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Calculating the greenhouse effect

Filed under: — gavin @ 21 January 2006

In another forum (on a planet far, far away), the following quote recently came up:

….the combined effect of these greenhouse gases is to warm Earth’s atmosphere by about 33 ºC, from a chilly -18 ºC in their absence to a pleasant +15 ºC in their presence. 95% (31.35 ºC) of this warming is produced by water vapour, which is far and away the most important greenhouse gas. The other trace gases contribute 5% (1.65 ºC) of the greenhouse warming, amongst which carbon dioxide corresponds to 3.65% (1.19 ºC). The human-caused contribution corresponds to about 3% of the total carbon dioxide in the present atmosphere, the great majority of which is derived from natural sources. Therefore, the probable effect of human-injected carbon dioxide is a miniscule 0.12% of the greenhouse warming, that is a temperature rise of 0.036 ºC. Put another way, 99.88% of the greenhouse effect has nothing to do with carbon dioxide emissions from human activity8.

We’ve discussed the magnitude of the greenhouse effect before, but it might be helpful to step through this ‘back-of-the-agenda’ calculation and see what the numbers really give. (Deltoid has also had a go at some of these mis-statements).

The quote comes from a lecture by an Australian climate ‘contrarian’ and frequent contributor to the southern hemisphere op-ed pages. Where did he get this from? One might assume that reference ’8′ was a scientific text, but one would assume wrong. It was in fact our old friend at Fox News, who may in turn have picked up his (junk)science from here. It is not clear whether this is the original source, but it’s close enough.

So, starting at the top:

  • “33 ºC” is the difference between the mean surface air temperature of the planet and the blackbody radiating temperature (i.e. the temperature a blackbody would need to radiate at to be in equilibrium with the incoming solar radiation given an albedo of about 0.3). So far so good. While that is one way to assess the strength of the basic greenhouse effect, another one is measure the amount of long wave radiation from the surface that is absorbed in the atmosphere (by greenhouse gases (incl. water vapour), clouds, aerosols, etc.). That is currently about 150 W/m2 and would be zero with no greenhouse effect at all.
  • “95% of this warming is caused by water vapour”. This is sourced to a couple of chaps who may have worked for Accu-Weather, but a) is misquoted – their ’90-95%’ is for both water vapour and clouds, and b) just wrong and c) irrelevant anyway.
    Dealing with b) first, if you remove all water vapour and clouds you still absorb about 34% of the long wave radiation, and conversely, if you only have water vapour and clouds you absorb 85% (calculations here). Thus the effect of water vapour and clouds is between 66 and 85% – the range being due to the spectral overlaps with the other absorbers. These calculations were done with the GISS GCM radiation code, which matches line-by-line codes to about 10% – but the numbers are very similar to Ramanathan and Coakley (1978), and so probably aren’t too far off what you would get with any decent radiation code. I’ll get to ‘c)’ below….
  • “The other trace gases contribute 5% … amongst which carbon dioxide corresponds to 3.65%”. That is just 100 minus 95% of course, but really it should be 15 to 34% – of which CO2 on its own is between 9 and 26% (op cit). If you were to naively estimate the total temperature contribution of the CO2 it would be between 3 and 9 ºC – but see below.
  • “The human-caused contribution corresponds to about 3% of the total carbon dioxide in the present atmosphere,”. This one is blatantly false and is erroneously credited to the US Dept. of Energy in the original source (their Table 1)! The ’3%’ number actually comes from comparing the human emissions with the gross emissions from natural sources while neglecting to consider the large natural sink. Because of the rapid cycling between the biosphere, the atmosphere and the upper ocean, that is an irrelevant comparison – kind of like comparing the interest on your bank account and your salary and expecting to be able to say something about your savings without thinking about your spending. The correct statement is that CO2 is around 30% higher than it was in the pre-industrial period, and all of that rise is due to human emissions (fossil fuel use and deforestation principally).
  • “Therefore, the probable effect of human-injected carbon dioxide is a miniscule 0.12% of the greenhouse warming”. That’s just 0.03*0.0365 of course – but even that is calculated wrong (it should be 0.11% by my calculator). But from our numbers, it would be between 3 and 8%.
  • “a temperature rise of 0.036 ºC”. More like 1-2.6 ºC actually, but although this gives numbers that are in the ballpark of the IPCC estimates (0.6 to 1.7 ºC warming for an increase of 30% in CO2 at equilibirum) this is not a sensible way to calculate climate sensitivty.

Why do I claim this is an irrelevant and not very sensible calculation? Firstly, it assumes linearity – all of the gases contributing according to their effects today when it is obvious that overlaps and saturation effects are large and important, and more importantly, it ignores feedbacks. The calculation above gives the impression that what you are calculating is the change of temperature that would result if you remove all the CO2. But since water vapour concentration is a feedback not a forcing, it can’t be assumed to remain constant as the planet cools. Water vapour does in fact change (roughly keeping relative humidity, as opposed to specific humidity, constant) and this has been shown in the real world as a function of volcanic cooling (Soden et al, 2002) and for longer term trends (Soden et al, 2005, discussed here), and is well reproduced in climate models.

What then is an appropriate calculation? Well, it’s simply the estimate of climate sensitivity for the present climate – how much would you expect the planet to warm if you doubled CO2? We’ve discussed this numerous times before, and in my opinion the best answer so far comes from looking at the difference between the last glacial period and the modern era – this gives a number around 3 +/- 1 ºC at doubling.

For the 30% rise in CO2 there has been so far, that would imply that would represent around 3% of the natural greenhouse effect – a good order of magnitude bigger than that suggested above. Of course, this is at equilibrium and not applicable to a transient change. If one takes into account the human-induced changes in the other GHGs (CH4, N2O, CFCs), you’d get something like double that. Given that even a 5 or 6 ºC cooling was associated with the huge ice sheets 20,000 years ago, and that 33 ºC cooling would reduce our planet to a near-snowball-like state, a potential increase of 5 to 6% of the natural greenhouse effect is not to be sniffed at… nor dismissed as irrelevent with highly misleading arithmetic.

One could make the point that my calculations are ‘just another web page’ no more and no less authoritative than the links above. In some sense that is correct (though I’d argue my sourcing is a little better!). But you will never find a peer-reviewed rebuttal of such a bizarre line of reasoning as we are dealing with here – basically because such a line of reasoning is highly unlikely to make it past peer-review itself. There are innumerable ‘proper’ references to estimates of the climate sensitivity though, and one should indeed hesitate to accept calculations like this example over the mass of peer reviewed studies.


240 Responses to “Calculating the greenhouse effect”

  1. 101
    David Nicosia says:

    Help me understand this…

    The earth’s climate in the “short” term (100s of years)
    is basically regulated by CO2 concentration if you
    hold the solar “constant” as constant, assume no significant orbital parameter changes or galactic dust changes, or no volcanic eruptions/meteor impacts.

    So a trace gas of 380 ppm has a huge impact on our climate even though without feedbacks a doubling from pre-industrial levels = .5 to .7K?

    Can someone explain the water vapor feedback again. I just don’t understand how water vapor and clouds are not the dominant GHG.

    I find it amazing that a trace gas can have so much impact on our climate system. Someone please explain.
    thanks

  2. 102
    Hank Roberts says:

    http://www.nytimes.com/2006/01/29/science/earth/29climate.html?_r=1&pagewanted=print

    January 29, 2006
    Climate Expert Says NASA Tried to Silence Him
    By ANDREW C. REVKIN

    The top climate scientist at NASA says the Bush administration has tried to stop him from speaking out since he gave a lecture last month calling for prompt reductions in emissions of greenhouse gases linked to global warming.

