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# Scientists have been puzzled by the seeming disparity between models

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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
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Passage breakdown

In the first paragraph, the author introduces a disparity and one explanation for that disparity:

• The disparity: the world isn't warming up as much as global warming models predicted.
• Michaels first thought that sulfate cooling could explain this disparity, but he later rejects this explanation.
• Currently, Michaels explains the disparity by saying that the models were wrong.

In the second paragraph, the author discusses an opposing explanation for the disparity:

• Santer disagrees with Michaels' conclusion that the models were wrong.
• Santer thinks that Michaels was partially correct about sulfate cooling, and also argues that the location of the oceans impacts warming.

For more on the process of breaking down RC passages, check out this article and our live RC videos.

Explanations for individual questions

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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
For question 3

I chose C.

I believe A and C fundamentally say the same thing.

"Scientists have been puzzled by the seeming
disparity between models of global warming based on
greenhouse gas emissions and actual climatological
data. "

"Thus, Santer
disputes Michaels’s claim that model predictions and
observed data differ fundamentally."

option C " Whether disparities between global warming models and climatological data can be detected"
option A " Whether climatological data invalidates global warming models".

I am perplexed as to how C could be wrong.
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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
For question 1, I don't understand why D is wrong? Can anyone help me with an explanation ?
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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
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Hi - can someone please help on the following queries

1 -- i dont understand why B is OA......

We read in the paragraph that Michaels did not even believe in sulfate cooling ...so how can we know if Michaels believed sulfate cooling is a short term phenomena when Michaels didnt even believe in the subject of sulphate cooling in the first place ?

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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
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Hello GMATNinja GMATNinjaTwo

The passage suggests that, in the early 1990s, Michaels would have been most likely to agree with which of the following statements about the disparity mentioned in lines 3-4?

A. This disparity is relatively less extreme in the Northern Hemisphere because of sulfate cooling.
B. This disparity is only a short-term phenomenon brought about by sulfate cooling.
C. This disparity is most significant in those parts of the world dominated by oceans.
D. The extent of this disparity is being masked by the temporary effect of sulfate cooling.
E. The disparity confirms that current models of global warming are correct.

For the above question, I was torn between B and E

Quote:
In the early 1990s, Pat Michaels sought to explain this disparity, suggesting that sulfate emissions in industrial areas had a cooling effect, thus temporarily retarding global warming

Michaels explained that the disparity is caused by sulphate cooling. In other words this would also mean that the global warming models could be/are correct. Is my understanding correct here?

I eliminated E because I thought Michaels would "more likely" agree with the point given in B than the point given in E. If we didn't have option B, would option E be correct then?

Waiting to hear back from you. Thanks
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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
jabhatta@umail.iu.edu wrote:
2-- why is A wrong over D please ......can some one

My thoughts below on this

Santer tells us that oceans are warmed more slower than lands are warmed . Does it say that oceans have a cooling effect? No it doesn't it. Read the below line

Quote:
Santer contends that, in general, global warming occurs more slowly in the south because this hemisphere is dominated by oceans, which warm more slowly than the landmasses that dominate the Northern Hemisphere

Also santer overall doesn't say anything regarding which hemisphere will heat faster. Nothing can be inferred. Rather he just disagrees to both the points michaels made i.e.
1. Sulphates didn't have a cooling effect
2. The model estimates are incorrect

Hope this helps
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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
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Question 1

pikolo2510 wrote:
Hello GMATNinja GMATNinjaTwo

The passage suggests that, in the early 1990s, Michaels would have been most likely to agree with which of the following statements about the disparity mentioned in lines 3-4?

A. This disparity is relatively less extreme in the Northern Hemisphere because of sulfate cooling.
B. This disparity is only a short-term phenomenon brought about by sulfate cooling.
C. This disparity is most significant in those parts of the world dominated by oceans.
D. The extent of this disparity is being masked by the temporary effect of sulfate cooling.
E. The disparity confirms that current models of global warming are correct.

For the above question, I was torn between B and E

Quote:
In the early 1990s, Pat Michaels sought to explain this disparity, suggesting that sulfate emissions in industrial areas had a cooling effect, thus temporarily retarding global warming

Michaels explained that the disparity is caused by sulphate cooling. In other words this would also mean that the global warming models could be/are correct. Is my understanding correct here?

I eliminated E because I thought Michaels would "more likely" agree with the point given in B than the point given in E. If we didn't have option B, would option E be correct then?

