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Duelling models

Climate models eh? If nothing else, they are at least the cause of some wonderfully convoluted arguments among climate scientists as they pore over the outputs like psychics gazing at the tea leaves in a saucer.

Recall, if you will, the story over the Sahel. GWPF put out a briefing pointing out that earlier claims that global warming was going to lead to perennial drought there were nullified by a long period of greening. This led to a cod debunking from Desmog, but later to a paper by Dong and Sutton, which claimed, on the basis of a GCM study, that the greening was in fact caused by greenhouse gases (background here).

The latest development is a new paper (£) by Alessandra Giannini of the Earth Institute at Columbia, which critiques Dong and Sutton. Her case is that there is a well-established link between sea-surface temperatures and Sahelian drought:

The generalized warming of the oceans attributed to GHGs, that emerged around 1970, is understood to have exacerbated drought persistence in the 1970s and 1980s3,7,8.

and because Dong and Sutton's computer model doesn't reproduce this link in its hindcast it is not to be trusted:

[O]ne reason why the model used by Dong and Sutton emphasizes the direct effect of GHGs may be its underperformance in reproducing the effect of historical SST on Sahel rainfall. Testing the version of this model made available in CMIP5 finds it does not reproduce the conclusion of SST influence reported in the literature (see refs 3,13, for example) that provides the scientific basis
for seasonal prediction.

Amusingly, the alleged underperformance is highlighted by means of comparing its hindcast, and that of a multimodel mean, to observations.

The multi-model ensemble mean correlation with observations is 0.46, significant at the 5% level. The correlation of the single simulation with HadGEM2 (solid orange line) is 0.30, not significant at the 5% level.

Perhaps a statistician might like to comment on how much weight we should put on a correlation of 0.46 as compared to one of 0.3, particularly in an autocorrelated time series.

So when we learn from reference 3 - also by Gianniani - and reference 13 that the "understood" link between sea-surface temperatures and the Sahelian drought is based on a computer modelling studies in which ocean temperatures were tweaked to see the effect on Sahelian rainfall, all we can do is stand in open-mouthed disbelief.

As everyone knows, climate models are barely capable of doing rainfall, and even less so at a regional level. Yet, if I understand correctly, Giannini is arguing that Sutton's model is wrong (a) because it doesn't reproduce things that other models do and (b) because its hindcast is marginally further away from the observations than the multimodel mean.

Is anyone actually convinced by this?


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Reader Comments (10)

The only conclusion to draw is that you get funded and published easier if you involve manmade greenhouse gases somehow. For once, Wikipedia is more even-handed...

"The Sahel drought was a series of historic droughts, beginning in at least the 17th century affecting the Sahel region, a climate zone sandwiched between the African Savannah grasslands to the south and the Sahara desert to the north, across West and Central Africa. While the frequency of drought in the region is thought to have increased from the end of the 19th century, three long droughts have had dramatic environmental and societal effects upon the Sahel nations. Famine followed severe droughts in the 1910s, the 1940s, and the 1960s, 1970s and 1980s, although a partial recovery occurred from 1975-80. While at least one particularly severe drought has been confirmed each century since the 17th century, the frequency and severity of recent Sahelian droughts stands out. Famine and dislocation on a massive scale—from 1968 to 1974 and again in the early and mid-1980s—was blamed on two spikes in the severity of the 1960-1980s drought period.[1] From the late 1960s to early 1980s famine killed 100,000 people, left 750,000 dependent on food aid, and affected most of the Sahel's 50 million people.[2] The economies, agriculture, livestock and human populations of much of Mauritania, Mali, Chad, Niger and Burkina Faso (known as Upper Volta during the time of the drought) were severely impacted. As disruptive as the droughts of the late 20th century were, evidence of past droughts recorded in Ghanaian lake sediments suggest that multi-decadal megadroughts were common in West Africa over the past 3,000 years and that several droughts lasted far longer and were far more severe.[3][4]".

The references behind this are quite interesting and strongly suggest that both these new papers are just plain wrong because neither natural variation nor rather more direct intervention from humans can be ruled out. I don't know how you can stand to read such dreck. At any mention of statistical significance I reject any paper.

Aug 28, 2015 at 11:06 AM | Unregistered CommenterJamesG

Notwithstanding that using frequentist stats on pseudo-Bayesian models is not justifiable...

Aug 28, 2015 at 11:08 AM | Unregistered CommenterJamesG

Is anyone actually convinced by this?
Of course. All those who wish to be.
"All models are wrong but some are useful" — useful for telling the story you want people to hear. Let us all sit back and enjoy the show. Gianniani is just one more in an increasingly long line of papers written either to reinforce the meme ahead of Paris or to limit any doubt that might creep into the minds of the faithful who see possible contradictions emerging.
Truth and accuracy are no longer of any importance and the writer will do whatever is necessary to see that the message conveyed is the "correct" one.

Aug 28, 2015 at 11:13 AM | Registered CommenterMike Jackson

The climate obsessed rely on circular arguments such as Dr. Alessandra Giannini's as a matter of course.

Aug 28, 2015 at 12:17 PM | Unregistered Commenterhunter

Is anyone actually convinced by this?

I'm sure if Gavin and friends are not convinced, they won't come to tell it; rather they'd just be on message. The science is settled, after all.

The major problem with climate science is not only crappy science, it is the mood of 'we against them', tribalism as Curry puts it out. It is OK to note there is a huge amount of bad science in circulation. It is just that some people do not like anybody mentioning uncertainty outside closed workshops and conferences.

