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Why we have a scientific consensus on climate change

Posted on 23 March 2011 by Thomas Stemler

A short piece for the general audience of RTR radio, Perth, Australia.
(listen to the original audio podcast)

Recently a research group analysed the current literature on climate science. Their aim was to find out how many of the active researchers in the field agree on man-made climate change. The answer is, 97 out of 100 agree that the climate is changing and that we are causing it.

From my own experience, such a high proportion is quite unusual. As scientists we are trained to be professional sceptics, who doubt everything and who moreover love a good debate. Therefore putting 3 scientists together in a room sometimes results in an argument with 5 different opinions.

While this is the more enjoyable side of science, the more important one is that being sceptic lets us identify errors and improve our understanding of nature.

Climate science is a very special science. It includes experts who study the dynamics and data from the atmosphere, the oceans, glaciers, and so on. Some of us specialise in building models, others use them to make predictions.

So how come that 97 % of the experts agree that the current warming is not natural but a consequence of burning fossil fuels?

First, it is because all our data show that the global mean temperature is increasing, that the glaciers and the arctic ice are melting and therefore sea levels are rising.

Second, we know that burning fossil fuel releases CO2 into the atmosphere. The properties of CO2 were first studied by John Tyndall in the late 1850s. Tyndall was an experimental physicist interested in how different gases absorb heat. John Tyndall's observations were remarkable. His pioneering work eventually inspired physicists to develop the theory of quantum mechanics, but his results about CO2 also led Arrhenius in 1896 to the conclusion that burning fossil fuel will result in global warming. So climate science is a very old science indeed; we have known about CO2 for more than 150 years.

Nowadays we know how much CO2 we put into the atmosphere by using it as our global garbage bin for fossil fuel. All our climate observations show a global increase in temperature. This increase is consistent with the well established properties of CO2.

Taking this into account it is no longer surprising that 97% of the professional sceptics working in the area of climate science agree that we are currently witnessing man-made climate change. The only question remaining is, what do we do? Ignore the facts or generate energy from other sources?

Dr Thomas Stemler is a physicist who is currently an Assistant Professor of Mathematics at the University of Western Australia. He is an expert in forecasting of complex nonlinear dynamical systems.

This podcast is now available on iTunes (or search for "Climate Podcasts from the University of Western Australia" in the iTunes store). Alternatively, you can subscribe to the stream via feedburner.

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Comments 101 to 107 out of 107:

  1. #96, Harry: Smug? Hardly. Factual? Yes. Directed at Gilles, who avoids fact-based argument whenever permitted? Also yes.

    "let's come up with a short, but better set of survey questions that are quantitative ... and post links to the survey here, and at WUWT"

    Yes, let's make scientific decisions by popular vote. How many think it would bemore effective if E = mc3? The ayes have it, so it must be true. Now, that was probably 'smug.'
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  2. @ Arkadiusz 98

    I don't really understand the point you are getting at in your first paragraph. Which is the "imperfect" model are you referring to?

    As DB said, when you are interpreting the result of the model, you should keep in mind what feedback the model captures. Is 1.94 degrees that far from the range? As someone pointed out elsewhere (don't remember where I read it), you should also keep in mind the model assumes that foliage increases, which is not necessarily true.

    Regarding the coal-fire plant paper:
    The paper says that while the emission of pollutants may induce a cooling effect in the short term, the control of pollutants down the road will remove this effect. And as far as I can tell the authors didn't suggest that the models don't capture the effect, it's just that the current way of quantifying the effect doesn't not reflect the regional variation.

    Regarding black death:
    So despite the long list of criticism of Scott and Duncan's hypothesis, despite the lack of concrete evidence, and despite the strong evidence of Y. pestis being the cause, you think Scott and Duncan overturned the consensus because you LIKED their writing?
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  3. "why don't you simply read AR4 instead of loosing your time here ?" I couldnt agree more! However, the reason this site exists because is people dont and worse a huge amount of disinformation is thrown out.

