# Why is Mars undergoing global warming?

**URL:** <https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778>\
**Category:** Great Debates\
**Created:** [March 31, 2006, 11:35pm UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778 "2006-03-31T23:35:43Z")\
**Posts on this page:** 20\
**Page:** 7

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**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\
**Post date:** [April 2, 2006, 10:35pm UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/121 "2006-04-02T22:35:27Z")

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> [@Flash Dancer](#):
>
> Obviously, I am not in a favorable positon now from your view point … what would you suggest I do correct it?

Engage the discussion with fewer observations about the persons with whom you are debating. Keep the remarks focused on the discussion, not the participants.

At this point, I will also note that EVERYONE needs to dial back the amount of personal remarks that border on _ad hominem_ (bad arguments) and insult (violation of rules).

However, you were the one who specifically called someone names, so you are currently being looked at more closely.

[/Moderating]

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**Author:** ![Flash\_Dancer](https://avatars.discourse-cdn.com/v4/letter/f/e495f1/32.png) [@Flash\_Dancer](https://boards.straightdope.com/u/Flash_Dancer)\
**Post date:** [April 2, 2006, 10:51pm UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/122 "2006-04-02T22:51:22Z")

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> [@GIGObuster](#):
>
> So far it shows you still don’t know how to spot evidence in your favor.
> 
> But speaking of data and statistics, the overall picture I get is that computer models were more accurate than the critics accept, usually they don’t accept the results because they point to human intervention as being a part in the warming:
> 
> [Pinatubo volcano research boosts case for hum | EurekAlert!](http://www.eurekalert.org/pub_releases/2002-02/rtsu-pvr021502.php)

I think we have most of the evidence needed for this excersise, the graphs were just to “show” the variance … now with almost 2,000 annual temperature measurements a solid sigma can be derived …

If you have other tabularized data sources please cite … we can also use them as additional sources for the variance …

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**Author:** ![Flash\_Dancer](https://avatars.discourse-cdn.com/v4/letter/f/e495f1/32.png) [@Flash\_Dancer](https://boards.straightdope.com/u/Flash_Dancer)\
**Post date:** [April 2, 2006, 10:52pm UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/123 "2006-04-02T22:52:39Z")

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> [@tomndebb](#):
>
> Engage the discussion with fewer observations about the persons with whom you are debating. Keep the remarks focused on the discussion, not the participants.
> 
> At this point, I will also note that EVERYONE needs to dial back the amount of personal remarks that border on _ad hominem_ (bad arguments) and insult (violation of rules).
> 
> However, you were the one who specifically called someone names, so you are currently being looked at more closely.
> 
> [/Moderating]

Again, I apologize, without comment … thank you …

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**Author:** ![GIGObuster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gigobuster/32/421_2.png) [@GIGObuster](https://boards.straightdope.com/u/GIGObuster)\
**Post date:** [April 2, 2006, 11:11pm UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/124 "2006-04-02T23:11:01Z")

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> [@Flash Dancer](#):
>
> I think we have most of the evidence needed for this excersise, the graphs were just to “show” the variance … now with almost 2,000 annual temperature measurements a solid sigma can be derived …
> 
> If you have other tabularized data sources please cite … we can also use them as additional sources for the variance …

You know Q.E.D was kidding about doing homework for you, now I wonder.

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**Author:** ![samclem](https://avatars.discourse-cdn.com/v4/letter/s/a9a28c/32.png) [@samclem](https://boards.straightdope.com/u/samclem)\
**Post date:** [April 2, 2006, 11:20pm UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/125 "2006-04-02T23:20:30Z")

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> [@Flash Dancer](#):
>
> Please show the significance / confidence level calculations, parameter values, their basis, etc., for your claim here? Sort of my field, would like to see it?

**Flash Dancer**. Without trying to be confrontational, you seem to have a math background interest in this subject. What exactly is your field of expertise?

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**Author:** ![Flash\_Dancer](https://avatars.discourse-cdn.com/v4/letter/f/e495f1/32.png) [@Flash\_Dancer](https://boards.straightdope.com/u/Flash_Dancer)\
**Post date:** [April 2, 2006, 11:37pm UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/126 "2006-04-02T23:37:09Z")

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> [@samclem](#):
>
> **Flash Dancer**. Without trying to be confrontational, you seem to have a math background interest in this subject. What exactly is your field of expertise?