Waiting to hear back from you. Thanks

Quote:
Michaels explained that the disparity is caused by sulphate cooling. In other words this would also mean that the global warming models could be/are correct. Is my understanding correct here?

In the early 1990s, Michaels thought that sulphate cooling might EXPLAIN the disparity between the models and the actual climatological data. This explanation doesn't make the disparity go away. The models do not match the data, so the models are not accurate (hence, there is a disparity). In other words, because there is a disparity between the models and the actual data, the models must not be correct, and choice (E) must be eliminated.

jabhatta@umail.iu.edu wrote:
3 -- Eliminated A because i dont think anywhere in the passage, the author talks about climatological data being better than global warming models -- where is this said ? hence i selected E ..

please let me know where am i going wrong

The data represent what is actually happening. The models represent what was PREDICTED to happen. If the actual data does not match what was predicted by the models, then this suggests a flaw in the models (invalidating the models).

Originally posted by GMATNinja on 29 Sep 2017, 15:39.
Last edited by GMATNinja on 15 Dec 2021, 08:49, edited 3 times in total.
Edited typo.
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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
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https://www.newscientist.com/article/mg ... ouse-wars/

FEATURE 19 July 1997
Greenhouse wars
By Fred Pearce

PAT MICHAELS, a belligerent sceptic about global warming, is in ebullient mood. “The truth is that what we sceptics say is always pilloried by the climate modellers, and then adopted as their own five years later. That would make a good theme for your article.”

Michaels, a climatologist at the University of Virginia, is convinced that the tide is about to turn in his favour, and that the efforts of the mainstream climate modellers, stalwarts of the UN’s Intergovernmental Panel on Climate Change (IPCC), are about to collapse under the weight of their own inconsistencies. “They can’t go on forever tinkering with their models, trying to make them fit reality. Ever heard of Ockham’s razor? It says the simple explanation is usually the best. Apply that in this case and you conclude that the climate just is not as sensitive to the greenhouse effect as they predicted.”

So what exactly is the problem for the climate modellers? Well, something strange has happened to global warming. For almost twenty years, while temperatures at ground level round the world have continued to rise inexorably, the warming has failed to penetrate the atmosphere. In wide areas some three kilometres above Earth, the atmosphere has actually been cooling. This is not what is predicted by the computerised climate models on which all estimates of global warming depend. They all say the warming should spread right through the troposphere, the bottom ten kilometres or so of the atmosphere.

Global warming sceptics have spent almost a decade challenging some of the basic tenets of the climate models. Ever since global warming became headline news in the late 1980s, they have been complaining that the prevailing view is skewed and overstates the problem. Their prime motivation seems to be indignation, coupled with a maverick instinct to buck the latest fashion. But they have also managed to secure some lucrative lecturing fees and consultancy deals with commercial concerns – such as the coal industry – who are anxious to undermine international efforts to control emissions of greenhouse gases such as CO2.

It is a year this month since the US’s under-secretary of state Timothy Wirth castigated the sceptics at a UN climate conference. They were “bent on belittling, attacking and obfuscating climate change science”. But the stubborn failure of most of the troposphere to warm continues to hearten the greenhouse outlaws. Are they right? Has the climatic apocalypse been postponed? Are the modellers on the run from reality?

On a tour of some of the main players, you dodge a constant crossfire of personal and professional abuse. In his home near Boston, the sceptics’ guru Dick Lindzen, a meteorologist from the Massachusetts Institute of Technology, accused the IPCC of being dominated by “guys from the bottom of the heap, such as geographers”.

Back in Virginia, Michaels slams the IPCC scientists for manipulating data, then settles into an explanation of how the key to Vice-President Al Gore’s challenge for the presidency next time round will be corrupt environmental journalists who he will use to peddle a fraudulent version of climate change.

In the greenhouse wars, the battle is bloody and many a good scientist has been conscripted by both sides. Take John Christy. For ten years he was a Baptist minister in Kenya before he took up science. Now, as professor of atmospheric science at the Global Hydrology and Climate Center, part of the University of Alabama in Huntsville, he catalogues data from satellite instruments operated by the US government’s National Oceanic and Atmospheric Administration (NOAA).

Since 1979, long before global warming was an issue, NOAA’s instruments have been measuring microwave radiation released by the atmosphere. The radiation comes largely from oxygen molecules, which release more as they warm, giving an overall picture of temperatures in the troposphere. So far, and in stark contrast with the ground-based meteorological stations, the satellites have apparently picked up little evidence of warming.

