Blowing the Whistle on Global Warming

[_Droopy]

http://www.powerlineblog.com/


Blowing the Whistle on Global Warming

David Evans was a consultant to the "Australian Greenhouse Office" from 1999 to 2005. He is a former global warming alarmist; however, he is also a scientist who goes where the evidence leads him. In this important article in The Australian, he blows the whistle on the fraud that many of the world's governments are in the midst of perpetrating:

I DEVOTED six years to carbon accounting, building models for the Australian Greenhouse Office. I am the rocket scientist who wrote the carbon accounting model (FullCAM) that measures Australia's compliance with the Kyoto Protocol, in the land use change and forestry sector.

FullCAM models carbon flows in plants, mulch, debris, soils and agricultural products, using inputs such as climate data, plant physiology and satellite data. I've been following the global warming debate closely for years.

When I started that job in 1999 the evidence that carbon emissions caused global warming seemed pretty good: CO2 is a greenhouse gas, the old ice core data, no other suspects.

The evidence was not conclusive, but why wait until we were certain when it appeared we needed to act quickly? Soon government and the scientific community were working together and lots of science research jobs were created. We scientists had political support, the ear of government, big budgets, and we felt fairly important and useful (well, I did anyway). It was great. We were working to save the planet.

But since 1999 new evidence has seriously weakened the case that carbon emissions are the main cause of global warming, and by 2007 the evidence was pretty conclusive that carbon played only a minor role and was not the main cause of the recent global warming. As Lord Keynes famously said, "When the facts change, I change my mind. What do you do, sir?"

There has not been a public debate about the causes of global warming and most of the public and our decision makers are not aware of the most basic salient facts.

You really need to read the whole thing to get the full impact, but here are a few highlights:

1. The greenhouse signature is missing. We have been looking and measuring for years, and cannot find it.

Each possible cause of global warming has a different pattern of where in the planet the warming occurs first and the most. The signature of an increased greenhouse effect is a hot spot about 10km up in the atmosphere over the tropics. We have been measuring the atmosphere for decades using radiosondes: weather balloons with thermometers that radio back the temperature as the balloon ascends through the atmosphere. They show no hot spot. Whatsoever.

If there is no hot spot then an increased greenhouse effect is not the cause of global warming. So we know for sure that carbon emissions are not a significant cause of the global warming. ...

2. There is no evidence to support the idea that carbon emissions cause significant global warming. None. ...

3. The satellites that measure the world's temperature all say that the warming trend ended in 2001, and that the temperature has dropped about 0.6C in the past year (to the temperature of 1980). ...

4. The new ice cores show that in the past six global warmings over the past half a million years, the temperature rises occurred on average 800 years before the accompanying rise in atmospheric carbon. Which says something important about which was cause and which was effect. ...

The last point was known and past dispute by 2003, yet Al Gore made his movie in 2005 and presented the ice cores as the sole reason for believing that carbon emissions cause global warming. In any other political context our cynical and experienced press corps would surely have called this dishonest and widely questioned the politician's assertion. ..

What is going to happen over the next decade as global temperatures continue not to rise? The Labor Government is about to deliberately wreck the economy in order to reduce carbon emissions. If the reasons later turn out to be bogus, the electorate is not going to re-elect a Labor government for a long time. When it comes to light that the carbon scare was known to be bogus in 2008, the ALP is going to be regarded as criminally negligent or ideologically stupid for not having seen through it.

The same will be said of any American government that ruins our economy is service of the global warming ideology.

[_Scottie]

The jury is still out for me as far as global warming is concerned.

I'd like to see what Gore's critics say about his documentary.