I would be amenable to disclose this to “A” Mod here who would promise to keep it confidential … I am very cautious about disclosing this since my identity could be easily discovered, even if I tried to mask it …

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**Author:** ![Flash\_Dancer](https://avatars.discourse-cdn.com/v4/letter/f/e495f1/32.png) [@Flash\_Dancer](https://boards.straightdope.com/u/Flash_Dancer)\
**Post date:** [April 2, 2006, 11:38pm UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/127 "2006-04-02T23:38:47Z")

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> [@GIGObuster](#):
>
> You know Q.E.D was kidding about doing homework for you, now I wonder.

Ahahaha! ok … 🙂

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**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\
**Post date:** [April 2, 2006, 11:55pm UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/128 "2006-04-02T23:55:17Z")

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> [@Flash Dancer](#):
>
> I would be amenable to disclose this to “A” Mod here who would promise to keep it confidential … I am very cautious about disclosing this since my identity could be easily discovered, even if I tried to mask it …

:rolleyes: Just in general terms, please, not specific school, program, and graduation date. Applied mathematics, statistics, computational climatology, acuarial science, what?

Stranger

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**Author:** ![Flash\_Dancer](https://avatars.discourse-cdn.com/v4/letter/f/e495f1/32.png) [@Flash\_Dancer](https://boards.straightdope.com/u/Flash_Dancer)\
**Post date:** [April 3, 2006, 12:12am UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/129 "2006-04-03T00:12:56Z")

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> [@Stranger On A Train](#):
>
> :rolleyes: Just in general terms, please, not specific school, program, and graduation date. Applied mathematics, statistics, computational climatology, acuarial science, what?
> 
> Stranger

BS, MS, PhD ~ Engineering

Thesis ~ carbonyl fluoride reactions / spacecraft retry / microscopic thermodynamics

Professor ~ Nuclear, Fluids, Adv Thermo, Laboratory Statistics

Numerous peer reviewed publications and presentations over the past few years ~ probability / statistics

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**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\
**Post date:** [April 3, 2006, 1:06am UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/130 "2006-04-03T01:06:57Z")

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> [@Flash Dancer](#):
>
> Professor ~ Nuclear, Fluids, Adv Thermo, Laboratory Statistics
> 
> Numerous peer reviewed publications and presentations over the past few years ~ probability / statistics

Okay. No offense, but I’m trying to square your credintials against the claim that [this graph](http://vathena.arc.nasa.gov/curric/land/global/tchgc.gif) and [this graph](http://vathena.arc.nasa.gov/curric/land/global/tchgb1.gif) demonstrate any meaningful, much less statistically assessable, data. Would you accept this in a student lab report?

Back to the topical discussion, the climate behavior on Mars, owing to a different atmospheric composition, complete lack of liquid surface water to provide evaporation, virtually non-existant cloud cover, and completely inert volcanism, is substantially different that that of Earth. Implying, as the OP did in the original post, that the absence of pollution sources on Mars invalidates their contribution on Earth is disingeneous to say the least. Manifest evidence has been provided, in the form of actual temperature data, that indicates a recent and fairly dramatic change in global temperature.

Blind extrapolation of global temperature trends leads to a substantial increase in the positive rate of change of global average temperature, though as always with extrapolation one must be careful to distinguish between what one speculates with regard to trending and what one actuallly knows about the behavior of the system; a complex, high perturbative, chaotic system like the Earth’s climate tends to defy absolute prediction even in the short term. However, even a conservative trend prediction of temperature increase indicates readily predictable alterations of regional ecospheres. Is this trend predictable with a human, rather than natural influences? Lacking a control case, it’s impossible to make the case of direct causation for certain, but the argument that pumping astonishing amounts of carbon dioxide and other heat-trapping gases into the atmosphere have correlated strongly with increased atmospheric contamination is persuasive, regardless of modest cyclical variations in the past.

This is in concert with the overwhelming majority of professional climatologists, of which I daresay we have none in company. That being the case, we can make reasonable speculation on the effect and result of climate change but lacking any credible evidence of a political conspiracy among climatologists we would collectively be hard pressed to dispense with the perponderance of opinion without clear contradictory data, which has not been presented.

