Scientific consensus on climate change

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Is there a scientific consensus on climate change?

The short answer is yes, in broad terms there is. That of course doesn’t mean that all scientists agree on everything having to do with climate change. First of, scientists are in general argumentative and stubborn: they will usually find something, be it a minor point, about which they disagree with someone else’s opinion or interpretation. But in light of that nature, the broad consensus about the recent climate chang is very strong indeed. This consensus is laid out in the IPCC reports (Intergovernmental Panel on Climate Change), by means of a thorough review of all recent scientific literature on the relevant topics. Minority opinions are also discussed in these reports, but are -as are all results- put in the context of the bigger picture of the literature as a whole. Indeed, this is how it should be done, for outsiders to get a proper view of what the current state of the science as a whole is.

 

What is the scientific consensus on climate change?

Short answer: Recent climate change is for a large part due to human activity.

Longer version:

  • Surface temperature readings jiggle up and down, but over the course of the past century, their overall trend is up. Rising global temperature is also confirmed by the global retreat of glaciers, melting of ice sheets, poleward migration of species and increased ocean heat content. Issues with individual measurement stations do not impact this rising trend.
  • The levels of carbon dioxide and other greenhouse gases in the atmosphere have also been rising. The concentration of CO2 in seawater has increased as well. The total observed increase is consistent with the amount of fuel humanity has burned and the amount of land it has cleared since the industrial revolution began. Isotope analysis confirms that the additional CO2 comes predominantly from fossil fuels.
  • Basic theory (known since at least 150 years) links these two trends. Because of greenhouse gases, a smaller fraction of the thermal radiation emitted by the surface escapes into space. The planet becomes a net absorber of energy. The surface heats up and emits more thermal radiation, until the total amount of escaping thermal radiation again balances the energy deposited by sunlight. The radiative properties of CO2 have been measured over 150 years ago (Tyndall), and the warming of the earth resulting from our emissions was predicted shortly thereafter (Arrhenius). His prediction was quantitatively in the same ballpark as was later confirmed. Since then, research has -by and large- backed these results up into a mountain of evidence. Current global warming is a prediction come true. That doesn’t happen all that often in science…
  • Natural factors, such as variations in the sun’s output, have been too small to account for the observed temperature increase.

See here for another discussion of what the consensus is all about. A bit more technical description is here. For more detail, see here.

Criticism on the consensus view

Most criticism concerns the first and the last points of the consensus view as stated above. The second and third points are hardly ever criticized, at least not by people minimally versed in physics. Indirectly however, they are often implied to be false.

  • There has been a more or less constant attack on the observed temperature trend, even when it has now significantly risen above the level expected from natural variability of the weather. Fact is, the trend is so overwhelming and there are so many observations, even of different physical quantities, pointing in the same direction, that it really starts to be laughable to contest that the globe is warming. Known problems such as the urban heat island effect are corrected for in all temperature series, and the procedures to arrive at a global temperature are very carefully thought out and publicly documented. Of course climate scientists are all for good quality control of the observations, which admittedly still have a lot of issues to be dealt with (see eg here and here the latest “controversies” in how to deal with such issues). But when such criticisms are driven by an obvious desire to discredit the entire temperature trend (and, by extension, any mitigation policies) without proper justification for such far reaching claims, then I take the criticism with a grain of salt.
  • Sometimes it is implicitly questioned that the current rise in CO2 is due to human activity, but in such a way that the claim is hard to recognize. E.g. by stating (correctly) that during the great ice ages the temperature rose before CO2 did, “skeptics” often conclude that the current CO2 rise is a consequence of warming rather than vice versa. But this last claim is patently false: we know for a fact that we put the CO2 in the air. (The cause-effect relation between CO2 and temperature goes in both directions; they can act as a feedback on each other. More CO2 causes warming; warming causes more CO2 emissions. It’s like the chicken and the egg.) As another example, the bogus documentary “The great global warming swindle” implicitly claims that the increased CO2 comes from the oceans (and thus, by extension, not from fossil fuel burning). This is so obviously wrong, it’s not even funny. (For a critique of this documentary, see e.g. here)
  • The third point is implicitly pushed aside when trying to promote or exaggerate the sun’s role in climate change of the past century. As if by making the sun responsible for global warming the known physics of greenhouse gases magically stops functioning. Just like there is no knob to switch off gravity on the earth, there is no knob either to switch off the radiative effects of greenhouse gases. It’s there, deal with it. If it wasn’t there, the earth would be a whopping 30 degrees C colder than it is, and life as we know it would not exist. But what if the radiative effects of greenhouse gases are smaller than what is currently thought? While there is some playing room for the climate sensitivity (the equilibrium temperature response to a doubling in CO2 equivalents) to vary, this playing room is rather limited by several constraints from e.g. paleo-climate and climate response to large volcanic eruptions (see e.g. here and here). You would still have to explain away a whole body of observations in order to come up with a substantially larger contribution of the sun to current climate change than laid out in the IPCC reports.
  • The sun’s energy output is huge, and variations in the sun have caused climate changes in the past. The sun’s energy output has not been as high as in the past century for thousands of years. True, but it only explains a small portion of the current warming, mainly in the early 20th century. Over the last 50 years the sun’s output has been roughly constant (decreasing weakly), so even with exotic and unsubstantiated magnifying mechanisms (e.g. cosmic rays, UV-dynamics feedbacks) the sun can not be held responsible for the recent global warming since 1975. Often you will hear the logical fallacy that “since the sun has been responsible for climate changes in the past, it must now also be responsible”. On an equal level are emotional arguments such as “How can we possibly influence something so big and complex such as the earth’s climate, when contrasting us little humans to that giant ball of energy in the sky?” Such arguments may sound plausible when listening to a radio-show; in a real scientific debate they are not taken seriously.
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20 Responses to “Scientific consensus on climate change”

