Occam's Razor and Climate Change

The simplest explanation is usually the correct explanation

Guest essay by Eric Worrall

Professor Keven Trenberth once campaigned for the scientific world to accept the alarmist view of climate change as the “null hypothesis”, the baseline theory against which all other theories must be measured.

http://wattsupwiththat.com/2011/11/03/trenberth-null-and-void/

The reason Trenberth faced an uphill battle to have his view accepted, and ultimately failed, is that the simplest explanation of contemporary climate change does not involve Anthropogenic CO2.

As Professor Phil Jones of the CRU once admitted in an interview with the BBC, the instrumental record contains periods of warming which are statistically indistinguishable from the 1990s warming – periods of warming which cannot have been driven by anthropogenic CO2, because they occurred before humans had made a significant changes to global CO2 levels.

Between 1860 and 1880, the world warmed for 21 years, at a similar rate to the 24 year period of warming which occurred between 1975 and 1998. There was simply not enough anthropogenic CO2 in the atmosphere to have driven the 1860s warming, so it must have been driven by natural variation.

warming_periods

So how does Occam’s Razor apply to this observation? 

According to the definition in Wikipedia, the principle of Occam’s Razor states “that among competing hypotheses, the one with the fewest assumptions should be selected. Other, more complicated solutions may ultimately prove correct, but—in the absence of certainty—the fewer assumptions that are made, the better.”

From Wikipedia, the reason why Occam’s razor is important:

“To understand why, consider that, for each accepted explanation of a phenomenon, there is always an infinite number of possible, more complex, and ultimately incorrect alternatives. This is so because one can always burden failing explanations with ad hoc hypothesis. Ad hoc hypotheses are justifications that prevent theories from being falsified. Even other empirical criteria like consilience can never truly eliminate such explanations as competition. Each true explanation, then, may have had many alternatives that were simpler and false, but also an infinite number of alternatives that were more complex and false. However, if an alternate ad hoc hypothesis were indeed justifiable, its implicit conclusions would be empirically verifiable. On a commonly accepted repeatability principle, these alternate theories have never been observed and continue to not be observed. In addition, we do not say an explanation is true if it has not withstood this principle.

Put another way, any new, and even more complex theory can still possibly be true. For example: If an individual makes supernatural claims that Leprechauns were responsible for breaking a vase, the simpler explanation would be that he is mistaken, but ongoing ad hoc justifications (e.g. “And, that’s not me on film, they tampered with that too”) successfully prevent outright falsification. This endless supply of elaborate competing explanations, called saving hypotheses, cannot be ruled out—but by using Occam’s Razor.”

Source: http://en.wikipedia.org/wiki/Occam’s_razor

In other words, if we reject the principle of Occam’s Razor, we open the door to accepting theories of arbitrary, ultimately infinite complexity. A theory created by researchers who do not accept the principle of Occam’s Razor cannot be falsified, because the theory can always be tweaked in arbitrary ways to avoid falsification.

So why does applying the principle of Occam’s Razor force us to reject the theory that anthropogenic CO2 is the main driver of contemporary climate change? The reason is that nature has produced periods of warming similar to the recent warming, without any significant contribution from Anthropogenic CO2.

So we have two competing hypothesis for what is driving contemporary climate change:-

1. Observed natural variation, which has produced periods of warming statistically indistinguishable from the warming which ended in 1998.

2. Observed natural variation + an unproven assumption that Anthropogenic CO2 is now the main driver of Climate Change.

Clearly the second hypothesis fails the test of Occam’s Razor. In the absence of compelling evidence that anthropogenic CO2 has overridden natural variation, we have to accept hypothesis 1 – that observed climate change is the result of natural variation.

The climate is not hotter than it was in the past, periods such as the Holocene Optimum, or looking further back, the Eemian Interglacial. The warming which ended in 1998 was not faster, or of significantly longer duration, than similar natural warmings which occurred in the recent past.

Nothing about the current climate is outside the bounds of climatic conditions which could reasonably be produced by natural variation – therefore, according to the rules of science, we have to reject hypothesis which unnecessarily embrace additional unproven assumptions, unless or until such assumptions can be tested and verified, in a way which falsifies the theory that natural variation is still in the driver’s seat.

