I know that temperature rises and falls. But there has been no overall upward trend over the past 10,000 years. Ie temperatures in the 1900s were no warmer than temperatures 10,000 years ago. So the Earth is not in some long term warming trend. It is actually in a long term slight cooling trend. The warming that bought us out of the glacial period was a rapid rise of 8C and that occured in a few thousand years over 10,000 years ago. So recent temperature rises cannot just be attributed to part of some long term warming trend that simply doesn't exist.

It's a physical reality. CO2 is a greenhouse gas and so "blankets" heat. Look at how hot venus is for example with it's co2 thick atmosphere.

That might have been true 10 years ago, but subsequent rises since then mean that most of the temperature rise has occured in recent decades.

The media did. But the scientists did not.

CO2 is not the only factor. You also have aerosol levels which cause a cooling effect (aerosols decreased since the 70s due to tighter pollution regulations) as well as solar (which could have been responsible for much of the early centuries warming). The warming trend due to co2 is on top of natural variability, not in place of it.

No, but I cannot see how the magnitude of recent warming can be attributed to a geologically slow process spanning 100K years

How do you define "coming out of an ice age"? Does a 10,000 year cooling trend constitute "coming out of an ice age?", or is there some other basis for saying we are coming out of one?

No, we are on an interglacial peak at the moment. Here is a graph that goes back a bit further from the other one. It's regional of greenland rather than global but it mirrors the overall large scale changes:



It's because there is a lack of natural explainations that can fit the fingerprints of the recent warming.

Now I see why we are disagreeing. You are talking about massive ice ages that occur over periods of millions of years wheras I am talking about ice ages that occur over periods of hundreds of thousands - ie glacial and interglacial periods. The massive ice ages you are talking about are composed of hundreds of up and down "teeth" which are glacial and interglacial periods. Ie:



I especially don't see how 100 years of warming can be attributed to whatever long term mechanism is responsible for trends over millions of years.

So what? What does 10,000 years mean to a 100,000+ year process? Can temperatures not rise, fall back, rise again, fall back again, and still be considered coming out of an ice age?
That simply isn't true. CO2, and other "greenhouse" gases, do not act as a "blanket". Perhaps you mistyped.

However, that is not the issue posed in my rebuttal to your assertion that increases in CO2 concentrations started the Earth on a warming trend 100 years ago. At no time in known history has increasing CO2 concentrations led temperature increases. Increases in CO2 concentrations have always lagged increases in temperature - in both directions.
Really? I'm sure you have a source for this. How much has the planet's temperature increased from 1950 to now?
Oh? What do you consider Steven Schneider?
But it's the only factor in the warming you claim over the past 100 years? It's certainly none of the forcings that are taking (or have taken, if you prefer) us out of the last ice age, right?
The warming of the past 100 years is not anomalous in the history of the planet. In fact, the planet has gone through several relatively rapid increases and decreases in temperature before we even showed up. Why is it so outlandish to imagine the planet cannot experience a rapid rise in temperature, a period of stasis (or even falling), before resuming its rise - perhaps even suddenly?
Well, we're still in one. There is ice at the poles, not a very common state for the planet to be in. It's getting warmer than it was when we had bigger ice sheets at the poles. We're not falling into an ice age (because it's getting warmer); we're not out of an ice age (because there's still ice at the poles); so that only leaves coming out of an ice age.
It's a "peak" because your graph can't predict the future. Is it impossible that, 100,000 years from now, your graph might simply be a tiny straight line in a longer general uptrend? I mean after all, isn't that what you're arguing - that the temperature is only going to keep going up?
And we know all the forcings that contribute to the planet's climate?
Well, "ice age" is defined as "having ice at the poles".
Why? In a process that takes millions of years to complete, do you expect the change to be linear in any way? Can there not be periods of warmth, then cold, then warmth again while the overall temperature trend remains generally up? Do you imagine that over the span of even a few years the planet reaches the necessary temperature to melt all the ice, then simply remains stable until the next forcing plunges the temperature to a level necessary to freeze all the water over the span of another few years? That simply doesn't make sense to me, doesn't jive with any of the known forcings, and doesn't jive with any of the empirical observations.