[_Droopy]

http://cei.org/pdf/5539.pdf

http://www.ff.org/centers/csspp/pdf/20061121_gore.pdf

http://www.johnstonsarchive.net/environment/gore.html

http://www.sepp.org/Archive/NewSEPP/Inc ... alling.htm

http://www.heartland.org/pdf/22835.pdf

http://canadafreepress.com/index.php/article/3784

http://www.co2science.org/education/rep ... itique.php

[_Tarski]

Can someone explain to me how one man's uncertainty on the causes of GW justifies Droopy's heroic certainty on the same subject?

http://julesandjames.blogspot.com/2007/ ... h-all.html

[_Tarski]

The jury is still out for me as far as global warming is concerned.

In case you would prefer certainty
one short cut you can take is this: Ignore the science completely. Just think of what the implications for your economic position might be. Then choose on that basis. Of course, if most climate scientists tend to disagree with your conclusions reached by the political method, it may create so much cognitive dissonance and need for justification that you will obsessively cull the Internet for support from any blogger or disaffected low level engineer or what have you and post volumes of it on a board about Mormonism (and probably myriad other places).

I'd like to see what Gore's critics say about his documentary.

They say plenty. It is smoothly stated, has the cadence of reasonableness (sometimes) but is often wrong and based in misunderstanding of climate science. Don't think that the supporters of the bulk of Gore's movie don't have rebuttals based in good science. That said, no documentary will ever be flawless or always perfectly accurate. The thrust of the movie is still basically right. They seldom give Nobel Prizes to total nuts.

[_Droopy]

Gore's film isn't a scientific documentary, but a propaganda film that effectively makes Albert Gore the Leni Riefenstahl of the modern political moment. Its not just that the film (and his Powerpoint presentation) are top loaded with junk science, in the form of extreme, implausible future scenarios supported by no empirical evidence and which even the IPCC would no longer feel comfortable condoning, but the shameless fudging of evidence and intellectual dishonesty. There are several examples of this in the film, but without doubt the worst of these is the 650,000 year proxy data reconstruction graph Gore uses in the film, in which C02 rise is claimed to precede warming. The actual empirical evidence demonstrates precisely the opposite, that warming always precedes CO2 rise by an average of 800 years, with the spread being 200 to 1,000 years.

One of the film's producers, Laurie David, even produced an indoctrination manual for children called The Down to Earth Guide to Global Warming, in which the fraud is taken a step further, with the mislabeling of the separate graph lines denoting CO2 and temperature:

http://scienceandpublicpolicy.org/other ... error.html

If this isn't enough, Gore even used the long discredited "hockey stick" graph created by another purveyor of tainted data, Michael Mann, that makes the really inconvenient MVP disappear.

Don't be fooled by Tarski, like so many others involved in promoting the hysteria, he's not really interested in the science, only the ideology.

Here's another excellent alternative analysis:

http://cei.org/pdf/5820.pdf

[_Tarski]

Don't be fooled by Tarski, like so many others involved in promoting the hysteria, he's not really interested in the science, only the ideology.

Since I am not hysterical or even slightly anxious, I guess you are wrong again-- aren't you.?

[_EAllusion]

Out of curiosity Droopy, do you read original scientific papers on climatology outside of those referenced and interpreted by denialist websites? Not that I trust your truth-telling skills, but I'm genuinely curious how far you go. Easy money is on "no."

I don't exactly search out climate science journals, but I do subscribe to Science. Science publishes major papers on the subject fairly routinely in addition to more informal discussion of the issues in other sections. My science education is such that I can read those papers with a good deal of scientific literacy. (The pure physics papers often fly over my head, and biology papers tend to be easy, light reading for me.) I also occasionally read original papers when reading about issues in climatology from various sources.

My personal favorite pop-site on climate science and climate change is www.realclimate.org. It's sort of the Pandasthumb of climate science. You'll find most of the classic and newwave denialist arguments you parrot with hysterical bluster devastated there.

