This was an email I sent to Brendan a few weeks ago. Thought I'd repost to get a response :)

I'm an environment-minded liberal democrat who loathes oil companies and believes without hesitation that we as a society need to do more to protect the earth. Having fronted this "green cred," however, I am perplexed by a paradox that seems to render the Anthropogenic Global Warming hypothesis dubious. It has to do with the fact that ice core data demonstrate that for hundreds of thousands of years, there's been an historic 800 year lag between CO2 levels and temperature. Temperature goes up, then 800 years later, CO2 levels go up. Temperature goes down, 800 years later, CO2 levels go down. Using Occam's Razor, this suggests that CO2 changes do not drive climate change, but rather that climate change drives changes in CO2 levels. I have read widely, and I cannot find a coherent (from the AGW perspective) explanation for this lag. Please see this blog entry for a more complete argument. <link>.

Can you (or another AGW expert) explain this lag in plain language?

Thanks!

Liberal Democrat; Global Warming Agnostic

Right. You're a Democrat. Sure. But to answer the general question --

In the past, increases in CO2 levels don't initiate the warming between ice ages. Other things besides CO2 affect the climate. It does NOT mean CO2 doesn't cause global warming. (In fact, without the green house affect, we'd be dead on an iceball.) It also does NOT mean that man-made CO2 level increases won't cause warming.

For a more complete explaination try this link: <link>

Of course, an actual answer wasn't what you were after.

Well basically you're missing the point entirely.

<link>

Using Occam's Razor, this suggests that CO2 changes do not drive climate change, but rather that climate change drives changes in CO2 levels.

That may be true in the natural climate cycle. But that's not what we're talking about, is it? We're talking about perturbing the natural cycle with a giant infusion of CO2. That this isn't what drives the natural cycles is hardly the point. In fact, it's completely irrelevant.

I am a very solid dem. Obama supporter in fact. And I'm all in favor of super strict environmental regulations. Hell, even if global warming isn't man made, I'm sure there are bad things we're doing to the planet that we haven't even identified.

I've actually read and parsed that realclimate.org post carefully - as well as that motl response post. Still seems the AGW argument is massively flawed. And even if the realclimate explanation holds up - let's just say it's completely right - it's at the very least incredibly dubious and intellectually dishonest that Al Gore (and other AGW enthusiasts) have glossed over the potential mischief this 800 year lag counterargument could have on the theory.

My only request is - let's be scientific! Science never "proves" an argument one way or another. It creates and tests hypotheses. But its conclusions and inferences can always be changed when new evidence comes to light. Newton's laws of motion, for instance, held up for ~200 years until Einstein introduced relativity. It often appears that pro-AGW advocates have enshrined their dogma as absolute truth. Perhaps the AGW models are right - but science is about looking hard at contradictory evidence, not brushing it under the table.

by the way, to address your points:

1) "It does NOT mean CO2 doesn't cause global warming." TRUE

2) "It also does NOT mean that man-made CO2 level increases won't cause warming." TRUE

3) "Of course, an actual answer wasn't what you were after." PARTIALLY TRUE, I'll admit :) I want to be provocative, but I also TRULY want to figure this out. I am willing to eat my hat, proverbially. I used to think global warming deniers/agnostics or whatever you want to call them were either complete lunatics or shills. Now I've kind of completely flip flopped. Only science and logic can save us from our emotional responses. And then, only some of the time.

" I want to be provocative, but I also TRULY want to figure this out. I am willing to eat my hat, proverbially. I used to think global warming deniers/agnostics or whatever you want to call them were either complete lunatics or shills. Now I've kind of completely flip flopped. Only science and logic can save us from our emotional responses. And then, only some of the time."

