The Instigator
Pro (for)
5 Points
The Contender
Con (against)
6 Points

Global warming is mostly anthropogenic

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Voting Style: Open Point System: 7 Point
Started: 6/14/2011 Category: Science
Updated: 6 years ago Status: Post Voting Period
Viewed: 8,158 times Debate No: 17055
Debate Rounds (4)
Comments (51)
Votes (2)




Resolved: Global warming is mostly anthropogenic


Global Warming: An increase in the Earth's average atmospheric temperature that causes corresponding changes in climate

Mostly: 75% or greater

Anthropogenic: Caused by humans

* Round one will be for acceptance only, no arguments!



I accept the challenge and am looking forward to a good debate.
Debate Round No. 1


I will begin round two by defining a few additional terms:

: One of two or more atoms with the same atomic number that contain different numbers of neutrons

Infrared radiation: Electromagnetic radiation which we humans perceive as heat

Troposphere: The lowest portion of Earth’s atmosphere

Climate forcing: An externally imposed perturbation in the radiative energy budget of Earth’s climate system

Now, on with the debate!

Carbon dioxide emissions are increasing rapidly. In 1870, the amount of carbon dioxide in the atmosphere was about 290 parts per million (ppm). As of April 2011, the amount of carbon dioxide in the atmosphere had risen to approximately 390 ppm (1). Very carefully calibrated measurements have confirmed that human activities are the primary cause of this increase, as I will demonstrate below.

There are two primary carbon isotopes: carbon-12 and carbon-13. Carbon dioxide produced from burring fossil fuels and clearing forests has a unique isotopic composition. This is because plants prefer lighter isotopes, that is they prefer carbon-12 over carbon-13. Fossil fuels like coal or oil are derived from ancient plants. Thus, when we burn fossil fuels, we’re releasing more of the lighter Carbon-12 into the atmosphere.

If human activities are the primary cause of the observed increase in carbon dioxide concentrations, we would expect to see the ratio of Carbon-13 to carbon-12 fall. Indeed, this is just what we observe. Measurements from the atmosphere (2), corals (3), and sea sponges (4) indicate that this ratio has declined greatly over the past 100 years.

Without a doubt, the rise in atmospheric carbon dioxide is almost entirely anthropogenic. As I will demonstrate, several lines of evidence indicate that the current warming trend is caused by this increase in carbon dioxide.

1) More Infrared radiation is returning to the Earth:

If carbon dioxide is responsible for global warming, more infrared radiation should be returning to the surface. Before presenting further evidence which affirms the resolution, I will provide a simple explanation of why this is so.

The Earth emits a large amount of infrared radiation into the atmosphere. Some of this heat is absorbed by carbon dioxide molecules, which then reemit infrared radiation in all directions. Some radiation spreads downward and ultimately comes back into contact with the Earth’s surface, where it’s absorbed. However, some of the radiation spreads upward. In the upper layers of the troposphere, carbon dioxide molecules are sparse, and this heat energy can eventually escape to space.

When additional carbon dioxide molecules are added to these layers, significantly more thermal infrared radiation from lower levels will be absorbed. Therefore, the place from which heat energy finally leaves the Earth will shift to higher layers. These layers are very cold, since temperatures decline greatly with altitude in the troposphere. Notably, the amount of energy emitted by an object is proportional to its temperature. Thus, these high altitude layers will emit significantly less radiation than the layers below, thereby retaining a large amount of heat energy.

As these layers accumulate heat, they will warm and emit an increasing amount of infrared radiation. Thus, more radiation will spread downward and reach the surface, causing the surface to warm as well.

Measurements from ground stations indicate that more infrared radiation is indeed returning to the Earth (5-6). When we take a close look at the spectrum of this radiation, we can determine how much each greenhouse gas is contributing to the warming effect. From these results, one scientist concluded that, “This experimental data should effectively end the argument by skeptics that no experimental evidence exists for the connection between greenhouse gas increases in the atmosphere and global warming” (6).

2) The upper atmosphere is cooling:

As greenhouse gases trap more heat in the troposphere, less infrared radiation reaches the upper atmosphere, beginning with the stratosphere. Therefore, if the increase in carbon dioxide is responsible for the current warming, we would expect to see cooling in the upper atmosphere. This has been observed by several scientific researchers (7-9).

3) The tropopause has risen:

Theoretically, global warming would also lead to an increase in the tropopause height. The tropopause is the atmospheric boundary between the troposphere and the stratosphere. Because the troposphere has warmed and the stratosphere has cooled, the tropopause has risen several hundred meters over the past three decades (10).

4) Oceanic heat content is increasing:

Ocean heat content is increasing, especially in the upper layers. This specific pattern of ocean warming, with heat penetrating from the surface, can only be explained by greenhouse gas warming. As Barnett et al. concluded, “[The increase in ocean heat content] cannot be explained by natural internal climate variability or solar and volcanic forcing, but is well simulated by two anthropogenically forced climate models. We conclude that it is of human origin, a conclusion robust to observational sampling and model differences. Changes in advection combine with surface forcing to give the overall warming pattern” (11).