This particular piece seems appropriate:

http://www.realclimate.org/index.php?p=94

The global cooling myth

Every now and again, the myth that "we shouldn't believe global warming predictions now, because in the 1970's they were predicting an ice age and/or cooling" surfaces. Recently, George Will mentioned it in his column (see Will-full ignorance) and the egregious Crichton manages to say "in the 1970's all the climate scientists believed an ice age was coming" (see Michael Crichton’s State of Confusion ). You can find it in various other places too [here, mildly here, etc]. But its not an argument used by respectable and knowledgeable skeptics, because it crumbles under analysis. That doesn't stop it repeatedly cropping up in newsgroups though.

I should clarify that I'm talking about predictions in the scientific press. There were some regrettable things published in the popular press (e.g. Newsweek; though National Geographic did better). But we're only responsible for the scientific press. If you want to look at an analysis of various papers that mention the subject, then try http://www.wmconnolley.org.uk/sci/iceage/.

Where does the myth come from? Naturally enough, there is a kernel of truth behind it all. Firstly, there was a trend of cooling from the 40's to the 70's (although that needs to be qualified, as hemispheric or global temperature datasets were only just beginning to be assembled then). But people were well aware that extrapolating such a short trend was a mistake (Mason, 1976) . Secondly, it was becoming clear that ice ages followed a regular pattern and that interglacials (such as we are now in) were much shorter that the full glacial periods in between. Somehow this seems to have morphed (perhaps more in the popular mind than elsewhere) into the idea that the next ice age was predicatable and imminent. Thirdly, there were concerns about the relative magnitudes of aerosol forcing (cooling) and CO2 forcing (warming), although this latter strand seems to have been short lived.

The state of the science at the time (say, the mid 1970's), based on reading the papers is, in summary: "…we do not have a good quantitative understanding of our climate machine and what determines its course. Without the fundamental understanding, it does not seem possible to predict climate…" (which is taken directly from NAS, 1975). In a bit more detail, people were aware of various forcing mechanisms - the ice age cycle; CO2 warming; aerosol cooling - but didn't know which would be dominant in the near future. By the end of the 1970's, though, it had become clear that CO2 warming would probably be dominant; that conclusion has subsequently strengthened.

George Will asserts that Science magazine (Dec. 10, 1976) warned about "extensive Northern Hemisphere glaciation.". The quote is from Hays et al. But the quote is taken grossly out of context. Here, in full, is the small section dealing with prediction:

Future climate. Having presented evidence that major changes in past climate were associated with variations in the geometry of the earth's orbit, we should be able to predict the trend of future climate. Such forecasts must be qualified in two ways. First, they apply only to the natural component of future climatic trends - and not to anthropogenic effects such as those due to the burning of fossil fuels. Second, they describe only the long-term trends, because they are linked to orbital variations with periods of 20,000 years and longer. Climatic oscillations at higher frequencies are not predicted.

One approach to forecasting the natural long-term climate trend is to estimate the time constants of response necessary to explain the observed phase relationships between orbital variation and climatic change, and then to use those time constants in the exponential-response model. When such a model is applied to Vernekar's (39) astronomical projections, the results indicate that the long-term trend over the next 20,000 years is towards extensive Northern Hemisphere glaciation and cooler climate (80).

The point about timescales is worth noticing: predicting an ice age (even in the absence of human forcing) is almost impossible within a timescale that you could call "imminent" (perhaps a century: comparable to the scales typically used in global warming projections) because ice ages are slow, when caused by orbital forcing type mechanisms.

Will also quotes "a full-blown 10,000-year ice age" (Science, March 1, 1975). The quote is accurate, but the source isn't. The piece isn't from "Science"; it's from "Science News". There is a major difference: Science is (jointly with Nature) the most prestigous journal for natural science; Science News is not a peer-reviewed journal at all, though it is still respectable. In this case, its process went a bit wrong: the desire for a good story overwhelmed its reading of the NAS report which was presumably too boring to present directly.

