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It's the sun
Climate's changed before
There is no consensus
Surface temp is unreliable
Models are unreliable
It's cooling
Ice age predicted in the 70's
Al Gore got it wrong
We're heading into an ice age
CO2 lags temperature
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Empirical evidence for anthropogenic global warming

The skeptic argument...

There is no empirical evidence or proof of anthropogenic global warming - it's all based on computer models.

What the science says...

There are multiple lines of evidence, independent of climate models, that show that manmade emissions are causing global warming. The logic is as follows:

CO2 is rising

Rising CO2 levels are based not on one station but over 300 stations in 66 countries (World Data Centre for Greenhouse Gases). Isotope ratios show the increase is due to anthropogenic CO2 emissions (Ghosh 2003). CO2 is rising and mankind is causing it.

CO2 causes warming

Climate sensitivity is commonly defined as how much global temperature increase if we doubled CO2. So what is our planet's climate sensitivity?

  • Annan 2006 uses a variety of independent methods and results from many studies to narrow climate sensitivity to around 2.5 to 3.5°C.
  • Tung 2007 calculates climate sensitivity to between 2.3 to 4.1°C using a model-independent analysis of observations.

These studies, using a variety of independent methods studying different datasets, estimate a climate sensitivity around 3.0 degrees. More on climate sensitivity...

Expected warming

Many lines of evidence show that the Earth has in fact warmed by an amount consistent with theory. Some aspects of the warming are unique to CO2 warming - the carbon "fingerprint".

Conclusion

There is a clear empirical evidence that CO2 is rising, CO2 causes warming and the expected warming is observed. This poses two problems for those who deny anthropogenic warming:

  1. What is causing the warming if not CO2?
  2. Why isn't rising CO2 causing the warming?

Related Arguments

Comments

  1. Will Nitschke (www.capitaloffice.com.au) at 19:27 PM on 19 December, 2007
    Perhaps it is simpler to point out that you can't actually 'prove' anything with absolute certainty in science. The best you can do is suggest a probability, and then usually only when you can perform experiments and directly check results. None of which applies to climate science. Almost all evidence becomes circumstantial in nature. Eventually you build up so much circumstantial evidence that its sheer weight compels you to accept the theory.

    However, your conclusion appears to be back the front. (I've read similar illogical reasoning expressed on the Real Climate web site.) If you want to propose CO2 as the main current driver of climate change, it is up to the proposer of the theory to provide evidence. It is not up to the critics to disprove the theory or offer alternate theories. It is enough for them to say 'we don't know the answer but your theory can't be correct because of reason X.'

    If I proposed that invisible pigs floated through the atmosphere and they caused temperature rises, the burden would be on me to provide supporting evidence. It would certainly not be on you or anyone else to have to disprove my theory. Science doesn't work that way.
  2. This post doesn't show evidence for the extra CO2 warming anything. So we are left with the models alone. Which we are of course disputing. If you go to Annan study you see that he is trying to infer CO2-warming from volcanic cooling and solar variation. Tung from solar variation alone.

    So the two of them simply assert this climate sensitivity business assume that CO2 causes warming, and allege the amount of that warming by reference to matters which are NOT CO2-warming.

    This is UNSCIENCE.
  3. The mistake here is to take the Watts-Per-Square-Metre assumptions for granted. By the time we get to what CO2 ought to do we have already processed the information to a very great degree. The attempt has been made to process everything so that "apples may be compared with apples" as it were. So that therefore CO2-warming is compared alongside solar warming as if they amount to the same thing. Whereas the former ought to be compared more to insulation and its effect globally would have to be considered speculative at best.
  4. Philippe Chantreau at 17:21 PM on 6 February, 2008
    What speculative large scale effect could stem from more insulation with unchanged energy input? Could it be similar to the effect of more energy input with unchanged insulation?