  1. malone Says:

    When you recommend RealClimate.org and their devastating critique of the swindle documentary, is it parts such as this

    “CO2 doesn’t match the temperature record over the 20th C. … They presented this as a major flaw in the theory, which is deeply deceptive, because as they and their interviewees must know, the 40-70 cooling type period is readily explained, in that the GCMs are quite happy to reproduce it, as largely caused by sulphate aerosols”

    that you are thinking of?

    This certainly does provide “accurate scientific information” in that it demonstrates that the writer is only somewhat distantly familiar with actual science.

    Specifically, to say that the drop of temperature is sorted because the models predicted it is a) absurd – I have a phd in data analysis and have seen more fiddled models from academics that you can shake a stick at, and b) is quite clearly “assuming the answer”, in that if we are going to assume the “models” are correct, no debate is required. The whole point is that I and many others think they’re nonsense and so would prefer some reason that has actual physical evidence, not models which are simply useless in predicting the state of such complex systems.

    Maybe a reason for the drop which is consistent with AGW exists, maybe not. But the folks at RealClimate certainly don’t have one, or they would trot it straight out. Do you, or do you know anyone who does?

  2. Bart Says:

    Yes, I do. And so do the folks at RealClimate and pretty much all climate scientists.
    The global temperature is the consequence of many things, not only greenhouse gases (though for the past 100 years, they have definitely been dominant). The main flaw in the Swindle’s argument is that they fail to see that simple fact. Changes in solar output, landuse and aerosols have also played a role. Then there’s volcanoes, El Nino/La Nina, and other short term (weather related) fluctuations. The global temperature change is therefore not in a one to one relationship with CO2, nor is it expected to be so. Real Climate has repeatedly made this point, and so will any serious climate scientist.
    The physical reason that aerosols cool the climate is that they reflect solar radiation and they influence cloud properties: More aerosols cause more (and thus smaller) cloud droplets, and therefore a more reflective and longer lasting cloud. This is known from basic physics and measurements alike, though the exact magnitude of the effect is highly uncertain. From the 40s to the 70s the amount of aerosol in the air has increased due to human activities, and since the late 70s they have decreased slightly (at least over Europe and North America) or stabilized due to air pollution regulation. These changes had a cooling and a slight warming influence, respectively.
    Models are not perfect, and they have major uncertainties, but that doesn’t make them useless. To be able to reproduce temperature changes over vastly different times in the history of the Earth means that they do some things quite right. And to the extent that they may be wrong, they can be wrong both ways: over- or underpredicting the climatic consequences of CO2 (or any other climate forcing for that matter). More uncertainty means more reason to be cautious.
    Besides, Anthropgenic Greenhouse Warming (AGW) doesn’t solely depend on climate models; it is based on many different lines of evidence, of which the models are only one.
    Finally, if you’re into data analysis, take a look over at tamino.wordpress.com; he’s a data analyst who enjoys looking at climate data first hand, using rigorous analyses.

