. “The question should no longer be is there a human component, but what is it?”
In a second paper Dr Judith Curry, from the Georgia Institute of Technology, questions this position, but argues that the discussion on the null hypothesis serves to highlight fuzziness surrounding the many hypotheses related to dangerous climate change.
“Regarding attribution studies, rather than trying to reject either hypothesis regardless of which is the null, there should be a debate over the significance of anthropogenic warming relative to forced and unforced natural climate variability,” said Curry.
Curry also suggested that the desire to reverse the null hypothesis may have the goal of seeking to marginalise the climate sceptic movement, a vocal group who have challenged the scientific orthodoxy on climate change.
“The proponents of reversing the null hypothesis should be careful of what they wish for,” concluded Curry. “One consequence may be that the scientific focus, and therefore funding, would also reverse to attempting to disprove dangerous anthropogenic climate change, which has been a position of many sceptics.”
“I doubt Trenberth’s suggestion will find much support in the scientific community,” said Professor Myles Allen from Oxford University, “but Curry’s counter proposal to abandon hypothesis tests is worse. We still have plenty of interesting hypotheses to test: did human influence on climate increase the risk of this event at all? Did it increase it by more than a factor of two?”
All three papers are free online:
Trenberth. K, “Attribution of climate variations and trends to human influences and natural variability”: http://doi.wiley.com/10.1002/wcc.142
Curry. J, “Nullifying the climate null hypothesis”: http://doi.wiley.com/10.1002/wcc.141
Allen. M, “In defense of the traditional null hypothesis: remarks on the Trenberth and Curry opinion articles”: http://doi.wiley.com/10.1002/wcc.145
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There is no point in quoting the IPCC as an unbiased scentific authority. I think we should remind ourselves that the IPCC rejects the null hypothesis and was established with the following mandate(see IPCC web site)
‘Principles Governing IPCC Work, “…to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation. IPCC reports should be neutral with respect to policy, although they may need to deal objectively with scientific, technical and socio-economic factors relevant to the application of particular policies.” ‘
I have a post on this at Climate Etc
http://judithcurry.com/2011/11/03/climate-null-hypothesis/
Aunty Freeze says:
November 4, 2011 at 3:16 am
It makes me sad that this is what science has become….
__________________________________
I am with you on that one.
I just went over to J.Curry’s blog – SAD.
Reversal of the null hypothesis? Really? This is simply another way of stating application of “The precautionary principle. If we go down this slippery slope we admit that global warming cannot be falsified, and the entire concept reverts to a “belief” rather than an application of science.
BrianSJ says:
November 3, 2011 at 10:56 am
“So, a safe null hypothesis would be temperature increases linearly with human population. Disprove that and the alarmists are doomed? No?”
Yes, that would be an interesting way to tweak the Null Hypothesis. However you’d need to specify the exact linear equation that supposedly relates global average temperature with human population. And that equation would be the new Null.
Suppose that you can reject that new Null with 95% or greater confidence. What have you actually shown? You haven’t ‘disproven’ the idea of AGW. You’ve simply shown that one particular linear equation has a lousy fit to the data.
If you cannot reasonably reject the new Null with 95% or greater confidence, what have you demonstrated? Nothing in particular. However Trenberth would be a happy camper. He would interpret that as ‘living proof’ of AGW.
Shevva says:
November 4, 2011 at 1:22 am
Hug[s] to the mods.
[AWWWWW…… -REP]
@ur momisugly Dave Springer , November 4, 2011 at 8:18 am
The issue is not one of “data trumping theory” . The theory is 19th century physics validated by more than a century of observation and experiment in addition to its mesh with the greater corpus of physical theory . It is readily testable , but climate science appears to have abandoned teaching by experimental demonstration .
This is about a maximally understandable and useful decomposition of the causes of observed phenomena . As elaborated in my Nature comment , adding any consideration of spectrum to the calculation of the temperature of a radiantly heated gray ball requires adding that additional function valued parameter to the code .