5) Observed precipitation trends can best be explained by increasing carbon dioxide:

Zhang et al. showed that models do a much better job of matching the observed precipitation trends when anthropogenic climate forcings were included. As they stated, “Anthropogenic forcing has had a detectable influence on observed changes in average precipitation within latitudinal bands, and that these changes cannot be explained by internal climate variability or natural forcing. We estimate that anthropogenic forcing contributed significantly to observed increases in precipitation in the Northern Hemisphere mid-latitudes, drying in the Northern Hemisphere subtropics and tropics, and moistening in the Southern Hemisphere subtropics and deep tropics. The observed changes, which are larger than estimated from model simulations, may have already had significant effects on ecosystems, agriculture and human health in regions that are sensitive to changes in precipitation” (12).

6) Most scientists believe that global warming is anthropogenic:

Several studies have surveyed climate scientists who are actively publishing climate research. All of these studies found that over 97% of climate experts are convinced that humans are the primary factor changing global temperature (13-14).

I look forward to my opponent's response!




I do not question that there has been an increase in human-produced CO2 or a general warming trend in climate since the end of the Little Ice Age, in the early 1800s. CO2 is indeed a greenhouse gas, and polls of climate crisis skeptics produce nearly unanimous agreement that anthropogenic CO2 causes some global warming. That's never been an issue. What is unproved and unlikely is the claim that 75% or more of global warming is due to anthropogenic CO2. If CO2 dominates climate, then global warming should have increased through the last decade, because CO2 has continued to increase. But global warming has at best stalled for a decade, and climate now is switching to a cooling trend.

Climate Sensitivity

If CO2 only acted according to the straight physics of greenhouse gases, the temperature increase would be small. Richard Lindzen, MIT professor of meteorology, explains:

"After all we are still talking about tenths of a degree for over 75% of the climate forcing associated with a doubling of CO2. The potential (and only the potential) for alarm enters with the issue of climate sensitivity—which refers to the change that a doubling of CO2 will produce in GATA. It is generally accepted that a doubling of CO2 will only produce a change of about two degrees Fahrenheit if all else is held constant." [1]

Doubling CO2 produces a 2 degree increase, Pro notes the actual CO2 increase has been about 30%. Climate crisis advocates claim that the effect is multiplied, and that is the issue. The multiplier is climate sensiivity.

"... current [CO2] climate models predict much higher sensitivities. They do so because in these models, the main greenhouse substances (water vapor and clouds) act to amplify anything that CO2 does. This is referred to as positive feedback. But as the IPCC notes, clouds continue to be a source of major uncertainty in current models. Since clouds and water vapor are intimately related, the IPCC claim that they are more confident about water vapor is quite implausible." [1]

The article further explains how the paleoclimatological evidence makes high sensitivity unlikely.

Atmospheric Temperature Profiles

CO2 global warming advocates do not claim that CO2 is causing the increased radiative reflectivity and the cooling troposphere, They claim that CO2 is increasing water vapor in the atmosphere which in turn produces the temperature profile. Thus the temperature profile is consistent with any theory that increases water vapor. There are many other possible causes, including changes in atmospheric convection patterns, changes in cloud cover, and ocean temperature changes.

Another possibility is that methane is the greenhouse gas culprit. Methane was once thought to be mainly a product of human activity, but data in 2007 showed that some natural effect caused a dramatic worldwide change in atmospheric methane. Natural methane changes may act to cancel other causes of temperature change. [2]

A decade of cooling defies CO2 models

Predictions of warming from 2000 to 2010 made by CO2 models were way off. Temperatures have been way below the error bands claimed for the models. [6,7]

A much better fit to observation is that the cyclical trends of the past several hundred years are continuing, with a small upward trend from increases in CO2. [7]

"The Pacific Ocean has a warm temperature mode and a cool temperature mode, and in the past century, has switched back forth between these two modes every 25-30 years (known as the Pacific Decadal Oscillation or PDO). In 1977 the Pacific abruptly shifted from its cool mode (where it had been since about 1945) into its warm mode, and this initiated global warming from 1977 to 1998. The correlation between the PDO and global climate is well established."

Much of the polar ice cap melted in the 1930s and before that in the 1880s, just as it did around 2007. In each case, colder climate followed, as is happening now. The question of what causes the PDO is unanswered.

Climate is complex

The theory of CO2 dominated climate hinges upon climate being simple, CO2 advocates say that in the past other factors like solar variations, earth orbit changes, and volcanoes contributed to climate, but that now none of that is happening so climate change must be entirely due to CO2. That idea is now so thoroughly discredited that a fresh look at climate science is required.

"What causes the deep meridian overturning of the ocean, redistributing heat around the planet? We don't know.

... [other basic unanswered questions] ...