The Hays paper above is the most notable example of the "ice age" strand. Indeed, its a very important paper in the history of climate, linking observed cycles in ocean sediment cores to orbital forcing periodicities. Of the other strand, aerosol cooling, Rasool and Schneider, Science, July 1971, p 138, "Atmospheric Carbon Dioxide and Aerosols: Effects of Large Increases on Global Climate" is the best exemplar. This contains the quote that quadrupling aerosols could decrease the mean surface temperature (of Earth) by as much as 3.5 degrees K. If sustained over a period of several years, such a temperature decrease could be sufficient to trigger an ice age!. But even this paper qualifies its predictions (whether or not aerosols would so increase was unknown) and speculates that nuclear power may have largely replaced fossil fuels as a means of energy production (thereby, presumably, removing the aerosol problem). There are, incidentally, other scientific problems with the paper: notably that the model used was only suitable for small perturbations but the results are for rather large perturbations; and that the estimate of CO2 sensitivity was too low by a factor of about 3.

Probably the best summary of the time was the 1975 NAS/NRC report. This is a serious sober assessment of what was known at the time, and their conclusion was that they didn't know enough to make predictions. From the "Summary of principal conclusions and recommendations", we find that they said we should:

1. Establish National climatic research program
2. Establish Climatic data analysis program, and new facilities, and studies of impact of climate on man
3. Develope Climatic index monitoring program
4. Establish Climatic modelling and applications program, and exploration of possible future climates using coupled GCMs
5. Adoption and development of International climatic research program
6. Development of International Palaeoclimatic data network

Which is to say, they recommended more research, not action. Which was entirely appropriate to the state of the science at the time. In the last 30 years, of course, enormous progress has been made in the field of climate science.

Most of this post has been about the science of 30 years ago. From the point of view of todays science, and with extra data available:

1. The cooling trend from the 40's to the 70's now looks more like a slight interruption of an upward trend (e.g. here). It turns out that the northern hemisphere cooling was larger than the southern (consistent with the nowadays accepted interpreation that the cooling was largely caused by sulphate aerosols); at first, only NH records were available.
2. Sulphate aerosols have not increased as much as once feared (partly through efforts to combat acid rain); CO2 forcing is greater. Indeed IPCC projections of future temperature inceases went up from the 1995 SAR to the 2001 TAR because estimates of future sulphate aerosol levels were lowered (SPM).
3. Interpretations of future changes in the Earth's orbit have changed somewhat. It now seems likely (Loutre and Berger, Climatic Change, 46: (1-2) 61-90 2000) that the current interglacial, based purely on natural forcing, would last for an exceptionally long time: perhaps 50,000 years.

Finally, its clear that there were concerns, perhaps quite strong, in the minds of a number of scientists of the time. And yet, the papers of the time present a clear consensus that future climate change could not be predicted with the knowledge then available. Apparently, the peer review and editing process involved in scientific publication was sufficient to provide a sober view. This episode shows the scientific press in a very good light; and a clear contrast to the lack of any such process in the popular press, then and now.

Further Reading:

Imbrie & Imbrie "Ice Ages: solving the mystery" (1979) is an interesting general book on the discovery of the ice ages and their mechanisms; chapter 16 deals with "The coming ice age".

Spencer Weart's History of Global Warming has a chapter on Past Cycles: Ice Age Speculations.

An analysis of various papers that mention the subject is at www.wmconnolley.org.uk/sci/iceage/.

(There are numerous hypertext links in the article)

[_EAllusion]

Whoops. It's actually in this thread: http://www.mormondiscussions.com/discus ... php?t=6941 that the "global cooling" gambit is made.

I guess I owe you one.

