What Does Climate Science Have to Say About the Claims of the AGW Denialists?
The community of climate scientists has put together an excellent website - RealClimate.org - which organizes links to the peer-reviewed professional journal papers on climate, distilling the essence for the general reader. It also provides a forum for anyone to ask questions or post objections, with climate scientists' answers. It was felt necessary to create RealClimate.org as an antidote to the loud misinformation spread by a shrill blogosphere and their political supporters. It includes a well organized wiki debunking the AGW denialist claims. I'm doing my own webpage here, specifically for the Cabrillo College student, but I'd recommend also that you spend time browsing the RealClimate.org site to get better informed. SkepticalScience is also a good place for locating published papers debunking the AGW denialist claims. The standard denialist nonsense has been debunked for many many years, and they count on you to NOT notice. Here's another list of claims debunked , dating back almost a decade.
Here's some very accessible (and entertaining) YouTube videos - Climate Crock of the Week - which show common denialist
tactics and myths. While these videos often have fun at AGW denialists
expense, take careful note that good reading of the scientific literature
is demonstrated explicitly as well. They contain a lot of genuine science and valuable visualizations and
are well worth seeing.
The "Urban Heat Island" myth
The "Temperature Leads CO2" myth (includes good visuals on Milakovitch cycles relation to Ice Ages)
The "Global Warming Stopped in 1998" myth
The "Medieval Warming" Myth (and validity of the "Hocky Stick" temperature plot of Michael Mann), also here
The "Solar Cycles Cause Global Warming" myth
The stolen emails ("Climategate"), what the emails actually say, and AGW Denialist tactics. and Part 2, and the Wrap
The "Greenland and the Arctic are Gaining Ice" myth
"Flogging the Scientists"; pretty sobering stuff, be forewarned
The American Denial of Climate Change (N. Oreskes, and the Republican directive renaming Global Warming as "Climate Change")
What We Know About Climate Science
So, these YouTube videos and many more point out some of the the ugliness in the AGW denialist camp. Despite these pathologies we can't use this as an argument to disregard all anti-AGW claims out of hand. There are also attempts to find alternate ideas contributing to global warming that were hoped to turn out to be good science. Not all critics of the AGW thesis are outright denialists. All ideas deserve a critical and fair examination.
Let's take our own look at the claims and ideas and see what the evidence says. In no particular order...
There is no consensus among climate scientists that global warming is caused by human activities (Richard
Lindzen is notorious for making this claim)
Why the claim is wrong: I can't say it any better than this - which summarizes several polls of scientists, climate scientists, and the general public. Scientists are in virtual unanimous agreement - today's global warming is caused by humans. Note below how this support is highly correlated with how deep is the knowledge and familiarity the respondent is with the science. Note how much lower is the agreement among the general public, thanks to the efforts of the AGW-denialist camp. They may not know their subject, but they know how to fool the people needed to accomplish their immediate goals. That global warming is caused by man is also a position held by the National Academies of Science of dozens of countries, with no dissenters, and dozens of scientific societies in our own country - see this in detail here. This piece by Lindzen on the Cato website, on the supposed lack of consensus, is amazing, and wrong on so many counts. There is not one reference cited to support his opinions. And after reading and re-reading, I can only conclude that Richard Lindzen's reasoning supporting "lack of consensus" boils down to the fact that Richard Lindzen is not part of the consensus (!). (scroll to the bottom of my webpage here for more insight on Lindzen). This paper too, in the Proceedings of the National Academy of Sciences, (Anderegg, etal 2010) finds 97-98% of active climate scientists agree that global warming is caused by man, and that the anti-AGW camp simply has no objective evidence to support their credibility in judging such things as climate change. Here is an interview discussing this study on YouTube.
of the World's Leading Scientists" have signed a petition rejecting
the idea of anthropogenic global warming
Why this Claim is Wrong: The quotation marks above stated by Bob Lutz, CEO of GM, in a well-remembered episode of "The Colbert Report". The infamous "Oregon Petition" arrived in the mail of vast numbers of people including some scientists (circulated in 1999 and again in 2007 and signatures summed). It urged their signature rejecting AGW by using a paper by Robinson, Robinson and Soon (RRS 2007) which is junk science at its most extreme. A primary strategy of junk science promoters is to publish in outlets unable or unwilling to give proper expert review. Note that RRS is published in the Journal of Physicians and Surgeons (that's right - not a typo! To say the least, this medical journal is not known for having competent climate referees!). The petition is not filled with the signatures of scientists - its definition of a scientist is: anyone who signed the petition. This is a petition who's layout only allows check marks for PhD, MS, and BS degrees, and who admits they did not check the authenticity of the signers. It's an oil and tobacco company sponsored petition carefully graphic designed to appear to be a scientific journal article, and whose ultimate signatures include an unknown number of real scientists. See this report by the UK's Guardian. Yet the internet is filled with countless blogs perpetuating this myth and angrily attacking the notion of AGW. Here is a site collecting numerous debunkings of this claim. Climate scientists at RealClimate address the fraud. Only 39 of the 32,000 signers claim to be "climatologists", and by far the largest category are holders of only a BS "or equivalent", in some subject or other (the lowest educational check box option provided). This "Climate Crock of the Week" video presentation covers the background of those behind the signature campaign. It's not pretty. Here's a collection of errors major and minor in the petition. In particular, this rebuttal by climate scientist Michael MacCracken is the most detailed, requiring 23 tightly written pages just to enumerate the distortions and falsehoods.
What of the 2% of climate scientists who are not convinced global warming is largely human-caused? Three of the most prominent in denialist writings are Richard Lindzen (more on him later), and John Christy and Roy Spencer. Christy and Spencer's scientific acumen doesn't appear to be very good, judging by their record.
