Anti-global heating claims - a reasonably thorough debunking

[Updated 9/15/07: Added myths #19 & #20, climate predictions aren't possible and volcanoes emit more CO₂ than people, respectively]
[Updated 9/14/07: Updated Myths #4, 8, 10, & 13]

The Earth is heating up, and human beings burning fossil fuels are the dominant cause. It’s not ocean warming that dominates, it’s not cosmic rays, it’s not variations in the Earth’s orbit and tilt toward the sun (Milankovitch cycles), it’s not solar irradiance - it’s us. But there is a very vocal minority that refuses to believe global heating (the severity of the problem requires more urgent language, and besides, 105 degrees isn’t warmer than 100, it’s hotter) is real.

Global heating deniers fall back on a variety of myths in order to buttress their position. These myths vary from logical fallacies to pseudoscience to poor math to scientifically valid but disproved hypotheses. Yet every single claim against global heating I’ve found has been debunked at one time or another, and at this point, the only hypothesis that fits all the data is that human civilization is heating up the planet.

I’ve gathered the top anti-global heating myths into the following list and provided a reasonably thorough debunking for every one. I’ve focused only on the scientific claims because they can be addressed with data, and there are probably a few I’ve missed that I’ll happily tackle in the comments as needed. There were a number of claims that tied together, so I addressed them all at once rather than independently. And if I could quote references that weren’t the IPCC Working Group I: The Physical Basis for Climate Change detailed report (not the summary for policymakers), I did - too many people reject the IPCC out of hand and it’s always better to use the original source if it’s available.

Table of Contents

Myth #1: All the CO₂ in the air at present comes from the mantle.

Myth #2: Increasing CO₂ in the air is due to gases coming out of solution as the ocean heats up.

Myth #3: Humans are not the source of the recent increase in atmospheric CO₂ concentration.

Myth #4: CO₂ is rising at 0.38% per year, not 1% per year as the IPCC Third Assessment Report claimed.

Myth #5: CO₂ is such a weak greenhouse gas that it cannot be the cause of the observed warming.

Myth #6: CO₂ concentrations are not correlated with global temperature due to periods in the geologic history when CO₂ was higher and the planet was in an ice age.

Myth #7: Temperatures during the Medieval Warm Period were warmer than modern temperatures.

Myth #8: The existence of the Medieval Warm Period has been ignored in order to support anthropogenic global heating.

Myth #9: Modern temperature increases are a direct result of the Earth’s climate exiting the Little Ice Age.

Myth #10: Global cooling between 1940 and 1970 happened even though anthropogenic CO₂ was rising at

Myth #11: Cosmic rays hitting the earth are behind global heating.

Myth #12: The Stefan-Boltzman law breaks the equations of global heating.

Myth #13: Computer models are too inaccurate to accurately predict a system as complex as the Earth’s climate.

Myth #14: The oceanic storage of heat is required to account for the differences between data and early models. But the updated models still require an unrealistically large oceanic depth of water to make them work right.

Myth #15: The oceans have already begun to cool in response to natural variations, so global heating is wrong.

Myth #16: Satellite measurements of tropical air don’t correspond to directly measured temperatures, so global heating isn’t actually happening.

Myth #17: Global heating will be good for the planet, not bad.

Myth #18: Water vapor is a more powerful greenhouse gas than CO₂, and since humans have almost no direct impact on the amount of water vapor in the air, humans can’t be the cause of global heating.

Myth #19: We don’t have enough climate data to make valid predictions of any kind.

Myth #20: Volcanoes spew more CO₂ into the air in a single eruption than humanity has emitted in its history.

 

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DENIAL MYTH #1: The source of all the CO₂ in the air is outgassing from the mantle (Source: George V. Chilingar’s (of the Department of Civil and Environmental Engineering, University of Southern California) paper titled On global forces of nature driving the Earth’s climate. Are humans involved?).
Debunking: This theory proposes that the bulk of the CO₂ in the air and oceans today is a direct result of outgassing from the Earth’s mantle, not from human consumption of fossil fuels. The key piece is this:

Recalculating this amount into the total anthropogenic carbon dioxide emission in grams of CO₂, one obtains the estimate 1.003×10¹⁸ g, which constitutes less than 0.00022% of the total CO₂ amount naturally degassed from the mantle during geologic history. Comparing these figures, one can conclude that anthropogenic carbon dioxide emission is negligible (indistinguishable) in any energy-matter transformation processes changing the Earth’s climate. (emphasis mine)