4. The new ice cores show that in the past six global warmings over the past half a million years, the temperature rises occurred on average 800 years before the accompanying rise in atmospheric carbon. Which says something important about which was cause and which was effect. ...

http://www.realclimate.org/index.php/ar ... -ice-cores

What does the lag of CO2 behind temperature in ice cores tell us about global warming?
Filed under:

* FAQ
* Greenhouse gases
* Paleoclimate

— group @ 9:42 AM - (Français)

This is an issue that is often misunderstood in the public sphere and media, so it is worth spending some time to explain it and clarify it. At least three careful ice core studies have shown that CO2 starts to rise about 800 years (600-1000 years) after Antarctic temperature during glacial terminations. These terminations are pronounced warming periods that mark the ends of the ice ages that happen every 100,000 years or so.

Does this prove that CO2 doesn't cause global warming? The answer is no.

The reason has to do with the fact that the warmings take about 5000 years to be complete. The lag is only 800 years. All that the lag shows is that CO2 did not cause the first 800 years of warming, out of the 5000 year trend. The other 4200 years of warming could in fact have been caused by CO2, as far as we can tell from this ice core data.

The 4200 years of warming make up about 5/6 of the total warming. So CO2 could have caused the last 5/6 of the warming, but could not have caused the first 1/6 of the warming.

It comes as no surprise that other factors besides CO2 affect climate. Changes in the amount of summer sunshine, due to changes in the Earth's orbit around the sun that happen every 21,000 years, have long been known to affect the comings and goings of ice ages. Atlantic ocean circulation slowdowns are thought to warm Antarctica, also.

From studying all the available data (not just ice cores), the probable sequence of events at a termination goes something like this. Some (currently unknown) process causes Antarctica and the surrounding ocean to warm. This process also causes CO2 to start rising, about 800 years later. Then CO2 further warms the whole planet, because of its heat-trapping properties. This leads to even further CO2 release. So CO2 during ice ages should be thought of as a "feedback", much like the feedback that results from putting a microphone too near to a loudspeaker.

In other words, CO2 does not initiate the warmings, but acts as an amplifier once they are underway. From model estimates, CO2 (along with other greenhouse gases CH4 and N2O) causes about half of the full glacial-to-interglacial warming.

So, in summary, the lag of CO2 behind temperature doesn't tell us much about global warming. [But it may give us a very interesting clue about why CO2 rises at the ends of ice ages. The 800-year lag is about the amount of time required to flush out the deep ocean through natural ocean currents. So CO2 might be stored in the deep ocean during ice ages, and then get released when the climate warms.]

To read more about CO2 and ice cores, see Caillon et al., 2003, Science magazine

Guest Contributor: Jeff Severinghaus
Professor of Geosciences
Scripps Institution of Oceanography
University of California, San Diego.

Update May 2007: We have a fuller exposition of this on a more recent post.

http://www.realclimate.org/index.php?p=94

The lag between temperature and CO2. (Gore’s got it right.)
Filed under:

* Arctic and Antarctic
* Greenhouse gases
* Paleoclimate
* Climate Science

— eric @ 2:45 PM

Eric Steig

When I give talks about climate change, the question that comes up most frequently is this: “Doesn’t the relationship between CO2 and temperature in the ice core record show that temperature drives CO2, not the other way round?"

On the face of it, it sounds like a reasonable question. It is no surprise that it comes up because it is one of the most popular claims made by the global warming deniers. It got a particularly high profile airing a couple of weeks ago, when congressman Joe Barton brought it up to try to discredit Al Gore’s congressional testimony. Barton said:

In your movie, you display a timeline of temperature and compared to CO2 levels over a 600,000-year period as reconstructed from ice core samples. You indicate that this is conclusive proof of the link of increased CO2 emissions and global warming. A closer examination of these facts reveals something entirely different. I have an article from Science magazine which I will put into the record at the appropriate time that explains that historically, a rise in CO2 concentrations did not precede a rise in temperatures, but actually lagged temperature by 200 to 1,000 years. CO2 levels went up after the temperature rose. The temperature appears to drive CO2, not vice versa. On this point, Mr. Vice President, you’re not just off a little. You’re totally wrong.