On the other side, the National Academy of Science is made up the most accomplished and highly regarded scientists in the nation. Here is a letter signed by 250 NAS members condeming the attacks by political forces on science in general and climate science in particular.Claim: Water Vapor is vastly more important than CO2 in the greenhouse effect. CO2 is a tiny component of the atmosphere and contributes only a tiny amount of greenhouse effect. And besides, the absorption lines of CO2 are saturated and so adding more won't add more greenhouse warming.
Why the Claim is Wrong:
1. Water vapor IS a bigger source of greenhouse warming than CO2. But it is precisely because CO2 is a small component that its dramatic and rapid rise has such a significant effect on climate. Because these CO2 absorption lines are saturated only in the central core wavelength, adding more CO2 adds opacity in the wings (wavelengths slightly different than the theoretical wavelength of maximum absorption) of the absorption lines and traps additional heat. Because of the saturated line core, detailed calculations show that heat trapped only rises as the logarithm of CO2 rise (not linearly), in agreement with observations. - More important, there is always a level in the atmosphere above which the absolute density of CO2 is low enough that the absorption lines are not saturated. As CO2 levels continue to rise, the mean altitude where the bulk of the re-absorption of IR radiation happens will slowly rise higher (but still far below the stratosphere). The saturated CO2 lines argument is just naive and false. If you'd like a little more detail, this link describes the situation well, even for the spectroscopically challenged. Here's another explanation of how bogus this argument is.
2. The water cycle is rapid. Water is evaporated from the surface, and precipitates back down to the ground with a time scale very short compared to CO2. This means that water vapor in the atmosphere is very close to equilibrium. However, when we burn coal and oil which has been buried underground and taken millions of years to accumulate, and we do it at a rate which will exhaust it in just a few hundred years, the Earth and oceans cannot absorb the resulting CO2 fast enough to take it back out of the atmosphere. This is why CO2 levels are rising so rapidly while water vapor levels are not - water vapor remains in approximate equilibrium because it can liquify and fall instantly out of the atmosphere as rain - CO2 cannot. Now however, if you warm the air, you raise the ability of air to hold water vapor. But then, that illustrates a dangerous positive feedback - raise temperatures by adding CO2 which can't be pulled out of the atmosphere fast enough to stay level, raises the average absolute humidity, which raises greenhouse warming due to water vapor. In other words, rising CO2 levels are the ultimate culprit, even when some of the additional heating of the earth is due to water vapor caused Greenhouse Effect. (Richard Lindzen would have you believe otherwise, but well-supported theory, climate models, and actual observations all show clearly that he's wrong. More on that later).
3. This reason is the most important: the basic physics of radiation absorption and transport described above for molecules is well understood. Though the calculations are non-trivial - we do need quantum mechanics and good Monte Carlo codes to calculate absorption coefficients vs wavelength for all the relevant molecules - they are nevertheless straightforward and confirmed to be correct in experiments. We know the density, composition, and temperature profile of the atmosphere and this allows us to take those calculations as confirmed by lab results and extend them to the atmosphere as a whole. There are no significant uncertainties. Therefore...
I can't emphasize this enough - AGW denialists not only need to come up with another culprit for observed global warming, they also need to come up with some sort of amazing physics which will somehow nullify a hundred years of solid atomic physics demonstrating the reality of a CO2-induced Greenhouse Effect.
CO2 levels have been measured with high precision. Note even the seasonal variance as northern hemisphere spring vegetation pulls CO2 out of the atmosphere, and reverse in fall and winter. Note too how levels are not just rising, they're accelerating as the Third World rapidly industrializes.
is a sign of dogmatism, group-think, unwillingness to consider other
views, and is analagous to religious zealotry. It is anti-scientific.
Why this claim is wrong: See this Soon and Baliunas editorial on the website of the Heartland Institute (an AGW denialist organization) taking this position with respect to climate science. It's an amazing claim, really. It is a slap in the face of science itself and shows the desperation for straws to grasp at as the science supporting AGW continues to expose the weakness and incredibility of "other views". The truth is - when scientists do their job WELL, THAT is when a consensus emerges! It signals the success of constantly improving computer power, technology, and years of effort on the part of very bright and dedicated people to bring evidence and logic to bear on the relevant questions. Scientists have reached consensus on many difficult scientific questions - for example, the quantum mechanics of semi-conductors and quantum electrodynamics. Does that mean that scientific conviction of the truth of these ideas too is only symptom of slavish adherence to the group-think (your Ipod wouldn't be possible without valid understanding of this physics!)? To argue that scientists who have reached consensus are no better than axe-grinding close-minded religous zealots....what a smear! what an insult to all scientists! What is the hallmark of scientic history? The ability of the peer-review system to check and verify results and generate genuine new knowledge - this should be overwhelmingly obvious to everyone. What is the hallmark of religious zealotry? Intellectual stagnation, increasing irrelevancy to progress and knowledge. To constantly refine knowledge and continue to subject new ideas to careful thought is of course a good thing. And so obvious as to not need stating. Not one scientist who is part of the consensus that GW is AGW would argue otherwise.
It is bizarre that the denialists try to posture as the lone defenders of scientific skepticism and hold up the example of Alfred Wegner and Continental Drift as a lonely heroic champion of the truth - since denialists current pronouncements that water vapor absorption blankets CO2 absorption, and land vegetation and the oceans would soak up any anthropogenic CO2 so we have nothing to worry about, date back 60 years to the rather naive status quo of the time, and it was the lone defender of better physics - Callendar (1938) - who, despite getting some physics wrong, showed that anthropogenic CO2 would indeed cause significant global warming. Since then, the evidence, observations, and physics have created a virtual unanimous scientific consensus that CO2 emissions are raising Earth's ground temperatures at a rapid and dangerous rate. There is no honor in being a scientific maverick, and there is no honor in being a member of the scientific consensus. There is only honor in having the Truth be your highest priority. And if your fellow scientists do the same and you find yourself in consensus, as is true in the climate science community, it speaks well of the integrity of those in consensus.