Kerry and Dan assert that the predictive power of climate models has plateaued and is not likely to improve until questions like these are answered." [3]


Pro's link only goes to the abstract of the survey; the paper hasn't been published. The abstract links to a page of how the survey authors compiled their list of 1372 climate scientists to survey. The authors divided climate scientists who, in the authors words are "convinced by the evidence (CE) for anthropogenic climate change or unconvinced by the evidence (UE) for ACC.." 903 are "convinced" of anthropogenic climate change and 472 are "unconvinced." Thus according to the authors, 34% of climate scientists are not convinced of anthropogenic global warming. So where does the 97% figure cited by the authors come from?

We don't know because the authors don't say exactly what questions they asked, who responded, or how many of the responses they kept. Although we don't know in this case, here is how climate crisis advocates have managed the feat in the past. Referring to a previous survey of over 10,000 earth scientists: " ... close examination of the source of the claimed 97% consensus reveals that it comes from a non-peer reviewed article describing an online poll in which a total of only 79 climate scientists chose to participate. Of the 79 self-selected climate scientists, 75 agreed with the notion of AGW.
" [5]

Of the 10,000 scientists surveyed in that effort, only 79 responded. The survey linked by Pro was conducted by Pratt and his associated, who are very vocal advocates of climate crisis. So who responded to the Pratt survey of 1372 scientists? It's likely that most skeptics did not bother responding.

The figure of 34% skeptics is on the low end of estimates made by Patrick Michaels [8], who puts it between 35% and 50%. A surveyed of degreed meteorologists in the American Meteorological society produced "Only 24 percent of the survey respondents agree with United Nations Intergovernmental Panel on Climate Change (IPCC) assertion, “Most of the warming since 1950 is very likely human-induced.”

Taking a prominent stand against climate crisis can cost a scientist his job, so skeptics tend to keep a lower profile than crisis advocates. For comparison, back in the 1960s the Steady State Theory was favored by about two-thirds of scientists over the Big Bang. The Big Bang is now stongly favored. Science is not determined by a vote.

Pro has the burden of proof to show 75% of global warming is anthropogenic. The science does not provide that proof.

Lindzen is widely acknowledged as the foremost expert on climate circulation models.







8. Shattered Consensus: The True State of Global Warming, Rowman & Littlefield, 2005

Debate Round No. 2


Transient Climate Sensitivity

The Earth has warmed approximately .8ºC since 1870 (1). I allege that at least 75%, or .6º, of this warming was caused by CO2. We can evaluate the truth of this statement by determining the transient climate sensitivity value which would be required to produce .6ºC of warming.

In essence, transient climate sensitivity is a constant which determines how much warming we can expect to see immediately following a change in atmospheric CO2. Transient sensitivity is lower than equilibrium sensitivity, due to the thermal inertia of ocean heat uptake. Fully equilibrating ocean temperatures would require thousands of years. Therefore, transient climate sensitivity is more relevant to determining near-term climate change than equilibrium climate sensitivity.

Transient climate sensitivity is equal to the observed temperature change divided by the radiative forcing which produced the change (2). So, to calculate transient climate sensitivity we first need to estimate CO2’s radiative forcing. We can use the following formula to do so (3):

∆F = 5.35 ln(C/Co)

C is the current concentration of atmospheric CO2, which is approximately equal to 390 ppm. Co is the pre-industrial concentration of 290 ppm. Therefore, CO2’s radiative forcing equals about 1.6 W/m2.

As I mentioned above, transient climate sensitivity can be calculated by dividing the magnitude of the observed temperature change (.6) by CO2’s radiative forcing (1.6). Doing so gives us a value of .375 °C/[W/m2] for transient climate sensitivity when three fourths of global warming is anthropogenic.

If this were the correct value, we would expect to see a 1.39ºC rise in temperatures immediately following a doubling of CO2 concentrations (2). However, climate models which are constrained by observational evidence indicate that we would actually see between 1.5º and 2.8ºC of warming (4). There is a 5% chance that this range is not correct (4), but this small of a percentage is hardly notable.

Thus, we can say with confidence that CO2 can account for more than 75% of the observed warming trend. This is because a temperature change is the product of CO2’s radiative forcing and transient climate sensitivity. For only .6º of global warming to be anthropogenic, climate sensitivity would have to be unrealistically low.

Equilibrium Climate Sensitivity

Equilibrium climate sensitivity is the global mean temperature change that eventually results from a doubling of atmospheric CO2. This temperature change can only be achieved over thousands of years. Thus, equilibrium sensitivity is quite larger than transient climate sensitivity, which I defined above.

My opponent believes that equilibrium climate sensitivity is 2ºF (1.1ºC) for doubled CO2. However, this value is inconsistent with the study I presented above. This research article determined that transient climate sensitivity is unlikely to be lower than 1.5ºC. Therefore, it’s virtually impossible that equilibrium climate sensitivity is as low as my opponent alleges.