In essence, Prof. Chilingar is claiming that anthropogenic (human sourced) CO₂ has had a negligible impact on the atmosphere over the last hundred years or so and will have no impact over next few hundred years because we are adding a fraction of the total CO₂ outgassed by the mantle over the course of the last 4.5 billion years. Unfortunately, as W. Aeschbach-Hertig, of the Institute of Environmental Physics, University of Heidelberg, says in his rebuttal, there is at least one major error, like the fact that the modern atmosphere had only about 3×10¹⁸ g of CO₂ in it (not the full amount every outgassed by the mantle, which is 100,000x greater), so adding 1×10¹⁸ g of new CO₂ is a massive percentage change (~33%). In addition, time scales matter here - increasing the amount of CO₂ by 33% over the course of a few decades would overwhelm any system (like the Earth’s climate) that has a time constant of centuries. Finally, Prof. Chilingar appeared to attack global heating by concluding that direct heating of the air by human activity (aircraft air friction, power plant thermal plumes, etc.) couldn’t possibly cause the observed heating - which every serious climate scientist (Prof. Chilingar is a petroleum scientist) would agree with completely. Climate scientists say that the greenhouse effect is the cause of global heating, not direct heating by human activity. (source above)

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DENIAL MYTH #2: The source of the CO₂ in the air is thermal heating of the ocean causing dissolved gases like CO₂ to come out of solution and enter the atmosphere (Source: “Apocalypse Canceled”, by Christopher Monckton as well as others).
Debunking: The main idea here is that, if you overlay CO₂ concentration data from ice cores with temperature data, you notice that CO₂ has always lagged after temperature. Because hot water cannot store as much dissolved gas as cold water can (this is fundamental physics), the data could lead people to reasonably conclude that the ocean is the source of the CO₂ in the air and always has been. Unfortunately, there are three problems with this argument. The first is the aforementioned “predictive appeal to history” logical fallacy - just because CO₂ has lagged after temperature in the past doesn’t mean it always will (or is this time - it isn’t). The second is that this theory has been tested and been found incorrect.

If heating oceans were the source of the CO₂ in today’s atmosphere, we could expect a historical trend of dropping CO₂ concentrations in the oceans, yet we see the exact opposite - CO₂ concentrations in the ocean have increased even as their temperature has risen, driving down ocean pH (making it more acidic) and will continue to do so (source: Impacts of Anthropogenic CO₂ on Ocean Chemistry and Biology, NOAA). In addition, if a hotter ocean were the source of CO₂, oxygen would be coming out of solution as well, yet the concentration of oxygen in the atmosphere is actually decreasing, not increasing (sources: Environmental Chemistry.com’s CO₂ Pollution and Global Warming page and IPCC Working Group 1 Report, Chapter 2, pages 138-139).

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DENIAL MYTH #3: We don’t know for sure where the added CO₂ in the atmosphere is coming from, but it’s not from human consumption of fossil fuels (Source: distillation of multiple people’s claims at Wikipedia.org).
Debunking: We know exactly where the added CO₂ is coming from, and it most certainly is from human activity (mostly the burning of fossil fuels, but some is from industry and slash-and-burn deforestation for agriculture). Carbon has two stable isotopes (atomic weights), C¹² and C¹³. Plants prefer to use C¹² over C¹³ (it takes slightly less energy to bond to C¹² than to C¹³), so the naturally occurring ratio of the two isotopes is skewed toward C¹² in plants. All fossil fuels were originally plants, and so if the C¹²/C¹³ ratio in the atmosphere is changing toward increased concentrations of C¹², then the source of the new CO₂ must be plants. In addition, since animal respiration isn’t enough to skew the C¹²/C¹³ ratio and simultaneously affect the concentration of CO₂ and oxygen in the atmosphere, the source must be fossil fuels. (sources: Environmental Chemistry.com’s CO₂ Pollution and Global Warming page and IPCC Working Group 1 Report, Chapter 2, pages 138-139)

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DENIAL MYTH #4: CO₂ rates are rising only 0.38% per year, not the 1% per year called out in the Third IPCC assessment report (TAR) (Source: “Apocalypse Canceled”, by Christopher Monckton as well as others).
Debunking: Basically, this claim was used by Mr. Monckton to attack the validity of the TAR’s assessment. I was unable to find the exact data that Mr. Monckton used, so I’ll use the fourth assessment’s (AR4) data to make a point about how this error could have been made by Mr. Monckton. The average rate of change of the atmospheric concentration of CO₂ over the last 250 years has been about 0.14% per year (100 ppm change, ~280 ppm starting point, and the change occurred over 250 years), but rate of change has not been constant. In fact, the average rate of change since ~1960 has been about 0.50% per year, and the average rate of change since 1995 has been about 0.68% per year. And if you look at the middle left graph in Figure 3.2 of the IPCC Working Group 1 TAR Chapter 3, on page 201 (shown above), you’ll see that the actual graph of the data looks almost identical to the equivalent IPCC AR4 graph (Figure 1, FAQ2.1, page 135, shown at the left) and the description above. In the case of Mr. Monckton’s data, I suspect that he assumed a linear progression where the rate of change has been accelerating rather than remaining constant. (Source: IPCC Working Group 1 Report, Chapter 2, , page 137)