You can not question, you can not use science, you can not use (or find) logic, you must accept not just global warming, but man made global warming as fact. Any thing else labels you as a:

1. Shill for big oil (whatever that is)

2. Republican talking point perpetrator

3. global holocaust denier

4. stupid, uneducated, uniformed, moron

5. All of the above.

You are not allowed to have or voice an opinion, even in the form of a question. Now, go to your room and start calculating the size of your carbon footprint.

roarmouse...from everything I understand, it's not that people are trying to sweep some 800-year lag under the carpet because people are "dishonest," or it could cause a big problem for the man-made global warming theory. The 800-year cycle is part of an accurate description of the natural cycle of how carbon acts in a natural environment. Temperature rises, carbon rises with it, and vice versa. However, we have artificially raised the carbon emissions, causing the present carbon levels to be an unnatural varient, something we haven't observed before. Carbon emissions are now running up and independently of temperature and other natural variables. Therefore, we can't really use the 800-year lag, because it is part of that natural cycle that we have now altered, leaving it up to models, etc to try to figure out what effect the raised carbon emissions could have on temperature and other variables.

hi ajb,

you're completely right that we're injecting unnatural amounts of CO2 into the atmosphere. No one with a brain would deny that humans are causing CO2 levels to spike (although there is a legitimate argument over how novel and important this increase is. volcanoes and other natural sources produce far more CO2 per year than humans do.)

The reason I think the lag is such a potentially big deal is that it suggests that the cause and effect relationship between CO2 and temperature may be inverted from what the pro-AGW models suggest. In other words, changes in temperature drive changes in CO2, not the other way around.

Here's a bad analogy. Let's say that we observe a person for a year. When it's cold out, she wears a sweater. When it's hot out, she doesn't wear a sweater. Our natural - and correct - assumption is that she puts on and takes off the sweater in response to the temperature outside. The converse argument - that when she wears a sweater, she causes it it be cold outside, and when she takes the sweater off, it heats up outside - makes zero sense. It's laughable. But that's exactly what's the pro-AGW contingent seems to be suggesting here with respect to CO2 and temp.

That there's a lag is beyond dispute. We have evidence of this continuous relationship going back hundreds of thousands of years. Temp goes up - then 800 years later, CO2 levels go up. Temp goes down, 800 years later, CO2 levels go down. It's a continuous phenomenon easily explained by "AGW skeptics" who contend that climate change is driven (mostly) by the sun. When the sun heats the earth, the oceans degas CO2, causing temps to rise (it takes 800 years according to models for CO2 to degas from the oceans). Conversely, when the sun cools, the oceans cool, and CO2 gets sucked back into the water. By the way, I believe methane levels follow the same trajectory as CO2 - piling on further evidence that CO2 has not historically been a (significant) driver of climate change but rather a consequence of it.

what do you make of this? would love to hear responses! thanks...

roarmouse:

what do you make of this? would love to hear responses! thanks...

Roarmouse , I think that question has been asked and answered multiple times already. Your whole argument seems to be based on; if event A causes event B, then B can't possibly cause A, which is an assumption without basis.

Nobody is disputing that the sun and Earth's orbit around it have caused fluctuations in Earth's climate in the past, or that these fluctuations resulted in increased atmospheric CO2. What people are saying is that there also exists a mechanism whereby increasing CO2 can result in climate change. Why do you assume these two ideas are mutually exclusive?

roarmouse:

I just wrote about this on another thread, but I'll post here. If you're really just trying to be provocative, I'm wasting my time, but I'll assume that you actually want to understand the issue.

It's true that, historically, increased CO2 levels have not been the original cause of warming periods. I'm an astrophysicist, so I know a little about this — there's an astronomical theory of climate change. The Earth's orbit changes in several ways on long time-scales (thousands of years), which affects how much sunlight the Earth gets. The Sun's activity varies on more like a decadal time-scale. The Sun's output can change on longer time-scales, too. The Solar System travels on its trajectory around the center of the Galaxy, and passes through dustier and less dusty parts of the interstellar medium. Supernovae explode and their high energy particles hit the Earth's atmosphere. I could go on.