But look at why equating consensus with religious zealotry accomplishes a great deal for the AGW denialist camp. It makes off-the-wall ideas now hallmarks of heroic struggle against the stale status quo. It legitimizes banner promotions of ideas which have already been debunked. It panders to a regretable but very human tendency - to try and avoid taking responsibility for bad behavior. It also taps into the need for heroism in just about everyone (unless you really pause and think about it for a moment). It therefore buys time for business-as-usual on the part of the oil and mining industries and those they financially sponsor (like the Exxon-sponsored George C Marshall Institute which funds Baliunas).
Here's a new theory (made up on the spur of this moment) - Moon dust kicked up by lunar meteorite impacts leaves the Moon's gravity and spirals down towards the Earth's atmosphere, where its low (6%) reflectivity causes a net warming, just like soot from Chinese coal plants. THIS is the cause of global warming, not people! I want my own theory, I want to swing for the fences, too. I want in on that gravy train of climate research money that the denialists say is out there. I want my theory put right up there next to AGW and without any mention of its scientific weaknesses. Why should I have to get my idea past professional climate journals and those killjoy referees anyway? Why can't I be considered a legitimate contender until hell on Earth arrives, hoping that someone will provide evidence which finally snatches victory for my pet theory from the jaws of apparent defeat? Aren't my credentials sufficient in themselves for everyone to believe my theory is just as credible as AGW? After all, I'm a PhD too! Make sure you get the name spelled right - the Nolthenius Theory! ...OK, fun's over. I'll calm down now.
What the Science Says: Unlike many claims, this one is not absurd on its face. I can imagine having a sense of excitement on realizing the possibilities of this idea. It's worth a careful look. First, let's summarize the supposed mechanism, which is a bit more complex than some other claims: High solar activity means a stronger solar magnetic field permeating the solar system, which tends to deflect galactic cosmic rays (very high speed ionizing atomic nuclei) from hitting the earth. Galactic cosmic rays (GCRs) create charged particles which are presumed to become cloud condensation nuclei (CCN) from which water droplets form. Thus, the more GCRs the more clouds and vice versa. Higher solar activity and hence fewer GCRs mean less clouds, reflecting less of the sunlight, and more is absorbed at the surface. Hence, the hypothesis claims - Fewer GCRs -> fewer CCNs -> less low-level cloudiness -> more sunlight absorbed by the Earth's surface -> higher temperatures.
First, it is true that more cosmic ray secondaries reach the lower atmosphere during solar minimum. The reason is that the solar magnetic field is weaker then, and therefore so is the shielding that it provides from cosmic rays from the Milky Way Galaxy in which we live (magnetic fields, as we learned in Astro 3 and Astro 4, cause a bending in the motion of charged particles).
Change in cosmic ray intensity
between 1700 and the present day from four independent
What about cosmic ray flux correlation with low clouds? It is a complex series of steps needed to go from a cosmic ray hit in the lower atmosphere to a cloud condensation nucleus to a nucleated particle big enough to be called a cloud droplet and scatter sunlight and affect climate. The physics shows that there are already far more than plenty of nuclei available for cloud formation, given the other conditions necessary to make a cloud. There are still large uncertainties in modelling the steps, however, even including reasonable ranges. Nevertheless, Pierce and Adams (2008) find that the number of cloud condensation nuclei caused by cosmic rays modulated by the solar cycle is only about 0.1% of the total cloud condensation nuclei, which is “far too small to make noticeable changes in cloud properties based on either the decadal (solar cycle) or climatic time-scale changes in cosmic rays.”. A good summary of the state of aerosols and cosmic rays and cloud nucleation as of 2009 is here.
So the theory of cosmic ray induced significant cloud cover looks pretty weak, but what about the observations of clouds? After all, maybe some mechanism other than ones considered may be at work and yet induce a significant effect? A good way to see if GCR's affect cloudiness is to study so-called "Forbush Decreases (FD's) ", which are significant and rapid drops in the GCR intensity over a time scale of a few days. Since the lifetime of clouds is of order hours, studying cloud cover over these time scales will at least test if there is any demonstrable mechanism for GCR's to affect clouds, although not over the decades time scale relevant for climate change. Svensmark (2009), using only 5 FD's, says there is an effect from FD's, but Kristjansson etal (2008) studied a larger sample of FD's and used MODIS satellite data, finding no correlation by several measures. NOAA (The National Oceanic and Atmospheric Administration) website summarizing global warming science, says "global analyses of cloud cover over land for the 1976-2003 period show little change". This site has a fairly comprehensive list of published papers (over two dozen) finding insignificant or no connection between cosmic rays and cloud cover.
More important, the ISCPP satellite data on global cloud cover (used in Svensmark's
work) is now known to be flawed, from the study by Evan etal (2007) - authors
and abstract given below...
"Arguments against a physical long-term trend in global ISCCP cloud amounts": Evan AT (Evan, Amato T.), Heidinger AK (Heidinger, Andrew K.), Vimont DJ (Vimont, Daniel J.), GEOPHYSICAL RESEARCH LETTERS Volume: 34 Issue: 4 Article Number: L04701 Published: FEB 17 2007
Abstract: The International Satellite Cloud Climatology Project (ISCCP) multi-decadal record of cloudiness exhibits a well-known global decrease in cloud amounts. This downward trend has recently been used to suggest widespread increases in surface solar heating, decreases in planetary albedo, and deficiencies in global climate models. Here we show that trends observed in the ISCCP data are satellite viewing geometry artifacts and are not related to physical changes in the atmosphere. Our results suggest that in its current form, the ISCCP data may not be appropriate for certain long-term global studies, especially those focused on trends.''