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Martin

From the article that Eric Worrall linked to:
D – Do you agree that natural influences could have contributed significantly to the global warming observed from 1975-1998, and, if so, please could you specify each natural influence and express its radiative forcing over the period in Watts per square metre.
“When considering changes over this period we need to consider all possible factors (so human and natural influences as well as natural internal variability of the climate system). Natural influences (from volcanoes and the Sun) over this period could have contributed to the change over this period. Volcanic influences from the two large eruptions (El Chichon in 1982 and Pinatubo in 1991) would exert a negative influence. Solar influence was about flat over this period. Combining only these two natural influences, therefore, we might have expected some cooling over this period.”
And instead of cooling from 1975-1998 we saw warming, which was clearly caused by Anthropogenic CO2 seeing that natural influences during that period had a cooling effect!

AKSURVEYOR

@ Martin
Ha ha ha, you just proved his point about occams razor ‘However, if an alternate ad hoc hypothesis were indeed justifiable, its implicit conclusions would be empirically verifiable.’

Occams razor doesn’t apply to climate science. For example, in a stunning example of convoluted eco-logic Joeri Rogelj et al[1] argues that the more complicated and uncertain the science becomes, the more urgently we need to take drastic action to reduce emissions.
“In conclusion, in light of the large uncertainties that still exist, the lack of consensus across different studies and lines of evidence, and the weak constraint that the observations provide, we argue that the possibility of lower values for ECS and TCR does not reduce the urgency for climate mitigation. On the contrary, a risk-averse strategy points to more ambitious reductions compared to what countries presented so far.”
Objections overruled. Simples.
[1] http://iopscience.iop.org/1748-9326/9/3/031003/article

Konrad

Trenberth demanding that the null-hypothesis be reversed in the case of the unproven radiative global warming hypothesis was one of those “how low can they go?” moments in climate “science”. But there have been so, so many…A veritable litany of shame.

Martin says: at 12:28 am
And instead of cooling from 1975-1998 we saw warming, which was clearly caused by Anthropogenic CO2 seeing that natural influences during that period had a cooling effect!
—————————————————–
So the natural non-anthropogenic CO2 had a cooling effect?

Perry

And yet since 1998, even with the increase of CO2 continuing, there has been no significant increase in warming. Just because someone wrote that warming from 1975-1998 was clearly caused by Anthropogenic CO2 does not make it so. Give it another 10 winters like the most recent, the citizens USA & Canada may have voted with their feet.

Village Idiot

Martin:
You’ve entirely missed the point of the good Professors piece. Bringing stuff like data, facts and physical laws into the mix, just making it more complex.
Let me try to again explain the simple beauty of the argument:
It’s been as hot or hotter as it is now during the last millions of years (without human emissions) therefore humans have no influence on climate now.
Try a bit harder. It’s really just a matter of faith 😉

Old'un

Martin at 12.28 am
– I am so relieved to learn that there are only two natural influences that could possibly affect global temperature. That makes everything so much simpler!
Great post Eric Worral – thank you

Clearly caused? On what planet? Not this one, which has thousands of natural influences…

dragineez

Uh, a non-scientist neophyte here, but I just haven’t bought into the entire idea that’s there is any such thing as a “global average temperature”. When discussing glowball warming with those that have never really examined the issue I always point out the fallacy of averaging things that are not measured. The entire point of this post is to accede to the warmunists that nonsensical arithmetic masturbation has meaning.
Well, that’s my take on it anyway.

Ben

Martin says 12:28 am:
“And instead of cooling from 1975-1998 we saw warming, which was clearly caused by Anthropogenic CO2 seeing that natural influences during that period had a cooling effect!”
Yes and you insist that Leprechauns did in fact tamper with the film.
Natural influences include ALL natural influences, including uncertain influences, and possibly unknowns influences, as well as poorly understood natural influences. Natural influences did it then, and could be doing it now and that is the simplest explanation.
It seems to me that you have reinforced the point of the blog, and the need for Occam’s Razor as an important tool in science. Otherwise you will need to prove that the influences you name are completely understood in their entirety, that they are the only natural factors that have any influence, and that when combined they do indeed influence the climate in the direction you claim, without any other influences on the climate other than Anthropogenic CO2. I suspect that nature is much bigger and less understood than you think.