    That insulation's extent has been verified. Changes over time of outgoing long wave radiation have been measured and shown to have decreased by the amount expected from increased GH gases:
    Harries et al, Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997, Nature. 2001 Mar 15;410(6826):355-7

    Abstract here: http://www.nature.com/nature/journal/v410/n6826/abs/410355a0.html
    "The evolution of the Earth's climate has been extensively studied, and a strong link between increases in surface temperatures and greenhouse gases has been established. But this relationship is complicated by several feedback processes—most importantly the hydrological cycle—that are not well understood. Changes in the Earth's greenhouse effect can be detected from variations in the spectrum of outgoing longwave radiation, which is a measure of how the Earth cools to space and carries the imprint of the gases that are responsible for the greenhouse effect. Here we analyse the difference between the spectra of the outgoing longwave radiation of the Earth as measured by orbiting spacecraft in 1970 and 1997. We find differences in the spectra that point to long-term changes in atmospheric CH4, CO2 and O3 as well as CFC-11 and CFC-12. Our results provide direct experimental evidence for a significant increase in the Earth's greenhouse effect that is consistent with concerns over radiative forcing of climate."

    It essentially means that there is more heat retained in the system in the bands of the mentioned gases. It is claimed that this additional heat is warming the climate. Is that such a bold claim?

    Now, I'm sure Will Nitschke will find objections. This is where the logic breaks down. When ample evidence has been gathered and critics of a theory continue to refute it, because no amount of evidence can ever be satisfying and they will not state what kind of evidence would be so, or define it in a way that they know is impossible to reach. Indeed, there is no such thing as absolute certainty.
  5. Den siste mohikanen at 09:00 AM on 19 March, 2008
    "here is a clear empirical evidence that CO2 is rising, CO2 causes warming and the expected warming is observed."

    -Yes, Yes and No. CO2 is rising and we expect that to cause warming. But "the expected warming" is not observed. If by expected you mean that we have seen warming that yes, but not from CO2 alone. In fact, the IPCC uses "aerosols" to explain the cooling from 1944 to 1975, and kindly explain that we do not know much about the climatic impact of aerosols. So to say that the "expected" warming is observed is to mislead: the expected warming from KNOWN factors (i.e. such the IPCC says we know lots about) would have been a steady increase from 1944, interupted by a few volcanoes and La Ninas.


    And to answer your question:
    "What is causing the warming if not CO2?"
    The suns irradiance, cosmic rays, a positive PDO, and a range of other factors, along with CO2.

    "Why isn't rising CO2 causing the warming?"
    Well, IT DOES, albeit not all of it, but from there, it's a long way to prove that a warming of half a degree until now will translate into an additional 5 degrees to year 2100.
  6. Philippe references the 2001 Harries study. I am assuming that he did not read all of it.

    If he would have actually read it, he would know that the change in outgoing radiation was mostly due to methane and CFC's, and that the change caused by CO2 was so small--it is well within the margin of instrument error.

    Doesn't mean much.
  7. Will Nitschke thinks:

    "It is not up to the critics to disprove the theory or offer alternate theories. It is enough for them to say 'we don't know the answer but your theory can't be correct because of reason X'."

    Well, actually, I was taught in high school one cannot PROVE a scientific theory, only disprove it. To this end it WOULD be up to the critics to disprove the theory of AGW, and it is certainly NOT enough to say "your theory can't be correct because of reason X."

    After all, I could say that the theory of evolution can't be correct because the Book of Genesis says that God created the world in seven days, but unless one is a rabid Fundamentalist this would constitute no argument at all.

    At the very least AGW deniers should give a detailed and defensible analysis of the weaknesses they perceive, and as this site shows there is very little in the current body of denialist understanding that holds up to scrutiny.

    I think too that Will Nitschke's needs to separate in his head the difference between 'proof' on the one hand and 'support' and 'corroboration' on the other.

    And his example of invisible pigs is a strawman - climate science DOES substantiate its models with a large body of empirical evidence, so the pigs are visible indeed, if one cares to open one's eyes and mind.

    Just look at the links above for starters, and remember that there are many more examples for those who have the wherewithall to find them.
  8. Will Nitschke (www.capitaloffice.com.au) at 19:26 PM on 19 June, 2008
    "Well, actually, I was taught in high school one cannot PROVE a scientific theory, only disprove it."

    That idea was proposed by Karl Popper (as I learnt in my university education when studying the basis of scientific theory building). Disproving a theory is not as easy as it sounds when you try to do it in practice.

    "Just look at the links above for starters, and remember that there are many more examples for those who have the wherewithall to find them."

    Have you looked at any of these links you proudly refer to, since the bulk of them are critical of AGW and don't provide the 'large body of empirical evidence' you seem to be imagining is there?

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