Not telling the real uncertainty gives a lot of room for Hansen, Gore, Cook and other climate activists / pests who live from the gullible, young, educated good-doers.

Aug 28, 2015 at 12:56 PM | Unregistered CommenterHugh

Is there some form of computer model designed to assess the accuracy of computer models?

None of the models predicted the pause/halt/slowdown/cessation in global warming. Is this because they were programmed by climate scientists who did not think that anything other than warming was possible?

In a housing boom, no one is paid to predict the next crash, for fear of triggering the next crash. Global temperatures are allegedly controlled by humans, so why do global warming alarmists only wail about excess heat? They ought to be celebrating the lack of warming, not bemoaning the fact they can't find any.

Or are climate models just controlled to produced the results required by climate scientists, thus rendering them all, climate scientists and their equally useless models, unfit for any purpose?

Aug 28, 2015 at 2:17 PM | Unregistered Commentergolf charlie

It really matters not a fig what these two GIGO models say. What matters is the reality on the ground- routinely ignored by "modellers" running around in their make-belief play-pens.

The fact of the matter is the sahel is greening (see these images

This greening is most likely due to increased atmospheric CO2 increasing the plants' water use efficiency, allowing colonisation of areas previously too arid,

Not bad for a molecule classed as a pollutant by the EPA.

Aug 28, 2015 at 3:07 PM | Unregistered CommenterBitter&Twisted

"...Not bad for a molecule classed as a pollutant by the EPA." --Bitter&Twisted

The EPA should know pollutants. After all, they are one.

Aug 28, 2015 at 7:51 PM | Unregistered Commenterjorgekafkazar

" paper (£) by Alessandra Giannini of the Earth Institute at Columbia, which critiques Dong and Sutton. Her case is that there is a well-established link between sea-surface temperatures and Sahelian drought:

The generalized warming of the oceans attributed to GHGs, that emerged around 1970, is understood to have exacerbated drought persistence in the 1970s and 1980s3,7,8."

Great way to start science research. Base one's research upon an assumption described in other research; in other words, base an assumption upon an assumption.

When one builds upon a foundation of shifting sand, one should not be surprised when the house of cards blow away.

Warming SST should cause higher evaporation over the ocean allowing the ocean winds to carry greater moisture.

When warm moist winds rise in elevation or hit cooler air masses, warm air forms clouds that usually leak.

When warm moist winds are cooled during nighttime temperature drops, a heavy dew forms. In many desert areas this moisture is a primary plant nurturing form aqueous solution.

Amongst my meager collection of orchids are some rupicolous, literally rock dwelling, Laelia species. Most of these rupicolous plants are succored in nature by night time dew and thoroughly dessicated during daytime full sun and dryness. These orchids, unlike many other orchids, greatly benefit from a thorough misting at dusk and dawn.

Warm moist winds condensing at night should definitely be good for desert areas.

A cooling world and SST will probably drench current desert areas causing gradual and perhaps drastic changes to formerly very dry areas.

When the Sahara was last a lush green land, the world was very chilly. Assumptions, are that this was caused by location changes in the various jet streams. Specific explicit cause(s) for jet stream relocation are unproved and therefore open to wide discussion.

But a warmist doesn't need proof, for proof does not matter in a world that should be warming. What ifs built upon what preferred ifs are great for obtaining research dollars.

Aug 29, 2015 at 5:45 PM | Unregistered CommenterATheoK

Working paper WP61 from the UK Tyndall Centre in 2004 had an interesting account of climate history in Africa:

Long term perspectives and future prospects, Nick Brooks, Saharan Studies Programme and Tyndall Centre for Climate Change Research, School of Environmental Sciences, University of East Anglia

“Long-term climatic and environmental change in the Sahel is associated with variations in the strength and position of the African Monsoon. At the last glacial maximum (LGM) some 21 thousand years ago (ka), the Sahara desert covered a much larger area than at present, as apparent from the dating of fossil dunes some 5° south of the present extent of mobile dunes (Talbot, 1983).

“Over the past 1.65 million years, approximately corresponding to the Quaternary period, there have been some seventeen glacial cycles, each lasting approximately 100ka (Goudie, 1992). Evidence from lake sediments in the central and southern Sahara indicates a succession of arid and humid episodes broadly coincident with glacial and interglacial periods respectively (Kowalski et al., 1989; Szabo et al., 1995; Cremaschi, 1998; Martini et al., 1998).”

“On multi-millennial timescales, shorter than those represented by the 100ka glacial cycles, monsoon dynamics are modulated by the Earth’s 21ka precessional cycle, which determines the angle at which the Earth’s axis is inclined to the plane of the ecliptic (the plane in which the planets orbit the sun) (Kukla and Gavin, 2004).”

“When this angle is large, the northern hemisphere is inclined more steeply towards the sun in summer, resulting in increased solar insolation or heating of the Earth’s surface, and a larger differential heating between the northern hemisphere land masses and the oceans, which intensifies the global monsoon system.

When the angle of inclination of the Earth’s axis is small, boreal summer heating is reduced and the monsoon system is weak. The 21ka and 100ka cycles interact, and an increase in boreal summer insolation is believed to have contributed to the process of deglaciation after the Last Glacial Maximum (LGM) (Goudie, 1992).

By around 10ka, maximum inclination had been reached, resulting in an increase in incident solar radiation at the Earth’s surface associated with intensified monsoon activity throughout the northern hemisphere subtropics (Tuenter et al., 2003).”

I suppose we have to ask the question, “what effect does anthropogenic CO2 have on the angle of inclination of the Earth’s axis?”

Aug 30, 2015 at 5:50 PM | Registered Commenterdennisa

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