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DENIAL MYTH #5: CO₂ is a sufficiently weak greenhouse gas that it could not be responsible for the level of climate change being modeled and observed (Source: distillation of multiple people’s claims at Wikipedia.org).
Debunking: CO₂ is a relatively weak greenhouse gas compared to methane or nitrous oxide. If we use the radiative forcing (RF) values from Table 2.1 (page 141) of the IPCC Working Group 1 Report, Chapter 2 and assume a linear relationship between RF and concentration in the atmosphere, CO₂ is about 0.0044 Watts per square meter per ppm (Wm^-2ppm^-1), compared to 0.2706 Wm^-2ppm^-1 for methane and 0.5016 Wm^-2ppm^-1 for nitrous oxide. This means that methane is about 62x as powerful a greenhouse gas than carbon dioxide, and nitrous oxide is about 114x as powerful as CO₂. The problem is that CO₂ concentration in the atmosphere is measured at 379 ppm, while methane is only 1.774 ppm (1,774 ppb), and nitrous oxide is only .319 ppm (319 ppb). Because there is 213x more CO₂ than methane, and 1188x more CO₂ than nitrous oxide, the fact that CO₂ is a relatively weak greenhouse gas is more than compensated for by concentration in the atmosphere. See also DENIER MYTH #18 below for a discussion of water vapor and CO₂.

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DENIAL MYTH #6: 450 million years ago was the coldest in 0.5 billion years and also had the highest CO₂ concentrations. Because of this, CO₂ is not actually correlated global temperature (Source: distillation of multiple people’s claims at Wikipedia.org).
Debunking: Scientists aren’t sure what happened in the late Ordovecian period, when the world plunged into an ice age while CO₂ levels were still very high (8-20x current levels). There are some ideas about what happened, however. A 1995 paper titled Reconciling Late Ordovician (440 Ma) glaciation with very high (14X) CO₂ levels suggests that the physical location of the megacontinent Gondwanaland may have had something to do with it, and later papers suggest that the problem could be one of resolution of the data - if we can’t tell what the CO₂ levels were at the moment of glaciation, then we can’t say whether CO₂ being removed from the atmosphere was the cause or not. And if the high CO₂ levels plunged due to geologic processes (namely the rise of the Appalachian Mountains and a subsequent carbon sequestration due to the weathering of the mountains), then there would be a mechanism to explain how the CO₂ was high while the temperature was also high - the data isn’t detailed enough to know better, so it was actually a lot lower than 8x-20x present day when Gondwanaland froze up. In fact, this identical process is proposed as the cause for the most recent spate of ice ages, with the Himalaya Mountains being the cause. However, ultimately we just don’t know enough about this particular instance to say for sure.

However, the correlation of CO₂ and global temperature is well established over the last 650,000 years using ice core data. The image (click for a larger version) is a composite created by the IPCC from multiple different sources for the WG1 AR4 chapter 6 on Paleoclimate, Figure 6.3, page 444. The black line shows a proxy for local temperature (deuterium), the green line is nitrous oxide, the red line is CO₂, the blue line is methane, and the gray line is a proxy for land ice (low=more glaciers/larger ice caps). Notice that not only is CO₂ concentration correlated with temperature, but so is methane concentration.But the most interesting part of this graph is the three stars in the upper right corner of the image. They are to scale with the associated lines and represent the 2000 concentrations of nitrous oxide (green star), CO₂ (red star), and methane (blue star).