Only if there is an overall warming trend surely, otherwise you aren't coming out of an ice age - you are stuck in it, or possibly sinking back into it slowly.

I didn't mistype. They do act as a blanket in that they keep heat in.

Not always. There are some situations where co2 rise predates temperature rise: http://mclean.ch/climate/figures/Vostok_CO2_2.gif. Although either way there are a lot of other factors in operation over thousands of years - not just co2. For example: http://www.ncdc.noaa.gov/paleo/abrup...es/figure5.gif which matches up against the glacial temperature variation quite well, especially more recently.

The co2 lags following temperature increase is by about 800 years wheras the warming continues much longer than that, meaning that any amount of the later stages of the warming could be due to the increased co2 levels as part of a feedback effect. Ie More temperature -> increased co2 after ~800 years -> further increase in temperature.

So orbital variation could have caused the initial temperature rise, which causes co2 levels to increase (somehow), which in turn caused to additional warming.

The situation is unique now in that we can be sure the recent co2 rise has nothing to do with temperature rise so I guess time will eventually put this issue to rest either way.

Here's a graph:


It's pretty close so I retract my claim down to saying it's about equal. Although just ten years ago the pre-1950 warming would have definitely been more, and I expect in 10 years time the pre1950 warming would definitely be less.

Here's a quote from one of Schneider's books (written in the 70s) that you won't find on any skeptic site:

So not a particularly good example of someone predicting future catastrophic cooling because of cooling trends from the 1950s to 1970s
Here's another that shows what his conclusions were based on, rather than what they were not:

These quotes and more involving the myth that scientists in the 70's were predicting a catastrophic global cooling can be found here: http://www.wmconnolley.org.uk/sci/iceage/

I don't claim that. The warming caused by the manmade co2 rise is on top of any natural variation in temperature. And natural variation will certainly exist. For example the contribution of solar activity to recent warming is factored in by climatologists.

It certainly won't be some of them such as orbital variation.

I agree

That in itself is not outlandish. But the idea that the last century of warming can be attributed to leaving an ice age is outlandish. What reason is there to attribute this centuries warming to coming out of an ice age?

There is nothing in past temperature records to give us any reason to have expected the 1900's to warm (or cool really as 100 years is too short an amount of time to be meaningful in any hundred thousand or million year trend)

In fact based on the past 10,000 year record alone we would actually expect the world at end of this millenium to be cooler than it is today.

There simply is no trend in past records that a man sitting in his room in 1890 could look at and use to predict the warming in the 20th century. So after the fact that is has warmed how can anyone simply attribute it to a historical trend that wasn't obvious before the warming?

On scale of the past few million years it is a very common state for the planet to be in. Interglacial periods (of which we are currently in one) are short lived compared to glacial periods.

We are out of a glacial period though. We might not be out of some long term million year span ice age, but on that scale the last 100 years is meaningless.

We are at the normal peak for interglacial periods. They don't really go any higher than this. I do think the temperature will continue going up but due to a unique cause.

A lot of them are known and the best one at the moment to explain most of the recent warming is enhanced greenhouse effect. There is correlation, mechanism and better compatibility with observations than other explainations.

That may be the long term million year long ice ages. But it cannot apply to glacial and interglacial periods as we are now described as having been in interglacial period for the past 10,000 years despite ice existing at the poles all that time.

No, but I don't believe you can attribute any 100 year trend specifically to such a long term process.

Yes but those periods of warmth and cold are caused by shorter term process than the process driving the temperature trend up gradually in the long term. There isn't just one process at work.

Also there is no overall temperature trend going up in the records. That has been my whole argument against attributing recent warming to such a trend from the start - the long term warming trend that recent warming is supposedly part of simply doesn't exist on a scale in which 100 years is relevant. You have to look above tens of million years of scale to find any upward trend and even then im not sure if there is one.