    … James E. Hansen … said in an interview that officials at NASA headquarters had ordered the public affairs staff to review his coming lectures, papers, postings on the Goddard Web site and requests for interviews from journalists.

    Dr. Hansen said he would ignore the restrictions. “They feel their job is to be this censor of information going out to the public,” he said.

    …. Dr. Hansen said that nothing in 30 years equaled the push made since early December to keep him from publicly discussing what he says are clear-cut dangers from further delay in curbing carbon dioxide.

    In several interviews with The New York Times in recent days, Dr. Hansen said it would be irresponsible not to speak out ….”

    He said he was particularly incensed that the directives affecting his statements had come through informal telephone conversations and not through formal channels, leaving no significant trails of documents.

    Dr. Hansen’s supervisor, Franco Einaudi, said there had been no official “order or pressure to say shut Jim up.” But Dr. Einaudi added, “That doesn’t mean I like this kind of pressure being applied.”

    The fresh efforts to quiet him, Dr. Hansen said, began in a series of calls after a lecture he gave on Dec. 6 at the annual meeting of the American Geophysical Union in San Francisco. …, warning to Dr. Hansen that there would be “dire consequences” if such statements continued, those officers and Dr. Hansen said in interviews.

    George Deutsch, a recently appointed public affairs officer at NASA headquarters, rejected a request from a producer at National Public Radio to interview Dr. Hansen, said Leslie McCarthy, a public affairs officer responsible for the Goddard Institute.

    …. Ms. McCarthy said Mr. Deutsch called N.P.R. “the most liberal” media outlet in the country. … Mr. Deutsch said his job was “to make the president look good”

    Mr. Acosta, Mr. Deutsch’s supervisor, said that when Mr. Deutsch was asked about the conversations he flatly denied saying anything of the sort. …. Mr. Acosta said that for the moment he had no way of judging who was telling the truth.

    … Larry D. Travis, an astronomer who is Dr. Hansen’s deputy at Goddard, …. said he walked into Ms. McCarthy’s office in mid-December at the end of one of the calls from Mr. Deutsch demanding that Dr. Hansen be better controlled….

  3. 103
    Coby says:

    Pat,

    You can see the forcings involved over the past 150 years as determined by GISS here: http://www.giss.nasa.gov/data/simodel/ There are links to details of each from that page, you may be able to find the actual data from there as well.

    The total forcings for 2000 relative to 1750 are shown here: http://www.grida.no/climate/ipcc_tar/wg1/figspm-3.htm

  4. 104
    Coby says:

    Can someone explain the water vapor feedback again. I just don’t understand how water vapor and clouds are not the dominant GHG.

    Firstly, H2O is the dominant GHG, but it is not a driver of climate change. What makes it a feedback rather than a forcing is the fact that, unlike CO2, if you pump it into the atmosphere, or suck it out of the atmosphere, it will return very quickly to its original levels due to its abundance in the oceans and its ability to quickly rain out. The level of stable H2O concentration is basically a function of air temperature, so that if the temperature rises by whatever means, water vapor will rise as well causing a feedback effect.

    Clouds, AFAIU, are complicated because they can both reflect incoming radiating back into space (cooling) and absorb outgoing radiation, reemitting it back to the surface (warming). They behave this way in different proportions depending on height, type, diurnal cycle, temperature and the size of the particles around which droplets form.

    I find it amazing that a trace gas can have so much impact on our climate system. Someone please explain

    The world is an amazing place! :) Sorry, I have no better explanation than that, but I think you can find countless examples where tiny things can have huge impacts.

  5. 105
    Pat Neuman says:

    In 101. David wrote … “Can someone explain the water vapor feedback again. I just don’t understand how water vapor and clouds are not the dominant GHG”.

    David,
    My explanations and projections in climate and hydrologic prediction are based in large part on observations, rather than modeled estimates of what’s happening. The accuracy of models for prediction is dependent on the quality of the input data, the quality of the model and the quality of the parameters derived from model calibration. Thus, model output is too dependent on qualities for me to give large weight to in my predictions. My explanations on the water vapor feedback is not dependent much on models either. I’ve observed CO2 in the atmosphere to be increasing, evidenced by the increase in CO2 at NOAA CMDL measuring stations. I’ve observed winter dewpoints to be increasing. I’ve observed that humid air thaws ice at higher rates than dry air of the same temperature (latent heat of condensation). I’ve observed a rapid decline in the number of weeks per winter/spring that river basins are covered by snow and ice. I’ve observed that soils can dry only after the frozen layer on top has thawed. Therefore, with fewer weeks of winter/spring snow and ice cover, more weeks of evaporation and transpiration take place, adding water vapor to the atmosphere. The difference between warming from increasing “trace” greenhouse gases and warming from solar radiation is the duration of warming from GHGs compared to solar radiation. Solar radiation increases and variation are sporadic and possibly short lived. GHG accumulation is continuous and long lived. If increasing in solar radiation were not sporadic and short lived, it would be difficult to distinguish warming due to solar vs from GHG, but solar doesn’t behave that way… making it pretty easy for me to see the effects from either. The water vapor feedback becomes very important in GHG warming because the warming triggers from GHGs are continuous and long lived.

    Coby,
    re your 102. comments, I have not looked at your suggested websites yet, regarding the warm late 1920s-early 1950s period, and the cooler period from the mid 1950s to early 1970s. I’m hoping that the explanations given at the sites you suggested have data which I can observe, not merely model output which would be too dependent on model quality to be convincing to me.

  6. 106
    Caio de Gaia says:

    I really would like to know how the heat content of the atmosphere has been changing. Temperatures are adequate for the public but as a physicist I would prefer true measure of energy change.

    About the topic of the post, the fact that back-of-the-envelope physics should not be applied to climate:

    Qian, Yun; Kaiser, Dale P.; Leung, L. Ruby; Xu, Ming. More frequent cloud-free sky and less surface solar radiation in China from 1955 to 2000. Geophys. Res. Lett., Vol. 33, No. 1, L01812, 10.1029/2005GL024586

    From the abstract:
    “The total cloud cover and low cloud cover have decreased 0.88% and 0.33% per decade, respectively, and cloud-free days have increased 0.60% and overcast days decreased 0.78% per decade in China from 1954-2001. Meanwhile, both solar radiation and pan evaporation have decreased in China, with solar radiation decreasing 3.1 W/m2 and pan evaporation decreasing 39 mm per decade. ”

    This is clearly counterintuitive. The authors attribute this to increased air pollution. It’s the kind of thing that can only be understood in a detailed model.

    There is another paper that shows why is so hard to get decent regional models:

    van den Broeke, Michiel; van de Berg, Willem Jan; van Meijgaard, Erik. Snowfall in coastal West Antarctica much greater than previously assumed, Geophys. Res. Lett., Vol. 33, No. 2, L02505, 10.1029/2005GL025239

    From the abstract
    “the Amundsen Sea sector of West Antarctica and the western Antarctic Peninsula, both data sparse regions, are found to receive 80-96% more accumulation than previously assumed. ”

    The key word here is “data sparse”. It’s a pity, we need models that work well at the regional level. The thing that makes me favor a human cause for GW is the Artic, but I would like to see a model that can predict consistently regional changes everywhere.