My opponent claims that 1.1ºC of warming for doubled CO2 is consistent with palaeoclimate evidence. To back up this suggestion, he cites an opinion article which concluded as follows:

“The notion that the earth's climate is dominated by positive feedbacks is intuitively implausible, and the history of the earth's climate offers some guidance on this matter. About 2.5 billion years ago, the sun was 20%-30% less bright than now, and yet the evidence is that the oceans were unfrozen at the time, and that temperatures might not have been very different from today's. Carl Sagan in the 1970s referred to this as the Early Faint Sun Paradox. It turns out that increased thin cirrus cloud coverage in the tropics readily resolves the paradox. In present terms this means that they would diminish rather than enhance the impact of CO2.”

For this claim to be accurate, an increase in thin cirrus cloud cover would have to provide a warming effect, and a decrease would have to provide a cooling effect (5). However, satellites indicate that the opposite of this statement is true (6-7). As Su et al. concluded, “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.

Therefore, an increase in cloud coverage cannot explain the “Early Faint Sun Paradox.” Rosing et al. found an alternate solution to this alleged paradox. As they noted, “Our model calculations suggest that the lower albedo of the early Earth provided environmental conditions above the freezing point of water, thus alleviating the need for extreme greenhouse-gas concentrations to satisfy the faint early Sun paradox” (8).

If these conclusions are correct, the “Early Faint Sun Paradox” cannot be used to determine climate sensitivity. Nevertheless, estimates of the Earth’s climate sensitivity can be deduced from other palaeoclimate data.

For example, Hergerl et al. used temperature reconstructions from the past millennium to quantify the Earth’s climate sensitivity. They determined that the Earth would warm between 1.5ºC and 6.2ºC (2.7 and 5.6ºF) if CO2 concentrations were doubled (9).

Climate Models

My opponent claims that climate models overestimate the Earth's climate sensitivity. However, this is not true. As it turns out, estimates of climate sensitivity from models are consistent with estimates from paleoclimate data (2).

Atmospheric Temperature Profiles

My opponent claims that, “CO2 global warming advocates do not claim that CO2 is causing the increased radiative reflectivity and the cooling troposphere.They claim that CO2 is increasing water vapor in the atmosphere which in turn produces the temperature profile.”

My opponent appears to have confused the troposphere with the stratosphere. As I demonstrated in round one, the troposphere is expected to warm as carbon dioxide increases. Nevertheless, tropospheric warming cannot prove that climate change is anthropogenic.

Meanwhile, as the greenhouse effect intensifies, the stratosphere is expected to cool. When CO2 traps more heat in the troposphere, less infrared radiation can reach the upper atmosphere. Therefore, if the increase in CO2 is responsible for the current warming, we would expect to see cooling above the tropopause. This has been observed by several scientific researchers.

Cooling in the stratosphere actually suggests that global warming is caused by an intensifying greenhouse effect. For example, if global warming were caused by the sun, we would expect to see warming in all layers of the atmosphere, including the stratosphere.

The Scientific Consensus

Here is the full paper of the study I presented in round one.

The authors “compiled a database of 1,372 climate researchers and classified each researcher as either convinced by the evidence for anthropogenic climate change or unconvinced by the evidence for ACC.”

In total, 903 of these scientists were convinced and 472 were unconvinced. However, this study did not attempt to determine how many researchers supported the IPCC’s conclusions. Instead, the authors of this study analyzed “the distribution of credibility of dissenting researchers relative to agreeing researchers and the level of agreement among top climate experts.” They concluded as follows:

“The [unconvinced] group comprises only 2% of the top 50 climate researchers as ranked by expertise, 3% of researchers of the top 100, and 2.5% of the top 200. This result closely agrees with expert surveys, indicating that 97% of actively publishing climate scientists agree with the tenets of ACC.”




Global Warming is measured from 1978, not 1870

Pro, says: "the Earth has warmed approximately .8ºC since 1870 (1). I allege that at least 75%, or .6º, of this warming was caused by CO2. We can evaluate the truth of this statement by determining the transient climate sensitivity value which would be required to produce .6ºC of warming."

Where did "since 1870" come from? If warming is judged from the Middle Ages (the Medieval Warm Period), when anthropogenic CO2 production started to be significant, then there has been little or no global warming. If we start measuring from the Little Ice Age (ending in the early 1800s) then there is gradual warming as Pro suggests. The earth cooled from the 1930s through the 1970s, so there are lots of choice in that period to pick a time as a basis for global warming to agree with many theories. The amount of global warming or cooling depends completely upon the time period selected.

"[In] Loehle's insightful paper. His analyses also reveal a long-term linear cooling trend of 0.25°C per thousand years since the peak of the interglacial warm period that occurred some 7000 years ago, which result is essentially identical to the mean value of this trend that was derived from seven prior assessments of its magnitude and five prior climate reconstructions. In addition, Loehle's analyses reveal the existence of the Medieval Warm Period of 800-1200 AD, which is shown to have been significantly warmer than the portion of the Modern Warm Period we have so far experienced, as well as the existence of the Little Ice Age of 1500-1850 AD, which is shown to have been the coldest period of the entire 3000-year record."