And it's true that increased temperatures lead to higher CO2 levels, on a roughly 1000 year time-scale. (okay 800, whatever.) This is because the ocean stores lots of CO2 — 50 times as much as is in the atmosphere. And CO2 is more soluble in colder water than in warmer water. It takes around 1000 years for the deep ocean to warm significantly after the surface starts to warm. So, the surface warms, several hundred years later, the ocean has warmed, and CO2 starts to come out of solution and go into the atmosphere. (Incidentally, there are comparable positive feedback loops for methane.)

That's all true. But it's also true that CO2 IS a greenhouse gas. Physicists can (and do) study the optical properties of CO2 in the lab. The molecule has well-known, well-characterized strong absorption bands in the infrared part of the spectrum. As a result, when there is more CO2 in the atmosphere, the greenhouse effect is stronger, and this contributes to rising temperatures. There is no (scientific) debate about this; it is fact.

So, the way this all works together is that, occasionally in the Earth's history, something causes temperatures to begin to rise; and several hundred years later, CO2 levels start to rise and contribute to increased warming. CO2, therefore, acts as an amplifier of the astronomical forcings of climate. It allows warming periods that would have lasted only 1 or 2 thousand years, and caused only a 2 or 3 degree (Celsius) rise in temperature, to instead last 10 thousand years or more, and cause a 12 degree (Celsius; 21 degree Fahrenheit) rise in temperature.

No one's sweeping anything under the rug. Al Gore's movie was not disingenuous at all. He never claimed that CO2 is typically the original cause behind global warming periods. The 800 year lag is real, is well-understood, and casts no doubt on CO2 as a potent greenhouse agent.

Sanjait: Very nice, pithy post.

Hi dslack and sanjait,

Thanks for your posts - very glad to be debating with an actual astrophysicist. I got a B.S. in geophysics from Yale but have since forgotten the vast majority of what I learned :)

As to your points:

sanjait:

1) "Your whole argument seems to be based on; if event A causes event B, then B can't possibly cause A, which is an assumption without basis."

I'm not saying B can't cause A. Obviously, when you're dealing with a complicated subject like climate, it's hubristic to make a simple connection like that. A and B clearly influence each other. CO2 obviously does impact the climate! The question is - to what degree has it done so historically? And I'm suggesting this lag thing casts doubt on the popular idea that CO2 has always and will continue to be the primary driver of climate change.

2) "Nobody is disputing that the sun and Earth's orbit around it have caused fluctuations in Earth's climate in the past, or that these fluctuations resulted in increased atmospheric CO2. What people are saying is that there also exists a mechanism whereby increasing CO2 can result in climate change. Why do you assume these two ideas are mutually exclusive?"

This is a good point. I should be more clear. Again, I'm not saying that CO2 can't drive climate change. I'm sure it does, to some degree. I'd have to be an idiot to argue that it has zero influence. And - who knows - maybe the realclimate explanation is correct. But what I'm saying is that the simplest possible way to explain the lag is to say that temp drives CO2. I'm not saying it's the right answer - just that it seems to be the simplest. Thus, using the principle of Occam's Razor, it should be given serious consideration as a scientific hypothesis.

dslack:

I am totally in concordance with you for your first three paragraphs.

My issues come here:

1) "So, the way this all works together is that, occasionally in the Earth's history, something causes temperatures to begin to rise; and several hundred years later, CO2 levels start to rise and contribute to increased warming. CO2, therefore, acts as an amplifier of the astronomical forcings of climate."

okay first point. what is that "something" and shouldn't that be the focus of our investigation? And if we assume that that "something" is the sun, we've fully explained why the lag exists - you in fact eloquently made this case when discussing how the oceans aspirate CO2.

second point. where in the data is the evidence that CO2 acts as an amplifier to climate change? this is the heart of the matter to me. I understand that there's a complex mathematical way to model that this can happen, but where's the proof in the pudding, the physical evidence?

third point. even if the CO2-as-amplifier model works to explain the data, why is this the almost-universally preferred interpretation among AGW enthusiasts? why does the temp-drives-CO2 argument not also merit scientific consideration? where's the ice core data (or other evidence) that categorically refutes the temp-drives-CO2 idea?