Naturally, the sceptics have adopted Christy’s data to suggest that global warming is a myth. In response, collectors of ground-based data have hit back. Jim Hansen, the NASA climate modeller who first put global warming onto the front pages back in 1988, claims that if the satellites can’t see evidence of warming “there’s something wrong with their data”.

Both are wrong, says an exasperated Christy. First, his short time-series – just 18 years – is skewed by warming at the start, caused by a short-term natural warming in the Pacific, and by cooling towards the end, from the eruption of Mount Pinatubo in the Philippines. Filter out those effects and he reports “a very slight warming trend”. But most importantly, says Christy, “the satellites don’t measure surface temperatures, but average temperatures through the troposphere”. Thus the surface and satellite data complement rather than contradict. Put them together, he says, and they show that the surface of the planet is warming, but the bulk of the troposphere, the so-called free troposphere, is not.

Ups and downs
Add archive data from weather balloons recently assembled at the British Meteorological Office by David Parker, another assiduous and independent-minded data-cruncher, and something even more surprising emerges. From the early 1960s to the late 1970s, there was strong warming in the free troposphere, at a time when the surface was cooling slightly. Then everything switched: the surface warmed strongly while at 1.5 kilometres and upward, temperatures were at least stable, if not falling.

Nobody can explain this reversal. Certainly, the temperature record of the past three decades does not match the predictions of the models, agrees Parker. In the models, the surface and the free troposphere are very closely coupled, so their temperatures should move together. But if this is right, why are the temperatures in these two regions moving in different directions? “The surface and mid-troposphere appear to be much less coupled than the models assume,” says Parker. “If the models don’t get tropospheric heating right, we are in trouble.”

After years of trying, the greenhouse sceptics finally feel that here they have found the Achilles heel in the climate models. If the models are wrong about how surface warming influences temperatures in the troposphere, they are also likely to be wrong about another fundamental feature: the movement of water vapour between the surface and the free troposphere. And that, argue the sceptics, means the models may have misrepresented, or even have invented, one of the vital mechanisms behind global warming itself: the positive water-vapour feedback.

Feedbacks are what turn the greenhouse effect from a benign curiosity into a potential apocalypse. Even sceptics agree that putting more greenhouse gases, such as CO2 from burning fossil fuels, into the atmosphere will tend to warm the planet. But even the doubling of CO2predicted for the late 21st century would only add about 1 °C to global temperatures. According to the models, however, this initial warming will be magnified by a series of positive feedbacks. In the most important of these, they predict that surface warming will increase evaporation from the oceans and push more water vapour into the atmosphere. Because water vapour is itself a strong greenhouse gas, this would amplify the effect of the CO2 – a positive feedback that might roughly double global warming.

But will it? Christy’s collaborator on the satellite data, Roy Spencer of NASA’s Marshall Space Flight Center, is doubtful. “I don’t think warming will be as big as people think,” he says. “The positive feedback theory assumes that, in practice, a warmer troposphere will actually hold more water vapour.” But he points out that if, as the satellite data suggest, the free troposphere is largely cut off from the surface, water that evaporates from the oceans will not necessarily mean more water vapour in the free troposphere.

This matters, according to Spencer, because water molecules in the troposphere could have a much bigger warming effect than ones that stay close to the surface. Higher up, the air is extremely dry, and Spencer argues that because of this, adding or subtracting relatively small amounts of water there could greatly alter the amount of heat trapped.

Not everybody agrees about the importance of the upper troposphere in driving water vapour feedbacks. One of Britain’s leading meteorologists Keith Shine, from the University of Reading, says: “The surface is at least as important here. Sure, a single molecule is more important aloft, but there are so many more molecules at the surface.”

But if Spencer is right, this would seem to pose a serious problem for the conventional view that water vapour would amplify the effect of CO2. The extra water vapour generated by warming at the surface would never make it to the regions where it could significantly increase the greenhouse effect.

Clouding the issues
And there is more. Some sceptics also argue that the complex physics of clouds could actually reduce the amount of water vapour that reaches the free troposphere – and so damp down global warming. The modellers are on weak ground in this discussion because individual clouds are too small to be modelled in any detail inside global climate models, which assume that their dynamics will be unchanged by warming.