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DENIAL MYTH #7: The Medieval Warm Period/Medieval Climate Anomaly (MWP) was warmer than conditions today (Source: “Apocalypse Canceled”, by Christopher Monckton among others).
Debunking: This claim has been addressed repeatedly, and every example I found basically summarized down to this: The evidence used by most scientists that believe this claim is anecdotal at best and that while this evidence applies regionally to the area between Greenland and the Ural Mountains, there is not yet enough evidence to support this claim on a hemispherical basis, never mind a global basis. In addition, there is a chance that the MWP and the Little Ice Age (see DENIAL MYTH #9 below) are both artificial and arbitrary and are actually representative a gradual cooling trend as opposed to a periodic oscillation in the global temperature. Check through all the sources for more detailed information. (Sources: Climate of the Last Millennium, by Raymond S. Bradley, Climate System Research Center, Dept. of Geosciences, University of Massachusetts, Amherst, IPCC Working Group 1 Report, Chapter 6, Figure 6.10 and Box 6.4, pages 467-469, Climate Over Past Millennia, by P.D. Jones and M.E. Mann, Medieval Warm Period and the Little Ice Age Myths)

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DENIAL MYTH #8: The MWP has been ignored in order to produce the desired conclusion (Source: “Apocalypse Canceled”, by Christopher Monckton as well as others).
Debunking: Even if this were true in the past (and the sources for Claim #7 above show it has been addressed repeatedly since the release of the TAR), the IPCC Working Group 1 Report, Chapter 6, Figure 6.10 and Box 6.4, pages 467-469 (shown at right) addresses this specifically. In essence, there is statistical evidence that the MWP was not warmer than the last 25 years (since 1980), but there are enough errors in the MWP data to warrant additional research into the scope (Europe? The entire Northern Hemisphere? Global?) and magnitude of the MWP. (source linked above)

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DENIAL MYTH #9: The temperatures we’re experiencing in the later part of the 20th century are a result of the global climate finally coming out of the Little Ice Age (Source: distillation of multiple people’s claims at Wikipedia.org).
Debunking: The Little Ice Age is a period of significant cooling in Europe, but there are questions as to whether this known regional change was truly global in dimension. However, if you look at the graph of the temperature data for the last 2000 years, there is no period where the reconstructed global temperatures have changed at a faster rate than in the last 50 years or so. I refer people to the IPCC Working Group 1 Report, Chapter 6, Figure 6.10 and Box 6.4, pages 467-469 (image shown above in Myth #8 above), but also to this NCAR press release that verifies that the basic conclusions of the original “hockey stick” remain accurate even using multiple different models.

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DENIAL MYTH #10: There was a significant period of global cooling between the 1940s and the 1970s. This cooling period existed as anthropogenic CO₂ levels were rising significantly. If anthropogenic CO₂ is more important than natural drivers, then this cooling period would not exist, yet it does (Sources: produced by Rcronk in the comments to Eastern seaboard of the United States to be much hotter, but also made in the Wikipedia.org claims).
Debunking: That this cooling period existed and was global in scope is not disputable as the scope of the MWP is - scientists were directly monitoring temperatures globally by this point, and these three decades were cooler than the decades preceding them and dramatically cooler than recent decades. So what caused the cooling?

First, there is a correlation between sunspots and solar irradiance (output) on the Earth. During this period, sunspots were less common and there was less solar energy reaching the Earth, allowing it to cool slightly. Second, there were several volcanic eruptions that released massive amounts of sulfur dioxide into the atmosphere. Sulfur dioxide is an aerosol that forms droplets of sulphuric acid in the high atmosphere and reflects solar energy back into space, so these two volcanic eruptions had some short- to medium-term effects. In addition, prior to the 1970s there were limited pollution controls, allowing pollutant aerosols to act as coolants via reflection of solar radiation. Ultimately, though, it is believed that sometime after 1970 the concentration of CO₂ rose to the point that solar forcing was no longer the dominant climate factor, anthropogenic CO₂ was. (Sources: Do Models Underestimate the Solar Contribution to Recent Climate Change?, Swindled!)

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DENIAL MYTH #11: Cosmic rays (very high energy particles) striking the Earth’s atmosphere is the cause of global heating (Source: distillation of multiple people’s claims at Wikipedia.org).
Debunking: According to this theory, cosmic rays are responsible for cloud cover - fewer cosmic rays means fewer clouds and less cooling in the summer (clouds reflect the energy) and more heating in the winter (as clouds hold heat in). Unfortunately, there doesn’t appear to be any statistically significant trend in the number of cosmic rays hitting the Earth, and the few experiments performed to date appear to be stricken with error or a failure to address key points. This could be an aggravating factor, but is highly unlikely to be the primary source of global heating. (Sources: No Link Between Cosmic Rays and Global Warming, Cosmic Rays and Global Warming, Recent Warming but No Trend In Galactic Cosmic Rays)

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DENIAL MYTH #12: The Stefan-Boltzmann Law (the relationship between radiation and temperature of an ideal “black body” radiator) breaks the calculations required to make global heating work (Source: “Apocalypse Canceled”, by Christopher Monckton as well as others).
Debunking: This issue was the hardest to make heads or tails of, because the only people who really use it are deniers. That said, Mr. Monckton claims that the real value of lambda (the response of the Earth to radiative forcing) of between 0.22 and 0.33 C/W. But this number is only valid for an ideal black body model of the Earth, and the Earth is not even remotely close to a black body. Unfortunately, because I can’t find examples of the math involved to walk through it, I can’t say that this claim has been as well debunked as I’d like it to be, and as most climate scientists claim it is. (Source: Cuckoo Science)