I don't imagine anything about change happening in a few years. It may happen in a couple of thousand.

How do you know the overall warming trend isn't still intact? Because the last 10,000 years show stasis? And it should take the planet less than 10,000 years to do whatever it's going to do? No process on the Earth takes longer than 2,000 years?
Does CO2 inhibit convection?
What study is this from? John McLean is a "computer consultant and occasional travel photographer". Though that doesn't matter, I would rather refer to the study that produced this graph. Even when he agrees with my position.

The caption that should appear below this graph, which appears on this page:

"It appears that temperature may have risen slightly before carbon dioxide 138,000 years ago but the important fact is that carbon dioxide levels remained elevated even as temperatures slowly fell. In fact it took more than 15,000 years for carbon dioxide levels to decline."

The problem with using graphs with such huge scales is that you get no detail. Distinguishing the 800-1200 years where CO2 lags a change in temperature is nearly impossible. Best to go right to the study.
But these factors have nothing to do with current warming?
Could be. Or it could be any number of other forcings - some of which we may not even know. What we do know is that CO2 concentrations have been much higher before and the planet didn't undergo runaway warming. So, obviously there is a disconnect in your "more temperature -> increased co2 after ~800 years -> further increase in temperature" paradigm.
About equal - despite the fact that the vast majority of CO2 concentrations over the past 100 years came after 1950. So, temperature goes up .5 C while CO2 concentrations experience a modest increase. Temperature goes up .5 C while CO2 concentrations experience a major increase. The relationship is so clear.
Yea, predictions are fun.
Here's another quote from Schneider:

"To capture the public imagination, we have to offer up some scary scenarios, make simplified dramatic statements and little mention of any doubts one might have. Each of us has to decide the right balance between being effective, and being honest."

Here's one from the NAS:

"There is a finite possibility that a serious worldwide cooling could befall the Earth within the next 100 years."

So, yes, scientists were promoting the idea that the world was headed for another ice age. And they were using the same scare tactics they use today. Denial is fine, but anyone could pick up Mr. Schneider's seminal paper on the subject and verify exactly what he espoused.
What's the error rate on these estimates of natural variation?
But it could be others? Perhaps even others we know nothing about?
Because the planet goes through periods of glaciation and de-glaciation with some regularity. Judging by what we know of this cycle, we seem due to move toward de-glaciation. Whatever forcings cause this to be so, it seems awful presumptuous and self-important to believe we mere ants are the cause when the planet's been doing it all by itself long before we showed up.
Of course, if you limit your history to 10,000 years. This planet has been going through its machinations for billions of years! That's three orders of magnitude longer than your graph. In short, you're missing the forest for the trees.
You write things like this and it's like you completely understand my point. I don't understand why we're having such a hard time.

Let me use your language:
Interglacial periods are shorter than glacial periods. In order to move from one glacial period (i.e. ice age --> ice-free age) you need to move through an interglacial period (perhaps many). The temperature will fluctuate up and down while still moving between a globe with ice at the poles, and a globe without ice at the poles. Therefore, it would not be unreasonable to assume that the increase in temperature over the past 100 years is a result of a continuation of the trend toward de-glaciation. In fact, it wouldn't be unreasonable for the planet to warm an additional 10C over the next 2,000 years or so before levelling off again - perhaps even going down modestly.
Eureka! Exactly! Yet we sure are attributing a lot to the past 100 years and it's measly 1C increase.
What? You make this assertion based on a database of, at most, three other occurrences? How in the world do you get "normal" from that?
Correlation, not causation; a mechanism with a disconnect; and observations based in computer models.
Why? Doesn't every series need minutia?
*sigh* There is no overall temperature trend going up in the records of the past 10,000 years. (Actually, there are several instances of the temperature going up for centuries, and going down for centuries. Seems familiar.) Does 10,000 years mean anything in a process which takes millions of years?
Even a couple thousand. Above, you agreed that the time between ice ages is millions of years. Do you imagine the Earth moves between ice ages within a few thousand years? That the temperature required to melt all the ice on the planet is reached within a few thousand years?