If one starts measuring warming from around the end of the coldest point n the past 3000 ears, a warming trend is inevitable. That doesn't mean the warming is due to CO2, even though it is consistent with a CO2 theory.

Since Pro didn't say in the challenge, we should be obliged to assume the common meaning of the global warming period, which is the dramatic warming from 1977 to around 2000, when the warming stalled. That period is entirely the grounds for claiming a climate crisis. Pro's reference to the climate survey, which Pro claims is dominated by experts, says the time of interest is the second half of the twentieth century, which recites the common understanding of the context of anthropogenic global warming. The bogus global warming hockey stick, presented in the 2000 IPCC report, purported to show that there had been no change in climate in the thousand years preceding the 1970s.

Pro picked the dates that agree with her theory. However, her analysis is wrong in any case. Lindzen gave the figure for CO2 warming assuming "all other things equal." That means that the result would occur if there is nothing that either amplifies or diminishes the effect of CO2. That's an interesting number, but it is not a claim that nothing else is going on. Therefore, Pro would have to at minimum prove that there were no positive or negative feedback mechanisms. She provided no such evidence. Crisis advocates say there are very strong positive mechanisms, while skeptics say there are probably negative mechanisms. Temperature cooled from 1870 to about 1910, then warmed sharply to the 1930s, then cooled to the 70s, then warmed to about 2000, then stabilized and now are cooling. That erratic behavior is inconsistent with a claim that all other things are equal.

One of the first books by skeptics, Michael's "The Satanic Gases", pointed to the gradual climate warming trend since the end of the little ice age, and used that to argue against anything unusual happening with CO2.

Temperature Profile of the Atmosphere

I agree that cooling in the stratosphere and warming of the troposphere is consistent with increased greenhouse gases. The question is what green house gas? CO2 crisis advocates do not claim that CO2 is the direct cause. They say that CO2 increases water vapor, and that water vapor is responsible for the temperature profile. I cited data that suggests that natural variations in methane might be the green house gas at work. An theory that has increased water vapor, such certain cloud theories, are also consistent.

Being "consistent with" does not mean "causes." A famous example is that increased ice cream consumption correlates with increased murder rates. That doesn't verify a theory that ice cream causes murder. Hot weather is the culprit in that case. The atmospheric temperature profile is consistent with many theories.

Climate Model Predictions

Pro argues that "However, climate models which are constrained by observational evidence indicate that we would actually see between 1.5º and 2.8ºC of warming." Tracking down Pro's reference 4, it depends upon work published in 2006. Publication delays and the availability of data implies that the "observational evidence" on which the conclusion is based was probably concluded around 2003. I established in previous round that the lower 5% error bound on the climate model predictions from around 2000 were falsified by observations from the whole decade. The lower bounds that had only a 5% chance of being wrong were found to be wrong on the low side.

Still, we are making progress in the debate. With Pro's claim that climate sensitivity is low, we agree that there is no CO2 induced climate crisis. In particular, that refutes the stand that that the alleged experts take in denouncing skeptics. Pro also does not dispute my claim that the CO2-
high-sensitivity models are certainly wrong, because they predicted dramatic increases since 2000, when deceases have been observed. Once one understands that the debate is about the temperature rise from 1978 to about 2000, that effectively concedes the debate.

The Survey of Alleged Experts

Pro agrees that at least 35% of climate scientists are unconvinced.

The idea of the survey is that the true experts among climate scientist are the ones who publish the most in some undisclosed list of journals selected by climate crisis advocates. The Climategate scandal revealed that CO2 crisis advocates put top priority on preventing skeptics from being published. A 2008 Conference of skeptics recounted seemingly endless cases of skeptics being denied publication by controlling CO2-crisis advocates.

A similar methodology applied in the Middle Ages would have identified all the real experts as supporting the theory that the earth is the enter of the solar system, dissenting publication being rare. One improvement over the Middle Ages is that dissenters now can publish in journals not controlled or accepted as valid by the ruling elite, and they can also publish in independent books and on-line. Note that Einstein only submitted one of his 300 papers to peer review. He would presently not be classified as an expert according to the methodology used.

Moreover, skeptics place strong emphasis on reconstructing past climate variations, on assessing the impact of climate change, and on assessing solar influence on climate. Crisis advocates do not count any of that as climate science. The famous "Hockey Stick" falsely made the Medieval Warm Period disappear. Climate reconstruction refuted that. It's easy to get government funding for trivial topics somehow related to global warming, but no such funding is available for dissenters.

The survey only proves that politics rules in climate science.

Debate Round No. 3


Alleged cooling

My opponent claims that the atmosphere cooled between 2001 and 2008. However, this does not imply that global warming has stopped. Even in a period of long-term warming, surface temperatures can show short-term cooling trends. For example, there have been 54 cooling periods lasting 9 years in the HadCRU dataset (1). Many of these cooling periods have occurred in the context of long-term warming.

As Dr. Liebmann concluded, the recent cooling trend between 2001 and 2008 was “neither statistically significant nor unusual in the context of trend variability in the historical record” (2). Therefore, the alleged cooling was probably due to natural variability, including a strong La Nina which occurred in 2008.