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DENIAL MYTH #13: Using computer models is inherently inaccurate, especially of long-term changes in a system as complex as the Earth’s global climate (Source: Pretty much all of the deniers use this one, so there are more sources than I care to link to directly).
Debunking: Models are inherently inaccurate - anyone who tells you otherwise is trying to sell you a bad modeling software package. However, models can be made to accurately average out to something that represents reality, and this is the case with the IPCC models. I suggest that everyone read IPCC Working Group 1 Report, Chapter 8, FAQ 8.1, pages 600-601 and IPCC Working Group 1 Report, Chapter 9, page 684 (shown at right) to get a better understanding of how the models work, and the fact that models without anthropogenic CO₂ simply don’t match the actual measured temperature changes. For more comments on using models for predictions, see Denial Myth #19 below.

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DENIAL MYTH #14: The Earth hasn’t warmed by the expected amount predicted in the IPCC TAR, and papers have suggested that oceanic storage of heat is the reason. However, the only part of the ocean that matters as a “thermal sink” for atmospheric heating is the top few meters and yet the calculations performed require that 1.25 miles of ocean are available as a “sink” to make the math work out. Unfortunately, deep ocean temperatures haven’t changed at all (Source: “Apocalypse Canceled”, by Christopher Monckton).
Debunking: First, the Earth has warmed even more than the TAR models predicted (see Myth #19 below), not less.

Second, let’s talk about what oceanic depths matter to climate. It’s true that only the top 90 meters or so of the ocean matters to short-term absorption of heat, but because of oceanic currents, the entire ocean does turn over eventually, if very slowly. So the entire ocean must be modeled in order to understand just what the effects of the oceans actually are. The IPCC TAR had to use a depth of 3000 m in order to correctly reconstruct existing temperature data using models, but the latest IPCC report (AR4) uses a depth of 700 m instead, with data correlations between the sea surface temperature, the 0-700 m ocean depth zone, and then down to 3000 m as well. These correlations were not possible back in 2001 when the TAR was released due to lack of data, and the data has significantly improved in the years since. Finally, most of the increase in the temperature of the ocean has bee in the top 300-700 m, and so no, the deep ocean temperature hasn’t changed a lot. Given that the time scales of interest when talking about the deep ocean are in the range of decades to centuries, it’s not a surprise and totally expected. (Sources: NOAA Office of Climate Observation: The Role of the Ocean in Climate, Warming of the World Ocean, 1955-2003, S. Levitus, J. Antonov, and T. Boyer)

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DENIAL MYTH #15: The ocean has already begun to cool as expected given recent changes in solar output, cosmic solar rays, etc. (Source: “Apocalypse Canceled”, by Christopher Monckton).
Debunking: A 2006 paper by John M. Lyman, Josh K. Willis, and Gregory C. Johnson published in Geophysical Research Letters suggested that the oceans had lost a massive amount of heat (~20% of all the heat it had absorbed since the 1950s) without the heat apparently going anywhere. This was latched on to by many global heating deniers to suggest that the ocean had begun to cool as required by numerous suggested methods to account for purely naturally-driven global heating, or that the estimates of ocean heating were just plain wrong. Unfortunately, Dr. Lyman and his colleagues discovered that, while they’d accounted for measurement errors, they’d missed measurement biases (deterministic offsets in temperature inherent to the equipment measuring it) in their measurement devices, and the data will have to be corrected to account for this bias. Until then, however, there is no reason to believe that the unexpected cooling will actually be anything more than a glitch in need of correction. (Source: Correction to “Recent Cooling of the Upper Ocean”)

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DENIAL MYTH #16: Global heating isn’t actually happening because satellite measurements of tropical temperatures have not been rising like directly-measured temperatures in the tropics (Source: distillation of multiple people’s claims at Wikipedia.org).
Debunking: The satellites used to measure tropical temperatures remotely were discovered to have been drifting in their orbit, producing temperature measurements that were not during the day as expected, but rather during the night, confusing the cooler evening and nighttime temperatures with warmer daytime temperatures. The paper this comes from is “The Effect of Diurnal Correction on Satellite-Derived Lower Tropospheric Temperature” by Carl A. Mears and Frank J. Wentz of Remote Sensing Systems. Unfortunately, there is not a .pdf of this document available that may be freely distributed. However, this was reported in U.S.A Today and Live Science, and if you search Google for “satellite balloon data error global warming” you’ll find a lot more.