    Finally, people only think about the Sun in terms of the “solar constant” (total energy flux) when the biggest impact of the solar activity is possibly in cosmic ray flux. This is still debatable, but I suggest (these are easy to read):

    Marsh, Nigel; Svensmark, Henrik. Solar Influence on Earth’s Climate. Space Science Reviews, v. 107, Issue 1, p. 317-325 (2003).

    de La Fuente Marcos, R.; de La Fuente Marcos, C. On the correlation between the recent star formation rate in the Solar Neighbourhood and the glaciation period record on Earth. New Astronomy, Volume 10, Issue 1, p. 53-66.

    Somewhat harder read, but shows that sunspots are not the only thing to consider when looking into cosmic ray fluxes

    Lockwood, J. A.; Webber, W. R. Intensities of galactic cosmic rays of ~1.5 GV rigidity at Earth versus the heliospheric current sheet tilt. Journal of Geophysical Research, Volume 110, Issue A4, CiteID A04102

    All of this research is still in its early stage, there are people conducting laboratory research in cosmic rays and cloud formation. At this stage they have essentially a series of correlations that may be an accident, but some support for a causal relation may be appearing. The problem is that people starting this research where astronomers and getting cloud people interested has not been easy. The fields had very little previous contact. So please when you dismiss solar activity explain if you are talking about “solar constant” changes or magnetic activity changes.

  7. 107
    Hank Roberts says:

    > amazing that a trace gas could have so much impact ….

    Those who’ve won Nobel prizes for work in atmospheric chemistry agree — from this page
    http://nobelprize.org/chemistry/laureates/1995/

    read the three speeches linked there for examples.

    In Crutzen’s speech, in particular, he says our life today “… could have been much worse” — how lucky we are, right now.

  8. 108
    David Nicosia says:

    Thanks. Here is what I am seeing…
    If the earth warms due to solar variability for example, there will be some additional water vapor feedback warming which enhances the initial forcing of the climate system from higher solar output. Now return the sun back to slightly less output…the water vapor feedback works in the opposite sense magnifying the change a bit toward more cooling. But the main point is that the earth returns back to where it was.

    It is the relatively “long” residence time of CO2 in the atmosphere that forces the additional enhanced warming due to the H20 absorption bands. So you force the earth to warm even .5K by GHGs and it gets enhanced by the H20 for a long time. Is there a “breaking” mechanism which slows down the effect of H20. there has to be or every time the earth warms for whatever reason there would be a runaway greenhouse effect. I assume it is more low clouds which leads to a higher albedo and cooling?

    Comment 105 points out that there are observations showing the warming and increasing dewpoints and hence H20 vapor. Is this warming do to C02 increase? How sporadic is solar variability? Can’t the sun increase its output slowly and slightly over 100s of years and with the huge amount of energy storage capacity of the oceans, the warming is showing up in the 20th and early 21st centuries? Could this explain the LIA to the modern warm period? We could be just observing an upswing in climate temperature-wise and the permafrost melting, glacier melting, sea ice retreat, higher dewpoints etc is an artifact of natural warming. With any kind of warming you would have this water vapor feedback which amplifies the forcing signal of the sun’s changes.

    The fact that there was a LIA, a medevil warm period suggests that there is natural variability of the climate. This weakens the hypothesis that changing a trace gas has led to the recent warming trend. And I don’t buy the IPCC’s claim that there was no LIA and medievil warm period. This does not make sense. How can you cool one part of the globe for a couple hundred years and there is no change or little change in the rest of the world given the current continental layout and ocean currents. Heat eventually redistributes itself as the atmosphere becomes well mixed in the long term. So to say that Europe and Greenland were cold for 2 centuries was just local…to me…does not make sense. What about the NAO and the AO? These are Northern hemisphere teleconnection patterns that effect a large part of the NH. Anyway, the LIA makes it confusing for me to believe that GHG increase is the main driving factor in the recent climate changes. It could be mostly natural with some small forcing from C02.

    Is there a smoking gun anywhere that would point to this CO2-H20 synergy leading to the current warming?
    Has anyone measured radiatively changes in absorption bands from spectrometers on satellites showing the combination of these two species leading to more long wave IR downwelling? I would love to see the observed changes in radiative transfer and not have to rely on a model to tell us that this is what is happening. I am a meteorologist and we use computer models all the time and they have so many assumptions and biases. I am leary about a model showing something and then that becomes accepted as an “observation”. It is not. It is just a model. we know the real world is so much more complex that our models.

    Anyway, any radiative transfer evidence of this h20-c02 feedback from satellite data? That would be awesome and would really be a strong case for AGW.

  9. 109
    Blair Dowden says:

    I have just arrived at this discussion, and I am disappointed that there was no response to post #3, where Andre demonstrated that a doubling of carbon dioxide will only lead to a 0.6 degree temperature rise, including water vapor feedback. One might think that our increasing carbon dioxide production was no big deal.

    But I do not follow his argument. First, he uses the Modtran program to claim doubling carbon dioxide will lead to a forcing of 3.2 watts per square meter, including feedbacks. This sounds a bit low to me, but I do not understand the meaning of all the parameters in that program. I wonder if Andre understands it, or is his result not valid?

    But then he uses a formula based on this web page to translate the forcing into a temperature change. Please help me here, this does not make sense. They do not mention that an IR absorbing layer radiates at a lower temperature, which is the basis of the greenhouse effect. I suspect the whole thing is rubbish, so Andre’s calculation is invalid. I would appreciate if someone can confirm this.

  10. 110
    Andy Lacis says:

    The first statement of the punching bag quote that the combined effect of terrestrial greenhouse gases is to warm the surface of the Earth by 33 C is basically correct. The second statement that 95% of this warming is produced by water vapor is clearly erroneous. Of the 33 C greenhouse effect, about 10-11 C is due to non-volatile greenhouse gases (i.e., gases that do not precipitate out from the atmosphere for the typical range of atmospheric temperatures). These non-volatile greenhouse gases are CO2, CH4, N2O, ozone, and CFCs. If the Earth’s atmosphere were totally devoid of water vapor, these non-volatile GHGs would support a surface temparature 10-11 C warmer than the -18 C equilibrium baseline (which corresponds to no atmospheric greenhouse effect). The rest of the 33 C greenhouse effect is due to feedback effects of water vapor which is a reaction to the radiative forcing due to the non-volatile GHGs and accounts for roughly half of the 33 C greenhouse effect, and clouds which provide roughly 6-7 C. As a crude analogy, the non-volatile greenhouse gases serve as a “skeleton” upon which vater vapor (and cloud) feedbacks can operate. (A horse without a skeleton upon which its muscles can exert their force would be laying sprawled out flat on the ground.) Accordingly, if the non-volatile GHGs (CO2, CH4, N2O, O3, CFCs) were removed from the atmosphere, the atmospheric water vapor and clouds would precipitate from the atmosphere, and the resulting surface temperature would drop to the baseline -18 C value. In this over-simplified model, the non-volatile greenhouse gases (CO2, CH4, N2O, O3, CFCs) provide an overall radiative forcing of about 11 C. The volatile component (water vapor and clouds) operate in the current climate system with an effective multiplicative feedback factor of 3 which multiplies the applied 11 C forcing to generate the total 33 C terrestrial greenhouse effect.