Of course, those who've been paying attention will recognize that Gore is not wrong at all. This subject has been very well addressed in numerous places. Indeed, guest contributor Jeff Severinghaus addressed this in one of our very first RealClimate posts, way back in 2004. Still, the question does keep coming up, and Jeff recently received a letter asking about this. His exchange with the letter writer is reproduced in full at the end of this post. Below is my own take on the subject.

First of all, saying "historically" is misleading, because Barton is actually talking about CO2 changes on very long (glacial-interglacial) timescales. On historical timescales, CO2 has definitely led, not lagged, temperature. But in any case, it doesn't really matter for the problem at hand (global warming). We know why CO2 is increasing now, and the direct radiative effects of CO2 on climate have been known for more than 100 years. In the absence of human intervention CO2 does rise and fall over time, due to exchanges of carbon among the biosphere, atmosphere, and ocean and, on the very longest timescales, the lithosphere (i.e. rocks, oil reservoirs, coal, carbonate rocks). The rates of those exchanges are now being completely overwhelmed by the rate at which we are extracting carbon from the latter set of reservoirs and converting it to atmospheric CO2. No discovery made with ice cores is going to change those basic facts.

Second, the idea that there might be a lag of CO2 concentrations behind temperature change (during glacial-interglacial climate changes) is hardly new to the climate science community. Indeed, Claude Lorius, Jim Hansen and others essentially predicted this finding fully 17 years ago, in a landmark paper that addressed the cause of temperature change observed in Antarctic ice core records, well before the data showed that CO2 might lag temperature. In that paper (Lorius et al., 1990), they say that:

changes in the CO2 and CH4 content have played a significant part in the glacial-interglacial climate changes by amplifying, together with the growth and decay of the Northern Hemisphere ice sheets, the relatively weak orbital forcing

What is being talked about here is influence of the seasonal radiative forcing change from the earth's wobble around the sun (the well established Milankovitch theory of ice ages), combined with the positive feedback of ice sheet albedo (less ice = less reflection of sunlight = warmer temperatures) and greenhouse gas concentrations (higher temperatures lead to more CO2 leads to warmer temperatures). Thus, both CO2 and ice volume should lag temperature somewhat, depending on the characteristic response times of these different components of the climate system. Ice volume should lag temperature by about 10,000 years, due to the relatively long time period required to grow or shrink ice sheets. CO2 might well be expected to lag temperature by about 1000 years, which is the timescale we expect from changes in ocean circulation and the strength of the "carbon pump" (i.e. marine biological photosynthesis) that transfers carbon from the atmosphere to the deep ocean.

Several recent papers have indeed established that there is lag of CO2 behind temperature. We don't really know the magnitude of that lag as well as Barton implies we do, because it is very challenging to put CO2 records from ice cores on the same timescale as temperature records from those same ice cores, due to the time delay in trapping the atmosphere as the snow is compressed into ice (the ice at any time will always be younger older than the gas bubbles it encloses, and the age difference is inherently uncertain). Still, the best published calculations do show values similar to those quoted by Barton (presumably, taken from this paper by Monnin et al. (2001), or this one by Caillon et al. (2003)). But the calculations can only be done well when the temperature change is large, notably at glacial terminations (the gradual change from cold glacial climate to warm interglacial climate). Importantly, it takes more than 5000 years for this change to occur, of which the lag is only a small fraction (indeed, one recently submitted paper I'm aware of suggests that the lag is even less than 200 years). So it is not as if the temperature increase has already ended when CO2 starts to rise. Rather, they go very much hand in hand, with the temperature continuing to rise as the the CO2 goes up. In other words, CO2 acts as an amplifier, just as Lorius, Hansen and colleagues suggested.