During La Nina, heat is transferred from the atmosphere into the ocean. Meanwhile, the opposite occurs during El Nino. These natural weather phenomena, which have occurred for thousands of years, can change annual temperatures by as much as .2ºC.

Over short time periods, atmospheric temperature trends closely reflect the behavior of these events. However, over time, the cooling caused by La Nina events balances the warming induced by El Nino events. Thus, these natural variations have practically no influence on atmospheric temperatures over long time scales. According to the World Meteorological Organization, data must be averaged over 30 years to eliminate nearly all year-to-year temperature variations (3).

Trends over time scales significantly shorter than 30 years clearly have little meaning. They’re highly uncertain and can't be used to accurately predict long-term trends. This undoubtedly applies to the cooling between 2001 and 2008. In essence, we cannot tell if global warming is continuing simply by looking at short-term atmospheric trends.

Nevertheless, it’s still possible to determine if global warming has continued in the past decade. We can do so by examining the heat content of the entire climate system, including the oceans, land, atmosphere, and ice. The planet’s total heat content is not influenced by natural variations like El Nino and La Nina. These oscillations simply redistribute heat throughout the climate system; they cannot create or destroy heat.

Researchers have found that the climate system as a whole has continued to accumulate heat since 2000 (4-5). This proves that global warming is continuing, regardless of the short-term atmospheric cooling trend.

Climate Model Validation

My opponent claims that climate models are inaccurate, citing two blog articles. I will begin by examining the second article, his reference number 7 in round 3.

This article purports to demonstrate that the cooling trend between 2001 and 2008 is inconsistent with model projections. However, this article compares temperature data to the IPCC’s projection of 0.2 degrees of warming per decade. That projection was based on several model runs averaged over many different initial conditions to eliminate natural variability. However, as I demonstrated above, the temperature record contains large amounts of natural variability on time scales less than a couple decades.

Clearly, the IPCC’s projection of the long-term global warming signal is not directly comparable to 8 years of temperature data. Instead, we should compare the temperature data to short-term model projections which include natural variability. When we do so, we realize that model projections are indeed consistent with observations. As NASA scientist Gavin Schmidt noted, “Claims that a negative observed trend over the last 8 years would be inconsistent with the models cannot be supported” (6).

I will now examine my opponent’s other article which supposedly demonstrates that climate model projections are inconsistent with observational data.

This article compares temperature data to model projections from 1990. However, these projections were based on an emissions scenario which assumed that methane concentrations would increase linearly from 1990 to 2030 (7). In actuality, the growth of methane concentrations slowed greatly in the first decade of the twenty-first century (8). Thus, it’s highly unlikely that the projections from 1990 would ever match the observational data.

Notably, this does not mean that climate models are inherently inaccurate. Emissions scenarios are not developed by models themselves, but rather by scientists and other experts. Creating highly accurate scenarios is extremely difficult, as no one can foresee what actions will be taken to mitigate global warming.

My analysis

My opponent had three main objections to my analysis which demonstrated that CO2 could account for more than 75% of the observed global warming since 1870. First, as my opponent stated, “Her analysis is wrong...Lindzen gave the figure for CO2 warming assuming all other things equal. That means that the result would occur if there is nothing that either amplifies or diminishes the effect of CO2. Therefore, Pro would have to at minimum prove that there were no positive or negative feedback mechanisms.”

This claim doesn’t make much sense. I did indeed account for the feedback processes, and Lindzen’s value was never even used in my calculation.

As I explained clearly, I was attempting to determine the transient climate sensitivity parameter which would be necessary to produce .6º of warming. By definition, this parameter is a measure of how greatly the climate system amplifies any radiative forcing (9). My calculations showed that transient climate sensitivity would have to be greater than .375ºC/W/m2 in order for the resolution to be valid. This is a positive value, meaning that the feedback processes must, as a whole, amplify CO2 induced warming.

I then compared this calculated climate sensitivity parameter to several climate model simulations. As it turned out, the models all simulated parameters larger than .375, indicating that there are indeed very strong positive feedbacks.

My opponent has also suggested that global warming should be measured from 1978. Although warming can be measured from this year, it doesn't necessarily have to be. It makes sense to measure global warming from the industrial revolution, when we started emitting carbon dioxide in significant quantities.

Nevertheless, I have conducted a similar analysis measuring global warming from 1980. I have also used observationally based estimates of the climate sensitivity parameter, as an alternative to climate model predictions.

Constraints on past warming attributable to CO2

The Earth has warmed about .5ºC since 1980. To determine how much warming is anthropogenic, we first need to estimate CO2’s radiative forcing relative to that year. As I’ve mentioned previously, we can use the following formula to do so.

∆F = 5.35 ln(C/Co)

C is the current concentration of atmospheric CO2, which is approximately equal to 390 ppm. Co is the concentration of CO2 in 1980, which equals about 345 ppm. Thus, carbon dioxide’s radiative forcing is .66 W/m2.

