2010-08-17 13:01:09Basic Rebuttal No.45: CO2 levels in the past
steve.oconnor

steve.oconnor@hotmail...
152.91.63.37

hi,

here's my suggestion for Basic rebuttal no.45: CO2 levels have been higher in the past.

---

Sure, CO2 levels have been higher in the past: the deep geological past.

According to some research published last year, CO2 concentrations in the atmosphere now are higher than any time for about 10-14 million years in a period called the Middle Miocene.

That's at least a full 8 million years before humans existed!
2010-08-17 13:33:06I think it needs more detail
John Cook

john@skepticalscience...
121.222.17.49
That doesn't really address the argument which is "CO2 was higher in the past and yet temperatures weren't always warmer - doesn't this disprove the warming effect of CO2". The general answer is that the sun was also cooler in the past - when you combine the effect of CO2 and sun, it matches well with climate records.
2010-08-17 14:10:06oops
steve.oconnor

steve.oconnor@hotmail...
152.91.63.37
yes sorry..i should have read the rebuttal more clearly first (newbie error!)
2010-08-19 15:35:44
watchingthedeniers

watchthedeniers@optusnet.com...
203.41.179.162
Should it also not be briefly stated that C02 levels have been relatively stable for the past 800k years and that the last 200 years have seen a rapid increase (i.e. a 38% increase above pre-industrial levels)
2010-08-20 23:11:30
John Russell

jr@johnrussell...
84.92.176.215

I'd certainly use the point you make as a punchline: but it does need the other info, Steve. And I agree with 'watchingthedeniers' suggestion.

When writing these rebuttals I always go first to the argument on the main site and read and assimilate the intermediate rebuttal, then try to reduce it to the 'plain English' basics. 

Best wishes,

JR

2010-08-30 12:26:10Basic Rebuttal No.45: CO2 levels in the past (2nd try)
steve.oconnor

steve.oconnor@hotmail...
124.171.104.220

how about this one?

---

Throughout most of its 4.5 billion year history, the Earth was a hot, tropical greenhouse. Does the geological evidence for glacier formation during past periods of high CO2 disprove the theory that CO2 drives climate?

It's important to remember that CO2 is just one of many things that can alter the climate. The Sun is the biggest driver of climate and it's well established that it was fainter in the past. Clouds, along with the level of aerosols in the atmosphere (volcanic haze, galactic dust etc), greatly influence how much of that sunlight reaches Earth and how much is reflected back into space. Ocean currents can also modify local climates by dictating how heat is transported around the planet. The position of land masses, the tilt and orbit of the Earth can all affect climate as well as many other things.

When gazing far back into Earth's history, we have to rely on very sparse data to construct theories, and some are more speculative than others. Geological proxies cannot provide cast-iron scientific proof and can only indicate certain aspects of past conditions if many assumptions are used. In the more recent past there is at least the luxury of having many more lines of evidence available that can be used for cross-checking and validation.

With all that in mind, it's likely that multiple events combining at just the right time can conspire to create the ideal conditions for glaciation to occur, even with CO2 levels many times higher than now. For example, about 450 Million years ago (Late Ordovician period) the Southernmost part of Gondwana was already cool as its tip was at the South Pole. With a fainter Sun it may have became cold enough for snow to accumulate year after year, eventually leading to continental glaciation as the layers of snow compressed. There may have also been additional factors: changing ocean currents and enhanced rock-weathering through to extra stardust from galactic arm movement have all been put forward as possibilities.

Interestingly, the premise that CO2 levels were many times higher during these glacial formations may turn out to be false: reconstructed CO2 levels over deep history are not yet sophisticated enough to resolve fluctuations that lasted less than a few million years. A reduction in CO2 levels for a million years or so cannot be detected by current methods, making it entirely possible that one of the major factors to past glaciations was indeed lower CO2.

2010-08-31 05:47:53What's the bottom line
nealjking

nealjking@gmail...
84.151.29.152
in the article just above?
2010-08-31 18:07:41Some comments
gpwayne
Graham Wayne
graham@gpwayne...
217.44.86.17

Hi Steve.

"Throughout most of its 4.5 billion year history, the Earth was a hot, tropical greenhouse". Sorry but I don't think this is accurate. The Earth goes through glacial periods, has been a giant ball of ice (snowball earth), and conversely has very hot periods too. It might be more accurate to state that the climate has gone through intense periods of hot and cold.

"Does the geological evidence for glacier formation during past periods of high CO2 disprove the theory that CO2 drives climate?" I don't think that is the argument. My reading is this: at previous times there has been very high levels of CO2 but no corresponding massive increase in temperature - or a runaway 'venus' effect. The argument is about the relationship between the proportion of GHGs and temperature, to which the rebuttal focuses on the missing forcing i.e. the sun being much less hot. It doesn't matter how much CO2 there is if there isn't any heat to trap.

2010-09-01 12:25:56confused
steve.oconnor

steve.oconnor@hotmail...
203.166.51.62

thanks for the initial feedback. ok, so i'm officially confused! i thought that i had to rebutt the following:

CO2 was higher in the past

"The killer proof that CO2 does not drive climate is to be found during the Ordovician- Silurian and the Jurassic-Cretaceous periods when CO2 levels were greater than 4000 ppmv (parts per million by volume) and about 2000 ppmv respectively. If the IPCC theory is correct there should have been runaway greenhouse induced global warming during these periods but instead there was glaciation."
(The Lavoisier Group)


Isn't the above specifically about lack of runaway greenhouse during the mentioned glaciation events, not generally about the past (maybe the title is misleading...)

I take your point about my first sentence, however i think we're both technically right. My research indicates that we had a hot greenhouse about 80% of Earth's history, and much much more than that if we only look at the last 500 million years when lifeforms other than bacteria roamed the planet ;)

hope someone can clarify!