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DENIAL MYTH #17: Some deniers don’t directly dispute that global heating is happening or that humans are the cause. Instead, they claim that global heating might just be good for the human race (Source: distillation of multiple people’s claims at Wikipedia.org).
Debunking: The effects of global heating have been investigated by many people and organizations with specific concerns in mind, ranging from the economy to public health to population migrations to political stability. Below is a sampling of the organizations who believe that global heating will not be good for the world and why.

• The Pew Center on Global Climate Change published “U.S. market consequences of global climate change in April 2004 where they estimated that global heating would be, using the most optimistic assumptions, a temporary boost to the U.S. economy by 0.7 to 1% by 2100, but that the most pessimistic assumptions would produce a reduction in GDP of approximately 3.0%. In addition, the benefits are almost exclusively in the agriculture and energy sectors and increasing temperature will ultimately reverse the gains in both sectors.
• According to Climate Change 2007: Impacts, Adaptation and Vulnerability, Working Group II Contribution to the Intergovernmental Panel on Climate Change Fourth Assessment Report - Summary for Policymakers (the full report is not yet available online), droughts will become more common as freshwater from melt and precipitation decreases, 20-30% of plant and animal species will be at increased risk of extinction and acidification of the ocean will adversely affect marine ecosystems, global agricultural productivity will increase slightly and then decrease as temperatures continue to rise, coastal flooding will cause serious problems (especially in Asia), and developing countries will be heavily hit by droughts, disease, and rising sea levels
• Lloyd’s of London, a major global insurance company and hardly a hotbed of liberal activism, released this 360 Risk Report titled “Climate Change: Adapt or Bust”. The gist of the report is that climate change is going to cause major losses to insurers if the risks aren’t managed carefully, and that the risks must be managed by working with businesses and governments as well as by updating internal risk models to account for a changing global climate.
• The CNA Corporation released a report on “National Security and the Threat of Global Climate Change.” The report is somewhat alarmist and the time scales described may be too aggressive, but the point that global heating will cause significant instability and impact U.S. national security is valid nonetheless.
• In a Pentagon report titled “An Abrupt Climate Change Scenario and Its Implications for United States National Security,” the authors propose an abrupt climate change situation that is unlikely but plausible and that results in massive food shortages, disruptions in energy supplies, droughts, and possibly even wars over access to fresh water, mass population migrations, and energy.

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DENIER MYTH#18: The influence of CO₂ cannot match the influence of water vapor, and since the impacts of water vapor are largely unknown and outside direct human control, human beings cannot be the source of global heating (Source: Comments on Digg.com’s post about this blog originally, but scattered around the net as well).
Debunking: First off, there is no doubt that water vapor is directly responsible for the bulk of the greenhouse effect (~60% according to Table 3 of “Earth’s Annual Global Mean Energy Budget”). As such, water vapor could far outweigh the direct effect of CO₂ in the atmosphere. Unfortunately, because of the complexity of the Earth’s water cycle, figuring out what the effects of water will be isn’t simple.

As the atmosphere heats up, it can hold more water vapor. As such, we can reasonably expect that the hotter the air is, the more humid it can be and, because water vapor is the most powerful greenhouse gas, the hotter the air will get. This positive feedback leads us to an obviously erroneous conclusion - that we should already be boiling. Since we’re not, there must be something that provides negative feedback to at least partly compensate for the positive feedback, and there is - precipitation in the form of rain, snow, sleet, hail, etc. Small local variations in temperature can create massive differences in the amount of water vapor present in the local atmosphere - a hot high pressure system drives the humidity down and stops precipitation, while a cooler low pressure system permits condensation and then rain or snow. All in all, this means that water vapor that enters the atmosphere persists there a very short period of time - about 11 days (see the right sidebar) - while CO₂ persists in the atmosphere for decades to centuries.

Now, since people can’t directly control water vapor, the only way we have to influence it is via temperature. If the greenhouse effect boosts global temperature somewhat, we should realistically expect that the amount of water vapor in the air should be increasing. Similarly, if global temperatures drop for some reason (for example, a large volcanic eruption dumping massive amounts of aerosols into the air), we should expect to see water vapor concentrations decrease. In the lower atmosphere, the available data points to increasing water vapor content, but because of large variations in local humidity from day to night, from day to day, and from season to season, no-one currently knows exactly how much more water vapor is going into the air (IPCC Working Group 1 Assessment Report 4, Chapter 3, “Observations: Surface and Atmospheric Climate Change”, page 273). And unfortunately, the upper troposphere (the region of the atmosphere believed to be most important for water vapor’s effects on global heating) has no conclusive direct data on water vapor concentrations. Instead, the increase in water vapor in this part of the atmosphere has been indirectly checked by the increase in this region’s temperature. Since water vapor is such a powerful greenhouse gas, any increase in temperature in this region of the atmosphere should be largely a result of the effects of water vapor (IPCC Working Group 1 Assessment Report 4, Chapter 3, “Observations: Surface and Atmospheric Climate Change”, Figure 3.21, page 275).