A good discussion of this viewing angle problem and how it's been used by the Svensmark camp is here. An article in EOS also shows how the claimed correlations are not actually present in the real data, here. The bottom line - claims of trends in cloud cover using this data set are not supported. As of mid 2010, it appears ISCCP has not issued corrected data.
And finally, from a discussion on the RealClimate.org site...Svensmark
and others pointed to an apparent correlation between low-altitude cloud cover
and cosmic rays. But after 1995, the beguiling fit of Svensmark's graph depends
on a "correction" of satellite data, and the
satellite scientists themselves say this is not justified.
Here’s a quote…
“I went to discuss this with the ISCCP scientists (downstairs) to
get their opinion and this is a rough summary of the issues:
1) ISCCP inter-satellite calibration is done by offsets for individual satellites, not through trends. For instance, calibration is done using the warmest and coldest deciles from the satellite radiances. Whenever a new satellite stream is introduced there will be offsets in various parameters (so far ISCCP merges data from 33 different satellites) since the calibrations are done for a limited selection of targets, the satellites sometimes see different things and there maybe subtle diurnal or angle related differences. Any new satellite can cause a jump, but it cannot produce a continuing trend. Calibrations are done directly against NOAA-9 (which was the best calibrated of all the satellites and serves as a gold standard for subsequent instruments). Thus the calibration of NOAA-14 (and NOAA 16 – from 2001) is performed directly against the NOAA-9 values, not with respect to overlapping satellites: http://isccp.giss.nasa.gov/JPEG/calib_be4after.jpg ). Thus there is no way the 1994 gap between NOAA-14 and NOAA-11 could have produced an ongoing trend in the ISCCP data.
2) The MS03 trend correction is based on the apparent difference between SSMI and ISCCP. But SSMI only sees water clouds and ISCCP sees both ice and water clouds, thus the trend could be a real effect, or it could be related to drifts in either or both instruments or to drifts in the calibration targets. It certainly can’t be assumed only to be a problem with ISCCP, and cannot have anything to do with the ‘gap’ mentioned above (since that would simply have produced an instantaneous offset).
Bottom line: there is absolutely no good reason to put in a trend correction because of a gap in the satellites."
From Laut (2003), showing the apparent correlation between cloud cover and cosmic ray flux breaks down after ~1995
From my reading of the papers and responses (including Svensmarks' here), my conclusion is that the cloud data is unfortunately not good enough to say much of anything with any confidence about Svensmark's hypothesis except that there is no apparent support from the full data. There appear to be on-going problems with calibrations, with the inability of the ISCCP to differentiate between low, mid, and high clouds, view angle problems, and intra-satellite calibration problems. Since we're concerned with trends on the decadal time scale, it may be some time before this particular data is sorted out. While there probably is some correlation between cosmic rays and global temperatures, the simplest and best supported explanation is the already verified change in solar luminosity with solar cycle. Less radiation -> cooler temps, and this just happens to overlap with Svensmark's unrelated hypothesis, since more cosmic rays arrive when the solar cycle is a minimum. With the cloud observations muddled at this time, in judging Svensmark's idea we therefore put more emphasis on the theoretical work, which appears quite confident that cloud formation is far more sensitive to other factors than to ionized particle availability created by cosmic rays. I discussed this with a personal friend who is also a leading professor of atmospheric science and who develops models of cloud formation, and he agrees.
More important - since the cosmic ray induced cloud feedbacks clearly must happen (if they happen at all)
on very short time scales (hours and days, not decades), and since there has been
no secular trend in cosmic ray or solar activity since the mid 1950's (see
the far right graph above), the Svensmark idea is a red herring as far
as its relation to AGW. It therefore cannot be an alternate explanation
for global warming.
Svensmark teamed with author Nigel Calder to write the popular-level book "The Chilling Stars" on his hypothesis. The Institute of Physics has reviewed the Calder and Svensmark book here. From my own reading of interviews with Svensmark, I have to say I am inclined to agree, unfortunately, with the book review's unfavorable judgments.
This 10 minute YouTube video "Climate Change - the Objections" is straight-arrow and shows good grasp on the science and gives a nice summary of the major problems with Svensmark's hypothesis, and also those of Richard Lindzen.
sun is causing global warming.
Why this claim is wrong: A large number of studies all show that the sun, whether by straightforward luminosity, or by UV flux, or by modulating cosmic rays, cannot account for more than a small fraction (if that) of global warming in the past 40 years. The sun's total luminosity does fluctuate slightly with the solar cycle, as magnetic field energy thermalizes and emerges as luminosity. However, it is weak, only 0.1% peak to trough. Since 1957, solar cycle maxima have been flat or decreasing in strength, and solar energy flux as well. And therefore too, all known variants of solar forcing show no trend. Meanwhile, this period shows the most rapid and accelerating global temperature rises, in lockstep with the rising and accelerating GHG emissions due to man's activities. Here's a good article with graphs and summaries of many published studies on the solar influence on climate. On the claim that somehow, through unknown physics, solar forcings must be higher than the purely irradiance effect, because look at how severe the "Little Ice Age" was, when the solar cycle virtually disappeared for several cycles. However, the Little Ice Age appears to have been a coincidence of several verified causes beyond the solar activity effect, including volcanic activity, reforestation pulling CO2 out of the atmosphere after the Black Death and Columbian Exchange (European diseases introduced to the New World) caused a large drop in global human population, for example.
The denialists will have you believe that global warming is a scam designed to pump up research dollars to the climate scientists. By this kind of logic, who would have more incentive than the Stanford Solar Center (where I worked for a time as a PhD student) to implicate the sun in global warming? Yet, see what they have to say here.
costs of halting CO2 rise is crippling to world economic progress, and we should
not commit to drastic action until we can prove with certainty that man and
fossil fuel burning is causing global warming.