2010-09-04 18:47:36I think the basic argument is that
nealjking

nealjking@gmail...
84.151.49.66

"CO2 was much higher in the past, so it can't be that bad for us."

And the basic rebuttal should be: 

"There is nothing INHERENTLY bad about high or low CO2 levels: The problem is that we are increasing the level so quickly that we are forcing a climate change IN A VERY SHORT TIME (about 250 years), and a huge proportion of our living organisms will not be able to adapt to that. We had 4000 ppm CO2 400 million years ago."

 

2010-09-06 16:56:51The basic argument
John Cook

john@skepticalscience...
121.222.93.62

Neal, yours is a slightly different argument. In general, I'm addressing the most common form of this argument which is that "CO2 was much higher in the past including times of ice ages therefore CO2 does not drive climate". The general simple answer is that you need to look at the combined effect of sun and CO2 as the sun was cooler in the Earth's deep past.

So the rate of change of CO2 is not quite as relevant. That's relevant to questions of species extinction and the ability to adapt to fast climate change. In the case of this argument, it's more elemental - the simple question, does CO2 cause warming?

Steve, I wonder if you should say "The Sun is the biggest driver of climate". It is a powerful driver of climate. But right now, it is not the biggest driver of climate - CO2 provides the strongest radiative forcing. So that statement can be misinterpreted or taken out of context.

2010-09-07 10:01:22Another try...
steve.oconnor

steve.oconnor@hotmail...
203.166.51.62

incorporating some of the above feedbacks & given it a trim. let me know what you think ;)

---
Over it's vast 4.5 billion year history the Earth has experienced many different climates, from extreme ice-ages lasting hundreds of millions of years through to conditions so hot even the poles were balmy.

CO2 levels roughly correlate with temperature over Earth's history, but there are periods where this appears to be false, such as 450 Million years ago (Late Ordovician period) where there is geological evidence of an ice-cap (glaciation) during a period of apparently high CO2.

It's likely that multiple events combining at just the right time can conspire to create the ideal conditions for glaciation to occur, even with CO2 levels many times higher than now. For example, during the Late Ordovician it's well established that the Sun was slightly weaker than it is today. Also, the Southernmost part of Gondwana was already cool as its tip was at the South Pole. Together, these effects may have made it cold enough for snow to accumulate year after year, eventually leading to continental glaciation as the layers of snow compressed into ice.

It's still speculative, but there may have also been additional factors: changing ocean currents and enhanced rock-weathering through to extra stardust from galactic arm movement have all been put forward as possibilities. A brief dip in CO2 levels may also be implicated as a potential trigger for the glaciations. It may be some time before we know the whole story with a large amount of confidence. 

2010-09-07 11:19:53
nealjking

nealjking@gmail...
91.33.100.6
"the past couple of millions years" => "the past couple of million years"
2010-09-17 20:04:38
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.232.67

CO2 levels roughly correlate with temperature over Earth's history, but there are periods where this appears to be false, such as 450 Million years ago (Late Ordovician period) where there is geological evidence of an ice-cap (glaciation) during a period of apparently high CO2.

Steve, see argument 109 - "CO2 was higher in the late Ordovician."

The glaciation process began 10 million years before the Hirnantian Glaciation, when CO2 levels were low. 

http://www.geology.ohio-state.edu/~saltzman/saltzman_young_05.pdf

A good summary here:

http://researchnews.osu.edu/archive/earlyice.htm

 

 

2010-09-20 21:48:00this is hard ;)
steve.oconnor

steve.oconnor@hotmail...
203.217.48.33

thanks for the comments dappledwater.

 unfortunately the paper is no longer there, but the summary seems good. the whole time period seems difficult and fraught if you ask me... the summary that you pointed to said that CO2 was a lot lower 10milion years beforehand:

"This particular ice age didn’t begin when CO2 was at its peak -- it began 10 million years earlier, when CO2 levels were at a low."

But this is flatly contradicted by the 'standard' CO2 model for paleo, GeoCarb III:

http://www.shef.ac.uk/aps/apsrtp/taylor-lyla/geocarbmodel.html

According to that, 10MY before the Ord glaciation, CO2 levels seem to dip only a tiny amount - from about 17x to 16x the present level. From what I can tell from other papers, proxy data for CO2 over this period are very sparse.

It's an intriguing theory, but I don't see how it alters the general thesis, especially as I mentioned that CO2 could have well be lower than generally thought. My reading of the literature so far indicates that there is still a lot of division over the details.

2010-09-21 06:02:44
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.245.170

Steve, I just checked, the Saltzman/Young paper is still there. Have a read, it's pretty compelling - the large deposits of quartzite sand, previously thought to be as a result of tectonic forces were in fact as a result of weathering (reduced sea level) and the find at two other sites show it was a global lowering of sea level. Note the later papers in John's argument too.

You mention the sparse data available back in deep time & that's how I think you should approach the rebuttal. Anyway get back to you later, gotta go to work. 

 

 

  

2010-10-01 17:14:40
steve.oconnor

steve.oconnor@hotmail...
203.166.51.62

i've gone through some more papers, and think i have a fuller understanding now. appreciate any feedback!

======
It's probably fair to say that the issue of glaciation during periods of ultra-high CO2 in Earth's deep past seems at first glance to contradict a fundamental tenet of climate science (ie. high CO2 = high temperature.)

Most controversial is the glaciation that occurred at the end of the Ordovician period (the so-called Hirnantian Stage) roughly 444 Million years ago. In its most intense phase it lasted perhaps only a couple of Million years and happens to coincide with a major extinction of marine life, indicating that while brief, it was intense.

It's important to keep in mind that although low CO2 is a necessary ingredient in triggering ice-ages, CO2 starts to build up in the atmosphere once the glaciation takes hold. Why? Because all that extra snow and ice reduces the air exposure of rock to the process of weathering, a key method the Earth uses to naturally remove CO2 from the atmosphere over long time periods.