Now, it there is a minor criticism one might level at Gore for his treatment of this subject in the film (as we previously pointed out in our review). As it turns out though, correcting this would actually further strengthen Gore's case, rather than weakening it. Here's why:

The record of temperature shown in the ice core is not a global record. It is a record of local Antarctic temperature change. The rest of the globe does indeed parallel the polar changes closely, but the global mean temperature changes are smaller. While we don't know precisely why the CO2 changes occur on long timescales, (the mechanisms are well understood; the details are not), we do know that explaining the magnitude of global temperature change requires including CO2. This is a critical point. We cannot explain the temperature observations without CO2. But CO2 does not explain all of the change, and the relationship between temperature and CO2 is therefore by no means linear. That is, a given amount of CO2 increase as measured in the ice cores need not necessarily correspond with a certain amount of temperature increase. Gore shows the strong parallel relationship between the temperature and CO2 data from the ice cores, and then illustrates where the CO2 is now (384 ppm), leaving the viewer's eye to extrapolate the temperature curve upwards in parallel with the rising CO2. Gore doesn't actually make the mistake of drawing the temperature curve, but the implication is obvious: temperatures are going to go up a lot. But as illustrated in the figure below, simply extrapolating this correlation forward in time puts the Antarctic temperature in the near future somewhere upwards of 10 degrees Celsius warmer than present — rather at the extreme end of the vast majority of projections (as we have discussed here).

Global average temperature is lower during glacial periods for two primary reasons:
1) there was only about 190 ppm CO2 in the atmosphere, and other major greenhouse gases (CH4 and N2O) were also lower
2) the earth surface was more reflective, due to the presence of lots of ice and snow on land, and lots more sea ice than today (that is, the albedo was higher).
As very nicely discussed by Jim Hansen in his recent Scientific American article, the second of these two influences is the larger, accounting for about 2/3 of the total radiative forcing. CO2 and other greenhouse gases account for the other 1/3. Again, this was all pretty well known in 1990, at the time of the Lorius et al. paper cited above.

What Gore should have done is extrapolated the temperature curve according this the appropriate scaling — with CO2 accounting for about 1/3 of the total change — instead of letting the audience do it by eye. Had he done so, he would have drawn a line that went up only 1/3 of the distance implied by the simple correlation with CO2 shown by the ice core record. This would have left the impression that equilibrium warming of Antarctica due to doubled CO2 concentrations should be about 3 °C, in very good agreement with what is predicted by the state-of-the-art climate models. (It is to be noted that the same models predict a significant delay until equilibrium is reached, due to the large heat capacity of the Southern ocean. This is in very good agreement with the data, which show very modest warming over Antarctica in the last 100 years). Then, if you scale the Antarctic temperature change to a global temperature change, then the global climate sensitivity to a doubling of CO2 becomes 2-3 degrees C, perfectly in line with the climate sensitivity given by IPCC (and known from Arrhenius's calculations more than 100 years ago).

In summary, the ice core data in no way contradict our understanding of the relationship between CO2 and temperature, and there is nothing fundamentally wrong with what Gore says in the film. Indeed, Gore could have used the ice core data to make an additional and stronger point, which is that these data provide a nice independent test of climate sensitivity, which gives a result in excellent agreement with results from models.

A final point. In Barton's criticism of Gore he also points out that CO2 has sometimes been much higher than it is at present. That is true. CO2 may have reached levels of 1000 parts per million (ppm) — perhaps much higher — at times in the distant geological past (e.g. the Eocene, about 55 million years ago). What Barton doesn't bother to mention is that the earth was much much warmer at such times. In any case, more relevant is that CO2 has not gone above about 290 ppm any time in the last 650,000 years (at least), until the most recent increase, which is unequivocally due to human activities.

(Again, there are numerous hyperlinks in the original links. They deserve to be read.)

[_EAllusion]

Out of curiosity Droopy, do you read original scientific papers on climatology outside of those referenced and interpreted by denialist websites? Not that I trust your truth-telling skills, but I'm genuinely curious how far you go. Easy money is on "no."

Still true.