    An early discussion of radiative forcing and climate sensitivity is given by Hansen et al. 1984 (Climate sensitivity: Analysis of feedback mechanisms. Geophysical Monograph 29, Maurice Ewing Vol 5, AGU, 130-163). This paper compares the radiative forcings due to doubled CO2 and to a 2% increase in solar irradiance, and provides a quantitative analysis of feedback contributions due to water vapor, cloud, lapse rate, and surface albedo changes. The paper shows that while feedback efficiencies of the different feedback processes can be compared linearly, the feedbacks combine in a non-linear fashion. In the Hansen et al. 1984 paper, the radiative forcing due to doubled CO2 was 1.2-1.3 C, with the overall feedback factor in the 3-4 range to produce a 4 C global equilibrium warming. More recent results (Hansen et al. 2005, Earth’s energy imbalance: Confirmation and implications. Science 308, 1431-1435) suggest that the total global feedback effect is in the 2.1-2.3 range giving a 2.7 C global warming for doubled CO2.

    Because of overlapping absorption and saturation effects, the greenhouse contributions of individual contributors depend on their atmospheric context. For example, the radiative forcing due to doubled CO2 in the current atmospheric context is about 1.2-1.3 C (with no feedbacks operating). But removal of the current CO2 amount produces a cooling of more than -7 C (with no feedbacks operating). Analytic formulas that describe the amount of radiative forcing due to different concentrations of atmospheric CO2, CH4, N2O, and CFCs can be found in Hansen et al. 1988 (Global climate changes as forecast by GISS three-dimensional model. JGR 93, 9341-9364). Again, the (applied) radiative forcing is provided by changes in the non-volatile GHGs, aerosols, or solar irradiance. Water vapor, clouds, and snow-ice albedo change in response to the applied radiative forcing and account for the overall global feedback factor which acts to magnify the applied forcing to produce the eventual equilibrium change in global surface temperature

  11. 111
    Hank Roberts says:

    > I am a meteorologist (David Nicosia)
    I know of a David Nicosia who is a meteorologist with the NWS. That you?

    I’m a reader here, not a climate scientist, but I think you’ll find your water vapor questions addressed in the discussion about water vapor — http://www.realclimate.org/index.php?p=142

  12. 112
    Tim Jones says:

    Blair Dowden wrote in comment #109:
    “I have just arrived at this discussion, and I am disappointed that there was no response to post #3, where Andre demonstrated that a doubling of carbon dioxide will only lead to a 0.6 degree temperature rise, including water vapor feedback. One might think that our increasing carbon dioxide production was no big deal.”

    The answer is found in Archer’s writings:
    http://geosci.uchicago.edu/~archer/PS134/ps134_notes.ch3.pdf

    I don’t think David Archer has set up the Modran 4 model to casually debunk his own assertions. But I too would like to see the refutation through a correct demonstration of the model.

  13. 113
    Tim Jones says:

    David Nicosia wrote in comment #108:
    “Anyway, the LIA makes it confusing for me to believe that GHG increase is the main driving factor in the recent climate changes. It could be mostly natural with some small forcing from C02.”

    Judith Lean wrote:
    http://www.gcrio.org/CONSEQUENCES/winter96/sunclimate.html
    (excerpt)
    “What is known of climate change prior to the Industrial Revolution affords additional insight. The well-documented surface temperature rise since 1850 can be viewed as but the most recent 60 percent of a warming of about 0.8°C since the 17th century (Fig. 3d) http://www.gcrio.org/CONSEQUENCES/winter96/article3-fig3.html, interrupted periodically by volcanic effects. Estimates of Northern hemisphere surface temperatures from 1610 to 1800–during part of the so-called Little Ice Age–correlate well with a reconstruction of changes in solar total radiation–around the time of the Maunder Minimum (Fig. 2c) http://www.gcrio.org/CONSEQUENCES/winter96/article3-fig2.html. This suggests, without proving, a predominant solar influence on climate throughout this 200 year, pre-industrial epoch. The reconstructions of solar radiation and surface temperature shown for these years in Figures 3a and 3d http://www.gcrio.org/CONSEQUENCES/winter96/article3-fig3.html tell of an increase in solar radiation of 0.14 percent and a coincident warming of 0.28°C. If we apply the same implied sensitivity to the period since 1850, the 0.13 percent increase in solar radiation in the last 140 years should have produced a warming of 0.26°C, or about half of that observed.

    If we apply the same relationship to the last 25 years, solar changes can account for less than a third of the warming observed (Fig. 5) http://www.gcrio.org/CONSEQUENCES/winter96/article3-fig5.html .”

    Is there more credible current research on her part or others which overturns this assertion? If not, then only about a third
    of the warming since about 1970 can be attributed to solar forcing and the other two thirds is attributed to AGHG forcing.

  14. 114

    Re #43:

    Pat, sorry for the delay in response. Sometimes one need do some homework instead of discussing climate change, to keep a balance in one’s marriage…

    About the attribution of solar and GHGs to polar amplification, just have a look at the temperature trends in the NH for the last century in Johanessen ea.. You will see in Figure 1a that small variations in lower latitudes (up to 55N) are fortified in the higher latitudes, and particular in the Arctic over 70N. This is to both sides, in cooler periods as well as in warmer periods. Of particular interest is the 1930-1940 period, where a small increase in temperature of 0-0.2 K in the 30-55N band is accompanied by a 0.8-1.2 K rise in temperature above 75N. That period was mainly solar driven.

    The recent warming is more pronounced, also in lower latitudes, and again fortified in the Arctic. Here we have certainly a mix of GHG warming and solar warming (as you know, the sun in recent decades is more active than in the 1930-1940s), but there is no pattern difference between the mainly solar 1930′s and the mixed warming after 1970, only a difference in amplitude. Thus it is quite difficult, if not impossible, to know what part is solar based and what part is GHG based in the instrumental record.

    Btw, the ECHAM4 models used in Figure 1b,c,d clearly overestimates GHG and aerosol forcing (+ feedbacks) and underestimates solar forcing (+ feedbacks).

    Further, don’t relay too much on regional evidence. Alaska certainly warmed with a (PDO related) jump after 1976. But other regions like Greenland were warmer in the 1930-1940′s, cooling thereafter and only reach the higher temperatures again after 2000.

  15. 115
    Tom Brogle says:

    RE William’s comments on 96
    Clarfying
    There are indications that the Antarctic was as warm at the begining of the 20th century as it was at the end but that coolng must have occurred sometime in between.
    See my post 90
    That the Urban Heat Effect has exagerated the Global temperature see my post 96
    That it must been warmer than it is now in historical times see my post 90
    There is no DIRECT proof that CO2 causes GW
    Attribution is not proof

  16. 116
    Hank Roberts says:

    David N (are you the David Nicosia, meteorologist, who works for the National Weather Service? I can’t find a different one, where do you work as a meteorologist?)

    You quote from 1996 US Gov’t Global Climate Change pages — their current pages are a decade newer, 2005-6, and they invite readers to ask questions right there — why not ask at the source first?

    The first few in their “Doctor Climate” page answer many of your questions about what is known now that wasn’t known a decade ago!

    If you want step by step, track the citations forward in the literature.

    See also here: http://www.columbia.edu/~jeh1/

    I’m trying to point out how to look things up, basically what I do when I find very old information online. Hope this helps you do the same.

  17. 117
    Pat Neuman says:

    re #114

    Ferdinand,

    I think solar radiation was high during the 1920s-1930s, evidenced by a surge in temperatures and very low humidity. The 1940s-mid 1950s were influenced by warm El Ninos. The mid 1950s-mid 1970s were influenced by cool La Ninas. By the late 1970s, the climate was similar to what it would have been without the 1920s-1930s peak solar radiation and subsequent El Ninos-La Ninas, possibly set in motion by the peak solar radiation of the 1920s-1930s.

    Thus, we shouldn’t put any of the blame for the rapid global warming we observe now on any increase in solar radiation. That would incorrect.