Why this claim is wrong: IEA report shows it is estimated to take only about 1% of world annual GDP from now till 2050 in order to reduce CO2 emission rates to 50% of current levels, which is estimated to confine global warming to an additional 2 degrees C above current levels. This is still very serious warming with serious consequences, but there is at least a chance it is not completely catastrophic, like the ~6 degrees C which the "business as usual" scenario calculations indicate. Halting CO2 rises no doubt will have a serious impact on oil and coal company profits unless they change their business models, but these business interests should not define themselves as the world economy. Here's a good link to the economics of global warming which itself links articles in peer-reviewed journals on costs vs various mitigation strategies.
Why this claim is wrong: Can't say it any better than this article - "cherry picking"! The 1995 claim is extreme cherry-picking. Chosing now back to 1995 is the longest period you can get away with and still just slightly fail the standard measure (95% confidence interval) of statistical significance. The notorious Richard Lindzen is the originator of this one, and later repeated in the denialist blogosphere in many places. The disingenuousness of it all is discussed here. Note too that 2010 is on course to be the hottest year in recorded history, despite the fact that the sun over most of the past decade has been going through the longest and deepest solar minimum in a 100 years. El Nino events, the solar cycle, and finite observational accuracy accounts for most of the year to year variance. Note the trend since 1880, about when fossil fuel use began to be widespread, and decide for yourself whether global warming has really stopped. Yet there are bizarre denialist blog sites that still claim we're headed into another Ice Age.
Cloud feedbacks from enhanced warming are negative (i.e. cause a net cooling),
so that climate is essentially stable.
Why this claim is wrong: This is Richard Lindzen's "Iris Effect" hypothesis, proposed in 1990. Hypothesis is perhaps a generous term - speculation is closer. The evidence and theory both point to cloud feedbacks actually trending towards increased warming, i.e a positive feedback. Brian Soden, a Princeton climate scientist, examined the tropical greenhouse effect in and out of El Nino conditions and finds that clouds behavior is opposite to that hypothesized by Lindzen (Soden 1997). And Lin (2002) finds "The observations show that the clouds have much higher albedos and moderately larger longwave fluxes than those assumed by Lindzen et al. As a result, decreases in these clouds would cause a significant but weak positive feedback to the climate system, instead of providing a strong negative feedback", opposite to Lindzen's hypothesis. And the most recent study again shows cloud feedback is positive (more CO2 warming leads to more cloud-cover induced warming), not negative. See more studies backing up this conclusion here and here. The current incarnation of Lindzen's idea is in Lindzen and Choi (2009), claiming that the ERBE satellite data show increased outgoing radiation from Earth to space when sea surface temperatures rise. But this work has a number of major flaws which are fatal to the hypothesis, pointed out (paper still in process) by Trenberth etal here. Lindzen is reportedly reworking his claims yet again. Given his original incarnation was published now 20 years ago, it seems like variants are going to be keep coming, regardless of how wrong they continue to be. The specific problems are not easily put into bullet points for the non-science major, so I would recommend the serious student follow the links to fully digest this. However, it's safe to say that climate models agree well with the global temperatures and Lindzen's ideas are quite outside what both theory and observations indicate. More disturbing, these studies above show Lindzen cherry-picking in time interval, cherry-picking in model heat flow parameters, and deeply flawed portrayal of the relation of the tropical system to global climate. On a larger time frame, this "Iris" hypothesis is obviously wrong, as relatively small changes in insolation at the arctic circle (Milankovitch cycles) are amplified by feedback to produce the great Ice Ages. We see the opposite happening today, as the arctic is melting rapidly due to the ~1 degree Celsius temperature already seen. There's another 0.6C or more "in the pipeline", even if we completely halt all CO2 production (i.e. shut down every car, every factory worldwide) today.
Claim: Climate scientist Michael Mann (Penn State University) is guilty of misusing confidential data and engaged in a conspiracy to withhold information, and manipulated or destroyed data to strengthen his case that human activity was changing the global climate.
Why this claim is wrong: The time scale for warming depends, of course, on the magnitude of the forcing and the thermal inertia of the system. If climates are relaxing from the last Ice Age, such that each incremental change in ice coverage means a bit warmer planet, leading to a bit less ice, etc, and if the ice is a mile thick and covering vast areas of the northern hemisphere, then yes - it can take thousands of years for quasi equilibrium to happen. That has nothing whatsoever to do with the current situation. There's only a small arctic ice cap remaining - mainly Greenland. And the forcing is not the relaxation described above, but a rapid and strong rise in greenhouse gases. As for thermal inertia: the thermal and CO2 capacitance of the ocean is vastly bigger than that of the atmosphere, due to its mass. But it is to the atmosphere that we are directly adding CO2. Next, the evidence is strong from both theory and observed correlation that the ice ages are primarily controlled by the Milankovitch cycles. These changes in the Earth's spin axis are straightforward to calculate by the laws of gravity for both the past and future. Currently we are finishing a period of decreasing insolation at arctic north latitudes, and global temperatures for the past centuries have shown a slow net cooling - until the rapid rise beginning about a hundred years ago. If we've been rebounding from the last ice age, why has there been centuries of cooling - until now? Makes no sense. Global temperatures rise at a rate depending on the magnitude and direction of the forcing mechanism. A study using a suite of climate models shows that the moderate temperature rise in the early 20th century is mostly due to the rising solar activity, while anthropogenic CO2 is responsible for the more rapid warming since then (Meehl 2004) We're currently adding a strong forcing upward by CO2 and methane emissions, and temperatures are responding rapidly, as calculations show they should - not the glacially slow progression out of an ice age ~19,000 years ago. The atmosphere response to forcing in general can be much faster than this claimed millenial time scale, most obviously by the response to volcanic eruptions as graphs on this page show. Coming out of true Ice Ages can take hundreds or thousands of years, due to the feedback of melting ice and resulting lowered albedo. Forcings which go directly to the atmosphere will be short, of order decades, or less. And that's exactly what we're seeing with current global warming.