Meanwhile, recent independent observations indicate that the Earth’s transient climate sensitivity parameter is .67ºC/W/m2, at absolute lowest (10).

We can now determine the minimum amount of global warming that CO2 is responsible for by multiplying .66 by .67. This gives us a value of .44ºC. Therefore, at least 88% of the .5º observed temperature rise since 1980 is anthropogenic. Clearly, the resolution is valid.


My opponent claims that, "The Climategate scandal revealed that CO2 crisis advocates put top priority on preventing skeptics from being published." However, this is not the case. The Independent Climate Change Email Review investigated the CRU scientists' actions relating to peer review. The investigation concluded that the CRU's actions were normal and didn't threaten the integrity of peer review (11).

Concluding Remarks

I urge everyone to vote pro! I've provided several research articles to support my claims, but my opponent has not provided a single one.

I'll post my references in the comments section.


The global warming time scale

Pro seems to me to be giving the false impression that the time scale of global warming does not matter. Global warming from 1978 to 2000 was at the rate of 0.20 C per decade. From 1870 it is about 0.8 / 14 = 0.06 C per decade, on average. If the 1978 trend is correct, we may have a climate crisis from anthropogenic global warming. If the 0.06 degree number is correct, then there is no crisis. In the first case a theory of positive feedback of CO2 is required to say that CO2 effects are multiplied by around three. If he 0.06 degree number is correct, then we know can try to figure out how much was due to natural warming after the coldest temperatures in 3000 years and how much was due to CO2. Perhaps negative feedback cuts the CO2 effect in half and other factors account for the warming. We do not know, and therefore Pro's case is unproved.

Cause and Effect

Pro did not establish cause and effect between observed global warming and CO2. For a decade, climate has been running below the 5% probability of error claimed for CO2 climate models. The explanation given for the large departure is that there are natural variations like La Nina that models do not account for and cannot predict. That's certainly true; models to not include such variations.

The problem is that conceding large unknowns means the warming from 1978 to 2000 may also be a product of those large unknowns. The alleged "lower bound based on observation" of CO2 effects cannot be trusted because observations always include all of the many long term and short term influences. If very high quality climate predictions are achieved, we would have confidence that everything has been correctly accounted for. That is not the case because the model predictions are truly awful.

Pro implies that the prediction errors in a decade are just short term blips that can be ignored as statistical, whereas the long term is well understood and predictable. Pro says, "the temperature record contains large amounts of natural variability on time scales less than a couple decades." The implication is clearly contradicted by the Pacific Decadal Oscillation that I cited, and which operates with a roughly 60 year cycle. 30 years of warming are followed by 30 years of cooling. There was a cooling trend ending in the 70s, followed by warming until about 2000, and now it seems we are starting a cooling cycle. Pro never claimed that this cycle does not exist or that it is in the models. The Pacific Decadal Oscillation exists, is long term, and is not modelled.

Pro claims that another reason for the models to err was that methane contributions inexplicably slowed substantially. Pro says, "In actuality, the growth of methane concentrations slowed greatly in the first decade of the twenty-first century." So why did they slow? (Some may recall that we were supposed to have been doomed by the methane from ever-increasing cow flatulence.) I cited evidence that methane may act as a natural negative feedback mechanism than moderates other warming effects, including CO2. Pro's new contention supports that theory. Climate sensitivity to CO2 can be much less than the minimum supposed by Pro.

Climate is complex

The amount of warming or cooling observed over some period is the sum of:

CO2 warming
+ PDO warming or cooling
+ Methane-change induced warming or cooling
+ Water-vapor-change induced warming or cooling
+ Earth orbit variation induced warming or cooling
+ Atmospheric sulphate induced cooling (mainly volcanoes)
+ Solar variation induced warming or cooling
+ Cloud-change induced warming or cooling
+ Other unknown factors that induce warming or cooling.

The methane and water vapor factors may depend upon the warming from other sources, so they do not exist if all other things are equal. Clouds depend upon water vapor, temperature, and other factors. The net warming depends upon all these condition summed at the start of the period and again summed at the end.

Now, consider that there was slight cooling from 2000 to the present. How much of that is due to CO2? Consider that there was about 0.5 degree warming from 1978 to 2000? How much was due to CO2? How about the 0.8 degree from from 1870 to the present; how much of that was due to CO2? In each case the question "How much is due to CO2?" only makes sense if the factors other than CO2 are known. That is what is claimed by CO2-crisis-advocates for the warming from 1978 to 2000. They say they looked and found nothing else that could account for the warming other than CO2 amplified by water vapor. Among the significant factors they overlooked is the long-term Pacific Decadal Oscillation.

If the present cooling is +0.02 from CO2 + 0.01 from water vapor - 0.01 due to methane - 0.025 due to PDO = -0.005, then how is the percentage due to CO2 even defined. I'm not claiming those numbers are accurate, I'm just illustrating the problem of proving the claim that 75% is anthropogenic CO2.