Henry Clark

Presentations against the “null hypothesis” tend to, in subtle implicit steps:
Step 1) focus on a stated fingerprint of human influence
Step 2) then spin around to act like it was responsible for all of around 0.6 degrees Celsius net warming over the past century compared to a cold part (the early 20th century), rather than how even total average temperature rise (let alone that from human influence alone) was far less, if any, compared to the late 1930s in non-rewritten data
Step 3) then spin around to pretend it will cause an order of magnitude more (several degrees) this century
But, while misrepresenting the history of natural forcings versus temperature is possible in text and in “adjusted”-data plots, otherwise a dominant influence of natural albedo change is blatant and fits history: from the MWP & LIA, to the warmth in the mid 20th century, to the 1960s-1970s global cooling scare, to the later global warming scare, and the subsequent “pause.” That can be seen in my usual http://tinyurl.com/nbnh7hq illustration.

Mindert Eiting

Interesting to see the significances in the table. You throw a coin and look for series of heads-only. And yes, those series are ‘significant’. Should we believe that the coin became biased in those short series or should we conclude that some statistical principles are violated?

Steve Case

Between 1860 and 1880, the world warmed for 21 years,
Hmmm, I’d say from 1850 to 1878, and who knows before 1850?
But then:
The 33 year period from 1878 – 1911 -0.6C° of cooling CO2 up  5 ppm
The 33 year period from 1911 – 1944   0.7C° of warming CO2 up 15 ppm
The 33 year period from 1944 – 1977 -0.4C° of cooling CO2 up 30 ppm
The 33 year period from 1977 – 2010   0.8C° of warming CO2 up 60 ppm
I’d say there’s a pattern in all of that, and it’s not CO2.

michel

What’s really needed is to establish the distribution of warming episodes and absolute temps, and then see if we are one or two sds north of the mean. Or if its not a normal distribution, where we are. Anyone know any study like that?

son of mulder

Occam’s Razor states “that among competing hypotheses, the one with the fewest assumptions should be selected. Other, more complicated solutions may ultimately prove correct, but—in the absence of certainty—the fewer assumptions that are made, the better.”
So then test the hypothesis ie make a prediction and check if it works out correctly. To predict one needs models, the models didn’t prove correct on the hiatus, the tropospheric hot spot etc.
Ergo hypothesis wrong.

Henry Clark

Additional note:
Unfortunately naive or careless in regard to temperature data source selection like many (most?) article writers, the article’s table incorrectly depicts 1975-2009 as if about the same rate of temperature rise as 1975-1998, so, while the source is not mentioned, it must be some extra fudged data published by the CAGW movement.
However, for instance, RSS satellite-measured global temperature went as follows since the satellites started returning data in 1979:
1979-1998 trend = +0.082 K/decade (warming)*
1998-now trend = -0.050 K/decade (cooling)**
Contrast to the article’s table!

If reading the article’s table alone, someone might assume (slightly different year start and endpoints or not) that the trend over both periods was 0.16 K/decade warming (way off).
This is, of course, repetitive if anyone has read enough of my comments over the months. But wrongness continues, so…
While my illustration is “cherry picking” 1998 in a way, the late 1990s were the turning point (for the reasons suggested in my usual http://tinyurl.com/nbnh7hq link, which are also why the mild cooling rate will become more later this decade).
* http://woodfortrees.org/plot/rss/from:1979/to:1998/plot/rss/from:1979/to:1998/trend
** (referring to 2014 up to now: http://woodfortrees.org/plot/rss/from:1998/plot/rss/from:1998/trend )

ConfusedPhoton

Ben D
If you were a climate “scientist” you would know that you have good CO2 and you have evil (fossil fuel produced) CO2. The evil CO2 leads to thermageddon, simples!
So cooling and warming are not inconsistent with AGW!

Martin
And instead of cooling from 1975-1998 we saw warming, which was clearly caused by Anthropogenic CO2 seeing that natural influences during that period had a cooling effect!
The conclusion that natural forcings should have produced a cooling effect from 1975 – 1998 implies the assumption that climate scientists have successfully catalogued all significant natural forcings, and correctly determined the magnitude of their impact on global temperature.
Considering that climate scientists can’t even pin down climate sensitivity to CO2 to a reasonably tight range of values, I am skeptical that understanding of other forcings is adequate to draw such a conclusion.

Dr. Strangelove

Steve
That pattern is PDO index. Roughly 30-year cycle matching the above warming and cooling periods. Roy Spencer studied this correlation and said 75% of 20th century temperature trend can be explained by PDO.

Between 1860 and 1880, the world warmed for 21 years,
Hmmm, I’d say from 1850 to 1878, and who knows before 1850?
But then:
The 33 year period from 1878 – 1911 -0.6C° of cooling CO2 up 5 ppm
The 33 year period from 1911 – 1944 0.7C° of warming CO2 up 15 ppm
The 33 year period from 1944 – 1977 -0.4C° of cooling CO2 up 30 ppm
The 33 year period from 1977 – 2010 0.8C° of warming CO2 up 60 ppm
I’d say there’s a pattern in all of that, and it’s not CO2.