Regarding the Little Ice Age - there is little doubt temperatures were lower for a few hundred years centered around the year 1600. It had been widely assumed that the Maunder Minimum in solar activity may have caused the Little Ice Age. However that was only a tentative assumpition as we had no data on solar output vs solar activity until recently. We now have good satellite data on insolation over the last several solar cycles, and the insolation only varies by less than 0.1% maximum to minimum in the solar cycle, so that a prolonged period of low solar activity such as the Maunder Minimum would not correspond to low enough solar heating to account for the Little Ice Age. This is confirmed by a recent paper by Feulner and Rahmstorf (2010) , (GRL paper here). Instead, recent papers show that during the Little Ice Age there were stronger and more frequent volcanic eruptions, which put sulfate aerosols into the atmosphere and cooled the Earth by reflecting sunlight, and that the Black Plague and Columbian disease spread to the New World caused a significant drop in human population during the late middle ages, leading to reforestation which took up enough carbon to account for the 10ppm of drop in CO2 associated with the Little Ice Age. This brief reference is interesting, though not a peer-reviewed paper.Claim: Why should we believe climate scientists now? In the '70's they were predicting we were headed for an ice age!
1.2 trillion tons of fossil fuel CO2 has been released into the atmosphere in the past 250 years. Fully half of that has happened just since 1975
CO2 levels for the past 150 years. Note the levelling off from the mid '30's to 1950, as World War II served as a distraction from fossil fuel burning by the great majority of people. This, and the reflective tropospheric sulfate air pollution which came with post-WWII industrialization counteracted greenhouse warming till ~1970, in agreement with observed temperatures and climate models.
Why this claim is wrong: Cherry-picking, basically is the answer. The cold high altitude interior of Greenland did have a net gain of snow during the '90's, but this was found to be consistent with global warming models, which include higher evaporation of warmer ocean water and deposition as snow at the very high elevations of the top of the Greenland ice cap, which was then still cold enough then to have the net snow balance be positive. However, the ERS-1 and ERS-2 satellite data used was not able to say much about the behavior of ice near the coastal areas, where in fact ice has been melting and sliding into the ocean at an accelerating rate. And, since the most often used study which AGW-denialists use to champion this myth was published almost 10 years ago, newer and better satellite data using gravity measurements show that the entire continent is net losing ice (this YouTube shows how GRACE works). A recent paper by Wu etal (2010) using a different calibration of GRACE data, still finds Greenland is losing its icecap, albeit at a smaller rate. The graph at left shows the change in the total ice mass of Greenland, interior+coasts. The regular up/down oscillations are due to seasonal summer melting vs winter ice accumulation, not observational error. Note that the rate at which the ice is disappearing has doubled in just this last decade - a decade during which the solar heating contribution has actually been dropping as we've gone from a solar maximum in 2001 to an unusually deep solar minimum in 2008/9. Ice loss is also happening in Antarctica (and here). A major factor is that the speed of Greenland glaciers is rising rapidly. Meltwater on the surface is observed to follow channels down to the base of the glacier, lubricating its gravity-induced motion towards the ocean. Without detailed images of the base of glaciers, it is not possible to model this accurately and to be conservative, the IPCC decided to not include this aspect in their AR4 report. Unfortunately, the result is a significant under-appreciation of the loss of continental ice at the poles due to global warming. Baffin Island, also in the arctic and the 5th largest island on Earth, has lost 50% of it's ice cap in the last 50 years. Globally, glaciers world wide are in rapid retreat (see graph below right - sorry for the poor reproduction!). See this video of congressional testimony which contains a nice animation of the GRACE data on where and when ice is being gained and lost on Greenland.
Change in total Greenland ice mass as determined from the GRACE data
Global Glacier Thickness Change: This shows average annual and cumulative glacier thickness change, measured in vertical meters, for the period 1961 to 2005. Explosive volcanic eruptions, which contribute dust to the stratosphere and cool the Earth's climate, can temporarily raise glacier mass balance. Four significant eruptions with worldwide impacts are shown on this graph and are generally associated with periods of increased mass balance due to lowered temperatures. Image courtesy of Mark Dyurgerov, Institute of Arctic and Alpine Research, University of Colorado, Boulder.
Claim: The domestication of rice and clearing of forests beginning near the dawn of civilization likely saved us from an Ice Age.
In past Milankovitch cycles, warming induced the release of CO2, which then added to further warming. Notice that we are in an unusually long period when the Milankovich cycles conspire to prevent this from happening again, until at least 50,000 years and perhaps 130,000 years from now.
Support for the Milankovitch theory of Ice Ages comes largely from the significant correlation between global temperatures and the insolation at 65N latitude. However, it is not perfect. Note the lack of interglacials during two insolation cycles ~160,000 years ago. The last 8,000 years have not cooled (moderately) as Milankovitch alone would have suggested.