So in fact, it's entirely consistent with climate science to have high CO2 during glaciations: the highest levels typically occur right at the end of an ice-age, just as the warmth from the extra CO2 begins to overpower the cold temperatures, tipping the climate back into a period of abrupt warming.

In the case of the Hirnantian glaciation, it was so brief that an adequate timeline of CO2 changes couldn't be accurately identified until recently, leading to many contradictory theories and speculation about cause and effect.

There seems to be added confusion because the entire Ordovician period was understood by many as a "super-greenhouse" and therefore unable to support any ice-age, even such a brief one. Improved techniques in fossil proxy reconstructions now show that the temperature of the oceans was much cooler than previously thought, especially at the crucial time just before glaciation.

The actual trigger for the Hirnantian glaciation is not known with absolute certainty, but seems to be a combination of enhanced rock weathering and a Sun that was about 4% weaker, raising the CO2 threshold needed to form an ice-cap on the Southern tip of Gondwana.

There may have been other contributing factors, such as altered ocean currents. Another suggestion is that global cooling from the massive Deicke volcanic eruption may have caused a smaller glaciation prior to the Hirnantian, acting as a "primer" for the main event. It's likely that the exact sequence of events will be argued over for some time.

The bottom line, however, is that very high CO2 levels during these ice-ages is normal and expected.

2010-10-02 02:13:39
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Sounds fair to say there's no KO blow for this argument because it's so reliant on anachronism, we don't have enough data to say definitively what happened. 

Steve, it might be worth emphasizing or reminding readers a little more directly of the relative weakness of the Sun during the Ordovician. something on the order of 2% less than today versus the ~0.6% change some skeptics employ to explain warming over the past 130 years. If the latter is true, that suggests sensitivity sufficient to explain past discrepancies between C02 and temperature based simply on stellar evolution. Skeptics can't really have it both ways. 

2010-10-02 08:51:12
steve.oconnor

steve.oconnor@hotmail...
203.173.14.233
ta Doug - updated to put in your suggestion
2010-10-02 11:15:55
doug_bostrom

dbostrom@clearwire...
184.77.83.151
Steve,  just to clarify, is your active version on the rebuttals preview, or here? I'm guessing on the preview? 
2010-10-02 12:48:00
steve.oconnor

steve.oconnor@hotmail...
203.173.14.233

i've just put it on the preview too & modified the summary to better reflect this rebuttal

2010-10-02 13:14:14
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.228.174

Steve, maybe?

1. "It's important to keep in mind that although low CO2 is a necessary ingredient in triggering ice-ages, CO2 starts to build up in the atmosphere once the glaciation takes hold. Why? Because all that extra snow and ice reduces the air exposure of rock to the process of weathering, a key method the Earth uses to naturally remove CO2 from the atmosphere over long time periods"

 

2010-10-02 13:27:38
steve.oconnor

steve.oconnor@hotmail...
203.173.14.233
good edits dappledwater - done!
2010-10-02 13:54:29Backstory
steve.oconnor

steve.oconnor@hotmail...
203.173.14.233

I'm not sure if this may be interesting to anyone, but although the skeptical argument quoted comes from Ian McClintock's "paper" for the Lavosier Group, he seems to have plaguarised from Ian Plimer's well-known work of fiction "Heaven and Earth":

from pp165

"The proof that CO2 does not drive climate is shown by previous glaciations. The Ordovician-Silurian (450-420 Ma) and Jurassic-Cretaceous (151-132 Ma) glaciations occurred when the atmospheric CO2 content was more than 4000ppmv and about 2000 parts per million volume (ppmv) respectively...."

"If the popular catastrophist view is accepted, then there should have been a runaway greenhouse when CO2 was more than 4000ppmv. Instead there was glaciation. Clearly a high atmospheric CO2 does not drive global warming and there is no correlation between global temperature and atmospheric CO2. This has never been explained by those who argue that human additions of CO2 to the atmosphere will produce global warming."

He repeats words to this effect a few additional times throughout his book.

2010-10-02 16:16:18A few suggestions
James Wight

jameswight@southernphone.com...
58.105.164.221
Avoid the phrase “fundamental tenet” – this language plays right into the hands of the “AGW is religion” crowd. Science doesn’t have tenets, it has conclusions.

“Million” does not need to be capitalized.

Where you say “ice-cap” I think the correct term is “ice sheet”. (As I understand it, ice caps are the relatively small masses of ice you get on mountaintops, whereas an ice sheet covers a substantial portion of a continent.)
2010-10-02 18:26:02wording-change suggestions
nealjking

nealjking@gmail...
91.33.101.215

 

"to contradict a fundamental tenet of climate science (ie. high CO2 = high temperature.)"

=> " to contradict a fundamental conclusion of climate science (i.e. high CO2 implies high temperature.)"

"In its most intense phase it lasted perhaps only a couple of Million years and happens to coincide with a major extinction of marine life, indicating that while brief, it was intense."

=> "In its most intense phase [comma], it lasted perhaps only a couple of Million years and coincides with a major extinction of marine life, indicating that [comma], while brief, it was intense."

"a key method the Earth uses to naturally remove CO2 from the atmosphere over long time periods."

=> "a key method by which CO2 is naturally removed from the atmosphere over long time periods."

 

"the highest levels typically occur right at the end of an ice-age, just as the warmth from the extra CO2 begins to overpower the cold temperatures, tipping the climate back into a period of abrupt warming."

=> "the CO2 levels building up until the increased heating brings the ice-age to an end. Shortly after that, the increased weathering rate brings down the CO2 levels within a few thousand years."

 

[I think this is the logic.  Is it accurate?]

 

"The actual trigger for the Hirnantian glaciation is not known with absolute certainty, but seems to be a combination of enhanced rock weathering and a Sun that was about 4% weaker, raising the CO2 threshold needed to form an ice-cap on the Southern tip of Gondwana."