2) "No one's sweeping anything under the rug. Al Gore's movie was not disingenuous at all. He never claimed that CO2 is typically the original cause behind global warming periods."

Al Gore shows a correlation between CO2 and temp stretching back hundreds of thousands of years and then breathtakingly assumes causation from it. He implies (if not outright states) that CO2 has always driven temperature. At the very least, the fact that he and other pro-AGW scientists rarely if ever address this 800 year lag issue should raise eyebrows because it's not scientifically easy to parse.

3) "The 800 year lag is real, is well-understood, and casts no doubt on CO2 as a potent greenhouse agent."

I take issue that it "casts no doubt" - as so do many reputable scientists. well, I'm not a scientist, but you get what I mean :)

thanks for this spirited and fun discussion. Again, I'd love to hear your responses...

roarmouse:

dslack:

I am totally in concordance with you for your first three paragraphs.

My issues come here:

1) "So, the way this all works together is that, occasionally in the Earth's history, something causes temperatures to begin to rise; and several hundred years later, CO2 levels start to rise and contribute to increased warming. CO2, therefore, acts as an amplifier of the astronomical forcings of climate."

okay first point. what is that "something" and shouldn't that be the focus of our investigation? And if we assume that that "something" is the sun, we've fully explained why the lag exists - you in fact eloquently made this case when discussing how the oceans aspirate CO2.

second point. where in the data is the evidence that CO2 acts as an amplifier to climate change? this is the heart of the matter to me. I understand that there's a complex mathematical way to model that this can happen, but where's the proof in the pudding, the physical evidence?

third point. even if the CO2-as-amplifier model works to explain the data, why is this the almost-universally preferred interpretation among AGW enthusiasts? why does the temp-drives-CO2 argument not also merit scientific consideration? where's the ice core data (or other evidence) that categorically refutes the temp-drives-CO2 idea?

Okay, great questions. In the interest of brevity, I eliminated some important details from the previous post.

first point: Historically (i.e., within the last several hundred thousand years), that "something" does not tend to be the Sun. For large swings in CO2 and temperature, that "something" has typically been changes in the Earth's orbit and rotation. There are several types of changes, and they have different periods, but these cycles operate on time-scales of tens of thousands of years.

second point: Based on the variation in orbital parameters, we can predict the changes in temperature and how long they should last. This is the "warming periods that would have lasted only 1 or 2 thousand years, and caused only a 2 or 3 degree (Celsius) rise in temperature" that I was referring to. The point is, we know how sunshine varied on the Earth's surface as a result of orbital changes, and those changes do not seem sufficient to explain 10,000+ year, 12°C warming periods. We also know how CO2 varied during that those warming periods, and when we take into account the infrared absorption of CO2 — the greenhouse effect caused by it (which I discuss below in response to your third question) — we see the the 12° higher temperatures are (relatively) easily explained.

Simply put, higher levels of CO2 have to lead to higher temperatures, as I describe below. When these higher temperatures caused by higher CO2 concentrations follow higher temperatures that were caused for some other reason, it is natural to say that the CO2 has amplified the original increase in temperature.

This is a positive feedback loop, because as temperatures go up, more CO2 leaves the oceans, and this in turn causes temperatures to go up more. Again, there is no real doubt about this (see below). This sort of positive feedback definitely exists. The extent to which it will lead to higher temperatures now is not entirely clear, because there are many other feedback processes at work too. But higher CO2 levels, all else being equal, definitely lead to higher temperatures. I can't emphasize this enough.