  3. malone Says:

    Ok, I agree with much of what you say. But I think it’s a little unfair to blame swindle for concentrating on CO2 – it is clearly the AGW people who are obsessed by this.

    I checked out the site. Better than most but still fundamentally missing the point. The situation with the models is in reality quite clear. Either they (or at least one) are predicting what will happen in the future with statistically significant accuracy, in which case they have earned the right to be listened to, or they’re not, in which case they should be IGNORED.

    People like to obfuscate this issue, but it really is that simple. None of the models from the 80s, 90s or early 2000s have made any predictions worth bragging about, so they are all to be ignored. Maybe the ones today are all 100% correct but we’ll only know in 10 years. But I know where my money lies.

  4. Bart Says:

    It is clear from reading eg RealCLimate that they have often stressed the fact that the global temperature is the consequence of many things, not only greenhouse gases (though for the past 100 years, they have definitely been dominant). I don’t see any “obsession” there or at other scientifically informed places. The role of CO2 in current warming is dominant, and its role is likely to increase rather than decrease (in a business as usual scenario that is). Moreover, curtailing its emissions is probably the major challenge amongst the different culprits, because it is most intimately linked with the energy system and thus with the very heart of our economy. Which is probably why it brings out such strong aversion in some people to do something about it: they are afraid it will hurt the economy (while forgetting how the economy will be affected if we don’t do something about it).

    What you call “quite clear” and “that simple”, is perhaps so in theory, but it is not as simple to assess. It’s not an all-or-nothing kind of game. When something is not worth bragging about, should it then automatically be ignored? Of course not. Models can be imperfect, yet still useful. I am not aware of evidence that the models of the past 25 years have faield miserably. I have seen evidence however that their predicitons have by and large come true. How else than by using models can we assess the likely consequences of our current and future actions?

  5. malone Says:

    Look, no’one acts like this with models in fields where anyone cares about the actual outcome. No drug is let loose on the market until the outcomes after its usage can be predicted with high statistical accuracy. No’one allows planes in the air until the evaluations of the state of the parts after usage agree with what was predicted. The incorrect models are only useful as a stepping stone to a correct one – until the desired predictive accuracy is acheived, they’re most valuable use is to tell you that the problem is not well understood. You can just assert that they’re useful if you like, but I disagree.

    “The role of CO2 in current warming is dominant, and its role is likely to increase rather than decrease (in a business as usual scenario that is).” Many others have this point of view – that of CO2 as the dominant factor – and so I find it hard to see the problem with Swindle concentrating on CO2 (especially when those who are responsible for the most carbon can be casually referred to as “culprits”).

    “I am not aware of evidence that the models of the past 25 years have faield miserably.” Sorry, but this is an absurd statement. How many of the proponents of AGW had models that predicted temperatures would level off from 1998 to now? We both know the answer is none, that they all predicted much more warming, the boy who cried wolf etc…

  6. Bart Says:

    Malone, you write that “No drug is let loose on the market until the outcomes after its usage can be predicted with high statistical accuracy. No’one allows planes in the air until the evaluations of the state of the parts after usage agree with what was predicted.” These are both good examples of the precautionary principle: you have to provide compelling evidence that something is safe, before actually doing/using it. This is common for actions that could have large negative effects. The warming effect of greenhouse gases has been known since the 19th century, so why not applying the same precautionary principle to their emission?

    I have used an airplane analogy in a previous post (http://ourchangingclimate.wordpress.com/2008/06/14/how-do-we-know-theres-a-consensus-and-why-does-it-matter/):
    “If a plane technician tells you that there is a 75% chance that the plane you are about to board will crash, would you board the plane? Would your action (presumably of not boarding) change if an economist points you to some screws in the wing of the plane that are perfectly in place, telling you that he therefore concludes that he regards it as totally save to board the plane? What if 99 engineers tell you it is unsafe and one tells you it is safe?”

    You mention that the effects of new drugs have to be accurately predicted before they are let loose on the market, though wouldn’t you acknowledge that these predictions are imperfect? It won’t take you long to find examples of drugs that later, sometimes long after their market introduction, were found to have serious side effects. That doesn’t make the predictions useless; we’d be worse off without them. But there is room for improvement, and the known imperfection of the prediction should actually make us more (not less) careful in allowing the potentially dangerous substance or activity.