Stranger

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**Author:** ![Flash\_Dancer](https://avatars.discourse-cdn.com/v4/letter/f/e495f1/32.png) [@Flash\_Dancer](https://boards.straightdope.com/u/Flash_Dancer)\
**Post date:** [April 3, 2006, 2:49am UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/131 "2006-04-03T02:49:27Z")

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> [@Stranger On A Train](#):
>
> Okay. No offense, but I’m trying to square your credintials against the claim that [this graph](http://vathena.arc.nasa.gov/curric/land/global/tchgc.gif) and [this graph](http://vathena.arc.nasa.gov/curric/land/global/tchgb1.gif) demonstrate any meaningful, much less statistically assessable, data. Would you accept this in a student lab report?

If they were attempting to display the variation / calibration of a measurement device … absolutely …

> [@](#):
>
> Back to the topical discussion, the climate behavior on Mars, owing to a different atmospheric composition, complete lack of liquid surface water to provide evaporation, virtually non-existant cloud cover, and completely inert volcanism, is substantially different that that of Earth. Implying, as the OP did in the original post, that the absence of pollution sources on Mars invalidates their contribution on Earth is disingeneous to say the least. Manifest evidence has been provided, in the form of actual temperature data, that indicates a recent and fairly dramatic change in global temperature.

Yep, lack of atmosphere, water vapor, CO2, ozone, volcanic activity, etc. etc., and still undergoing global warming … pretty interesting huh? …

> [@](#):
>
> Blind extrapolation of global temperature trends leads to a substantial increase in the positive rate of change of global average temperature, though as always with extrapolation one must be careful to distinguish between what one speculates with regard to trending and what one actuallly knows about the behavior of the system; a complex, high perturbative, chaotic system like the Earth’s climate tends to defy absolute prediction even in the short term. However, even a conservative trend prediction of temperature increase indicates readily predictable alterations of regional ecospheres. Is this trend predictable with a human, rather than natural influences? Lacking a control case, it’s impossible to make the case of direct causation for certain, but the argument that pumping astonishing amounts of carbon dioxide and other heat-trapping gases into the atmosphere have correlated strongly with increased atmospheric contamination is persuasive, regardless of modest cyclical variations in the past.
> 
> This is in concert with the overwhelming majority of professional climatologists, of which I daresay we have none in company. That being the case, we can make reasonable speculation on the effect and result of climate change but lacking any credible evidence of a political conspiracy among climatologists we would collectively be hard pressed to dispense with the perponderance of opinion without clear contradictory data, which has not been presented.
> 
> Stranger

Nothing blind here at all … this is a very simple problem … what is the probability, based on historical temperature variations and periodic warming / cooling trends, that the current “warming” trend is statistically significant or not? …

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**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\
**Post date:** [April 3, 2006, 3:18am UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/132 "2006-04-03T03:18:01Z")

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> [@Flash Dancer](#):
>
> If they were attempting to display the variation / calibration of a measurement device … absolutely …

I find that to be astonishing. Failing to place any origin or indices on a graph should result in a significant loss of credit.

> [@Flash Dancer](#):
>
> Yep, lack of atmosphere, water vapor, CO2, ozone, volcanic activity, etc. etc., and still undergoing global warming … pretty interesting huh? …

Interesting, yes. Directly applicable to the Earth’s climatologal behavior? No. One might as well estimate the number of sharks in the ocean from a count of crappie in the local reservoir.

> [@Flash Dancer](#):
>
> Nothing blind here at all … this is a very simple problem … what is the probability, based on historical temperature variations and periodic warming / cooling trends, that the current “warming” trend is statistically significant or not? …

You seem to be missing something fundamental here. You want to treat temperature variation as a strictly random occurance; that it occurs, or doesn’t occur, per some kind of standard or normal distribution.

However, mean global temperature variation isn’t random; it occurs because of specific events or combinations of events, or as part of a complex, multi-variant cycle of actions. Since our data set is limited to temperature data, and correlated with some amount of information about volcanic activity and atmospheric composition along with variance of solar output, we can make some educated guesses about what triggers climate changes. We know that change in atmospheric “greenhouse” gases result in significant changes in the ablity of the Earth to retain heat, and increases in suspended particulates and condensed water vapor block or reflect incoming solar radiations. From these general principles, climatologists have created mathematical models in an attempt to correlate known data to predicted behavior. To that end, looking for correlations between industrial increases in greenhouse gases (which is incontrovertible) and alterations in global mean temperature and climate behavior which fit the established, if still somewhat crude models, is perfectly legitimate.