--- Let me return to your question though. ---

What sort of physical evidence (pudding) would satisfy you? To me, it's a pretty good explanation to say that the astronomical forcings cannot explain the observed duration or amount of warming, whereas including the thermal effect of the concomittantly rising CO2 concentrations does explain the duration and amount of warming. If this is not a convincing argument to you, again, what sort of argument would you find convincing?

third point: I'm not really sure what you mean. Temperature does drive CO2, and CO2 also drives temperature. The feedback loop is well understood. If I were an omnipotent being, and, BAM!, I raised the temperature of the Earth by 10°C for 1000 years, the CO2 level would go up. If I alternatively raised the CO2 concentration by 200 ppm for 1000 years, the temperature would go up. As it works out in the real world, long-term temperature increases lead to higher CO2 concentrations, and those in turn lead to further increased temperatures.

roarmouse:

2) "No one's sweeping anything under the rug. Al Gore's movie was not disingenuous at all. He never claimed that CO2 is typically the original cause behind global warming periods."

Al Gore shows a correlation between CO2 and temp stretching back hundreds of thousands of years and then breathtakingly assumes causation from it. He implies (if not outright states) that CO2 has always driven temperature. At the very least, the fact that he and other pro-AGW scientists rarely if ever address this 800 year lag issue should raise eyebrows because it's not scientifically easy to parse.

Look, Al Gore has a limited amount of time in his slideshow to make a point. He didn't give a perfectly detailed explanation. He didn't explain precisely how infrared photons scatter off CO2 molecules. And he didn't mention the lag, as far as I can remember. I'm not here to defend his movie (even though I guess I tried to earlier), which I don't remember perfectly and may be flawed.

But the point is, as Sanjait and I have been emphasizing, it's not a simple matter of causation, like A causes B or B causes A. It's a situation where, historically, A and B amplify one another. It's a feedback loop. The physical processes at work in the loop — the optical properties of CO2 and its solubility in water — are well understood.

roarmouse:

3) "The 800 year lag is real, is well-understood, and casts no doubt on CO2 as a potent greenhouse agent."

I take issue that it "casts no doubt" - as so do many reputable scientists. well, I'm not a scientist, but you get what I mean :)

thanks for this spirited and fun discussion. Again, I'd love to hear your responses...

Okay, I guess you're being kind of picky here when I said it "casts no doubt", I meant it casts no legitimate doubt.

Scientists, even many reputable ones, can be wrong (though I think you'll find scant few physicists who doubt the infrared opacity of CO2). When Einstein published his paper on General Relativity, a group of physicists who didn't like the idea published a pamphlet titled, "100 Physicists Against Einstein". Einstein's response: "If I were wrong, it would take only one to show it." I'm not calling myself Einstein here. But I am saying that laboratory studies of the rotational and vibrational modes of CO2 have conclusively shown that it absorbs and re-emits (i.e., scatters) infrared light efficiently.

No serious, knowledgeable scientist doubts that CO2 is a potent greenhouse gas. The fact that lay people do only demonstrates the extent to which oil companies etc. have succeeded in obfuscating this basic fact.

I'm not at all claiming that there is agreement on the precise amount of warming that a given amount of additional atmospheric CO2 is likely to cause, because the atmosphere is a dynamic system with all sorts of interconnected climatic feedback loops. But it is fair to say that with all else being held constant, the thermal effect of a given addition of CO2 CAN be precisely predicted. The reason there are disagreements is that, in the real world, all else is not remotely held constant. But I emphasize: it is the many other feedbacks, not the optical properties of CO2, that (serious, knowledgeable) people disagree on.

Dslack,

Thanks so much for taking the time to lay out such a detailed and nuanced and compelling case! At the end of the day, I don't think we're so far apart. I want to reflect on your points in more detail, but alas I have a crushing work deadline for a project due Sunday at noon. I'll post a response after that, if you want to continue this conversation...

Hi dslack, not sure if you're still reading this, so I don't want to post a long reply...

but thanks again for your long thoughtful answers. lots to reflect on