- Question: How would one arrive at a conclusion of enhanced rock weathering? This seems to stick out.

- Suggestion: "Gondwana" => "the ancient continent of Gondwana"

 

"The bottom line, however, is that very high CO2 levels during these ice-ages is normal and expected."

=> "The bottom line, however, is that very high CO2 levels towards the end of these ice-ages is normal and expected."

2010-10-02 21:04:02
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.194.7

Yup, the "Goldilocks Zone" for these basic rebuttals sure is difficult with many topics, either too wordy/jargon-ese or not enough detail.

I like Richard Alley's take on CO2 as a thermostat for global temperature - crank up the CO2 and the increased weathering lowers it, cool the Earth too much and the ice cover lowers weathering causing CO2 to build up again until it warms enough to melt the ice, whereupon the increased weathering sequesters CO2 again.  

He also explained the puzzle of the apparent mismatches with high CO2 and glaciations in deep time - a few years back there were a lot of apparent contradictions, but as new discoveries are made it turns out that more and more we see CO2 acting as a global thermostat, as we might expect it to be. The videos I've seen, he didn't cite any specific examples though.    

2010-10-04 10:52:22
steve.oconnor

steve.oconnor@hotmail...
124.171.100.174

Thanks for the suggestions Neal. I re-ordered some of the paras and (hopefully) tidied up the timeline. i also thought i needed to contrast recent ice-ages with ancient ones as they use different mechanisms. comments appreciated.

===

It's probably fair to say that the issue of glaciation during periods of ultra-high CO2 in Earth's deep past seems at first glance to contradict a fundamental conclusion of climate science (ie. high CO2 implies high temperature.)

Most controversial is the glaciation that occurred at the end of the Ordovician period (the so-called Hirnantian Stage) roughly 444 Million years ago. In its most intense phase, it lasted perhaps only a couple of million years and coincided with a major extinction of marine life, indicating that while brief, it was intense.

The actual trigger for the Hirnantian glaciation is not known with absolute certainty, but it is now known (through improved fossil proxy techniques) that the temperature of the oceans was much cooler than previously thought and that CO2 levels had been declining over a long period prior to the event. A Sun that was about 4% weaker would have raised the CO2 threshold needed for the initial glaciation to form on the Southern tip of the ancient supercontinent Gondwana, while positive feedback mechanisms (such as the ice-albedo effect) would have ensured that the nascent ice formation accelerated.   

It's important to keep in mind that although low CO2 is a necessary ingredient in triggering ice-ages, CO2 starts to build up in the atmosphere once the glaciation takes hold. Why? Because all that extra snow and ice reduces the air exposure of rock to the process of silicate weathering, a key method by which CO2 (from volcanic activity) is naturally removed from the atmosphere over long time periods. For primordial ice-ages the highest levels of CO2 typically occur right at the end, just as the warmth from the extra CO2 begins to overpower the cold temperatures, tipping the climate back into a period of abrupt warming. Recent ice-ages don't show this effect because they weren't long enough and were driven mainly by orbital changes.

Some researchers have pointed to other possible contributing factors, such as altered ocean currents while another suggestion is that global cooling from the massive Deicke volcanic eruption may have caused a smaller glaciation prior to the Hirnantian, acting as a "primer" for the main event. It's likely that the exact sequence of events will be argued over for some time.

The bottom line, however, is that very high CO2 levels towards the end of ancient ice-ages is normal and expected. In the case of the Hirnantian glaciation, it was so brief that an adequate timeline of CO2 changes couldn't be accurately identified until recently, leading to some conflicting theories about cause and effect.

2010-10-04 16:26:07
nealjking

nealjking@gmail...
84.151.46.226

steve,

Some stylistic changes:

"The actual trigger for the Hirnantian glaciation is not known with absolute certainty, but it is now known"

Would be nice to use a different verb.

 

 

"silicate weathering, a key method"

=> "silicate weathering, a key mechanism"

The term "method" implies an intention on someone's part, and a goal. I didn't catch this the first time.

 

 

"For primordial ice-ages the highest levels of CO2 typically occur right at the end, just as the warmth from the extra CO2 begins to overpower the cold temperatures, tipping the climate back into a period of abrupt warming. Recent ice-ages don't show this effect because they weren't long enough and were driven mainly by orbital changes."

There is something about the first two phrases that bothers me: the "just as" confuses me about the causal connection between the high CO2 levels and the warmth from the extra CO2. Actually, this sentence structure suggests to me that the high level of CO2 are due to the extra warmth (but which is then attributed to the extra CO2): It has a chicken-or-the-egg quality to it. Maybe it would be better to spell it out, like so:

"For primordial ice-ages, the highest levels of CO2 have typically occurred towards the end: This suggests that the expected radiative forcing from this extra CO2 was in fact the mechanism for tipping the climate into a phase of abrupt warming, thus bringing the ice-age to a close. Recent ice-ages..."

I think this is what you mean.

 

2010-10-04 21:56:53
steve.oconnor

steve.oconnor@hotmail...
124.171.100.174

thanks again Neal - i think you're right.. it was a bit ambiguous. i have reworded it a bit based on your suggestions.

===

It's probably fair to say that the issue of glaciation during periods of ultra-high CO2 in Earth's deep past seems at first glance to contradict a fundamental conclusion of climate science (ie. high CO2 implies high temperature.)

Most controversial is the glaciation that occurred at the end of the Ordovician period (the so-called Hirnantian Stage) roughly 444 Million years ago. In its most intense phase, it lasted perhaps only a couple of million years and coincided with a major extinction of marine life, indicating that while brief, it was intense.