In considering 1870 to the present, they say that all the other factors are short term variations that can be ignored over the long term. However, that isn't true. Where one is in a 60 year cycle at the start and end of the selected period will be significant. Also, longer term cycles are much more difficult to identify, like what caused the Medieval Warm Period and the Little Ice Age.

The claim that 75% of global warming is due to CO2 is unproven. It cannot possibly be proved until models are complete and proven reliable, and that has not happened.

The Survey of alleged exerts

Some committee that investigated Climategate said they found no evidence of successful attempts to block publications by skeptics, even though the desire to block them was clearly expressed. We can be equally confident that a committee appointed by the medieval Church would find no wrongdoing in blocking the theory that the sun is the center of the solar system. However, I cited substantial evidence that skeptical publications are blocked, and Pro offered no rebuttal to that.

I also claimed that whole notion that science is determined by a vote of experts is an unsound one, and Pro did not rebut that.

Some debate issues:

1. I did not agree to waive the limit of 8000 characters by including supplementary material in comments. Pro's doing so is a conduct violation, albeit a mall one I can likely survive. However, the extra material should not be considered as part of the debate. That makes Pro without references for her R4 claims.

2. There is nothing wrong with using a blog post or a Wikipedia article as a reference, if the cited article references through to published material. Pro did not claim the data cited was incorrect, only that the person citing it did not meet her requirements. Moreover, in modern climate science, journal articles are as likely to be bogus as anything else. Mann's Hockey Stick is the classic example, but I cited both the reasons and other examples.

At the high level we are debating, summary statements by reputable climate scientists are usually more valuable than individual research papers. A paper typically has a long list of assumptions and caveats that are ignored in citing the conclusion, In fact, if doesn't have a long list of assumptions and caveats, it isn't good science. The paper's conclusions may have been overturned by later papers, but only an active climate scientist would know what has been sustained and what has been overturned. For example, Mann's hockey stick paper, complete with bogus conclusion that climate did not change for a thousand years before the 1970s, is still available for citation. It was reviewed by his fellow like-thinking climate scientists, while the errors where in the statistical methods.

Debate Round No. 4
51 comments have been posted on this debate. Showing 21 through 30 records.
Posted by QT 6 years ago
@ Roy

Can I see this research?
Posted by RoyLatham 6 years ago
I'm curious: what is the resolution that is being debated in the comments?

There is some interesting new research that suggests that with the same solar input, earth's climate may have multiple stable states. If there is a lot of ice, that reflects away the solar radiation and preserves the ice. If there is little ice, the solar absorption makes it difficult to form. There is also an intermediate state where ocean currents keep an ice cap at equilibrium. This is not at all well understood.
Posted by QT 6 years ago
Just to clarify, are you suggesting that the average global temperature could increase by 15ºC without any major consequences?
Posted by QT 6 years ago
Notably, a change of only 10ºC over several thousand years is enough to produce an ice age:
Posted by QT 6 years ago
If that study does exist, it was probably funded by ExxonMobil or some other biased source.
Posted by QT 6 years ago
Is that a direct quote?
Posted by sadolite 6 years ago
Tell me if you belive this study I read. It stated: The eaths average temp could fluctuate as much as 15 to 20 degrees celcius all over the planet every year and it would have no ill effects on the planet. I will give the source after you answer.
Posted by sadolite 6 years ago
For every source you show I can show one that says the opposite. The "global warming" debate, Oh excuse me the "Climate change" debate or what ever they are calling it now is a waste of resources and a waste of ones breath. It is 100% politically driven not scientifically driven. Absolutely not one dime of govt funds is given to skeptics who would attempt to analyze and find flaws using the scientific method in any govt funded study. And that sir is not conducive with and in line with the scientific method. You will never, ever see an open forum debate with a panels of scientists willing to put their reputations on the line as scientists to state emphatically and without any doubt any change in climate is caused by any one thing. Follow the money trail and you will find your source of global warming or is it climate change. I live in Florida I have an igloo l you real cheap.
Posted by QT 6 years ago
@ Sadolite

What is the source of your claims?

Clearly, the SCIENTIFIC evidence I've presented shows that they are not valid.
Posted by QT 6 years ago
As my opponent states, no scientist really doubts that the Earth has experienced a warming trend.
2 votes have been placed for this debate. Showing 1 through 2 records.
Vote Placed by Cliff.Stamp 6 years ago
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Total points awarded:32 
Reasons for voting decision: Interesting, odd statements from Con with a geo-defense of scientific consensus, drops on the industrial revolution etc., but Pro needed a more focused approach as most of the OP was not evenly strictly needed and blogs as science references? 3:2 pro
Vote Placed by ExNihilo 6 years ago
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Total points awarded:24 
Reasons for voting decision: Conduct violation, con points out. I think pro won the consensus argument. However, consensus is not, in itself, a reason to vote for Pro (esp with 35). On the other issues, Con was able to ameliorate the weight of Pros evidence, especially with the 75 analysis. Thus, pro did not meet the bop.