What overall warming trend?

Yes that is the short term trend. A century of temperature change is less meaningful on longer term trends. Ie in a long term trend of 1C increase per 1 million years the trend within a particular century is pretty meaningless.

The records show that interglacial warming occurs in a few thousand years, never longer than 10,000 years.

That's not the only way of trapping heat. I didn't say CO2 is a blanket, I said it was like a blanket in terms of trapping heat.

The Vostok ice cores http://en.wikipedia.org/wiki/Ice_core

I don't really care about whatever site that image is on. I haven't read that site. I simply googled for images for "vostok temperature". Pick any of them: http://images.google.com/images?q=vostok%20temperature

The 800 year lag is figured out from such ice core data on huge scales (http://icebubbles.ucsd.edu/CaillonTermIII.pdf). So are you now saying the lag might not even exist and might just be a side effect of using such a large scale?

No, orbital forcings operate on scales of thousands of years. The amount of orbital change in the past 100 is too miniscule to have any measureable effect on temperature. This is true of other long term forcings like overall volcanic activity of earth. They produce gradual ups and downs over hundreds of thousands and millions of years but not ups and downs within a few decades or a century. They don't variate that quick.

That is because on geological timescales co2 is not the primary forcing. Volcanic activity and orbital variance are larger factors on those time scales. Temperature over long periods of time will follow orbital variance and volcanic activity more than co2. Any warming from co2 will be over the top of these. So in a very simple example high co2 levels may cause a 4C warming effect, but if an orbital low is causing a -8C cooling effect then that will mask the warming from co2 at that point in time.

Not all positive feedbacks lead to runaway effects. The relationship between temperature increase and co2 increase is logarithmic, meaning that a doubling of co2 has a constant warming. So doubling co2 from 100ppm to 200ppm has the same warming effect as doubling it from 200ppm to 400ppm. So as more co2 increases the less warming effect each additional ppm has. This alone hampers any runaway warming.

I have already noted that there is natural variation that co2 is on top of. Every century has wobbles. You would only expect to see a perfect correlation between co2 and temperature last century if co2 was the only temperature forcing. I already pointed out that solar activity is likely to have caused some warming last century.

I don't know which site you got that from, but here is what he actually said:

What the skeptic sites have done here is shortened what Schneider did say and remove all the conditional statements. Ironically this is clearly done to make an "effective" rather than "honest" argument.

I see more parallels between the tactics of evolution skeptics and global warming skeptics all the time. Use of quote mining is just one tool of creationist sites employ. It seems global warming skeptic sites are engaging in the same strategy.

Another quote mine. This is what they actually said:

So it has been quote mined to put it out of context. All parts in bold were either omitted or modified. The 1975 NAS report is discussed here: http://www.wmconnolley.org.uk/sci/iceage/nas-1975.html

Quite clearly they were not. I cannot guarantee there weren't one or two scientists saying this, but as a whole the scientific consensus at that time was definitely not scare tactics that the world was headed for another ice age. Scientists were not sure what effect climate change would have at that time and were hypothesising about warming AND cooling effects. The skeptics cherry pick their hypothesis on cooling only and modify quotes to make it look like the skeptics were making certain predictions.

Often the skeptic sites simply strip out the conditions. For example if I say "If the sun were to turn off there would be a catastrophic cooling" the skeptic sites would strip it down to "onon predicted a catastrophic cooling".

If I claim "The future trends are uncertain. The influence of manmade co2 release may lead to warming over the next century that could be catastrophic. Another alternative is that increased aerosols lead to a cooling effect that could result in another ice age. More information is needed concerning co2 and aerosols."

The skeptic sites would say "onon predicted that increased aerosols will lead to a catastrophic cooling that could lead to an ice age".