    What, if not models, would you suggest we use to inform ourselves about the likely outcome of current and future activities? Or would you suggest that we don’t change the course of our activities until we have models that reach a certain level of accuracy? Even if climate scientists say that the models are good enough to predict that such a business as usual scenario is going to be extremely problematic? In terms of my airplane analogy, would you board the plane, and if so, why? Are you into taking large risks or do you have good reason to believe that those 99 engineers (read: 99% of climate scientists) are entirely wrong?

    Re Swindle: CO2 is not the only climate forcing, so you can’t expect a one to one relationship between CO2 and climate. Claiming that climate scientists say that it should is simply false.

    Global warming hasn’t stopped in 1998. See the previous point: there are multiple factors influencing climate, and even more that influence the weather over timescales of a few years (El Nino, volcanoes). See eg http://www.realclimate.org/index.php/archives/2008/01/uncertainty-noise-and-the-art-of-model-data-comparison/langswitch_lang/en

  7. malone Says:

    Ok, I admit me saying models are useless is not helping. I think the GW ones are useless, but i know that really I should say models that have reached acheived some measure of success in predicting real world outcomes can be considered useful, and define what the degree of success might be. And some of those that are deemed useful by this criteria can later be deemed useless because of more data which contradicts an assumption of the model. And the reverse can happen as well – sometimes a model deemed to be correct according to current data can suprise everyone, when say a drug kills someone unexpectedly, meaning the model and/or the criteria must be changed. The first thing to do then is acknowledge that one or more of the assumptions in the model are incorrect – but what you don’t do is just make up reasons ie. “it was because he ate 7 cans of tuna the day before”. Maybe he did and maybe no other user of the drug did, and maybe you can prove that everything else was identical, but however plausible this seems you don’t state that as the reason until there is some direct evidence and it has been experimentally verified. Because as anyone who has worked on complex systems knows, they NEVER STOP SURPRISING YOU. (I’m referring here to things like “Global warming hasn’t stopped in 1998. See the previous point: there are multiple factors influencing climate, and even more that influence the weather over timescales of a few years (El Nino, volcanoes).” – you can’t just “say” things liek this without ackowledging that they could be totally wrong).

    But it’s just so boring and long-winded to write like that. It’s more fun to just say they’re useless ie. that they have never made a prediction worth bothering with. Ok, my bad.

    I’m sorry to be direct – you seem like a nice polite person and all – but I just don’t know where to start with what you said, it’s all over the place. You’re making things far too complicated. The “precautionary principle”? And what the engineers “tell me”? And an economist? You’re completely and totally missing the point. The fact that there are 10,000 flights a day – all according to broadly similar standards and principles – which result in a handful of crashes each year is what you go on, what people SAY in the face of such evidence is largely irrelevant.

    And if, as you suggest, a flight engineer says something is wrong and this is outside what would normally be deemed acceptable, then you don’t ask the engineer for his opinion on what will happen – HE DOESN’T KNOW. He might think he knows but planes are unbelievably complicated – he doesn’t, he’s only at best guessing. Would I board the plane? No, of course not. Complex systems are ALWAYS SURPRISING YOU and, further, the gulf in complexity and understanding of aeronautics and climate science is so large that comparing flight engineers to climate scientists and acting or not acting to me boarding the plane is just not going to, erm, fly. The models should concentrate on bridging this gap (although I for one would bet large sums climate forecasts will NEVER be successful).

    What you’re doing is taking the fact that human generated CO2 in the atmpsohere is the (as you say in statistics) null hypothesis ie. assuming it is true, and trying to show that what we know is consistent with this.

    However, the null hypothesis is really that things are fine. I want some evidence before we start saying that CO2 emissions are going to cause problems. I think we should cut our dependence on fossil fuels and recycle and in general keep a close eye on the chemicals released into the environment, because they are good things to do. But thus far I have seen precisely zero evidence that CO2 has a MEASURABLE effect on the temperature. Sure, it’s a greenhouse gas and will have some. But the point is, there are so many other factors that have a larger effect, that trying to measure the influence of CO2 is trying to measure something which is smaller than the noise ie. fundamentally impossible, not to mention pointless.

    Why is this the null hypothesis? The situation now is that there are no problems, there is nothing dangerous about current temperatures. The danger is in the future, is predicted – so the null hypothesis is that there is nothing wrong and you must demonstrate that something is afoot. If there is evidence for this, I am yet to see it.