    The late-1920s-1930s surge in solar radiation was temporary only. After the 1930s, solar radiation fell back to it’s pre-1920s levels, and have remained nearly constant for 1940s to present. The global warming being observed now is entirely a result of human activity, mostly from GHG emissions (and subsequent global warming feedbacks).

    Thus it is not impossible to know what part of our global warming is solar based and what part is GHG based, it’s very clear to me.

    It would also become clear to some others if they reviewed the referenced temperature plots from 1888 to current within the Midwest, Great Plains, Northwest and Alaska, at:

    http://pg.photos.yahoo.com/ph/patneuman2000/my_photos

  18. 118
    Hank Roberts says:

    Oops, my bad editing in #115, I mangled an attempt and ran together replies to two previous items, sorry for mistake. The link, at least, is good, it’s to Hansen’s articles — the Columbia page. He covers a lot of this.

  19. 119
    JimR says:

    In #117 Pat wrote:

    “The late-1920s-1930s surge in solar radiation was temporary only. After the 1930s, solar radiation fell back to it’s pre-1920s levels, and have remained nearly constant for 1940s to present.”

    This statement is incorrect. During 1920s to 1930s the Sun was much less active than any other time in the 20th century. Since the 1920s to 1930s solar forcing has increased as the Sun has become more active. In fact following the increase started in the 1940s every solar cycle since has been more active than those relatively calm the 1920s-1930s.

    http://sidc.oma.be/html/wolfaml.html

    And several studies show that solar forcing is still increasing:

    http://www.nasa.gov/centers/goddard/news/topstory/2003/0313irradiance.html

    http://www.fel.duke.edu/~scafetta/pdf/2005GL023849.pdf

  20. 120

    Re #117,

    Pat, it is unclear to me where you have seen these solar data you mention. Several indices (sunspots, sun cycle length, magnetic AA index) give an increase 1900-1955, a decrease until 1975 and an increase thereafter to the current high level (higher than in the 1930′s, or even the past 8,000 years).
    Just look around for the different observations and the reconstructions of TSI (total solar insolation at the top of the atmosphere). Wikipedia has a good oversight…

  21. 121
    Hank Roberts says:

    The NASA page you link says:
    ” … the inferred increase of solar irradiance in 24 years, about 0.1 percent, is not enough to cause notable climate change, the trend would be important if maintained for a century or more.

    I suppose the sun’s behavior could change. So could ours.

  22. 122

    Re #49:

    Wayne, I did write that the even IF the current Arctic warming was 100% solar driven, that would not be distinguishable from the pattern of GHG warming. That doesn’t imply that this is the case. It probably is a mix. And depending of the climate model and the choice made for solar reconstrcution, the increase in global temperature of the past two decades is estimated up to 30% solar driven.
    It is clear that there is a polar amplification of small disturbances in the lower latitudes (and primary in the tropics). That there are record global (and consequential Arctic) high temperatures, while there is no El Nino and we are near a sunspot minimum, points to a longer term warming anyway.

    But IMHO most models underestimate longer term solar sensitivity. For Pat Neuman’s intention too: even if there was no increase in solar output after 1940 (but there clearly was), the intensity is higher than let’s say begin 1900. While air and surface temperatures do follow the sunspot trend rather fast, an average increase need much more time to reach a new equilibrium, due to slow responses of the oceans (30 years for the mixed layer to 1,500 years for the deep ocean overturning), ice cover, glaciers, vegetation,…

  23. 123

    Re #121:

    Hank, the NASA underestimates the short-term climate change the “only” 0.1% increase in solar strength causes. According to empirical evidence and interpretations of past cycles, the increase in global temperature of the past two decades is estimated 10-30% by solar strength increase.
    See Scafetti and West.

    [Response:But see this comment by Urs Neu on that paper as well... - gavin]

  24. 124
    Mikel Marinelarena says:

    Re #94- Joel, thanks for addressing all the issues I raised in my post #92. I have read through the links you provided.

    You surely have a point when you say that at some stage action should be taken if evidence is mounting that we face catastrophic events. In such a scenario we couldn’t wait until all scientific uncertainties were resolved. Alright. But are we really at that stage? What specific catastrophes can we be reasonably confident that we’ll suffer (or prevent) if we don’t act (or do act) now? Didn’t the American Academy of Sciences issue a report in the seventies that led Science magazine to conclude in it’s March 1, 1975 issue that a long “ice age is a real possibility”? Would it have been wise then to “take action” in order to prevent the “catastrophic” global cooling ecologists and reputed scientists were announcing?

    [Response: It wasn't Science, and there was no consensus for action - see our post on the Global Cooling myth-gavin]

    In any case, I am against the very costly actions that already ARE being taken. But I believe that that’s not the kind of discussion this forum was designed for.

    Regardless of what politicians are doing now about AGW, I’m sure you will agree that, as I said, much more research should be done in order to eliminate scientific uncertainties and take better informed actions, if necessary. Gavin, for one, didn’t object to point d) in my post #76.

    As for your answers to my questions, I continue seeing a lot of ad-hoc explanations for data that were found not to conform to the AGW theory forecasts. Wouldn’t it be much better to have a scientific theory that, as such, can explain and forecast empiric data in advance?

    1) The models you mention indeed generate graphs that visibly support the AGW theory. But models are as good as relevant and accurate are the data you feed them with. How close are climate modelers to knowing all relevant data that would generate a realistic output of past and future climate? Meterologists still struggle to generate accurate predictions beyond 3-4 days with their models. And some prominent climatologists dismiss current model-based climate predictions altogether, since models can only predict what might happen under a given set of conditions, not what WILL happen in the future.

    2) If I am allowed to give credit to prominent scientists such as Pielke, Craig and Sherwood Idso or (of course) Spencer and Christy my information on the lower troposphere temperature trends is not out-of-date. A difference with the surface trends continues to exist and the anticipated warming of the lower troposphere at a faster pace than the surface fails to be validated by available data, in spite of the efforts dedicated to correct and reanalyse it.
    http://blue.atmos.colostate.edu/publications/pdf/naturecomments.pdf
    http://climate.uah.edu/maps/26yeargraf.jpg
    http://www.co2science.org/scripts/CO2ScienceB2C/data/temperatures/temps.jsp

    3) Again, you give me a link where Eric and Gavin do an excellent job at explaining why data from Antarctica do not behave as expected: “there are very reasonable explanations for the recent observed cooling, that have been recognized for some time from model simulations” and put a lot of faith in their eventually behaving “well”: “In short, we fully expect Antarctica to warm up in the future”.

    4) My understanding of the whole debate is that the basic physical principles that you mention end quite early in this discussion (possibly at the 0.99 degrees C of global warming directly generated by the anthropogenic increase of CO2, as discussed above from Gavin’s explanations) and are followed by very complex relations when all feedbacks are considered. If that were not the case, we wouldn’t have any debate and Seitz, Singer, Michaels, Lindzen, Balling. etc would not be able to generate more attention than, say, creationists would in a debate on paleontology.