My impression is that one can have a well paid career in climate science never even understanding the 150 year old observation that a radiantly heated gray ball , however light or dark , will come to the same equilibrium temperature , Albedo is a fuzzy concept . I really think it should only be defined for flat ( gray ) spectra . In that case it falls out of the calculation of temperature . Otherwise , it must be defined with respect to some other spectrum . It’s only the assumption that the albedo of the planet with respect to the sun’s spectrum is different than the albedo of the planet with respect to the near 0k spectrum of all other directions around us which matters to the planet’s mean temperature . I wonder how many reading this know how to calculate the albedo between 2 arbitrary spectra . I know of no place to learn it on the web . Given any set of source , sink , and sphere spectra , one can calculate the temperature of the sphere . It’s the sort of thing which in other areas of applied physics would be a homework assignment .
Dave , do you have a reference with the details of those moon measurements , in particular their latitude ? It is very hard to explain how those measurements could be so cold as 249k . It’s particularly strange because by the same extreme computation which gives the earth with an assumed albedo ( wrt the sun ) of 0.29 a temperature of 255k , the 0.16 you assert for the moon predicts a temperature of 267k .
I have seen a claim ( since lost to the ether ) that the observed mean temperature of the moon is around 271k , only about 8c less than a gray ball , implying a much less extreme spectrum .
The notion that the spectrum of earth’s surface is like the moon’s is absurd on its face . There’s no blue , there’s no white , there’s no chlorophyll green on the moon . It’s the difference between the spectral map of the earth’s surface as it is and the it’s spectrum as seen from outside which defines the atmospheric greenhouse effect . Assertions about what it might be as a dry naked lifeless ball are irrelevant .
Russ says:
November 3, 2011 at 1:40 pm
I thought Trenberth was still out there chasing that “missing” ocean heat content. How does he have time to write stuff like this?
Q. What is the difference between a Climate Scientist and a mosquito?
A. One is a blood sucking parasite and the other is an insect.
Good one, ferd burple!
Arrrghh. I messed up the tags. Moderator, please delete my previous comment. Thanks.
Point taken, but not because any part of it [Trenberth’s assertion] requires proof of being ridiculous. It is a completely ridiculous assertion. It is self-evident. But here it is modified …
This should be turned around on him quickly and with no mercy. Everyone should now pester all Scientists and climate cult members with a simple question: “Do you agree with Trenberth’s assertion that Climate Science is settled and the Scientific Method no longer applies?“
The aliens are here to conquer us!! I have the data to prove it – all I need is to reverse the null hypothesis and then YOU have to prove that they are not ….
In the meantime I need a bit of founding.
It was reading though these posts and wondering:
Do you folks actually believe Trenberth is a drooling idiot?
It’s like when you get to climate science you have an on – off switch –
When it comes from someone like Trenberth, or Santer, or Hansen you switch OFF and that’s that.
Trenberth has never implied the Scientific Method no long applies, come on, can we get serious?
Have you folks considered the thought:
“The AGW is the null hypothesis because it is the only one that is consistent with our understanding of physics and Earth observations over past century. If it were NOT happening, we have to find an explanation.”
Please tell me how this guy still has a JOB
citizenschallenge says:
November 5, 2011 at 12:58 pm
Do you folks actually believe Trenberth is a drooling idiot?
No, his turning of scientific principle on its head is quite deliberate, and means he’s no scientist, but probably not a “drooling idiot” as you put it, although all the evidence may not be in yet on that.
he dazzled me with nonsense.
More like a desperate rent-seeker trying to keep the spigots open.
citizenschallenge says:
November 5, 2011 at 12:58 pm
Have you folks considered the thought:
“The AGW is the null hypothesis because it is the only one that is consistent with our understanding of physics and Earth observations over past century.”
Citizenschallenge, your comment shows that you do not understand the Null Hypothesis. That’s not how it’s defined. And for good reason.
The Null is a blunt instrument. Yes, in principle, it’s tweakable. So what? In the continuous case, tweaking the Null cannot lead to any interesting results. And from a mathematical perspective, it would be extremely difficult to tweak the Null in the way that Trenberth suggests. See my earlier posts in this thread on the subject.
Larry Fields is right, citizenschallenge does not understand the null hypothesis.