Milankovitch cycles show no new ice age for at least another 50,000 years (NOAA source) . (NOAA = National Oceanic and Atmospheric Administration. The principle federal science agency on ocean and atmospheric science)
A discussion with Ruddiman on his idea, and his eventual concession that early man's agricultural influence can only account for about 1/3 of claimed Ice-Age avoiding warming, is here. In this post by Ruddiman, you'll see that his hypothesis was refuted by Siegenthaler et al 2005 and by Spahni et al 2005. Ruddiman disputes these papers because they aligned data to a past interglaciation when insolation values were at a local maximum, and he says it should instead be aligned with a local minimum since we are at a local minimum in insolation today. This complaint by Ruddiman makes no sense, since it is from 8,000 years ago going forward that he claims early Man prevented an ice age by the development of agriculture, and 8,000 years ago did indeed correspond to a time of local insolation maximum, as the Milankovitch cycle insolation graph above shows. Also, in searching this and other discussions, I am surprised to see no one pointing out that the absolute level of insolation in his favored analog period of 400,000 years ago, is only 460 watts/square meter, a very large 20 watts/square meter less than current values, and much lower still than the ~520 watts/square meter which prevailed 8,000 years ago. The paleoclimate record indicates it would seem extremely unlikely than an ice age could be triggered at a time of such high insolation. His idea seems to assume that only the direction of changing insolation matters in inducing an ice age, not the absolute amount of heating. Ruddiman's hypothesis was tested recently using one of the many sophisticated climate computer models we have designed - the GENESIS climate model, and found that dropping CO2 and CH4 levels to Ruddiman's estimated non-human-caused levels, and see a 2 deg C temperature drop, which is only 1/3 of the temperature drops associated with ice ages, and Ruddiman concedes this. So what was Ruddiman's basis for the dramatic "Ice Age" claim? I have to admit it certainly did make the idea an attention-getter for his popular-level book "Plows, Plagues, and Petroleum: How Humans Took Control of Climate". Note also that we are now no longer in a realm of rapidly dropping Milankovich-induced cooling, and too that CO2 levels now are far higher thanks to fossil fuel burning in the last 60 years, than at any time in the past ~800,000 years.
The rapid rise in global temperatures in the last century is the AGW issue, and therefore Ruddiman's hypothesis would also seem to be a red herring in this regard. What's really interesting is how AGW denialists have latched onto Ruddiman's hypothesis as somehow helping their cause. They couldn't be more wrong. A great article with links on this bizarre logic is here.
The Little Ice Age has several contributing causes, not just solar. Robock (1979) finds that enhanced volcanism during this period provides the best fit to the data, while fitting to solar acitivity gives a very poor correlation. Also, the Black Plague de-populated and re-forested Europe and the Columbian Exchange (disease from European colonization of the New World) together caused significant de-populating of the Earth, and the resultant re-forestation of the landscape acted as an efficient remover of CO2 (10ppm = 3% by observations) from the atmosphere. In any case, we have accurate satellite measurements of insolation for several complete solar cycles now and therefore have a good idea of how to translate observed sunspot numbers and cosmic ray evidence into insolation estimates for past centuries. Even another dramatic Maunder Minimum would not induce an ice age (Fuelner and Rahmstorf 2010)
We clearly can't run an experiment on the entire Earth itself from 8000 years ago to today in order to rule Ruddiman's hypothesis completely - but the weight of evidence is clear: The validity of the idea is highly unlikely. Anyone teaching this as a reputable idea is doing a great disservice.
can't be Global Warming. We're having record low temperatures here in 2009
Why this Claim is Wrong: Basically, it's the difference between weather (short term variances due to moving cold and warm fronts), and climate (the average of weather over time scales of decades, so that daily and seasonal effects average away, revealing slower secular changes. Imagine getting down on your belly and examing a mountain stream from 2 inches away, and trying to predict what it would look like 2 seconds later. You'd find the task of making the prediction very tough at these tiny scales where mathematical chaos is important. But now stand on the high cliff over that same stream and try and predict what it'll look like in 2 hours. Much easier; it'll be nearly the same. And in 5 weeks? Maybe a little less water flow as summer continues. It's pretty obvious, really. So when you hear AGW denialists claiming the cold winter of '09 disproves global warming, it's a crock. Note also that 2010 was the hottest year on record.
can you trust climate models, they don't even include clouds!"
Why this Claim is Wrong: This was a stunner when I first saw it in Fall 2009. Climate models have included clouds for decades. It's a gross misrepresentation. As just one example from several years ago, see Hansen etal 2005, which includes both low and high level clouds in its climate model, see also earlier references therein. That said, cloud modelling has been difficult and until recently, progress in improving the models was slow. Cloud behavior in most models in the past has been done by parameterizations based on observations. This is a good approach when the complex physics doesn't have sufficiently known boundary conditions to model directly from first principles. It does not mean that the models are nonsense in what they produce. The evidence shows otherwise. Clouds are important to get right since about half of all insolation reflected back out to space is reflected by clouds. The IPCC AR4 identifies cloud modelling as one of the main contributers to the remaining spread in confidence about future temperature trends. But since 2006 the situation has improved substantially, with the advent of the "A-Train" group of satellites observing coherently the same wide regions from space across a wide range of wavelengths in order to measure simultaneously aerosol content, spectroscopic identification of components, albedo, and droplet sizes from reflection properties. Published results show the pollution aerosols make for smaller water droplets and ice crystals and less rainfall from those clouds (Jiang etal GRL 35, L14804 (2008)). We've confirmed also what we've known since 1989; that large concentrations of sulfate aerosols (e.g. from fossil fuel burning lead to smaller water droplets and brighter clouds (for the same water content), and that the smaller droplets inhibit precipitation and lead to longer lived clouds. So pollution adds a net cooling, on average. Since the industrialization of Asia has added to aerosols net world wide, we expect a net cooling from this effect, yet clearly global temperature continue to rise despite this. We also see that cloud feedbacks are positive feedback, meaning that CO2-induced warming alters cloud properties so that they accentuate the warming further. Cloud models have not all been equal in getting clouds right. According to a study by Clement etal (2009) studying 55 years of COADS cloud data in the southeast Pacific, rising sea surface temperatures cause a decrease in low clouds and a further increase in low level temperatures. This positive feedback, if correct, accentuates global warming beyond that forecast by the IPCC's 2007 report. The UK Met office's HADGem1 climate model closely matched the behavior of low clouds very well, and also is showing positive feedback.