The sceptical position here is that warming might make clouds more efficient at producing rain, leaving less water vapour behind to moisten the free troposphere. It works like this: most of the water vapour that evaporates from the oceans does not stay in the air for long. It forms clouds and quickly returns to the surface as rain. But some re-evaporates from clouds and heads off into the clear air of the free troposphere. Change the amount of water that leaves the clouds as rain, says Spencer, and you change the amount of water vapour left to re-evaporate from the clouds, and hence the amount of water in the free troposphere. ( See Diagram.

Two opposing views on the effect of water vapour on global warming.
)
This is where Lindzen comes in. Though he is highly regarded for his innate ability, Lindzen’s ideas are notoriously difficult to pin down. Colleagues complain that too few of them turn into peer-reviewed papers and too many emerge as invective in newspaper articles. Shine says: “Lindzen is painfully clever. But he keeps changing his arguments.” Even so, John Houghton, co-chair of the IPCC’s science panel, once described him as the “most serious” of his sceptic foes.

Lindzen argues vehemently that water vapour operates a negative rather than a positive feedback. He says “all the data show” that if clouds are warmer, they will turn a greater proportion of their moisture into rain. Result: less water re-evaporating from clouds, a drier free troposphere and a negative water-vapour feedback. In other words, changes in the tropospheric water vapour would compete with, not reinforce global warming caused by CO2.

Here, even some fellow sceptics back off. “It’s intriguing, but it’s a theory, that’s all,” says Spencer. “There is no actual evidence for a negative feedback.” Shine agrees. “The idea that precipitation efficiency is better in warm clouds is at best contentious. I think what is alarming us more about Lindzen’s comments is his assertion that the answer is known.”

But Lindzen’s opponents know that he is attacking them at a weak point. Evidence of a positive feedback is not overwhelming, either. The IPCC’s most recent review, its Second Assessment published in 1996, admits to serious gaps in knowledge about water vapour and concedes that feedback “remains a substantial uncertainty in climate models”.

Simon Tett, one of the Met Office’s top modellers and a leading IPCC author, agrees that recent studies suggest the positive feedback may have been overestimated. “I believe the upper troposphere is probably drier than the models suggest,” he says. Though the evidence for a negative feedback is, if anything, even weaker, the sceptics still believe things are moving their way.

Lindzen for one argues that if the models get the detail wrong, they will get the big picture wrong, too. But modellers say the proof of the pudding is in the eating. “We think there is good evidence that our models reproduce past climate change reasonably well,” says Tett. “That is good evidence that they are basically correct.”

But here too the modellers are being challenged. “The simply fact,” says Michaels, “is that even at the surface the world is not warming up as much as the modellers say it should.” Hansen agrees: “Models driven by greenhouse gases alone give warming about twice as large as observed over the past 150 years – about 1 °C rather than the observed 0.5 °C to 0.6 °C.” For recent years, says Christy, “the models suggest a warming three times what we see”.

Michaels was one of the first scientists to propose an explanation for this. In an article he wrote for New Scientistin the early 1990s, he suggested that sulphate smogs emanating from industrial areas were casting a thin pall over sufficiently large areas to mask much of the warming (“Global pollution’s silver lining”, 23 November 1991, p 40). By late 1994, modellers at the Met Office had adopted the idea and claimed that combining predictions of warming from CO2 and cooling from sulphate produced a good fit of actual climate change – a fit that persuaded John Gummer, Britain’s environment secretary of the day, to pronounce himself convinced that global warming was for real.

Yet today Michaels is a vociferous opponent of this theory. The problem is geography. Sulphate only survives a few days in the air. Since most sulphate is emitted in the northern hemisphere, its cooling influence should be largely limited to that hemisphere. So if sulphate cooling is important, Michaels says, the southern hemisphere should be warming faster than the north. Until the late 1980s, that was what was happening. But since 1987, warming has virtually ceased in the southern hemisphere – notably in the mid-latitude region between 1 and 1.5 kilometres above the surface, where warming was previously most intense – while it has surged ahead in the north.

For Michaels, that condemns the sulphate theory to the dustbin. And he scorns modellers who don’t follow his lead. One of Michaels’ most violent verbal attacks on fellow scientists is against Ben Santer of the US government’s Lawrence Livermore National Laboratory in California. In a paper in Naturelast summer, Michaels implied that Santer bolstered a claim that sulphates were cooling the planet by arbitrarily ending his analysis of temperature trends in 1987, the year the southern warming ceased. Santer’s data finished in 1987, but Michaels argues that there are other datasets that Santer could have used to extend his findings. In a subsequent letter to Nature, Michaels argued that the models and reality were diverging. “Such a result… cannot be considered a `fingerprint’ of greenhouse-induced climate change,” he claimed.