That we’ve established a first order concurrence between prediction and data indicates that, in fact, the injection of carbon dioxide and other gases into the atmosphere in unprecidencted (in recent history) rates is _a_ very likely causitive mechanism for global temperature increase, aside from other mechanisms and cycles that are occuring. If we suddenly discovered behavior that completely contraindicated predictions by current models then we’d be back at Sqaure One. But we’re not.

In short, climate behavior is not random. You can’t treat it as such. If you’re as experienced with design of experiments as your abbreviated CV indicates, then you should know this.

Stranger

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**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\
**Post date:** [April 3, 2006, 4:21am UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/133 "2006-04-03T04:21:43Z")

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> [@Flash Dancer](#):
>
> If they were attempting to display the variation / calibration of a measurement device … absolutely …

Please explain how to do a statitical analysis of variation using those graphs.

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**Author:** ![XT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/xt/32/456_2.png) [@XT](https://boards.straightdope.com/u/XT)\
**Post date:** [April 3, 2006, 5:40am UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/134 "2006-04-03T05:40:19Z")

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> [@Flash Dancer](#):
>
> Yep, lack of atmosphere, water vapor, CO2, ozone, volcanic activity, etc. etc., and still undergoing global warming … pretty interesting huh? …

It would be…if you bothered to proved this. I have yet to see ANY data proving or disproving that there is more than localized climate changes occuring on Mars…which is what I THOUGHT this thread was supposed to be about after all. There hasn’t even been a presentation on historical trends as far as the purported melting of the caps goes for gods sake. 😛

Do you have any proof that in fact Mars is undergoing GLOBAL warming (or even a global climat shift of some kind)? Do you have temperature data for all (or even part) of Mars…and historical data to show a trend? Aren’t these, um, kind of necessary to show that Mars is (or isn’t) undergoing global warming?

Seems kind of basic to me…though granted I’m no professor. 😉

-XT

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**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\
**Post date:** [April 3, 2006, 7:22am UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/135 "2006-04-03T07:22:24Z")

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> [@Flash Dancer](#):
>
> Huh? Please explain.

I would. But I’m not sure you’d pay attention, me being from Africa and all…

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**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\
**Post date:** [April 3, 2006, 8:43am UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/136 "2006-04-03T08:43:32Z")

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**Flash dancer** , since you ignored this post the first time around in GQ, could you address it now, in GD?

> [@SentientMeat](#):
>
> Both Earth and Mars have gone through cycles of heating and cooling in their history, with solar cycles palying a large part. So, Mars and **Earth before around 1980** can be explained “naturally”.
> 
> However, those explanations break down after around 1980 in the case of Earth. Look at [these graphs](http://www.ipcc.ch/present/graphics/2001syr/large/02.01.jpg). You’ll note that before around 1960, none of these greenhouse gases were _too_ far off the historical equilibrium concentration (eg. 280 parts per million for CO2). However, after that date you’ll note the concentrations begin to rocket, and their increase is still exponential today. This is why attempts to explain current warming trends **naturally** fail for post-1980 data, while Anthropogenic Climate Change (ACC) models are largely accurate.
> 
> There are almost no ACC-deniers in professional or academic climatology any more.

As for your “variance”, what do you suggest the variance is for [those graphs](http://www.ipcc.ch/present/graphics/2001syr/large/02.01.jpg)? Pretty high, yes?

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**Author:** ![Crowbar\_of\_Irony\_3](https://avatars.discourse-cdn.com/v4/letter/c/f08c70/32.png) [@Crowbar\_of\_Irony\_3](https://boards.straightdope.com/u/Crowbar_of_Irony_3)\
**Post date:** [April 3, 2006, 12:09pm UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/137 "2006-04-03T12:09:33Z")

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> [@Flash Dancer](#):
>
> The graph, regardless, of scale, etc., shows there has been variations in the Earth’s temperature not associated with man’s presence here. One of the more recent “warming” effects is now associated with a volcanic eruption.

The graph in context  
[http://vathena.arc.nasa.gov/curric/land/global/climchng.html](http://vathena.arc.nasa.gov/curric/land/global/climchng.html)

According to the article, it was just a “slight” change. The whole article seems to be supporting that the presence of humans are causing climate changes, but also state that it’s was not so in the past.