  8. Bart Says:

    Global warming is a prediction come true: it was predicted well over 100 years ago that increasing the levels of CO2 in the atmosphere would raise the Earth’s temperature. See e.g. http://www.aip.org/history/climate/co2.htm
    When you look at the history of climate science, the null hypothesis actually was that whatever humankind would dump in the atmosphere couldn’t possibly change the climate (or affect our health). With more evidence coming in, this null hypothesis was rejected in favor of the hypothesis that “yes, we can”. And it only got more strongly backed up by evidence as time went by. If you can refute or falsify that AGW is a reality, be my guest. You’ll be instantly famous. But as for now, you saying that you don’t trust the models isn’t going to convince many people (except those who have an extreme dislike of the perceived policy implications of global warming). The evidence is there for everyone to see and read. I’m sure you’ve been referred to the IPCC reports before though. Perhaps try the abovementioned website/book. It’s excellent, from what I’ve read.

    How much longer do you suggest we keep postponing measures to curtail our emissions? Will you ever be satisfied that we gathered enough evidence? You wouldn’t board the plane (in my example above), yet you’re willing to continue this world-wide experiment in the face of (what most scientists consider to be) compelling evidence that it’s changing the climate. Strange. My comparison to boarding the (deemed unsafe) plane is about acting in the face of an uncertain, yet probable risk. As such, it entirely flies.

    You state that you “would bet large sums climate forecasts will NEVER be successful”. I know of some people who would be quite willing to take you up on that, e.g.

    http://julesandjames.blogspot.com/2005/06/betting-summary.html

    The only bet taken up so far (at $10,000 hopefully a large enough sum for you) is about a comparison of global surface temperatures in 1998-2003 with those in 2012-2017 (6 year average in both cases). Your bet is also eagerly awaited at http://backseatdriving.blogspot.com/2005_05_01_backseatdriving_archive.html#111700433898143899
    Good luck. I hope you win.

  9. malone Says:

    “The evidence is there for everyone to see and read”, “How much longer do you suggest we keep postponing measures to curtail our emissions?”, “extreme dislike”, “Will you ever be satisfied that we gathered enough evidence?”, “what most scientists consider to be” – give me a break. Just admit it, you think the null hypothesis is that there is a problem and I should prove otherwise. We’ll all feel better.

    The whole point of bringing up planes is to show that consensus science just doesn’t exist and that to rely on a consensus is to admit that things are not clear. To want to the whole world to do what you want them to based on consensus science (ie. confusion) is something I have no time for.

    PS. I’m not willing to bet that I know what will happen, i’m betting no’one knows.

  10. Bart Says:

    Anthropogenic global warming originally was (past tense) the alternative hypothesis. Over time the accummulating evidence has made it the mainstream scientific consensus position. The consensus grew in response to the growing body of evidence; it is the result of the application of scientific standards (see eg this presentation by Oreskes). As such, the existence of a strong consensus is entirely relevant.

    The reason I brought up my plane analogy is to show that a consensus of risk amongst experts should not be ignored.

  11. Beata Says:

    Well written article.

  12. Brian Schmidt Says:

    Bart – thanks for the link.

    Malone – I have bets specifically designed to challenge those who claim we can’t predict future temps. See, e.g.:

    http://backseatdriving.blogspot.com/2006/01/i-will-bet-that-temperatures-will-drop.html

  13. Jurrie Says:

    Dear Bart,

    We spoke online earlier today in my quest for some basic answers, whilst trying not to drown in agitation of loads of text and very little reliable substance. I read your consensus article and the discussion that followed. I opened your link to a presentation of someone named Oreskes. Loads of text and suggestive things, without giving me what I want to know.

    Could you please show me a link to the argumentation that make your 99% of climate-scientists embrace the hypothesis of a anthropogenic cause of global warming? The presentation doesn’t provide me any information on where you come to a valid conclusion that warming is triggered by CO2. Just that the two rise together cannot be the basis of a main current hypothesis your almost your entire field of science, can it??

    I must say I feel some truth in the question of Malone of how come you have the hypothesis of things being wrong already? I would like to know as well.

  14. Bart Says:

    Jurrie,

    Oreskes doesn’t explain or provide physical evidence for human induced warming, but she does explain very well how the scientists got to know what they know, and why it is relevant that their collective knowledge converged onto a consistent broad picture of what’s happening and why.

    If you want to know instead how our knowledge got shaped thatt way, including more physical explanations, I’d recommend Spencer Weart. As I replied to Malone, global warming is a prediction come true: it was predicted well over 100 years ago that increasing the levels of CO2 in the atmosphere would raise the Earth’s temperature.