Why, if natural cycles theories were not in such disrupt I would say you have noticed a recurring natural cycle and that might be a some sort of a clue that might lead towards the physical cause of the cycle if we studied the matter.
Or it could just be the evil, magic molecule CO2 up to its old tricks. Did you know the magic bullet of Nov. 1963 was made of CO2?

Roy

Have supporters of the consensus ever claimed that natural variation is properly understood? If not their claim that the science is settled was clearly bogus from the start – and they knew it.
On the other hand, if they really do think that natural variation is understood have they published an explanation of it anywhere on the web that could be understood by a lay person?

KNR

Trenberths’ need to demand that the null-hypothesis be reversed, was a reflection of facts increasingly going against his claims and that his arguments were so weak they could not stand up to any good review. Its was the equivalent of child answering the question why did they eat all the sweets by loudly shouting ‘because’
Any other area of science this approach would have been usual , but in climate ‘science’ its says much about the area that is was normal stuff that hardly got noticed.
I am increasingly of the view that if I wanted a nice easy PHD , climate ‘science’ is the way to go , as they seem to accept any old rubbish as long it offers unquestioning support to ‘the cause’

Frederick Davies

Great (and more importantly, clear) post.
FD

Mindert Eiting

Michael at 1.52 am. Do you mean this? Take a temperature record of many years. Randomly select with a computer program series of adjacent years of any length. Compute the slope of linear regression in those series. Make a plot of series length on the x-axis and slope on the y-axis. You will get a scatter in the size of a big triangle. In very short series you will have many extreme positive and negative slopes. In very long series the slopes will centre about zero. You can draw 95 and 99 percent confidence zones. If temperature series did not contain auto-correlation the sampling distribution of regression slopes would suffice.

lgl

Fine, but what is the ‘simplest explanation’ for the 1880-1998 rise?

Henry Clark

Clicking on the link* of Eric Worrall (the author of this article, in his name in his prior comment), he writes that those “who wrote the emails have been officially cleared of wrongdoing” and describes as “real scientists” involved with how “our tax money is spent in the pursuit of greater knowledge” while having http://www.realclimate.org as the prime suggested reading there.
More than a bit over the top.
*
https://itunes.apple.com/us/app/climategate/id386480628
Hmmm. The choice of temperature data in the article’s graphic (see my prior comment at 1:58am slightly up on this page) wasn’t necessarily a coincidence.
This reminds me of another recent WUWT article submitter, e.g. the exchange with username RichardLH in and after http://wattsupwiththat.com/2014/03/16/crowdsourcing-a-full-kernel-cascaded-triple-running-mean-low-pass-filter-no-seriously/#comment-1591709 .

David, UK

Martin says:
March 22, 2014 at 12:28 am
From the article that Eric Worrall linked to:
D – Do you agree that natural influences could have contributed significantly to the global warming observed from 1975-1998, and, if so, please could you specify each natural influence and express its radiative forcing over the period in Watts per square metre.
“When considering changes over this period we need to consider all possible factors (so human and natural influences as well as natural internal variability of the climate system). Natural influences (from volcanoes and the Sun) over this period could have contributed to the change over this period. Volcanic influences from the two large eruptions (El Chichon in 1982 and Pinatubo in 1991) would exert a negative influence. Solar influence was about flat over this period. Combining only these two natural influences, therefore, we might have expected some cooling over this period.”
And instead of cooling from 1975-1998 we saw warming, which was clearly caused by Anthropogenic CO2 seeing that natural influences during that period had a cooling effect!

Yeah, the old logical fallacy that supposes that in order for a heat source to cause a body to warm, said heat source must be continually increased. And yet even a child knows that if a pot is simmering away on a low flame, and then the flame is turned up in a single step, the pot will gain heat over some period of time afterwards, as it seeks equilibrium. The flame is “about flat over this period” and yet the pot continues to warm. Get it? If you do then you understand more than most climate scientists.