And that charge drew blood. For Santer was the main author of a key chapter in the IPCC’s Second Assessment which concluded, largely on the basis of this work, that there was “an emerging pattern of climate response to… greenhouse gases and sulphate aerosols in the climate record”. In other words, the human fingerprint could now be seen in climate change.

But is it that simple? Santer, who admits to being “troubled” by Michaels’ assault on his integrity, responds vigorously. He denies selective use of the data and says that the datasets available when he wrote his paper for the years after 1987 were not compatible with his own data. He says that the relative cooling of the southern hemisphere since 1987 does not contradict the models. In fact, the models explicitly predict it. His case is that what we are seeing is the interaction between two different effects happening on two different timescales.

Blowing hot and cold
Basically, the first effect, global warming, is bound to happen more slowly in the southern hemisphere than the north. This is because most of the southern hemisphere consists of oceans, which heat up more slowly than the landmasses which dominate the north. But the picture has been confused by the second effect, sulphate cooling, which peaked in the north in the mid-20th century. It slowed warming in the northern hemisphere so much that the southern hemisphere, oceans and all, raced ahead. But since 1987, the growing force of the greenhouse effect has reasserted itself, and the north has again taken the lead. “The contention by Michaels that model predictions and observed data differ fundamentally is simply incorrect,” says Santer.

Michaels dismisses this. He says the data actually show that the southern hemisphere is not simply warming more slowly, as Santer maintains. It has actually been cooling since 1987, which no models predict. This, he says, makes a nonsense of both the theory of sulphate cooling and the models of global warming – a double-whammy that he relishes.

And, if anything, the more recent raw data quoted by both sides tends to bear Michaels out: the past five years was more than 0.2 °C cooler on average than the previous five. But, says Tett, “that’s probably just natural variability. You can’t dismiss a 30-year warming trend on the basis of a blip at the end.” Again, the jury is out.

Meanwhile, the argument is moving on. In a paper published in Sciencein November last year, Tett added ozone depletion in the stratosphere to the equation. It has been clear for some years that ozone depletion in the stratosphere is causing cooling there. More recently, modellers have suggested that this cooling is being transmitted to the upper levels of the troposphere as well. “Between 1960 and 1995, adding ozone depletion dramatically improves the fit between reality and the model,” Tett said. This is compelling, in particular because it helps explain why the upper troposphere has failed to warm as the models first predicted.

Michaels thinks there might be something in this. But he scoffs that constant tinkering with the climate models to make them fit reality is deeply unscientific. “It’s like a doctor who prescribes an aspirin for a headache and then claims the body’s problem was a lack of aspirin. They don’t have a proper diagnosis.” There is a clash of scientific cultures here.

Stripped of the polemic, Michaels analyses the two possible explanations for the slowness of global warming to date. Either, as the modellers say, the warming is being masked by something else, such as sulphate or ozone depletion. In which case, the mask must eventually slip as the greenhouse effect intensifies. Or, as the sceptics say, the climate is simply less sensitive to the warming effect of greenhouse gases than the models predict. And the positive feedbacks are largely illusory.

The modellers’ belief that they can create the future in climate simulations are undoubtedly shaken by the constant revisions to the models. The problem for the sceptics, however, is that they still lack a coherent story about how the atmosphere is working. And whenever they can find any uncertainty in the way that the atmosphere works, they tend to use this to claim that there will be no problem with greenhouse warming.

As Shine says of Lindzen: “He always falls back on uncertainty. Sure there is uncertainty, but he then claims that all the uncertainty will work in his direction. Why should it?”

Parker admits that “there are a lot of things we don’t know”. But, he adds, that doesn’t disprove global warming, or the models. “Sceptics tend to elevate one element in a complex system above all the others. You cannot do that, however clever you are. You have to integrate every influence to find out what they might mean when all acting together. And the models are the only way of doing that.”

Is there any common ground? Of all people, Michaels insists there could be. “When it comes to it, the modellers and the sceptics are not so far apart,” he says. Indeed, if pressed, Michaels, Lindzen, Spencer and other sceptics suggest a doubling of CO2 in the atmosphere would raise average temperatures by between 1 and 1.5 °C. And 1.5 °C is the bottom end of the modellers’ range of predictions.