But perhaps most importantly, the fact that the concentration of water vapor does increase and decrease along with external temperature changes was proven as a result of the 1991 eruption of Mount Pinatubo. The temperature dropped for several years, and the amount of water vapor in the atmosphere dropped at the same time, and roughly in the same pattern (Figure 2, to the left). When the authors of the paper looked at their general climate models, they discovered that, once they corrected for an El Nino that occurred right after Pinatubo erupted, the model only produced roughly equivalent cooling if water vapor feedback was included in the model (Figure 4, to the right).

What does all of this mean? Basically, water vapor is a more important greenhouse gas than CO₂, but because CO₂ will cause heating independently of water vapor, as man-made CO₂ increases global heating, water vapor will increase too, boosting the amount of warming with a positive feedback loop. How much exactly is up for debate, and there’s not a long enough data series on water vapor in the atmosphere to know everything. But just because humans can’t increase or decrease water vapor in the air directly doesn’t mean that CO₂ heating of the air won’t do so indirectly.

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DENIER MYTH #19: We don’t have enough climate data to make valid predictions of any kind. We have so many problems predicting the weather that there’s no way we’ve got enough data to predict how the entire climate functions (Source: multiple sources).
Debunking: Allow me to draw a detailed analogy from my professional field, electrical engineering. Please bear with me - I’ll try to keep the math and technical jargon to a minimum. The image to the left shows a simple electrical circuit called a difference amplifier. Using two fundamental relations derived from some of the laws of physics (specifically Kirchoff’s Voltage and Current Laws, derived from conservation of energy and conservation of charge respectively), and knowing a couple of key bits of information about resistors and operational amplifiers (op-amps), we can crunch through some basic algebra to come up with the following equation that describes mathematically how the output voltage V_OUT is related to the input voltages V_IN1 and V_IN2.

If you notice, the name “difference amplifier” comes from the fact that V_OUT is related to a difference between V_IN1 and V_IN2, and in fact if you select the resistor values correctly (R₂=R_F, R₁=R_G), you get a simplified equation below.

Given that I’ve described the circuit mathematically, do I have enough information to accurately predict how the circuit will respond? Yes and no. This equation accurately describes the operation of the circuit if the circuit perfectly represents reality. But the circuit doesn’t perfectly represent reality. Reality is quite a bit more complex, as the image shows. This circuit illustrates a much more accurate picture of reality in that it includes terms such as bias current, offset current, and offset voltage, and this equation is the corrected equation for the operation of the circuit (this equation is still missing two of the larger corrections, input and output resistance, because I didn’t want to re-derive the equations - it gets really tedious really fast).

But sometimes that’s still not a good enough model of reality. Every single term is a function of temperature, so as the temperature of the op-amp and the resistors change, their values change. Not only that, but depending on the precise nature of the parts, how the parts change with temperature will vary - some will increase as temperature increases, some decrease, some increase for a while and then decrease, some don’t change at all. Not only that, but if the circuit is expected to operate for an extended period of time, every term (including the temperature term) may change totally differently as the part ages. How each component operates varies with air pressure, humidity, radiation exposure, proximity to electromagnetic interference, how the component is packaged, what materials it’s made out of, mechanical stresses, manufacturing imperfections, device noise, input noise, and power supply variations. And this list is still too small to include all the possible variables - it’s just the list I came up with after 10 minutes of thinking of all the factors I’ve been expected to consider over the years. There are probably dozens more I haven’t even considered. Given the massive number of factors that might, or might not, affect the operation of the difference amplifier above, it’s simply not always possible to make detailed and exact predictions of how it will react at any given instant even though the circuit’s gross functionality will alway be predictable.

Predicting climate using models is like me predicting how the difference amplifier works at a basic level - I don’t need to know how the exact devices will react to air pressure and temperature in order to derive the basic equations. But if we want to use climate models to predict the weather, that’s a lot more like me trying to predict how my difference amplifier will operate given every possible input condition and variable.