    On a side note, you may be surprised to learn that, in fact, there are many countries where there is NO debate on AGW, including quite a few European ones. All relevant mass media adhere to the PC trend and constantly bombard the population with catastrophic predictions purportedly supported by ‘Science’. I have seen global warming gladly related in the media to tornadoes, hurricanes and even tsunamis!! Recently a right-wing newspaper in Spain held a set of 5 online chats with GW ‘experts’. 4 of them were environmental activist and the only scientist (a physicist) turned out to be the local representative of some “Concerned Scientists” association. This gentleman informed us that if we don’t act fast in 100 years the Greenland icecap will melt, which will provoke a 400,000 years long ice-age and that the current global warming is 1,000 times faster than any previous one experienced by the planet: http://www.elmundo.es/encuentros/invitados/2005/09/1670/

    How can vote-dependant politicians take wise decisions in face of such a state of public opinion? Would you really like to see this debate-less situation to generalize to the whole of the world? If I were a climatologist seriously dedicated to AGW research I would indeed be very concerned. Concerned by the dangerous snowball that the way this research is being publicized may provoke in society and economy.

  25. 125

    Well the sun seems to be in a spotlight of some sort. Lets go not so far back to 2 prominent years in all time high temperatures, 1998 and 2005, a surprise awaits sun activity adherents, 1998 and 2005 occurred when sun spot activity was at their lowest points. There is no need to strictly go back to the 30′s when things don’t quite work in the 90′s and the 21st century.

  26. 126
    Pat Neuman says:

    Coby,

    The link at:
    http://www.grida.no/climate/ipcc_tar/wg1/figspm-3.htm shows very low level of scientific understanding on a small amount of solar forcing for 2000 compared to year 1750.

    The link at: http://www.giss.nasa.gov/data/simodel/ on forcings over the past 150 years determined by GISS does not explain 1880-2005 globally averaged surface temperature plots by NOAA and NASA, nor 1888-2005 climate station plots for the U.S. at:
    http://pg.photos.yahoo.com/ph/patneuman2000/my_photos

    The explanation for the warm 1930s, cool 1960s and rapid global warming we see happening now is best explained by the case I made in #117. ie. “The late-1920s-1930s surge in solar radiation was temporary only. After the 1930s, solar radiation fell back to it’s pre-1920s levels, and have remained nearly constant for 1940s to present. The global warming being observed now is entirely a result of human activity, mostly from GHG emissions (and subsequent global warming feedbacks)”. …

  27. 127
    David H says:

    Re # 117, how do we know with any accuracy the solar radiation from 1920?

  28. 128

    Re #123 (comment):

    Gavin, thanks for pointing to the response of Urs Neu, as I couldn’t react on that anymore, the topic was already closed.

    Here follows my response:
    There are of course problems with this kind of estimation of solar sensitivity, as the geographical spread of temperature measurements of the oceans before 1955 was not very good. And of course, the ENSO influence is not completely filtered out (but that goes to both sides), neither volcanic. Both influence the amplitude. Despite that, it gives a good indication of solar sensitivity for 11 and 22 year cycles (0.11 K/Wm-2 and 0.17 K/Wm2 resp.). Comparable to earlier work which used completely different methods, by Douglass and Clader (0.10 K/Wm-2 for the 11 yr cycle) and White ea.(0.10 and 0.14 K/Wm-2).

    Further, as already discussed a few times here and on other subjects, this doesn’t include the longer term (over 22 years) response to the increase in solar forcing (+ feedbacks) since begin 1900.

  29. 129
    Robert says:

    #126 Pat,

    Merely repeating your prior conjecture does not make it correct. You have been given numerous references correcting your hypothesis.

    Solar activity it at a high, it warms the oceans, it warms the atmosphere, this takes time, the themal “momemtum” could carry global temperatures upwards for some time to come.

    Quoting from http://www.fel.duke.edu/~scafetta/pdf/2005GL023849.pdf

    Thus, while the theoretical models approximately
    predict the relative climate sensitivity ratio Z8/Z7 and the
    response time-lag, they seem to disagree from each other
    about the actual climate sensitivity to solar variation and
    significantly underestimate the phenomenological climate
    sensitivities to solar cycles as we have estimated.
    >

    Note that the Leanet al. (1995) diagram, and the others co-graphed at:

    http://www.grida.no/climate/ipcc_tar/wg1/fig6-5.htm

    – Hoyt and Schatten (1993, data updated by the authors to 1999)
    – Solanki and Fligge (1998)
    – Lockwood and Stamper (1999)

    All indicate the same thing, Solar activity is high. The correlation of sunspot activity (2nd order) with solar activity is strong in all of the plots. When sunspot numbers are changing rapidly and/or the numbers of sunpots are high, then solar activity is high.

    As a side note, geometry and albedo effects would reduce the effects of solar activity nearer the poles. The forcing by solar activity would be most prominent nearer the equator, where we are seeing the results.

    IMHO It’s not that GHG are not causing some of the warming, they just don’t do very much. These are trace gases, 400 ppm is a tiny amount, there is no catalytic effect (as for Ozone and CFCs), they are not virii that will reproduce. The effects of CO2 are simply overwhelmed by the “noise” of other effects in the system.

  30. 130

    Re #126,

    Pat, the scientific understanding of solar forcing is very low, that only points to the fact that there is a lot of discussion and differences in interpretation possible (as good as is the case for aerosols)…

    The IPCC forcing graph, as good as the GISS model forcings only are about forcings, without all positive and negative feedbacks that are typical (and different) for the different forcings, which ultimately lead to climate changes.

    About your last paragraph: if you don’t provide a scientific source for that opinion, then it is your opinion, but not based on any scientific evidence…

  31. 131
    Pat Neuman says:

    # 127

    Robert,

    Is this your first post to RC?

    In previous posts to RC, I wrote that when CO2 in the atmosphere is high, effects from other things are overwhelmed by the effect of the high CO2 concentration. When CO2 concentration is low (below 300 ppm) variations in other factors besides CO2 (orientation of the earth, orbital and solar radiation fluctuations, etc… can even trigger ice ages. No need for worry about ice ages any time soon, not with CO2 already high. The worry is from rapid CO2 accumulation and rapid global warming.

  32. 132
    Joel Shore says:

    Re #108 (“Is there a ‘breaking’ mechanism which slows down the effect of H20. there has to be or every time the earth warms for whatever reason there would be a runaway greenhouse effect.”)

    It is fallacious reasoning to say that the water vapor feedback would necessarily cause a runaway greenhouse effect in the absence of some braking mechanism. To see this, consider the following example: Say that an increase in CO2 causes (without water vapor feedback) a 1 deg rise in temperature. Then let’s suppose that the water vapor feedback due to this 1 deg rise causes an additional 0.5 deg rise. Then the feedback on that feedback causes an additional 0.25 deg rise. And, then a 0.125 deg rise and so on. The point is that you get a converging geometric series with the 1 deg rise in temperature caused by CO2 without feedback being translated into a 2 deg total rise once the water vapor feedback (including all the feedbacks on itself) is fully included.

    Of course, in this simplistic example, I haven’t given any proof that such a convergent series is a realistic assumption for our atmosphere. However, I once did a back-of-the-envelope calculation of a simplistic model of the greenhouse effect with water vapor feedback…and within that simplistic model, one indeed got precisely the result corresponding to the sum of a geometric series! As, I recall the two parameters that determined the strength of the feedback were the increase in water vapor concentration due to an increase in temperature (which I assumed followed the law of keeping the relative humidity constant…in which cause this number was accurately known) and the increase in temperature due to a certain increase in water vapor concentration. I didn’t have a good number for this latter parameter although I seem to recall that the number I would have had to use to get the water vapor feedback magnifying the “bare” warming by a factor of say 2-4 looked reasonable to me.