    See also the three links in the middle of my blog post for more technical details. It is explained there (and Spencer Weart, link above) that it’s much more than just correlation: GHG have radiative effects, which have been known since the 19th century (see also the third point in the blog post). Without GHG, Earth’s average temperature would be -18 deg C. More GHG means more heat is trapped. That is a basic physical feature, and indeed, the onus is on someone who claims this is not the case to explain how that could possibly be.

    Based on the primary literature and conferences it is clear that most scientists find the evidence indeed very strongly pointing to a dominant human influence on current climate changes. See e.g this recent survey, where it’s found that 97% of publishing climatologists agree with that.

  15. Jurrie Says:

    Hi Bart,

    Thanks for the information! I read the whole thing and I’m going to read it a-hundred times more. My first reaction of the Spencer Weart article is that I still find it a bit incomprehensable how fast the hypotheses that CO2 levels rising cause the warming has been embraced after ’40 with all noted other research findings in the article. Of course it’s a possibility, but to say that it’s proven remains a giant mystery to me. I can’t find how it got so called ‘accepted among most scientists’. They have predominantly been looking at behaviour of CO2 in small timeframes until that point.

    I see lots of very specific studies with variying results on very small timescales in an immensely complex system that have specific outcomes, but when it comes to icecore studies it seems there is a very large (800 years) lag of the rise of researched phenomenon. CO2 concentration will still have effect for some centuries. How can that not say a bit about the accuracy of measurements in short timescales? Let alone predictions? It seems to me there is a very reasonable chance that there are still so many possibilities not even known of yet that drive our planet to behave like it does.

    I read about ‘consensus in this part of science’. What part of science is that? Is that even reasonably possible with what we have now?

    Right now I highly doubt that can be true, because to me it seems it’s just not realistic to have consensus on the accuracy of predictions on things we haven’t even scratched the surface of. Let alone me reading articles from a lot of (sometimes retired) Professors in Geology or Physics and other disciplines that are sceptical about a lot of basic assumptions. What about them? The recently published article calling for worldwide action with Kyoto, murders any possible dialog on this subject by stating there is agreement and we should do what is said by IPCC and others.

    I truely hope in some way the so called ‘99% of all climatologists agreeing’ are right, because if it turns out the models are not right and all these efforts on reducing CO2 don’t have the effect they are assumed to have right now, I think science focused on synthesis will lose its credibility bigtime. And I’d say that’s far worse than being cautious with what we see as ‘the truth’ right now.

    I’m going to dive into the material indepth the coming weeks much more than I have now and let you know what I find.

  16. Jurrie Says:

    Regarding to what you said:

    As I replied to Malone, global warming is a prediction come true: it was predicted well over 100 years ago that increasing the levels of CO2 in the atmosphere would raise the Earth’s temperature.

    But that doesn’t say anything about CO2 driving temperatures, just that there might be a relation. As far as I know it could be something totally different both react on roughly the same way.

  17. Bart Says:

    “But that doesn’t say anything about CO2 driving temperatures, just that there might be a relation. As far as I know it could be something totally different both react on roughly the same way.”

    Not without violating basic radiative physics. Greenhouse gases absorb IR radiation and re-emit in all directions. Part of that energy therefore remains within the earth-atmosphere system, that would have otherwise escaped to outer space. There is a solid grounding in physics of the temperature effect of greenhouse gases.

  18. Bart Says:

    Jurrie,

    I truly hope that the 97% (as per Doran and Zimmermann) of climatologists are actually wrong. Because if they’re right, we could be in for some serious trouble if we don’t start cleaning up our collective act real soon.

    Which hypothetical situation is worse: Having reduced our greenhouse gas emissions when later it appears that global warming is not as severe as expected, or not having reduced our greenhouse gases when later it appears that global warming is as or even more severe than expected?

  19. Martha Says:

    It seems like a reasonable thing to say: “Let’s just start reducing our emissions because that is a good thing anyway, even if there is no GW caused by humans.” However, what happens when we start trading off that goal (reducing GHGs) with other environmental factors? What if we find an energy source that releases a toxin for certain animals but has no emissions? If we have years of fear-mongering that GHGs are going to destroy the planet, it seems likely that a hasty decision might be made.

    I think we should stop polluting as much as possible, but if we’re going to have to make trade-offs in environmental policy, we should go into those decisions as unbiasedly as possible.

  20. Global Warming Says:

    Global Warming

    Scientific consensus on climate change | My view on climate change

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