We don’t need to have all the data in order to have valid predictions. We need to have an understanding of the basic physics, the basic feedback and forcing mechanisms, and of the inputs and outputs of the Earth’s climate system. Climate scientists have a great deal of this information and have included it in the climate models (the illustration above illustrates the progression in increasing model detail from early models to the latest used by the IPCC). The climate models aren’t perfect, but neither are the basic equations of a difference amplifier circuit.

Do we have enough data to be able to claim, as I have, that the climate models are good enough to qualify as “basic equations”? Well, the IPCC Working Group I Fourth Assessment Report Summary for Policymakers says that they have “very high confidence,” 90% or more (see the image to the right for how the IPCC AR4 defines all the various confidence levels), that human beings have heated up the planet since 1750 (Box TS.1 on page 22-23 of the describes the percent confidence/likelihood indicated by the language). The Summary also says that the data and models have improved since 2001 when the likelihood was only “likely,” or greater than 66%, that humans were causing global heating (see the image to the right for how the IPCC Working Group I Fourth Assessment Report Technical Summary defines different likelihoods)

What increased the likelihood in the view of about 620 authors representing 42 different countries? It was partly that two of the key predictions of the IPCC Third Assessment Report (TAR) were accurate when compared with the actual data. First, the IPCC predicted that the temperature would increase by about 0.5 degrees C as per the image to the left. If you look at this blown up image, you’ll see that the actual data, approximately 0.7 degrees C, exceeded the global expected change significantly (indicated by the orange intersection I added). Some variation from the model over the short term is reasonable, so the fact that we’ve exceeded the expected range isn’t necessarily cause for concern that the models are underestimating global heating. Second, the TAR predicted that sea level would rise by between 1 and 5 cm from 1990 to 2006, with the expected range from the models somewhere between roughly 2.5 and 4 cm (Click on the image below for a more readable blow-up). If you look at the red and blue lines representing ocean station data and satellite altimeter data, you’ll notice that both track very closely to the maximum, but are both within the range of the IPCC TAR model. (Unfortunately, there’s significant confusion and contention about whether the TAR and AR4 models are similar, whether the unknown factors are included or not. See here for one side of the discussion, here for the other.)

In addition to the data closely matching the models, the scientists also have five or six more years of climate data of all types, improved data due to better measurement techniques, and more data from a wider geographical area. Combine the new and improved data, measured correlation between the old models and the new data, and improved climate models that, when properly vetted and compared with historical climate reconstructions, and you end up with a very compelling global heating theory that has convinced 620 authors from 42 countries that both the theory and the predictions are accurate. (Other sources: Real Climate’s page on sea level rise)

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DENIER MYTH #20: Volcanos emit more CO₂ in a single eruption (or per year) than humanity does, dwarfing anthropogenic emissions (source: comment below by BobCook)
Debunking: Volcanoes emit a lot of gases, including significant amounts of CO₂. Unfortunately, according to papers from back in the late 1990s, “Volcanoes contribute about 110 million tons of carbon dioxide per year while man’s activities contribute about 10 billion tons per year.” This means that anthropogenic CO₂ emissions are 100x greater than volcanic CO₂ emissions. In addition, as mentioned above in Myth #18, volcanoes generally cause global cooling through the emissions of cloud-forming sulfur dioxide and water-cycle feedback. Finally, the USGS says “The most significant impacts from these injections come from the conversion of sulfur dioxide to sulfuric acid (H₂SO₄), which condenses rapidly in the stratosphere to form fine sulfate aerosols” at this site

Over geologic time, volcanoes and mantle outgassing have emitted more CO₂ than humanity ever will, but that’s over the course of 4.5 billion years. See Myth #1 above for more information.

Additional information for how volcanic CO₂ emissions compare to anthropogenic CO₂ emissions is available at Gases: Man vs. the Volcano.

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At one point or another, each of these claims represented a real problem with the science of global heating. But no longer - the scientific evidence has become overwhelming. However, it’s the minority composed of global heating deniers who continue to hunt for flaws in climate science, so the deniers serve a valuable scientific purpose - when they find a real hole, or just think they have, addressing their claims are what has made the science of global heating as bullet-proof as it now is.It comes down to this simple fact: the overwhelming majority of the scientific evidence points to human-induced global heating, and every claim made by global heating deniers has been effectively debunked. And because the consequences of doing nothing are so severe, we must act now even as the data continues to improve - we can no longer afford to wait.[Crossposted: The Daedalnexus]NOTE: This post was inspired by a blog Whythawk posted a couple of weeks ago entitled Life Earth will end climate change the way Live Aid ended poverty in Africa - Er… where one of the comment posters, “2008Voter”, posted the links to some of the sources used for this blog.