Henry Clark
Clicking on the link* of Eric Worrall (the author of this article, in his name in his prior comment), he writes that those “who wrote the emails have been officially cleared of wrongdoing” and describes as “real scientists” involved with how “our tax money is spent in the pursuit of greater knowledge” while having http://www.realclimate.org as the prime suggested reading there.
What are you saying? Are you suggesting I am some kind of climate 5th columnist, contributing to WUWT on a regular basis and publishing an app full of climategate emails and “intriguing” links as part of a secret mission to help the cause of climate alarmism?

cedarhill

Facts are not a deterrent in the warmist political campaign. After all, how many Americans under the age of 30 are not aware the Earth circles the Sun? Regardless, facts and logic are still fun things.

hunter

Trenberth was using sciencey stuff to keep the political class on board and keep the trough full for himself and his pals.
He should have known he was just arm waving. No one could be so stupid as to think reversing the null hypothesis would work over a reasonable period of time in science. Religion, yes- you have to reverse the null. Science, no.

Konrad

lgl says:
March 22, 2014 at 2:39 am
“Fine, but what is the ‘simplest explanation’ for the 1880-1998 rise?”
—————————————–
Solar activity.
Climastrologists claim that because TSI varies so little between solar cycles it can not possibly be the cause.
But climastrologist do not understand how the sun heats the oceans. Due to the mis-application of blackbody calculations to transparent materials they claim a temperature for the oceans of -18C in the absence of DWLWIR. This figure is provably incorrect. The number they were looking for is +80C in the absence of atmospheric cooling. The reason is that solar SW and UV penetrates to depth in transparent water and heating is cumulative due the the slow speed of non-radiative energy return to the surface.
While TSI only varies ~0.1% (after the solar record has been thoroughly stamped flat), it is the higher frequencies that vary most. Great variation is evident in solar UV. Some claims indicate an increase of 6% or greater since the little ice age.
And the strength of solar UV-A at 50m depth is still in the order of 10 w/m2. 50m is below the thermocline where energy can more easily accumulate over time.

RichardLH

lgl says:
March 22, 2014 at 2:39 am
“Fine, but what is the ‘simplest explanation’ for the 1880-1998 rise?”
That the temperatures followed this, apparently repeating, natural ‘cycle’.
http://climatedatablog.files.wordpress.com/2014/02/hadcrut-giss-rss-and-uah-global-annual-anomalies-aligned-1979-2013-with-gaussian-low-pass-and-savitzky-golay-15-year-filters1.png
The other ‘choice’ is that somehow Volcanos, SO2 and CO2 came together in just the ‘right’ timing and magnitude with zero lag to provide exactly the same curve.

Merrick

And, Village Idiot, the CO2 concentration *now* is so much higher than the mean 1975-1998 value and the cooling forcings conjectured are *not* as prevalent as during the 1975-1998 period, but that’s not “data and evidence” in the same manner you declare for t75-1998 period? Thermometers, qou basis?
Damn editor. Auto correcting my typing then deleting characters I’m not trying to delete again. Sorry if that last sentence or so is a bit garbled in a couple places.

AlecM

No truly professional engineer or physicist agrees with the central premise of the ‘enhanced greenhouse effect’, the assumption that the Earth’s surface emits to the atmosphere net real IR energy as if it were a black body in radiative equilibrium with absolute zero.
This juvenile mistake, predicting three times intrinsic CO2 warming, is from incorrect physics taught in Meteorology and Climate Science. It is our era’s equivalent of the 18th Century’s ‘Phlogiston’, also debunked when real scientists did real experiments. The analogy is apposite because Phlogiston was supposed to be a 5th Greek Humour, emitted from heated bodies!
However, there is too much investment in politics and careers for the principal researchers to back down despite recent work by John Christy showing that 102 of the latest climate models predict three times too high warming: http://hockeyschtick.blogspot.co.uk/2014/03/john-christy-climate-models-overcook.html
3 times too high folks: if the cap fits, Climate Alchemy, wear it……….:o)
PS the real AGW in the 1980s and 1990s was probably the aerosols from Asian industrialisation reducing cloud albedo, hence the heating of the oceans. That effect saturated about year 2000. The hiatus is probably because the atmosphere self-regulated the intrinsic CO2 effect, an evolving story I will relate at another time.

Merrick

Thermometers. Quo Vadis?

johnmarshall

I go along with that. Good post many thanks.

lgl

RichardLH
Thanks, but the ~60 yrs cycle does not explain the 1880-1998 rise (~120yrs*2 ?)

walker808

lgl says:
March 22, 2014 at 2:39 am
Fine, but what is the ‘simplest explanation’ for the 1880-1998 rise?
There has been a slow rise in temperature since the end of the Little Ice Age in the nineteenth century. Climate changes , that is the nature of the beast.