Claim: Aerosols Are
Not Even Considered in Climate Models
Why this Claim is Wrong: This was another stunner when I first saw it in Fall '09. Of course aerosols are considered in climate models, and have been for many, many years! This graph at left is from Hansen etal 2007, which shows climate forcings due to the sun, snow coverage, land use, water vapor, ozone, well-mixed GHG's (methane, CO2, NO2...) and several different aerosol types, all using the Goddard Institute for Space Science's Climate Model E. Note that most aerosols act to cool climate by reflecting some sunlight back out into space before it can reach the ground. Only CO2 gas has a strong upward and accelerating positive temperature forcing and for fully 70 years now greenhouse gases have dominated all other effects except temporarily during volcanic eruptions, in line with observed temperatures. We certainly want to understand the detailed physics of aerosol formation better than we now do, as currently we need a mixture of basic physics and fitting to observed data to parameterize the behaviors under different relevant conditions. But note that even with the unusually frequent volcanic stratospheric aerosol injections since 1960 (including Mt. Agung, Mt. St. Helens, and Mt. Pinatubo) - volcanic eruptions being most powerful net cooling forcings - yet this is precisely the time when global temperatures have actually accelerated upward. While the aerosol forcing curves are likely to move a bit as we gain better understanding and ability to model, even if we're off by 100% on each aerosol curve, it won't come close to changing the net result and net conclusion - aerosols are not the reason for global warming.
Follows Temperature, Not the Other Way Around"
Why this Claim is Shamefully Misleading: This was the most stunningly naive (or deliberate red herring) claim of all when I first saw it in Fall '09. Look at the logic this claim attempts to persuade with: Because many past instances in the paleoclimate record show temperatures rising from low levels, followed 200 to ~800 years later with rising CO2 levels, this means that current CO2 rise is causing global warming today. If your response is puzzlement and a struggle to grasp the logic, be reassured - there is no logic to grasp. Before mankind was pumping huge amounts of carbon into the atmosphere in a geological instant, the large slow temperature changes were primarily caused by the Milankovitch cycles in the Earth's orbit, the best-supported theory of the primary cause of the Ice Ages. When temperature rises due to orbital change, the rising ocean temperature brings more CO2 out of solution and into the atmosphere (Callion etal 2003). The increased CO2 in the atmosphere then causes further temperature rise by the Greenhouse Effect, which induces more CO2 out of the ocean, etc. This positive feedback is sufficient to bring Earth out of an Ice Age into an interglacial. It takes many centuries for this process to happen as the CO2 transfers into and out of the ocean are quite slow because deep ocean currents are slow. A good discusion with figures is here, and another is here. Today's global warming is happening not on the thousands of years time scales of the "CO2 Follows Temperature, Not the Other Way Around" cannard, but a few decades. And the record clearly shows CO2 rise is happening followed closely by temperature rises. It's not at all like the examples pointed to in the paleo record. 10,000 years ago, humans comprised about 0.1% of the land vertebrate biomass. Today, we comprise over 99%, and drastically altering the atmosphere to support such a staggering figure.
Claim: Cities have grown during the 20th century and their asphalt, concrete and
buildings absorb much more heat than vegetated countryside. This biases temperature
measurements - this "urban heat island" effect accounts for much or all of
global warming, not CO2.
Why this Claim is Wrong: This effect is and has been very well known and has been carefully calibrated out for decades. The denialist claim is disingenuous in the extreme and aims itself at the naive, who don't realize how obvious and for how long this effect has been understood by climate scientists. The latest IPCC report in 2007 finds that urban heat island effects have been determined to have negligible influence (less than 0.0006 °C per decade over land and zero over oceans) on these measurements.
And Finally: On Richard Lindzen
Richard Lindzen is the highest profile and considered the most prestigious (Sloan fellow at MIT) of the AGW denialists. So it's disturbing that he uses his MIT position (earned by reputable work that was not AGW-denialist oriented back when he was a young man) while making misrepresentations in the Wall Street Journal and other non-journal outlets about climate science and the scientific evidence for global warming, without references, without support. Here is an account of his testimony in front of the UK's House of Lords and the outright falsehoods about the scientific consensus. A quote from this article: "when a panelist specifically asks ‘how far your view of the role of water vapour is shared by other scientists?’ (Q144), one cannot honestly answer ‘That is shared universally’ when no other scientist in the field has made a case for a negative water vapour feedback. This is probably the most egregious mis-statement in the whole testimony and is deeply misleading."
Here are links to his conflicts
of interest with regard to taking oil money, and to his own
grad students' testifying that Lindzen feels a strong need to prove his status at the expense of others, bringing into further question his ability to be objective and truth-oriented: “If
you want to prove yourself a brilliant scientist, you don’t always
agree with the consensus,” said Daniel Kirk-Davidoff, a former
student of Lindzen’s
at MIT. “You show you’re right and everyone else is wrong. He certainly
enjoys showing he’s right and everyone else is wrong,” Kirk-Davidoff
continued. “If you have a ten minute conversation with him, you can
Collection of links on Lindzen's strikingly poor record on climate change ideas, and his funding by oil money
Response to Lindzen's Newsweek interview
A variety of online videos of Lindzen talking - gives a good flavor for his way of making statements without supporting references, and which are false, but given in such a disarmingly breezy way that unless you know the facts, you can get taken in.
Here's another good video on the junk science of the objections to AGW, the final few minutes of which does a good summary of the poor science in Lindzen's "Iris" hypothesis. No responsible person sincerely desiring to know the truth can afford to simply take his unsupported pronoucements on faith, just because he's an MIT professor - the classic logical fallacy of "the argument from authority". Give credibility to a scientist because he's supported his case in solid peer-reviewed scientific journals, not because he's got a prestigous position earned earlier.
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