  33. 133
    Joel Shore says:

    Re #124: In response to your specific numbered comments–

    (1) Well, of course one could always question the models and the inputs to the models. However, the point is that your initial implication that the behavior of the global temperatures in the period from ~1940 to ~1970 has not been explained is not correct. You may not like the explanation…but that is a different thing entirely. As for the 3-4 day prediction thing, you are confusing the prediction of weather and climate…two very different things. There are also independent ways to verify the strength of the feedbacks predicted by the models by looking at past climate changes, such as glacial-interglacial oscillations and responses to volcanic eruptions.

    (2) I don’t think Sherwood Idso is considered to be a serious climatologist by most of the community and the co2science.org site is not a real credible source. And, while Spencer and Christy’s lower troposphere analysis still shows less warming than is measured at the surface, I believe that this difference is barely outside of their error bars. And, other groups that have reanalyzed the data come up with higher numbers. And, the history of Spencer and Christy’s numbers is that they trend higher and higher with time as the years go by, largely because they keep having to make corrections as errors are pointed out to them.

    (4) The reason that Seitz, Singer, Michaels, Lindzen, Balling, etc. generate so much attention probably has more to do with the politics and economic interests than with the science. And, if you think creationism (e.g., intelligent design) isn’t getting much attention, that is only because you are on the wrong (or, more accurately, the right) side of the Atlantic. Here in the U.S., probably more people believe in global warming than believe in evolution and people like Behe who promote intelligent design get lots of attention. In fact, the analogies between in motis-of-operation of the deniers of evolution and the deniers of anthropogenic climate change are strong.

  34. 134
    Tom Brogle says:

    In the comment on my post 7
    “But do you really consider a single anecdote from over 100 years ago to be cause to doubt the millions of temperature measurements”
    Look at the Wickepedia definition of anectdotal
    Nansens attempt to reach the N pole in is not anectdotal it a well documented piece of polar exploration.
    Millions of temperature readings weren’t made in the 1890s in polar seas. We have only the witness of Nansen and others as to the extent of the Polar ice cap.
    It appears that the extent is greater now than then.

  35. 135
    David H says:

    Re #131, “No need for worry about ice ages any time soon”. Really?

    So far as I can see from the ice core data, after death and taxation another ice age is the next best certainty. The consequences seem so awful I can’t see why we are not worrying about it.

    Can some one tell me if we have climate models that will explain Ice ages? My guess would be that any such model would need a much higher sensitivity for solar forcing than would be convenient for the AGW debate.

  36. 136

    Re #131,

    Pat, have a look at the work of Prof. Fujio MASUDA (Kyoto University), who discovered the 11-year solar cycle in fossil wood from the Cretaceous. You know, a period when CO2 levels were 4-12 times higher than today and global temperatures were 12(-20) K higher.

    Thus even with these high CO2 and temperature levels, the (+/- 0.1 K) solar cycle is detectable and not suppressed.

    [Response: You cannot make a clear attribution to solar - all you can say is that decadal variability is ubiquitos, but there are many sources of decadal varaibility - read Garric and Huber (2003) for instance. - gavin]

  37. 137
    Chris O'Neill says:

    Re #129

    The solar irradiance reconstructions at http://www.grida.no/climate/ipcc_tar/wg1/fig6-5.htm indicate that average irradiance over the sunspot cycle has increased by about 2W/m2 since the 19th century. This corresponds to an average increase over the whole of the earth’s surface of one quarter of this, or 0.5W/m2. This compares with the forcing produced by the increase in CO2 since the nineteenth century, which can be calculated from the formula quoted by the IPCC to give 1.6W/m2. Thus forcing from anthropogenic CO2 is 3.2 times as much as forcing from increased solar irradiance.

  38. 138
    Mikel Marinelarena says:

    Re #133

    Joel,

    The reason why I’m not an enthusiast of anthropogenic attributions to all global temperature changes observed on the surface in the 20th century is because some of them are comparable in size to previous known changes (even in Thomas Mann’s reconstruction of the last millennium climate) and obviously those had hardly any anthropogenic origin.

    I am by no means confusing climate with weather prediction. Instead I am contrasting the reliability of computer model simulations in two areas of science closely related.

    I am quite willing to disregard Sherwood Idso’s opinions and the information released on the co2science.org website (that seems to come from 3rd party, independent, sources) if you explain why I should do so. But please bear in mind that certain personal disqualifications work both ways and, more generally speaking, I don’t trust conspiracy-type theories too much. Still, you may be right in your explanation that economic interests and concerns promote attention in the US and a few European countries to the opinions of prominent scientists who don’t agree with AGW (no wonder, I would say).

    Let’s have a look at the debate from a different, simplified perspective. We have a scientific theory (AGW due to increased GHGs) that predicts:

    a) Global warming at a rate of about 0.2 ºC – 0.5 ºC per decade on average, given a business as usual scenario (where Kyoto makes a negligible impact).

    b) A faster warming of the lower troposphere than of the surface.

    c) An amplification of the warming in the polar regions, especially in Antarctica in winter, where the CO2 concentration relative to water vapour is at its highest.

    How well do empiric data validate this theory (which should be applied at least since the 80s, when aerosols are supposed to have stopped cooling the atmosphere)? What empiric data should be produced so that the theory has to be seriously reconsidered?

    [Response: (a) The models "predict" about 0.2 oC/decade, currently, and thats what is observed. Cue the familiar http://www.grida.no/climate/ipcc_tar/wg1/figspm-4.htm
    (b) Yes: see http://en.wikipedia.org/wiki/Satellite_temperature_measurements (c) You have the science mostly wrong here: see the recent RC post on polar amplification; also my post - William]

  39. 139
    Mikel Marinelarena says:

    Gavin,

    Thanks a lot for the link you gave me in post #124 http://www.realclimate.org/index.php?p=94

    It’s a magnificent job on the state of the climate science in the seventies and a very informative comparison between the global cooling myth prevalent in those days and the current global warming scenario. Looking inside the papers that William reviews and comments it seems apparent that at the time the idea of a coming ice-age was very strong in different media and to different extents managed to make its way inside scientific circles and even into the National Academy of Sciences.

    I was a teenager deeply concerned with environmental issues at the time and, in fact, I happen to remember distinctly the global cooling scare of those days. That was also the time when I began practising mountaineering. In spite of the cooling trend we were supposed to be in, I remember very well that we took it as a fact that mountain glaciers were generally retreating all over the world. As for the Alps and the Pyrenees we had many documents and images from the early explorers (most notably Whimper) that showed a much larger extension of these glaciers in the 18th century.

  40. 140

    Re #92 and “1) Why did surface temperatures cool down from the ’40s through the ’70s, while CO2 and some other GH gases were rapidly growing in the atmosphere?”

    Someone later gave the answer as particulate pollution. I’m wondering, would it be correct to think that World War II might have played a significant role? A lot of cities burned, and a lot of the soot must have gone into the stratosphere, which would then cause a slight antigreenhouse effect (the soot warms, the surface cools). Or would it have settled out right away?

  41. 141
    Pat Neuman says:

    re: 140.

    Barton,

    A chart showing radiative forcings, including stratospheric aerosols is at a link which Coby referenced in one of his messages. In reply to Coby I reviewed the charts (second link in 126. below) showing 1) Stratospheric aerosols and 2) Sum of 10 Forcings. The 10 forcing chart shows positive forcings from the 1940s through the 1970s except for a narrow dip (1963-1967).

    126. (repeated below to try to make things easier to follow).

    The link at:
    http://www.grida.no/climate/ipcc_tar/wg1/figspm-3.htm shows very low level of scientific understanding on a small amount of solar forcing for 2000 compared to year 1750.