Or if I say "We are in an interglacial period, and eventually we will fall into a period of cooling and descend into the next ice age. This may take thousands of years, or possibly hundreds"

The skeptic sites would say "onon predicted that we will fall into an iminent ice age"

The last IPCC science report contains a diagram for this:

http://www.grida.no/climate/ipcc_tar/wg1/figspm-3.htm

Could be. Any scientific theory can potentially be overturned by future observations.

We have put co2 levels to at least a 650,000 year high, possibily even higher than for millions of years back. We might be ants, but we are a lot of ants and can cause change.

A change in 100 years is totally meaningless in geological trends.

It is not reasonable for the planet to warm an additional 10C over the next 2,000 years because such a large and rapid change is unlike anything seen in millions of years (possibily even more)


http://cdiac.ornl.gov/trends/temp/vo.../tempplot5.gif


http://en.wikipedia.org/wiki/Image:6...ate_Change.png

We are on the left hand side in both of these graphs at temperature 0C. A 10C rise is off the top of the first graph and is equivalent to temperature 50 million years ago in the 2nd. So a 10C rise in the next 2000 years due to natural processes is very unreasonable.

How can a 1C increase be "a lot" and "measly" at the same time? On geological scales of millions of years the last 100 years is meaningless. Warming trens on large scales do not change much in any 100 year window. The short term "wobbles" over hundreds of years have nothing to do with those long term trends.

I have posted plenty of graphs and all kinds of different scales. The one over the past 5 million years shows more than just 3 occurences, it shows a couple of dozen since glacial and interglacial periods began:


http://en.wikipedia.org/wiki/Image:F...ate_Change.png

Mechanism is causation. The mechanism doesn't have a disconnect, it's a very simple case of co2 contributing to the greenhouse effect which warms the earth. More co2 = more greenhouse effect. That's the mechanism. The observations are not restricted to computer models. For example one observation is cooling in the stratosphere which is a signal of enhanced greenhouse effect.

In this case have nothing to do with the long term trend

Yes caused by short term forcings such as solar variation. They have nothing to do with a hundred thousand, let alone million year geological and orbital processes that are the likely cause for iceages. Yet you seem to be saying we can attribute every short term change in temperature on a scale of millions of years to the same cause. At least you give absolutely no indication how to differentiate the two. You say the warming last century can be attributed to the same million-year scale process that is bringing the earth out of an iceage. So was the medieval warm period also attributable to that same long term process? What about the little ice age? Isn't it far more likely that all these short term perbutations are due to processes that change on the short term, not processes that change slowly over millions of years?

Even in millions of years there has been no overall upward trend. Where specifically is this trend you are talking about? When does it begin?

I am talking about glacial periods and interglacial periods in which the change does happen in a few thousand years. On scales of major ice ages the last century is absolutely totally meaningless.

The one that began about 600,000 years ago. Here's your source:

Notice the upward trend beginning about 600,000 years ago. Even though temperature eventually tops out and falls several times, the overall trend is up. Each interglacial a little higher than the last, each glacial a little higher than the last. But all collectively serving to take us out of the Pleistocene - "The Great Ice Age".
We're not talking about interglacials. The OP asked about ice ages.
lol! Nice backtrack. Were you under the impression I thought you meant CO2 was a real blanket? No, I understand analogies, and this one doesn't fit. A blanket inhibits convection between the area under it and the area above it. CO2, and other "greenhouse" gases most certainly do not inhibit convection. Therefore, they are not "like a blanket" in trapping heat.
This is a link to an encyclopedia article on ice cores in general. I would like the study. There have been several studies on Vostok ice cores. In all the ones I've read, CO2 lags temperature. Which study does your source reference?
Well, perhaps you should think about reading the actual studies rather than looking for data which support your conclusions? As I pointed out before, trying to devine causation from graphs of such massive time scales is nearly impossible.
You're the one maintaining that CO2 concentrations began increasing 150-odd years ago and lead to increasing temperatures. I'm asking where the data your conclusion is based upon came from, remember?
Oh. So, other forcings work for a little while, then stop working? I've got to try and cut this short, onon, because I'm running out of time. You're attibuting the entire warming of the past 150 years to CO2. Or at the very least, you're denying other forcings (like those taking us out of the current ice age) have any impact at all. That was the statement I replied to originally. In effect what you're arguing is that all other forcings take a back-seat to CO2. A ridiculous proposition.
Doesn't matter. At some point your "more temperature -> increased co2 after ~800 years -> further increase in temperature" paradigm breaks down. In fact, it breaks down for the exact reason I've been trying to exlain to you from the beginning: it's a complex system and we don't know nearly enough to make the exclusive statements you've been making. You claim CO2 has caused the rise in temperature over the past 150 years (if there has been a change), yet other forcings have been working right along with it the entire time. Some we know about. There are probably others we know nothing about.
Not according to your paradigm. It's circular.
Then the "recent" warming could be attributable to anything - including whatever is working to bring us out of the current ice age.
I see no material difference between your quotes and mine.
We could've saved a whole lot of time if you would've said this originally. You wrote "the scientists did not" claim the world was headed for another ice age. Clearly, there were those who did. Consensus means nothing.
I don't have the time to read through this report. What I'm asking is if you can tell me how much temperature would vary if CO2 were the only forcing, and what is the error rate. For example: if CO2 were the only climate forcing, temperature would vary 1 degree (+/- .5 degree) for every 100ppm.
Then it could be the same forcings which are taking us out of the current ice age.
No doubt. You just have to prove we're doing this whole lotta' change with a 60% increase in a trace atmospheric gas to the exclusion of all others.
No, it's not totally meaningless. It's part of the trend. You're claiming that my one step from California toward New York means nothing because it's only one of billions.
You've been arguing that the 8C rise between 12,000 y.a. and 10,000 y.a. is "normal". Is an extra 2C so unreasonable? In fact, the graph you posted shows a pretty rapid ascent from ~-9C to ~+3C about 140,000y.a.. Rapid and large temperature changes are quite common, judging from your sources.
Too bad the planet doesn't know how to read graphs.
I wrote "we are attributing a lot to the past 100 years and it's measly 1C increase". The "a lot" describes what we are attributing to the 1C increase (it's all caused by CO2, it's an unprecedented increase in temperature, the planet is going to continue warming unless we stop putting CO2 into the atmosphere, cats and dogs are going to start living together, etc...); an increase in temperature which is "measly".
We're not talking about interglacials and glacials. We're talking about ice ages. There have been, to the best of our knowledge, only four ice ages in the planet's history. One of which we are in right now.
No, it is not. Mechanism is my car's engine. Just because it's running, doesn't mean my car is moving. CO2 has shown no ability to cause the earth to start warming.
It does. You said yourself that it is self-limiting. If the mechanism did not have a disconnect, we would be living on a star.
Yes, they are. With any non-linear, chaotic system empirical evidence is impossible. You can find data which supports your conclusion, but that's very different from observing changes in a controlled environment. We don't know all the machinations of this planet, and we don't know how they interact.
Just as one tree means nothing to a forest?
Why can it not? Especially if that "cause" is a confluence of several different processes working in concert which have been driving this planet since its birth?
The OP asked about "ice ages", not interglacials.

You get the last word, onon. I simply don't have time, nor desire, to rehash this argument.

My response to the OP: yes, it is quite possible that the increase in temperature over the past 100 years can be attributed to coming out of an ice age. The planet seems to vascillate between ice ages normally, and the past 100 years could be just one of the many hundreds of baby steps the planet takes towards getting from one ice age to another with a period of no ice in between. This is going to take millions of years, and we will probably experience colder temperatures (glacials), a subsequent expansion of ice sheets, followed by a warmer period with it's subsequent retreat of ice sheets (interglacials), and then another cold period, and so on. This will continue an unknown number of times before the planet finally succeedes in melting all the ice on the planet. At that point, we will be out of the current ice age and can expect to slip into another over the following millions of years. That is if we don't blow the planet up before then.