The actual trigger for the Hirnantian glaciation is not known with absolute certainty, but it is now understood (through improved fossil proxy techniques) that the temperature of the oceans was much cooler than previously thought and that CO2 levels had been declining over a long period prior to the event. A Sun that was about 4% weaker would have raised the CO2 threshold needed for the initial glaciation to form on the Southern tip of the ancient supercontinent Gondwana, while positive feedback mechanisms (such as the ice-albedo effect) would have ensured that the nascent ice formation accelerated.   

It's important to keep in mind that although low CO2 is a necessary ingredient in triggering ice-ages, CO2 starts to build up in the atmosphere once the glaciation takes hold. Why? Because all that extra snow and ice reduces the air exposure of rock to the process of silicate weathering, a key mechanism by which CO2 (from volcanic activity) is naturally removed from the atmosphere over long time periods. As the CO2 accumulates, the temperature rises due to the greenhouse effect, and at some critical point the coldness is overpowered and the ice-age comes to an abrupt end. Recent ice-ages don't show this effect because they weren't long enough and were driven mainly by orbital changes.

Some researchers have pointed to other possible contributing factors, such as altered ocean currents while another suggestion is that global cooling from the massive Deicke volcanic eruption may have caused a smaller glaciation prior to the Hirnantian, acting as a "primer" for the main event. It's likely that the exact sequence of events will be argued over for some time.

The bottom line, however, is that very high CO2 levels towards the end of ancient ice-ages is normal and expected. In the case of the Hirnantian glaciation, it was so brief that an adequate timeline of CO2 changes couldn't be accurately identified until recently, leading to some conflicting theories about cause and effect.

2010-11-04 18:43:29
Glenn Tamblyn

glenn@thefoodgallery.com...
121.219.107.173

Steve

John has just given me entry to the forum and this particular sceptic claim has always been one of my pet peeves. Its a month since your last comment on this but I haven't seen the rebuttal posted on the site yet so I assume it is still in the works. So just some personal opinions that may or may not be useful.

I have lost count of the number of times I have countered this sceptic argument, often when someone points me to this graphic from Monty Hieb's site www.geocraft.com (about 1/2 way down the page) Jo Nova has even copied it into one of her sceptics handbooks. Although the graphic is a simplification it is actually a useful representation of the past.

When challenged with this the arguments to me have take 2 forms. One is the form of the argument that John's rebuttal focuses on - "If CO2 is meant to warm things, how could there be Ice Ages when CO2 was high?". This is the most simplistic form of the argument and the most emotive. However it rests on the Hirnantian not being correllated with CO2 drop.

The other form of the argument I have seen focuses on the periods of stable temp's - "How could Temp's be stable when CO2 is falling. Doesn't that say CO2 has no effect?"

John's initial rebuttal and yours focuses most on the first form and only gives modest prominence to the second, hence the focus on the causes of the Hirnantian since it has seemed the odd one out.

But a vigorous rebuttal of the second form opens the possibility of actually counterattacking against the sceptics and highlighting a major misrepresentation. I have never understood why those on the Pro-AGW side haven't prosecuted this line strongly because I feel it is actually a major argument FOR AGW if used strongly.  And the fact that sceptics don't mention any of this can reduce their credibility.

Here is why, although it is possibly too long for a basic rebuttal

The Sun was Colder (not fainter - stronger, simpler language) when the Earth was first formed over 4 Billion years ago. It only produced around 7/10ths as much heat as it does today. We know this from 'The Standard Solar Model' (perhaps a link to wiki on this) that is at the heart of a branch of Astronomy called Stellar Physics which studies how stars work (this brings in that this understanding comes from outside Clmate Science). The SSM has existed for nearly 1/2 a century and been extensively tested.  If you have ever heard an Astronomer (or even Star Trek) refer to an M or G Type star, they are referring to the scheme for classifying stars based on the SSM.

Nearly 40 year ago it was recognised that this had implications for the Earth. If the Sun was so much colder at the dawn of time, the Earth would have been colder as well; so cold in fact that liquid water could not have existed - the Earth would have been a snowball. But we know from ancient geology that there was liquid water on the Earth. So something must have been warming it - a lot. This question was called the 'Faint Young Sun Problem' (link to wiki again) And the best explanation for what warmed the Earth was the Greenhouse Effect - lots and lots of it, much more than today. Huge levels of CO2 as well as equally huge levels of Methane, Ammonia (a GH gas that isn't present in the air today) and other gases; research is still continuing into other gases that may have existed then before life evolved and started adding Oxygen to the air.

Fast forward ariubd 3.5 Billion years to 600 Million years ago, the period covered by the graph. The Sun is now hotter but still not as hot as today. Most of the other gases are gone but CO2 is still there, but not at as high a level as in the past, but STILL MUCH higher than today. And for much of the period shown in the graph, temperatures were stable. CO2 fell as the Sun got warmer, keeping things steady except for the periods when Ice Ages happened (more on this later)

Just like a house. If it is cold outside you need the heating turned up high. Then as the temperature outside warms, you turn the internal heating down to keep the house temperature stable. Just like the Thermostat on your heater.

So what is this Thermostat that makes the CO2 level go down as the Sun warms up, all very slowly over 100's of millions of years? The process is called Chemical Weathering of rocks. Not erosion but chemical reactions on the surface of rocks. It works like this: Some of the CO2 and Water in the atmosphere have a chemical reaction producing a mild acid called Carbonic Acid; This falls out in rain and reacts with bare rock producing silicate and carbonate minerals that are washed down to the oceans and eventually form rocks such as limestone. This is a slow, very slow, but continual pump removing CO2 from the air over very long time periods - millions of years. At the same time, slowly over Millions of years, Volcanoes add small amounts of CO2 to the atmosphere that can slowly build up. So the 'pump' pulls CO2 out of the air and volcanoes add CO2. What the CO2 level is, over the very long term, depends on the balance between these two.

