Arnold Kling  

My Global Warming Question

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I posed it here.

what are the most persuasive reasons for believing that the rise in temperature is due to increased atmospheric carbon dioxide?

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COMMENTS (19 to date)
Dennis Mangan writes:

Al Gore said so?

mgarcia writes:

Over the last 2 centuries, fossil fuel that accumulated under the earths crust over millions of years has been burned, releasing carbon dioxide as a by-product of combustion. The current rate of release is 3.2 billion tons of atmospheric carbon dioxide per year

There is no evidence that the world is a carbon sink of infinite capacity. The measurable accumulation of atmospheric carbon dioxide is evidence to the opposite.

In our solar system, the surface temperature difference between Venus and Mars is largely due to greenhouse gases in their atmospheres.

Carbon dioxide is demonstrated to be a greenhouse gas in Earth's atmosphere.

Let me guess. I lose points because I went over 20 words.

If atmospheric concentrations of carbon dioxide went down, to concentrations along those of the 1600's, 1700's, and temperatures continued to climb, a lot of scientists would have egg on their face.

If the climate skeptics didn't have a history of moving the goalposts (temperatures are not rising... ok, temperatures _are_ rising, but it is not due to fossil fuel use... ok, temperature rise _is_ due to fossil fuel use, but carbon caps will have a catastrophic economic effect... ad infinitum), and if climate skeptics didn't embrace every technique in the "art of controversy", I would less inclined to think they are not arguing in good faith.

The Pope said there is no global warming. So, reasonably, the evidence is inconclusive. Can we please rise above this level of argumentation?

Stan writes:


Stephen Forde writes:

I think it is the expression of faith in authority.

"I don't think that many scientists would just something like this up."

"So you think Al Gore, David Suziki, and all of these people are full of s***?!"

Two immediate responses from people I knew when I said that I was somewhat skeptical about the whole global warming thing.

mjh writes:

mgarcia: 1 assumption, then 3 questions:

Assumption: C02 can only absorb limited radiation frequencies.

1) If the assumption is true, doesn't that mean that there's a diminishing return on how much temperatures can rise from additional C02?

2) If that's true, then aren't the additional heat that's predicted require other positive feedback effects?

3) If that's true, why didn't these positive feedback effects kick in when in the past the C02 levels and temperature levels were much higher than today?

Dr. T writes:

mgarcia strings random facts and theories together and thinks it is evidence.

Stephen Forde thinks that scientists wouldn't make up a theory of carbon dioxide causing global warming. He is very wrong: scientists make up stuff all the time; it's called generating hypotheses. The problem is that some scientists fall in love with their hypotheses, ignore contradictory data, and alter statistics and models in ways that lend unwarranted support to their favored hypotheses. This process has occurred with the "carbon dioxide increases are the main cause of global warming" hypothesis. Add to this the fact that scientific journal editorial boards, grant agencies, and politically-oriented climate groups are suppressing publication and funding of contradictory studies, and you get a false sense of scientific consensus about CO2 and warming.

With CO2 accounting for less than 5% of "greenhouse" gases in the atmosphere, it is hard to believe that relatively small changes in CO2 concentrations over the past few decades have caused global temperature increases. Unlikely hypotheses require rock-solid evidence, and we don't have that for CO2 and warming.

xmath writes:

[Comment deleted for supplying false email address.--Econlib Ed.]

william Lanford writes:

1. The surface of the earth is warmer than if would be if there were not atmosphere. This follows from simple energy balance between energy received from the sun and energy radiated by earth.
2. CO2 is one of the gases in the atmosphere that contributes to the warming at the earth's surface.
3. The amount of CO2 in the atmosphere has been increased by burning fossil fuels by a large amount, ~35%.
When sleeping, if I add a blanket, I feel warmer, but I am not sure I could prove that I was warmer.

shayne writes:

The specific mechanism related to CO2 that is assumed to be the warming (radiative forcing) factor is the molecule's ability to absorb solar radiation across a fairly wide frequency spectrum, but re-radiate absorbed energy in the infrared band (heat) only, as it's energy level decays back to steady-state. Presumably, the CO2 in the atmosphere on the Sun-ward side of the planet absorbs solar radiation (broadband as well as IR/heat), and when the solar radiation source is removed - night-side of the planet - the CO2 energy level decays, providing re-radiation in IR band only. In other words, higher frequency solar radiation impinging on the planet, that would otherwise not result in heating, is "converted" to heat by virtue of CO2 absorption and re-radiation characteristics.

While I understand and accept the CO2 absorption/re-radiation mechanism, I remain (what some would consider) a skeptic. In the first instance, global warming is "caused" ultimately by the Sun. Without extensive and long-term data on Solar radiation patterns, it is clearly a low probability exercise to attribute "global warming" to a single molecule. If you read the IPPC report, or even the technical summary, you will note that Solar radiation patterns have only been monitored for 28 years, and only short-term (11 year) radiation cycles have been observed. Additionally in the IPCC report, the scientific community admits that, with the sole exception of CO2, their level of understanding of Solar radiation effects and forcing effects of every other atmospheric constituent is either "low" or "very low".

Suffice to say, the report and any related evidence supports further study to help address the "low" to "very low" level of understanding of the scientific community. It does NOT support making wholesale changes to entire national and global economies. Again, read the book, skip the movie.

