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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Curry has the correct approach : the issue is to determine the extent of human effect. The problem always encountered in science when stats are used to reject the null is that in doing so, even if you can reject the null, you haven’t provided any useful information. We don’t really care that the effect is non-zero. We want to know whether the effect should be something of concern. After all, there is no other reason for doing the research in the first place. If you demand a null hypothesis, it should be that “Human activity has no significantly harmful effects re global warming.”
I wonder if Dr. Trenberth would comment on the amount of gray literature in the report he cited? I still have yet to see them reject the null, so why change the rules now? Oh yeah, it’s too mushy of a subject to make rejecting the null easy one way or the other. This is a simple case of changing the rules in the middle of a game when you think it’s too hard. It smacks of whining.
Ramon Leigh:
I would actually say it should be “The economic damage of action on climate change outweigh the future benefits of action.”
In a private email to me Trenberth claimed that the key evidence for AGW is sea levels.
Who in their right mind would take this scammer seriously ?
Does that mean all the climate money now has to flow to those doing research that proves against this new null hypothesis?
So long as the null hypothesis remains that wheat, corn, rice, and soybeans do not grow well in snow then I have no problem with the null hypothesis being that human activity is causing warming. The crux of the matter for me is whether the earth is at its optimal temperature and atmospheric CO2 content already or whether more warmth and atmospheric CO2 will move it towards or away from the optimum. Given that both CO2 and global average temperature are far below the norm for the past 500 million years and primary production in the food chain is also far below the norm then I’d say we probably shouldn’t worry about it until we at least have temperate forests covering Antarctica again and the threat of a cold ending to the Holocene Interglacial is not a concern.
Trenberth long ago gave up science for politics. His very statements now are not those of a scientist, but a propagandist.
cms says:
November 3, 2011 at 11:26 am
I agree. To sum up, recent global temperatures, weather, polar ice and sea levels are consistent with our knowledge of corresponding Holocene climate variability measures when man was not a factor to be considered. Ergo, the null hypothesis of natural variability easily rebuffs attack by pseudo scientists such as Trenberth.
Dave Springer says:
“…I have no problem with the null hypothesis being that human activity is causing warming.”
But that is the alternative hypothesis to the null hypothesis. Trenberth is desperate to make his alternative hypothesis the null hypothesis, but the problem is that skeptics are then being put into the position of having to prove a negative.
The null hypothesis states that the current climate is within the parameters of the Holocene prior to the industrial revolution. To falsify the null, one or more parameters must be exceeded. But temperatures, trends, rates of increase and declines have all been much greater during the Holocene. Thus, the null hypothesis remains unfalsified. Now Trenberth wants to reverse the scientific method, and place the onus on skeptics to prove that humans are not causing climate change. But Trenberth asserts that AGW is happening, so it is up to him to provide testable, empirical, falsifiable evidence. He hasn’t been able to provide any evidence for his ‘hidden heat in the pipeline’, so now he wants to change the rules.
In the past century and a half the planet’s temperature has gone from ≈288K to ≈288.8K, an extremely minor change compared with past rises, which happened when CO2 levels were much lower. Trenberth needs to face the fact that his predictions are being falsified by the ultimate Authority: the planet itself. Trying to put the onus onto scientific skeptics is a non-starter. But it shows that Trenberth is very concerned about the validity and importance of the null hypothesis, and the fact that it falsifies his alternative CO2=CAGW conjecture.
The proposal is that human-kind affect the climate and this is the reason that global temperatures are increasing.
The null hypothesis, on the other hand, is that climate changes anyway – it is ‘natural’; climate has always changed, even in the distant past long before there was any possibility of human influence. All scientists (and every other informed person) acknowledges that this expression of the null hypothesis is true. In the past climate has changed much more rapidly and much more abruptly than anything seen today.
So,If someone wishes to conjecture that climate now varies for some other reason, i.e. humans are the cause, the onus must be on them to ‘prove’ their conjecture – not the other way around.