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**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\
**Post date:** [April 3, 2006, 12:21pm UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/138 "2006-04-03T12:21:28Z")

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> [@Sam Stone](#):
>
> The graph on the top is the infamous ‘hockey stick’ graph, which I believe has been discredited. Read [Technology Review](http://www.technologyreview.com/articles/04/10/wo_muller101504.asp) for a layman’s description of the flaw in the analysis.
> 
> Here’s the [Web Site](http://www.uoguelph.ca/~rmckitri/research/fallupdate04/update.fall04.html) of the researchers who have found problems with the hockey stick, and their explanation of what’s wrong with it.

**Sam** , it has not been discredited. There is still plenty of legitimate debate in the field of these temperature reconstructions over the last couple of millenia using climate proxies and some reconstructions do show more variations over the last 1000 years than Mann et al. show. However, these different studies all tend to agree that the warming of the late 20th century is unprecedented (at least in the Northern Hemisphere where the data is better) over the last 1000 years. And, most of the criticisms of M&M have been shown to be specious. See [here](http://www.realclimate.org/index.php/archives/2006/02/a-new-take-on-an-old-millennium/). Of course, this is written Michael Mann, one of the authors of the original hockey stick, but it provides references to recent peer-reviewed work on the subject.

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<div class="post-metadata">

**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\
**Post date:** [April 3, 2006, 12:23pm UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/139 "2006-04-03T12:23:07Z")

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> [@jshore](#):
>
> And, most of the criticisms of M&M have been shown to be specious.

That sentence should say that most of the criticisms **by** M&M of the hockey stick graph of Mann and coworkers have been shown to be specious.

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<div class="post-metadata">

**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\
**Post date:** [April 3, 2006, 12:47pm UTC](https://boards.straightdope.com/t/why-is-mars-undergoing-global-warming/350778/140 "2006-04-03T12:47:47Z")

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At the risk of beating a dead horse, [here](http://www.realclimate.org/index.php/archives/2005/01/the-global-cooling-myth/) is a good reference from Real Climate entitled the “Global Cooling Myth”. The basic point is that, far from providing evidence that we should ignore current scientific concerns about global warming because some scientists talked about global cooling in the 1970s, the evidence from what actually occurred shows how well science worked.

In particular, in the 1970s as scientists were first really gearing up their work on global climate, they knew that there were both warming mechanisms (such as CO2 and other greenhouse gases, whose warming effects had been estimated by Arrhenius around 1900) and cooling mechanisms (sulfate aerosols from pollution and the natural mechanisms that would eventually take us out of our current interglacial and into another ice age in the absence of any anthropogenic forcings). A National Academy of Sciences report rightly concluded that not enough was understood to yet be able to make predictions about future climate and thus more study was needed. In other words, they realized there was no consensus in the scientific community yet regarding what would happen to the earth’s climate in the future.

Now, 3+ decades later, more research has been done and the U.S. National Academy of Science and the National Academies of 10 other nations (Canada, France, U.K, Germany, Italy, Japan, Russia, China, India, and Brazil) recently issued a statement (PDF file) that says that we definitely understand enough now to take prompt actions:

> [@](#):
>
> There will always be uncertainty in understanding a system as complex as the world’s climate. However there is now strong evidence that significant global warming is occurring. The evidence comes from direct measurements of rising surface air temperatures and subsurface ocean temperatures and from phenomena such as increases in average global sea levels, retreating glaciers, and changes to many physical and biological systems. It is likely that most of the warming in recent decades can be attributed to human activities (IPCC 2001). This warming has already led to changes in the Earth’s climate.
> 
> …
> 
> The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action. It is vital that all nations identify cost-effective steps that they can take now, to contribute to substantial and long-term reduction in net global greenhouse gas emissions.
> 
> Action taken now to reduce significantly the build-up of greenhouse gases in the atmosphere will lessen the magnitude and rate of climate change. As the United Nations Framework Convention on Climate Change (UNFCCC) recognises, a lack of full scientific certainty about some aspects of climate change is not a reason for delaying an immediate response that will, at a reasonable cost, prevent dangerous anthropogenic interference with the climate system.
> 
> …
> 
> Carbon dioxide can remain in the atmosphere for many decades. Even with possible lowered emission rates we will be experiencing the impacts of climate change throughout the 21st century and beyond. Failure to implement significant reductions in net greenhouse gas emissions now, will make the job much harder in the future.

The point is that science evolves over time and the uncertainty in the 1970s that led some scientists to predict warming and others to predict cooling has given way to a general consensus on global warming (even if some uncertainties still remain concerning the magnitude and effects of these changes).

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