Michael Jacobowitz writes:

How could a model predicting global warming have any accuracy if it cannot predict the date of the next ice age? Of course, no model purports the ability to address that issue. Absent dependable prediction of glaciation, it is difficult to believe the eggheads have a serious understanding of global warming or cooling.

Matt writes:

On Consensus...

The US Senate questions whether there is consensus on the cause of GW. Pretty interesting:

Morgan writes:

The burden of proof is clearly the other direction. We are pumping huge amounts of pollution into the air and earth. We can see the pollution in the air. The temperature of the earth is rising. If it rises too much, we know there will be dire, and perhaps apocalyptic consequences. We know asthma and cancer have been on the rise. Prove to me that the pollution that you emit into my air and into my environment isn't harmful.

xmath writes:

[Comment deleted for supplying false email address. Email the webmaster at to request restoring this comment and your posting privileges.--Econlib Ed.]

Barkley Rosser writes:

Well, it is hard to prove that it is the most
important cause, although the "skeptics" are not in agreement on what is the alternative (that is, the skeptics who agree that warming is occurring). However, there is a scientific theory that says more CO2 should lead to a greenhouse effect that I have not seen refuted (although some claim there is not enough CO2 in the atmosphere to make any difference), and, as has been pointed out, CO2 concentrations have increased by about 35% in the last half century, almost certainly entirely due to human activity, and since the mid-1970s average global temperature has also increased.

Max writes:

The most convincing argument is that the rate of burning fossil fuels has increased dramatically compared to past natural cycles (dy/dt >> 0)
that CO2 capability to irradiate which has been proven in laboratory.

However, uncertainities remain at large and we can't even predict the next few years. Also, sensitivity of the CO2 capabilities are pretty limited (larger amount of atmospheric CO2 does not mean linear increase in temperature, because the CO2 properties are actually decreasing with a rise of concentration).

So, while it is a convincing argument for rising temperatures (at least about 0.2-0.4 °C), it is not a good argument for something "catastrophic", because of nature itself:

a) it is unlikely that positive feedback forces would prevail, or we would have been boiled some million years ago to the core of our planet.

b) There are several other "ingredients" like Methan or even the amount of solar irradiance that can account for and counter-balance eventual climatic changes. After all, we can't really predict the way our sun will burn..

This doesn't say (and truthfully no serious sceptic ever claimed otherwise) that CO2 increases don't change temperature or even raise it, but rather that the effect is greatly exaggerated and put together with much doom and gloom...

Barkley Rosser writes:


That nonlinear feedbacks may work over certain ranges does not mean that they work over all ranges. There are cross-cutting effects. So, the standard theory on how CO2 works is that its direct effect has a diminishing returns effect, essentially a logarithmic effect. So, there is one counterweight. There are other positive feedback effects, however, especially reflectivity ("albedo") off of ice.

The geological record in fact suggests that the periods when we moved from ice age temperature and back were very short in geological time scales. So, it is very likely that historically we have seen episodes of nonlinear feedbacks operating over periods of time during these de facto discontinuities, only to reach limits of one sort or another with a new equilibrium setting in.

aaron writes:

Shayne, (this is simplified to get the basic concept across, it's flawed and I won't address re-emittance)

CO2 is effectively transparent to the shortwave radiation emitted by the sun (the shortwave energy bands that are absorbed by CO2 are essentially fully absorbed by the planet and other gasses, so more CO2 will not trap more energy from the sun). Where it is less transparent is over some longwave IR bands which are emitted from the earth (I believe most of which is a by-product from absorbtion of shortwave solar radiation by the other gasses and particles in the atmosphere, water, and land). Not all of the longwave radiation in the bands that CO2 absorbes are captured by CO2 and other gasses, so adding more CO2 increases the amount absorbed (and is turned into heat). This raises the temperature until the point that the higher temperature results in emission of more IR to space (returning to balance with incoming solar shortwave energy).

I think the theoretical impact of CO2 alone is quite low (lower than the commonly purported 1.2C for CO2 doubling).

There are diminishing returns to the increase, as mentioned in comments above. The low concentrations of CO2 would suggest to me that we are in the steeper part of the curve, but I don't know what % of these bands are already being absorbed (we should see less warming for each incrimental increase in CO2, but I don't know whether it is slight or big).

Emperically, over the century, we have seen about a .6C increase in temperature and about half of it is purported to be due to anthropogenic forcings (including, but not limited to CO2). This is with a 35% increase in CO2. If the entire anthrowarming is attributed to CO2 (slightly less than .3C), then getting all the way up to a full doubling (560 ppb) would give us at most another .36C of warming.

Ken Ring writes:

Burning fossil fuels does NOT add emissions to the atmosphere. It only puts back what was previously removed. Remember that a tree grows by absorbing CO2 from the air. A carbon atom+ a water molecule=a carbohydrate, the building block of nature. Therefore a log of firewood is just stored CO2, ready to be returned to the air again when combusted. It is CO2-in-the-bank. Same with coal, oil and gas. Otherwise, how does anyone think these materials were formed? So please, no more nonsense about the planet being in crisis etc. The only thing in crisis is our gullibility when it comes to smart-talking entrepreneurs like Al Gore, who goes around the world selling carbon credits to governments. Okay, so we may be adding these emissions back quickly. The planet can cope. What difference would it make to my deposit if I walked to the bank or ran?
Ken Ring
longrange forecaster
New Zealand

GeneA writes:

Ken Ring is right on the money, brilliant! If CO2 is not absorbed by growing vegetation, then what are "forest sinks"???
I am now a skeptic!

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