But Michaels has, as ever, a twist. “You can’t make a case for a global apocalypse out of a 1.5 °C warming. It destroys the issue. If politics weren’t driving this we could all meet on common ground.”

But, of course, he thinks the politics is all on the other side.

Further reading: see for example “The missing climate forcing” by J. Hansen and others, Phil.Trans. Roy. Soc. London B, vol 352, p 231 (1997)
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Question 1

line 7 ~ line 10
In the early 1990's, Pat Micheals sought to explain this disparity, suggesting that
sulfate emissions in industrial areas had a cooling effect, thus temporarily retarding
global warming.

: We should concentrate on a word ' temporarily'

B. This disparity is only a short-term phenomenon brought about by sulfate cooling.

-> temporarily = short-term phenomenon

Question 2

A. It will become a more serious problem in the Southern Hemisphere than in the Northern Hemisphere in spite of the cooling influence of oceans in the south.
-> more serious? : not mentioned
B. It is unlikely to be a serious problem in the future because of the pervasive effect of sulfate cooling.
-> in the future? not mentioned
C. It will proceed at the same general rate in the Northern and Southern Hemispheres once the temporary influence of sulfate cooling comes to an end.
-> will proceed at the same general rate? not mentioned
D. Until the late 1980s, it was moderated in the Northern Hemisphere by the effect of sulfate cooling.
-> Correct
Line 14 ~ Line 17, there is a mention about D
'Yet since 1987, ~ while warming in the north has accelerated'
It means that before 1987, the north has not accelerated.
We can infer 'not accelerated' to 'moderate'
E. Largely because of the cooling influence of oceans, it has had no discernible impact on the Southern Hemisphere.
-> no discernible impact? No. The passage argues that there is a difference between Northern and Southern Hemisphere

Question 3

Line 32 ~ Line 34
'Thus, Santer disputes Michael's claim that model predictions and observed data differ fundamentally.'

Michael's claim : global warming models themselves may be flawed
(model(line 4~6) : global warming based on greenhouse gas emission and actual climatological data)

Santer : disputes Michael's claim

So, A is correct
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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
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jabhatta@umail.iu.edu wrote:
Hi - can someone please help on the following queries

1 -- i dont understand why B is OA......

We read in the paragraph that Michaels did not even believe in sulfate cooling ...so how can we know if Michaels believed sulfate cooling is a short term phenomena when Michaels didnt even believe in the subject of sulphate cooling in the first place ?

---------------------------

Hello,

Michaels changed her idea in line 11: "Michaels later came to doubt this idea".

First, in the early 1990s, she "sought to explain this disparity, suggesting that sulfate emissions in industrial areas had a cooling effect, thus temporarily retarding global warming." (lines 8-10)

Second, she had doubt "pointing out that since most sulfate is emitted in the Northern Hemisphere, its cooling influence should be largely limited to that hemisphere" (lines 12-14)

Note that the question explicitly asks about Michaels' opinion "in the early 1990s".

Best,
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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
pulkitsharma9991 wrote:
For question 1, I don't understand why D is wrong? Can anyone help me with an explanation ?

Pat Michaels sought to explain this disparity, suggesting that sulfate emissions in industrial areas had a cooling effect, thus temporarily retarding global warming.

It means sulfate emissions has cooling effect and temporarily retarding global warming--leading us to option B this disparity is short-term
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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
Any advice on how to accelerate comprehension on passages similar to this?

I tend to get confused with passages with a large number of comparisons(disparities, disputes, etc.) and change of levels (increase/decrease on multiple items, etc.).

So far, I have been taking short notes, but my speed in passages similar to this one have been on the slower side. Any tips will be highly appreciated

Thanks!
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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
P1 - two models, not true what they suppose to, reasons given.
p2 - another theory, opposite to this one.

Main point - 2 opposite theories given on why models are not accurate.