    And so the science gets discussed. Debate is worthwhile so long as debaters back their claims and so debate is on the basis of the facts available dont you think?
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  4. Consensus – it would never be considered part of modern science and the scientific method. To me, going back to first principles always tends to shed some enlightenment. Science is most fundamentally about observation, hypothesising and experimentation of a controlled and repeatable nature. Without the latter it certainly is not science – at least not my understanding of it.
    Many fields of study call themselves a Science (like Social sciences etc) from the Latin “scire” to know but that has a very different meaning to orthodox science. One can have scientists working in many fields including management but that does not make those fields science.
    As an illustration of consensus the aether “theory” was “well founded.” Michelson and Morely carried out some brilliant experiments in the late nineteenth century to prove its existence. Their experiments proved otherwise but, it still took years for the consensus to dissolve and abandon the aether.
    As a novice surely no one can dispute that we must contribute to carbon based emissions – intuitively it seems so (deforestation, industrialisation, population etc) but more importantly the data confirms it through C isotope measures. But that is a different question to AGW of an extreme type.
    Consensus is not the answer (that doesn't mean scientists don't talk about it but consensus measures seem quite silly).
    One question puzzles me about the CO2/temp hypothesis. Given that there has been an increase of over 100ppm of CO2 in the last 200 years and the current level is about 30% higher than at any time in the last 500K years why is our current temperature not the highest temperature of that period.
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  5. TonyM, you're getting things a little backward. The science of AGW isn't robust because we have consensus amongst climate scientists - we have consensus amongst climate scientists because the science of AGW is robust!

    In that regard, the consensus is merely an indicator for non-scientists that there is a very high probability that the AGW hypothesis is correct. It's not evidence supporting AGW in & of itself, though there's plenty of that around.

    Regarding the CO2/temperature thing - you're forgetting thermal inertia. Current radiative forcing is ~1.6 W/m2, if I recall correctly. To heat the oceans by 1ºC takes a phenomenal amount of energy - multiplying 1.6W/m2 by the surface area of the earth (~510e12 m2) is a lot of energy, sure (about 816 TW, if I've done my sums right), but it's only enough to heat up the mass of the oceans by ~0.005ºC per year (assuming complete mixing, of course!). On that basis, you'd expect ~0.5ºC per century. We're currently seeing about three times that, I think, which is mostly down to the oceans not being well-mixed (plus some of the heat gets absorbed by the land & atmosphere).

    So, basically, it takes centuries at best, and possibly millennia, for the full warming effect to be realised. This is why focussing on projected warming to 2100 is a dangerous thing. The scientists do it because it's a handy reference point, far enough out to see some real effects that they can highlight to policy-makers. But in the high-emissions (or business-as-usual) scenarios, warming doesn't end there, by any stretch of the imagination.
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  6. Bern, thanks for your comments. I will leave the issue on consensus open as it would need to also canvas possibilities other than the one you have focussed on. I suggest if the science is so robust it does not need a survey on consensus. I have never heard of such a survey in the hard sciences even if its intent was to educate the public.
    So I guess what you are telling me is that the temperatures we experience today reflects CO2 of perhaps 200-1000 years ago. This sounds like a strange consensus science community when the controversy surrounding hockey sticks, hidden data and ocean rises is all so contemporary but the real cause is somewhere in the past. No wonder Gore is reported to have bought a property on the coast.
    In addition the CO2 we are spewing out now will have an effect in 200-1000 years. But, non mixing oceans right now are causing faster temp rises so that many of our pollies wrongly attribute it and some extreme natural events to CO2 rises rather than, say, God.
    As the last half million years have seen no runaway effect with CO2 increases (and there is plenty of it available in the oceans etc) why would I want to worry about the level of CO2 rising now. Besides technology will have caught up sufficiently and energy, say from fusion, will be so cheap that we can sequester all the CO2 we want in a few hundred years if that is required.
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    Moderator Response: You've wandered across quite a few topics other than the one that this post is about. Click the "Arguments" link in the horizontal bar at the top of this page, and skim the resulting list for appropriate posts. Further off topic comments on this thread will be deleted.
  7. TonyM, the confusion and conflation of issues and non issues in your post are so dense that I will not even bother to begin adressing them. All the answers are out there and easy to find if you actually want to look.

    As for why it is important to show that a consensus exists in climate science, that is because the assault on it is of a scope and ferocity that are unprecedented. Even the tobacco campaigns pale in comparison. The merchants of doubt have managed to create a perception that there is lack of agreement among scientists on the basics tenets. There is not. It is important to point that out. Science is not done by consensus and never was, that applies to climate as well.

    The consensus is one of research results. Climate scientists working on various aspects of the science reach similar or identical conclusions through different means. These conclusions impose themselves to anyone studying the science seriously. That is what consensus means.
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