And just how fast CO2 is being 'pumped' down depends on 2 things: How much bare rock is available for the reaction to occur on, and how warm it is. Like many chemical reactions, the reaction runs faster when it is warmer. So if the temperature is too high the reaction goes faster and the 'pump' runs faster and lowers the CO2 level, cooling things. If the temperature is too low the 'pump' slows down and CO2 builds up again to warm things.

And slowly over the eons, as the Sun gets warmer, the pump keeps going to lower and lower CO2 levels to compensate for the warmer Sun.

Without the Greenhouse Effect of CO2 and other gases the Earth would have started life as an extremely cold planet. Possibly too cold for life to have ever started. And without the CO2 'pump' as well, as the Sun warmed all that huge amount of CO2 would have made the Earth an inferno. Without CO2, an iceball and no life. With CO2 but no 'pump', an inferno and no life. But with both, a 'goldilocks' world.

Humanity owes its very existance to CO2, the GH Effect and the Thermostat!

So why do Ice Ages happen? Basically, because sometimes circumstances arise where the themostat has a hiccup. Sometimes for quite a long time. Major periods of volcanic activity (not just a single large volcano, that's not enough) can add CO2 to the atmosphere so fast that the pump can't keep up and temp's rise for a time. Or periods when the amount of bare rock increases can make the pump run faster without temperatures first changing, sucking CO2 levels down and lowering temp's - The collision between India & South Asia that started around 50 million years ago, pushing up the Himalayas may have started the cooling leading to our current cycle of Ice Ages.

Another important factor in creating Ice Age conditions is the position of the continents - to have Ice Age conditions you need land near the poles where ice can build up such as Antarctica & Greenland today. As ice builds up it reflects more sunlight back into space, creating conditions much like the Earth was in the distant past. Essentially more Ice has the same effect as when the Sun was colder. But CO2 levels are lower than in the more distant past so the planet turns cold.

A major earlier Ice Age starting around 300 Million years ago was associated with the time of the break up of the ancient supercontinent of PanGaia as parts of the continent drifted towards the poles and ocean currents changed significantly. Also part of this period was called the Carboniferous - the Age of Carbon. This was the point in time when major forests first evolved and covered the land, being then laid down to form the Coal we are digging up today. So this was sucking more CO2 out of the air.

The old geological record is quite consistant with CO2's role as a Greenhouse gas and that effect continues right up to very high levels indeed. We might never have been here without it.

If someone tells you that the geological record shows that CO2 isn't connected to temperatures in the distant past, that is like saying that the temperature in your house isn't related to how high the heating system is running, without first checking to see how cold it is outside!

2010-11-04 19:15:30Better link
Glenn Tamblyn

glenn@thefoodgallery.com...
121.219.107.173

Steve

Better link to Monty Hieb is http://www.geocraft.com/WVFossils/Carboniferous_climate.html

Glenn

2010-11-04 20:43:26
Rob Painting
Rob
paintingskeri@vodafone.co...
118.92.86.142
Glen, sounds like you've established a blueprint for the advanced version (hint, hint)
2010-11-07 13:05:19
steve.oconnor

steve.oconnor@hotmail...
124.171.101.46

hi glenn,

thanks for taking the time to comment. the thermostat is a great mechanism, but my first impression in reading your post is that you've left out another important mechanism for CO2 drawdown: life! the early to mid ordovician period saw an explosion of life in the ocean that drew down CO2 and cooled the oceans quite a bit (this was an important precursor for the hirnantian glaciation). as Trotter 2008 puts it:

"The clear paleontological evidence of increased biomass throughout the water column and consequent increased carbon burial, an important controller of atmospheric CO2 concentration, probably contributed to this cooling trend."

I've seen that graph you pointed me towards before, but i'm not sure how much i trust it: from the papers i've studied the temperature is not in fact stable through the ordovician (the only period i've looked at in depth) and the CO2 levels don't resolve "fine" enough detail to cover the glaciation event. Although a lot more is now known about the hirnantian now as was several years ago, the detailed picture is still quite complex and there are remaining questions over cause and effect.

i'm reworking the rebuttal as we speak and i'd be grateful for further feedback when i post it up. i hope i didn't misunderstand your post, so please correct me if i'm off base.


2010-11-08 19:43:17
Glenn Tamblyn

glenn@thefoodgallery.com...
121.214.15.248

Steve

My point in referencing that graph is that it is the one frequently used by the sceptics when making this claim.

Life is most certainly a factor. Something that it easy to forget when looking at a graph covering that period is that it covers virtually all of the history of the evolution of complex life on Earth. So changes in the biosphere certainly will have an impact.

My take on what is likely to have been the scenario over the Earth's history is as follows. On the very longest time scale, out to billions of years, Co2 emissions from background vulcanism is balanced to the Sun's changing output by 'the thermostat'. On the next time scale down, perhaps tens of millions of years, the new factors at play become the evolution of life and the resulting changes in the size of the biosphere, episodic periods of much higher levels of vulcanism and consequent CO2 outgassing, and the breakup and movement of continents, affecting ocean currents and the predisposition to Ice Ages. And CO2 levels in the atmosphere are then driven further by the changing carrying capacity of the ocean due to temperature changes.

Specifically on the impact of life, its major influence in changing climate will tend to be when their are events that have a major impact on the size of the biosphere. Big evolutionary changes, mass extinctions, major climate variations due to other factors etc. When the size of the biosphere is stable, then the size of the carbon sink it represents won't be changing much and won't contribute to climate perturbations much. If the size of the sink grows or shrinks significantly, this can have a big impact on carbon fluxes. So major biosphere changes potentially trigger climate changes. Or act as a feedback to other changes.

Glenn

2010-11-09 09:55:02
steve.oconnor

steve.oconnor@hotmail...
152.91.63.37

ok, cool. thanks again for the feedback.

one area that i find fascinating is how bacteria, vegetation and litchens etc can alter that thermostat by radically accelerating the speed of silicate weathering (up to a factor of 1000 i believe.) it's a real lovelockian daisyworld, but vastly more complex! 