(Book Question: 92)
The passage suggests that, in the early 1990s, Michaels would have been most likely to agree with which of the following statements about the disparity mentioned in lines 3-4?

suggesting that sulfate emissions in industrial areas had a cooling (10) effect, thus temporarily retarding global warming. Michaels later came to doubt this idea, however, pointing out that since most sulfate is emitted in the Northern Hemisphere, its cooling influence should be largely limited to that hemisphere. Yet, since 1987, (15) warming in the Southern Hemisphere, which had been relatively intense, has virtually ceased, while warming in the north has accelerated. Thus, Michaels not only doubted the idea of sulfate cooling, but came to feel that global warming models themselves may be (20) flawed.
*************************************************
A. This disparity is relatively less extreme in the Northern Hemisphere because of sulfate cooling. - no
B. This disparity is only a short-term phenomenon brought about by sulfate cooling. - correct
C. This disparity is most significant in those parts of the world dominated by oceans. - no
D. The extent of this disparity is being masked by the temporary effect of sulfate cooling. - no
E. The disparity confirms that current models of global warming are correct. - no
----------------------------------------

(Book Question: 93)
According to the passage, Santer asserts which of the following about global warming?
p2
A. It will become a more serious problem in the Southern Hemisphere than in the Northern Hemisphere in spite of the cooling influence of oceans in the south. - no
B. It is unlikely to be a serious problem in the future because of the pervasive effect of sulfate cooling. - no
C. It will proceed at the same general rate in the Northern and Southern Hemispheres once the temporary influence of sulfate cooling comes to an end. - no
D. Until the late 1980s, it was moderated in the Northern Hemisphere by the effect of sulfate cooling. - has to be the right answer. other can be eliminated easily. following lines needed to conclude this. ----------- But, according to Santer, the situation remains complicated by sulfate cooling, which peaked in the north in the mid-twentieth century.
E. Largely because of the cooling influence of oceans, it has had no discernible impact on the Southern Hemisphere. - extreme answer, use of no
---------------------------------------------
(Book Question: 94)
The passage suggests that Santer and Michaels would be most likely to DISAGREE over which of the following issues?

Thus, Santer disputes Michaels’s claim that model predictions and observed data differ fundamentally.

A. Whether climatological data invalidates global warming models - straight A.
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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
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teaserbae wrote:
workout GMATNinja gmatexam439 AjiteshArun u1983 GMATNinjatwo @abhimanha
Can you please Q1 I read the above explaination but I am still not clear why A and D are wrong and B is correct ?
Look at it this way (I'm assuming numbers):

1. Global warming was expected (predicted by models) to be (say) 5°.
2. Actual warming observed was only (say) 2° (less than what the models predicted).
3. The disparity between predicted and actual temperature increases was 3° (5 - 2)°.

4. In the early 1990s, Michaels thought that this difference was attributable to sulfate emissions, which had a temporary cooling effect. That was the reason that the actual figure (2°) was less than the predicted figure (5°).
5. He later had doubts about this explanation, because (a) most sulfate is emitted in the Northern Hemisphere and (b) after 1987, warming in the Southern Hemisphere ceased while warming in the Northern Hemisphere increased.

The question is asking us what Michaels would have been likely to agree with in the early 1990s about the disparity mentioned in lines 3-4. The disparity mentioned in those lines is the difference between predicted and actual temperature increases.

Option A: This disparity is relatively less extreme in the Northern Hemisphere because of sulfate cooling.
Michaels did not ever think that the disparity between the predictions by the models and actual warming was less extreme in the Northern Hemisphere. In fact, we have no idea about what the models predicted for the Northern and Southern Hemispheres (separately).

Option B: This disparity is only a short-term phenomenon brought about by sulfate cooling.
This is exactly what the passage says (Michaels sought to explain this disparity, suggesting that sulfate emissions in industrial areas had a cooling effect, thus temporarily retarding global warming).

Option D: The extent of this disparity is being masked by the temporary effect of sulfate cooling.
"The extent of this disparity is masked" means that the actual disparity was greater than what was seen ("masked" means "hidden"). That is, the actual disparity was greater than (5 - 2 = 3)°. Let's say the actual disparity was 4°. That is not what Michaels thought. Michaels said that the reason that the disparity was 3° was sulfate emissions. That is, if sulfate emissions had not been present, the disparity would have been smaller, not greater, because actual global warming would have been closer to what the models predicted.
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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
how much time should be taken for this passage ideally? i got all 3 right but took 10 mins.
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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
sarat0994 wrote:
how much time should be taken for this passage ideally? i got all 3 right but took 10 mins.

Definitely 10 minutes for 3 questions is not an ideal time. Ideal time is under 6 minutes but as it is a 700-Level passage so 7-7.5 minutes are fare enough but not more than this.
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Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
For question 1 , how do we know if the disparity is a short-term phenomenon?
Re: Scientists have been puzzled by the seeming disparity between models [#permalink]
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