RichardLH

lgl says:
March 22, 2014 at 4:35 am
“Thanks, but the ~60 yrs cycle does not explain the 1880-1998 rise (~120yrs*2 ?)”
Indeed. First you would need to remove that shorter term ‘cycle’ from the observed figures and look at the residuals.
http://climatedatablog.files.wordpress.com/2014/02/hadcrut-15-year-ctrm-and-75-year-s-g-curves.png
The greater than 75 years trend when you do so is too short, as yet, to call for any ‘cycle’ that may be present, all we have for sure is the rising edge of some longer term function.
The only clue that I can see is that the current shorter term ~60 years ‘cycle’ is, if it is indeed a ‘cycle’, ending too early to suggest that the underlying trend is still continuing upwards. It too may well be flattening off.
The observed data is also consistent with the longer term function also being driven by natural factors, rather than having to rely on co-incidental Volcanos, SO2 and CO2.

lgl

Ok, so the ‘simplest explanation’ is some unexplained natural variation.

Don’t look now but with the new February data NCDC says 2014 is not even on pace to be a “top 10” year. With every month that goes by the alarmist’s call to The Pause (TM) gets more complex, and Occam’s call gets louder…

Harry Passfield

markstoval says:
March 22, 2014 at 2:11 am

“Or it could just be the evil, magic molecule CO2 up to its old tricks. Did you know the magic bullet of Nov. 1963 was made of CO2?”

Ahh, Mark, that’ll be the same magic molecule that managed to make the flag flutter on the moon landing! 😉

RichardLH

lgl says:
March 22, 2014 at 5:18 am
“Ok, so the ‘simplest explanation’ is some unexplained natural variation.”
Occam’s razor would say that, yes. If you look at the available data, there are natural variations which are of smaller/similar magnitude. From everything above Annual and upwards. At 2, 3, 4 and 12 years below 15 years and on to ~60 years as well. Why would it need some other explanations for the longer series?

Steve Case

Dr. Strangelove said at 2:06 am
… That pattern is PDO index. Roughly 30-year cycle matching the above warming and cooling periods. Roy Spencer studied this correlation and said 75% of 20th century temperature trend can be explained by PDO.
And it needs to be stated more often. Repetition is a technique that works.

Village Idiot

@ lgl
You’ve got it in a nutshell. What we are best at here in the Village is sniping at climate scientists and their explanations – not necessary to explain anything ourselves

lgl

Richard
It wouldn’t, but natural variation is just a description, not an explanation imo. You have to explain how.

Kristian

Konrad says, March 22, 2014 at 3:13 am:
“lgl says:
March 22, 2014 at 2:39 am
“Fine, but what is the ‘simplest explanation’ for the 1880-1998 rise?”
—————————————–
Solar activity.”

Konrad,
lgl has been presented with this answer a multitude of times. He still ignores it. You can see it in the way he chooses to give his reply to RichardLH only, not to you. Deep down inside he knows your answer is the correct one. That’s why he systematically avoids addressing it. “No! It’s the CO2 what done it! It has to be!”
On a slightly different note, the ‘solar pond’ shows us pretty well how quickly and efficiently solar heat stores up in water that is not allowed to convectively/conductively cool. In reality the cooling of course happens at the surface and primarily through evaporation, but the principle stands. Thermal radiation alone could not adequately cool the oceans being heated by the sun. Not until they got really hot, close to boiling.
http://en.wikipedia.org/wiki/Solar_pond

Kirk c

Lgl: It wouldn’t, but natural variation is just a description, not an explanation imo. You have to explain how.
It is an explanation….. but you forgot the original question.
Q: “Why is there warming in the late twentieth century”?
A: it’s part of a long term natural variability.
Q: what causes the natural variability?
A: Not sure exactly. But we can rule out short term human causes ..so keep looking.

Tom in Florida

Occam’s Razor does NOT say “The simplest explanation is usually the correct explanation”.
The principle states that “Entities should not be multiplied unnecessarily.”
Two different concepts.
The most useful statement of the principle for scientists is:
“when you have two competing theories that make exactly the same predictions, the simpler one is the better.”
Simple example:
1 + 1 = 2, there is no need to say (5-4) + (6-5) = 2
Both are correct but the first is the simpler one and better to use.
Occam’s Razor is often used incorrectly by those who do not understand it or by those who know better and are trying to justify something that isn’t true. Incorrect usage of the principle immediately sets off my sceptic alarm.