2010-11-09 19:16:34
Glenn Tamblyn

glenn@thefoodgallery.com...
121.214.139.47

Steve

I hadn't heard about the lichen effect. I am working on the advanced rebuttal for this claim (it might take a while - work pressures, making money, groan, whinge etc) so do you have a reference of some sort on this?

G

2010-11-10 15:02:10
steve.oconnor

steve.oconnor@hotmail...
203.166.51.62

Here ya go!

"A study of Hawaiian basalt flows of known age indicates that there is an acceleration of chemical weathering on the order of at least 10 to 100 times for lichen covered surfaces relative to bare rock
...
We propose, therefore, that chemical weathering under biotic conditions is significently enhanced relative to abiotic continental crust exposed to similar rainfall, temperature and PCO2 conditions. The enhancement factor is uncertain; the key role of soil stabilization combined with other biotic effects suggests factors on the order of at least 100 to perhaps > 1,000."

"Biotic enhancement of weathering and the habitability of Earth" Schwartzman & Volk, Nature 1989 (340)

2010-11-11 13:59:57here goes...
steve.oconnor

steve.oconnor@hotmail...
203.166.51.62

Generally speaking, the further we look back into Earth's past, the harder it becomes to recreate exact climate histories. Dramatic events are often preserved in fossil records, but usually only a fraction are accessible for analysis. Many valuable pieces of the puzzle are either lost in time or too degraded to get meaningful results from. Plausible hypotheses are thus created and constantly re-tested as evidence accumulates and techniques improve. A consistent narrative emerges.

One such hypothesis (backed by an increasing body of theoretical work) is that CO2 is the major "control knob" that regulates the Earth's climate, so any evidence found to contradict this is extremely useful for scientists to examine. One of the most controversial events to recently challenge the prevailing wisdom is evidence for a major glaciation (ice-cap) that formed on the ancient supercontinent of Gondwana roughly 444 million years ago (during the Hirnantian Stage of the Late Ordovician period.)

This glaciation is unique not just because of its short duration (it lasted a 'mere' million years or less) but because it happened at the same time as one of the biggest extinctions in Earth's history and coincided with a major disturbance to the global carbon cycle.

Not only that, but according to some it occurred when CO2 levels were sky-high; as Ian Plimer states in 'Heaven and Earth', pp165:
 
"The proof that CO2 does not drive climate is shown by previous glaciations...If the popular catastrophist view is accepted, then there should have been a runaway greenhouse when CO2 was more than 4000 ppmv. Instead there was glaciation. Clearly a high atmospheric CO2 does not drive global warming and there is no correlation between global temperature and atmospheric CO2."

It seems at first glance like the skeptics are right! However, this polemic argument is a somewhat superficial view of something rather more complex and interesting. In order to unravel this apparent contradiction, several key pieces of information have to be taken into account. 

Firstly, models of energy production in the sun's interior (hydrogen converting to helium by nuclear fusion) indicate it was about 4.5% dimmer during the Late Ordovician. This result - combined with the logarithmic forcing effect of extra greenhouse gases - means that the maximum CO2 concentration needed for ice-caps to exist is much higher than now (in the order of 3000 ppmv.)

It's also important to realise that geochemical CO2 reconstructions in the deep past (such as Berner's GEOCARB model) are invaluable but subject to huge uncertainties. Berner himself cautions:

"This type of modeling is incapable of delimiting shorter term CO2 fluctuations (Paleocene-Eocene boundary, late Ordovician glaciation) because of the nature of the input data which is added to the model as 10 my or longer averages. Thus, exact values of CO2, as shown by the standard curve, should not be taken literally and are always susceptible to modification."

Many contrarians, including Plimer, state as fact that CO2 levels were more than 4000 ppmv during the glaciation, but this is simply not scientifically accurate. Not only are the upper and lower bounds very large in the GEOCARB model, this particular glaciation represents about a tenth of a single time-step.
 
The ocean temperature leading up to the glaciation (through the Early-Middle Ordovician) is now known to be lower than previously thought thanks to improved proxy reconstructions. This seems to have created ideal conditions for a huge spurt in marine biodiversity and also a large drawdown of CO2 from the atmosphere through carbon burial in the ocean. A large period of mountain-building was also underway (the so-called Taconic orogeny) increasing the amount of rock weathering taking place and subsequently lowering CO2 levels even further.

With the CO2 low enough, glaciers would have started to form on a small scale (perhaps at slightly elevated altitudes.)  The close proximity of the ocean would have provided significant thermal inertia, keeping temperatures low enough for snow to accumulate during the Summer months, while the ice-albedo feedback effect would have further accelerated this process, leading to widespread glaciation.

As more of the continent became covered in ice, this would have reduced the ability of rocks to absorb excess CO2 accumulating in the atmosphere (through volcanic activity.) At a critical point, the CO2 levels would have been enough to tip the climate into a new regime, where rapid warming took place and the glaciation ended.

The hypothesis that CO2 is a major regulator for the Earth's climate (past, present and future) is supported by the current body of scientific evidence. Hopefully this example makes it clear that many other factors can (and do) come into play, which is why simplistic narratives are often simply wrong.

2010-11-14 08:27:28thumbs up
jimalakirti

jimalakirti@gmail...
76.113.66.180
Nice job. I think the level of linguistic and scientific sophistication is very good.
2010-11-18 22:53:12
Riccardo

riccardoreitano@tiscali...
192.84.150.209
Good job. I'd only add, in the last sentence, what John keeps repeating, always look at the full body of evidence.
2010-11-19 14:32:00
steve.oconnor

steve.oconnor@hotmail...
203.166.51.62

I've changed the last paragraph from:

The hypothesis that CO2 is the major regulator for the Earth's climate (past, present and future) still remains to be challenged.

to

The hypothesis that CO2 is a major regulator for the Earth's climate (past, present and future) is supported by the current body of scientific evidence. Hopefully this example makes it clear that many other factors can (and do) come into play, which is why simplistic narratives are often simply wrong.

based on Riccardo's feedback - i think it reads a bit better... let me know what you think

2010-11-26 12:16:04
Andy S

skucea@telus...
66.183.167.232

I'm new to this rebuttal and it's remarkable to read the entire thread and see how the article has evolved. It started out as a overly simple  few lines and grew into a longish article that I enjoyed reading. (I actually think that it's now a bit too advanced for a Basic Rebuttal, but never mind.)