What would we expect from the null hypothesis? We know that the world is currently warming from the last ice age ( and more recently from the little ice age). Moreover, we know that ice ages occur with regular frequency on our planet, every 100,000 years, and they are interspersed with inter-glacial periods (like the one we are in now) in which the world warms up, This has been the regularly repeating pattern for millions of years on this planet. A good question to ask is, what were temperatures like in previous inter-glacial periods? Such as the Eemian 100,000 years ago? Well, we know from ‘settled science’ that the Eemian was warmer than today, and so the null hypothesis suggests that our inter-glacial (the Holocene) should continue to warm naturally – at least until it reaches the level of previous inter-glacials. Until this is achieved, all warming is merely evidence of the null hypothesis, i.e. the world should warm to the level of previous inter-glacials.
According to the IPCC’s own Arctic Impact Assessment Report (2005) the previous inter-glacial period 100,000 years ago (the Eemian) was warmer than it is now. In Section 2.7.3.1 it states “…during the Eemian the winter sea-ice limit in Bering Strait was at least 800 km farther north than today, and that during some summers the Arctic Ocean may have been icefree. The northern treeline was more than 600 km farther north”
So the null hypothesis points to warming, and the temperature record of the last century supports the null hypothesis as well as much as anything else.
“Is this circular reasoning, or what?”
It IS circular reasoning, AND a con-game! There is too much money to be made writing papers that “prove” AGW, and too long a list of sleight of hand tricks played with data, for AGW to be declared the null hypothesis. My null hypothesis is that if you follow the money, and the agendas of the liberal media, watermelon environmentalists, and “progressive” politicians, you will arrive at a huge lie.
So, essentially, he provides circular argument of anthropogenic garbage by referencing IPCC 2007 report, yet IPCC has stated they do not do science but put together different scenarios using grey literature, propaganda, news clipping, and the supposed science K.T. does.
And they wonder why they are viewed as highly irrational and unstable people?
Trenberth WAS a scientist, now he is a plain huckster.
On the sandlot, this is called taking your bat and going home.
“Very likely” is surely equivocal. So the IPCC report is “unequivocal” and “equivocal” at the same time.
At the risk of straying into Orwellian realms of cliché, very doublespeak!
@ur momisugly JJ
Answer: It’s a
sciencemoney thing. Youwouldn’tunderstand.““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.””
It is not clear at all that our effect is large and there is no evidence of any kind that our supposed effect emerges from natural variability.
In fact, looking at the long tern record, nothing in any measure is doing anything unusual. The only unusual aspect arises when the time frame is cherry-picked to ignore things like the Medieval Warm Period and the LIttle Ice Age or to ignore the 1938 recent warm peak and only focus on 1978 on so that 1038 is left out. Or they cobble the data with value added to create warming on paper.
Or do not adjust the data to account for obvious error bias. Just recently a data set from a site, in Texas I believe, was known to have a serious warm bias due to siting problems. The data handlers were told to include the data without adjustment—of course, the result showed warming. The contention is that the urban heat island effect is too small to be a problem, but it can easily be shown that rural sites do not show the warming shown by the urban sites, a significant different is involved.
Of course, then Trenberth quotes that oh so scientific IPCC report that concludes that all climate change is due to humans. It’s a political statement and he thinks it’s scientific? Check. He’s not a scientist.
I thought Trenberth was still out there chasing that “missing” ocean heat content. How does he have time to write stuff like this?
I have serious problems with discarding the standard null hypothesis to match the “consensus view” of AGW. Not only does it stand centuries of science on it’s head, but also because they blame greenhouse gases, specifically CO2, for AGW. Once you concede that AGW is real, that opens the door for the various anti-carbon schemes – carbon trading, carbon taxes, decarbonization, mega-engineering projects and the wholesale replacement of inexpensive, reliable hydrocarbon energy with very expensive, unreliable green energy.