    The link at: http://www.giss.nasa.gov/data/simodel/ on forcings over the past 150 years determined by GISS does not explain 1880-2005 globally averaged surface temperature plots by NOAA and NASA, nor 1888-2005 climate station plots for the U.S. at:
    http://pg.photos.yahoo.com/ph/patneuman2000/my_photos

    The explanation for the warm 1930s, cool 1960s and rapid global warming we see happening now is best explained by the case I made in #117. ie. “The late-1920s-1930s surge in solar radiation was temporary only. After the 1930s, solar radiation fell back to it’s pre-1920s levels, and have remained nearly constant for 1940s to present. The global warming being observed now is entirely a result of human activity, mostly from GHG emissions (and subsequent global warming feedbacks)”. …

    Comment by Pat Neuman â?? 29 Jan 2006 @ 5:31 pm

  42. 142
    JimR says:

    re #141

    “After the 1930s, solar radiation fell back to it’s pre-1920s levels, and have remained nearly constant for 1940s to present.”

    Once again this information is incorrect. The calmest period of solar activity of the 20th century was the 3 solar cycles from 1900 to 1930, solar cycles 14, 15 and 16. Since that time the Sun has been more active with every one of the 7 solar cycles since that time more active.

    http://sidc.oma.be/html/wolfaml.html

    http://www.gcrio.org/CONSEQUENCES/winter96/article3-fig3.html

    While there isn’t full agreement on increasing solar activity over the last few decades there is complete agreement that solar activity was lower in the early part of the 20th century and beginning in the 1940s rapidly increased and has remained high.

  43. 143
    Joel Shore says:

    Re #138: I agree with you on being leery of conspiracy theories. However, it doesn’t take much of a conspiracy theory to argue that there may be some individual scientists who, while having a scant publication list in refereed journals on the subject of climate change, do have strong political views or economic ties that cause them to have a strong bias. That is why it is best to stick to the peer-reviewed literature or at least sources who have a strong publication record in the peer-reviewed literature on this subject.

    On the other side of the fence (and I am not implying that you fall into this category!!), it does take a very conspiratorial mind to argue, as some do, that the whole field of climate science has been hijacked by a strong bias so that one cannot trust the conclusions of the IPCC, the National Academy of Sciences, or the councils of the AGU {American Geophysical Union) and AMS (American Meteorological Society). [And, even that companies like BP, Shell, and Ford are either part of or duped by the conspiracy (or that they are cowed by the all-powerful environmental movement, as I have seen some argue).]

    Re #139: There are many competing effects in the climate system including (on longer timescales) the natural glacial-interglacial oscillations, as well as the different anthropogenic forcings due to greenhouses gases, soot, and aerosols. Thus, it is understandable that in the 1970s there were concerns expressed both in regards to warming and cooling. However, what is important to note is that the National Academy of Sciences concluded that, given that we still did not have a very good understanding of all of these competing effects, more research was needed rather than taking any specific actions to prevent warming or cooling. That was exactly the right conclusion given the understanding at the time…and their more recent conclusion that it is now time to take action is exactly the right conclusion given our current understanding.

  44. 144
    Pat Neuman says:

    re 142.

    Jim,

    The Scientific Basis Working Group I, Climate Change 2001: shows VERY LOW LEVEL of scientific understanding for solar forcing. Justification exists to be skeptical about global warming attributed to variations in solar forcing, even for the late 1920s – 1930s period. How do you explain the record heat and very low humidity from 1927-1936?

    103 Years of Twin Cities Dew Point Temperature Records: 1902-2005
    http://climate.umn.edu/doc/twin_cities/mspdewpoint.htm

    VERY LOW LEVEL of scientific understanding for solar forcing:
    http://www.grida.no/climate/ipcc_tar/wg1/figspm-3.htm

  45. 145
    David H says:

    Today in the UK every news bulletin on every radio and TV channel has led with the dire warning from our chief scientist that we have most probably gone past the point of no return and cataclysmic GW is now most likely. We have been treated to clever graphics showing how little of the UK will remain above sea level and pictures showing huge chunks of ice falling off ice sheets into the sea. So maybe we should all go off and do something useful like building boats.

    But why is that that so many are still sceptical and new people keep joining them after the largest sustained media campaign in the history of science?

  46. 146
    JimR says:

    re #144

    I agree it’s a good point that the IPCC acknowledges the low level of understanding on the solar contribution. Obviously there is still much to be learned regarding the Sun and climate.

    Regardless of this point I don’t believe you can reconstruct solar forcing from dew points in the Twin Cities. That would be regional climate and solar forcing is reconstructed from the number of sunspots, beryllium-10 and carbon-14 isotopes. All sources agree that the 1920s to 1930s showed a slight lull in solar activity, lower than at anytime since 1940.

    You should seek another explanation for the dry 1920s-1930s in your area.

  47. 147
    Steve Bloom says:

    Re #145: Public opinion surveys clearly show the opposite. As has been pointed out with increasing frequency over the last year or so, the debate over whether climate change is happening is done; the task before us now is getting the right public policies in place to deal with it.

  48. 148

    Re #141 & #144

    Pat, the “scientific understanding” has to do with the fact that there is not a 100% sure relationship between solar activity indices (sunspots, cycle length, 10Be, 14C and other cosmogenic nucleides, magnetic AA index) and the change in TSI (total solar irradiation), of which we only have accurate data for the last two decades. Even less understanding is how this affects climate, beyond the direct radiation, while there are statistically proven links between solar cycle(s) and climate like cloud cover, jet stream position, precipitation, (sea) surface temperatures,… with effects far beyond the changes in direct forcing.

    Thus lack of scientific understanding is about how large the effect on climate is and what the physical base is for the solar-climate connection. There is no scientific doubt at all that solar activity now is higher than in the 1930-1940′s, or the LIA or even the past 8,000 years. If you aren’t willing to accept this, then further discussion is impossible, as you reject all available scientific evidence, without pointing to any evidence of the opposite view.

    Btw, there is even less scientific understanding about the impact of aerosols, which are the main cause for the 1945-1975 global cooling according to all climate models (but IMHO, by far overestimated)…

    [Response: Not so. There is plenty of scientific doubt about how sunspots, cosmogenic isotopes and magnetic indices are related to irradiance or solar activity in general. That there was a rise (of unknown magnitude) at the start of the 20th century seems probable, that there was a period of reduced activity at the Maunder Minimum (not the LIA in general) is probable, that the activity is higher now (i.e. in 1950) than in the last 8000 years is highly debatable (since it depends on all of those uncertain connections plus problems with tying the satellite obs, to sunspots, to the pre-anthropogenic 14C records). In all of these statements, confidence is low, and new results could overturn them (or reinforce them). Aerosols are indeed similarly uncertain. - gavin]

  49. 149
    Hank Roberts says:

    Mikel, what’s your source for your statement:
    “since the 80s, when aerosols are supposed to have stopped cooling the atmosphere)”? Who said that, what basis?

    I looked for that and couldn’t support it. I found:

    Strong present-day aerosol cooling implies a hot future http://www.nature.com/nature/journal/v435/n7046/abs/nature03671.html

    Related article with extensive quotes from several current research articles is here:
    http://scienceweek.com/2006/sw060120-6.htm

  50. 150

    Re #136, Gavin’s response:

    Thanks Gavin for the interesting link, which points to several short cycles in the Cretaceous climate, of which the 11-year solar cycle may be visible, or attributed to internal climate cycles… Anyway, that doesn’t change the fact that relative small variations in temperature are visible, even at extreme high CO2 levels and temperatures…


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