I don't like the very last line. I would change that to something like: Carbon dioxide is indeed the Biggest Control Knob but it's not the only factor that influences climate and if we try to argue that there is an overly simple relationship between climate CO2 and climate, we will get important parts of the story wrong

I added a link to Richard Alley's great talk . Incidentally, I wish there were more links in this article to good references. One of the very best things about SkSc is the links to further reading and I would like to see some links or references added (Berner's article, for example) to this one.  

Nevertheless, thumbs-up.

2010-11-26 12:27:56
steve.oconnor

steve.oconnor@hotmail...
152.91.63.37

thanks andy s!

Actually, I wasn't happy with the last line either, as i think that sometimes simple narratives *can* be right too (eg. add CO2 and you get warming, all else being equal) so i might rewrite that along the lines your suggesting (mebbe this afternoon after a nice cup of tea.)

I was not sure whether to put references in or not.. what's the consensus? 

2010-11-26 13:50:14
steve.oconnor

steve.oconnor@hotmail...
152.91.63.37

Reading through this again, I'm inclined to agree with andy s that this might be a bit long-winded for the Basic version, however, the intermediate is already done and the advanced is currently earmarked by Glenn Tamblyn (there's no preview, but not sure how much work he's done on this.)

I also think that a graphic or two may be a good idea to help clarify things.. perhaps something like the following:

Ordovician Glaciation 

 sorry for the bad formatting... it was just a quickie (the numbers are all made up)

2010-11-26 17:03:42
steve.oconnor

steve.oconnor@hotmail...
152.91.63.37

changed the last para to:

The hypothesis that CO2 is a major regulator for the Earth's climate (past, present and future) is supported by the current body of scientific evidence. However, CO2 is not alone in influencing the climate, and if we ignore other factors we will get important parts of the story wrong.

2010-12-02 13:40:41Here's a *really* basic version - note that graph is quick mock-up only
steve.oconnor

steve.oconnor@hotmail...
152.91.63.37

Geologists refer to ancient ice-cap formations and ice-ages as "glaciations." There was one such glaciation that happened about 444 million years ago (long before dinosours existed) that has got climate contrarians excited. It happened in the last part of the Ordovocian era, thus is popularly known as the Late Ordovician glaciation.

Unlike other glaciations in the last 500 million years, this one was exceptionally brief, lasting perhaps only a million years or so, and it happened when CO2 levels were apparently sky-high:

"The proof that CO2 does not drive climate is shown by previous glaciations...If the popular catastrophist view is accepted, then there should have been a runaway greenhouse when CO2 was more than 4000 ppmv. Instead there was glaciation. Clearly a high atmospheric CO2 does not drive global warming and there is no correlation between global temperature and atmospheric CO2." [from Ian Plimer's "Heaven and Earth" pp165]


On the surface, this may seem to contradict what climate scientists are currently saying about the link between CO2 and warming, but that's not really the case.

Plimer and other climate contrarians are reading off CO2 levels from a well-known geochemical model called GEOCARB, which is not really suitable for such short events. It has time-steps of 10 million years plus huge uncertainties around that time period. Recent research has uncovered evidence for a cooler ocean back then and a dip in CO2 levels (caused by rock weathering and carbon burial in the ocean) that wouldn't have been picked up by GEOCARB.

What's more, the sun was several percent dimmer in the Ordovician, which would have raised the threshold for glaciation to around 3000 ppmv. The illustration below shows what real CO2 levels may have possibly looked like:

 

Example only

Although CO2 is a key player, it is not alone in influencing the climate. This glaciation is a great example of how multiple factors combine to complete the story.

2010-12-09 15:06:51Pragmatic thumbs-up
James Wight

jameswight@southernphone.com...
112.213.154.195

This rebuttal has languished for too long. Thumbs up to either the long or short version.

2010-12-09 15:34:12Weird
James Wight

jameswight@southernphone.com...
112.213.154.195
I meant to give you a thumb but the thumb icon seems to have disappeared.
2010-12-21 16:38:07Thumbs up to either short or long version
James Wight

jameswight@southernphone.com...
112.213.166.150
The thumbs are back.
2010-12-21 16:42:15
Glenn Tamblyn

glenn@thefoodgallery.com...
121.220.25.32
Good to Go
2010-12-23 09:33:39final version
steve.oconnor

steve.oconnor@hotmail...
152.91.63.37

thanks for the comments etc.

i wasn't happy with the tone of my previous version (stridently anti-denier) which on second thoughts is perhaps not that helpful to our cause. so my final version (with fixed up diagram and more neutral tone) can be seen via the rebuttal list.

sorry for making so many changes.. i will strive to do better in the future.

2010-12-24 08:18:40Published
John Cook

john@skepticalscience...
123.211.206.13

Great diagram, Steve, I love how you communicated so much so simply - the dotted line with the glaciation threshhold is awesome. And your rebuttal made me realise how I'd answer the "CO2 was higher in the past" argument very simply:

  • Back when CO2 was higher, the sun was cooler - without the higher CO2, the earth would be frozen. 

Simple as that - turn their higher CO2 argument on its head - it's actually EVIDENCE for the warming effect of CO2. Very nice way of putting it.

Just curious, what program did you use to create your graphic? Did you guestimate the shape of the CO2 line?