I have no doubt humans have changed the climate somewhat, not through GHG emissions but through deforestation and land-use changes. I also have no doubt that much of the warming is overstated, primarily because of bad data, bad methodology, poor quality control and a gross underestimation of the UHIE on the land station data. But if you turn the null hypothesis back-asswards, discovering the truth will never happen.
R. Gates once complained that skeptics have no answers. First of all, that wasn’t a question. More importantly, our focus on the GHG boogeyman is keeping us from looking at other possible causes. We will never find the answers as long as we keep looking in the wrong place.
Abdul Abulbul Amir says:
November 3, 2011 at 10:29 am
It seems obvious that since humans of long ago learned to use fire and increase the amount of soot in the air that there has been some impact on climate. The only real question is the degree of that impact. The alarmist view is that impact is substantial and a disaster in the making. The skeptic view is that since there has been no climate change observed that is at odds with historical variability, the alarmist case is not only unproven, but suspect.
________________________________________
If we make the Assumption that Human Soot production has effected the climate during the entire Holocene, what do the charts of temperature tell us?
140K years of temp data from Vorstok. Holocene is on the left Eemian on the right. http://3.bp.blogspot.com/_cHhMa7ARDDg/SmDoZBIkB3I/AAAAAAAABAc/KkUzrz2abwI/s1600-h/Vostok-140Kc.jpg
Notice how nice and level the temperatures are in the Holocene
This is a close up of the last 2000 years (chart by Dr. Spencer): http://www.drroyspencer.com/library/pics/2000-years-of-global-temperature.jpg
The temperature varies plus/minus 0.6C where the Vorstok graph shows a 10C variation and the Eemian ~2.5C variation.
I have just PROVED that humans keep the temperature constant with in plus/minus 0.6C /sarcasm>
…said Professor Myles Allen from Oxford University, “but Curry’s counter proposal to abandon hypothesis tests is worse. …..”
.. because many of us climate scientists might lose our government funding and our children would go hungry. These bully conservatives are trying to take the food out of their mouths. Please, save my starving children from them! Help! Help!
Ugh! Trenberth gets an “F” in the graduate research course I used to teach. Obviously, he has no concept of what a “Null Hypothesis” is, much less how to word it or how to go about rejecting it. AGW is unraveling because it was never anything more than a theory, backed by a lot of delusional computer models that have never been proof of anything!
This insanity is all explained by the fact that Trenberth and many of his cohorts, are becoming desperate as real world data and observation continue to elude the predictions of the models. As the practice of science goes, the behavior of these AGW proponents is pathetic and disgraceful.
Trenberth is a totalitarian. eom
Maybe there are few who would go so far as to say, humans have had no effect on the climate. Reversing that as a null hypothesis could even make some sense.
But that is NOT THE hypothesis.
The hypothesis IS that human influence on the climate has and will continue to drive the climate to a catastrophic state that we already have no retreat from.
And that hypothesis is, I am afraid, total nonsense.
Myles Allen suggests that “some observed weather events will have been made more likely by human influence on climate, some less likely, and it is a legitimate and very important field of scientific enquiry to work out which are which.”
He appears to conclude that some – if not all – weather events are somehow affected by human activity, but then offers no clear explanation as to how he arrives at this kind of conclusion. This kind of position first demands clear evidence to back up the existence of human contribution.
Add to this, there is no stated means of distinguishing between which events are made “more” or “less” likely due to human activity, or what type of human activity is at the source – which makes the entire assertion rather useless.
The onus is on those claiming human causation to show a clear evidence of of that causation – evidence that would clearly distinguish asserted “human influence” and any resulting effects from any and all natural variations and their resulting effects. It goes without saying that such a position would first require a clear understanding of all elements that contribute to natural climate variation and all the resulting alteration to weather patterns – both past and present. Without this in place, there will always be a very high risk of error when attempting to assign human origins to any specific (or assumed) influence or change.