How do we know there’s a consensus, and why does it matter?


Investigating the consensus

In a study of over 900 scientific articles that had the keywords “climate change”, Oreskes found none (!) that disagreed with the consensus position (see here). That doesn’t mean that there weren’t any articles promoting a different view than the consensus position. (Articles that didn’t have the keyword “climate change” in their listing were not included in Oreskes’ review after all.) I’ve read quite a few papers myself that oppose the consensus view. But they can hardly be very many, relatively speaking. Otherwise Oreskes’ review would not have resulted in zero “skeptical” articles.

Almost all relevant scientific organizations and National Academies of Science endorse the consensus view that recent climate change is for a large part due to human activity. Even the most recent statement from the organization of petroleum engineers (!) acknowledges that recent climate change is linkes to human activity. A large scale review of the scientific literature, undertaken and endorsed by many, many scientists working in the field, is more trustworthy than any individual’s book or article or website. (Yes, that includes this one. You’ll get the most complete and balanced picture of climate change by reading the IPCC reports)

A recent survey of scientists having authored a recent journal article on climate change found that the majority concurred with the IPCC position. A sizeable minority was of the opinion that the IPCC reports overstate the importance of and/or certainty regarding CO2 compared to other forcings (both natural and anthropogenic!). Only very few respondents were of the “skeptical” opinion that warming is predominantly natural. Nobody denied that the globe is warming. A large minority found the IPCC too cautious, understating the human influence on climate and/or the seriousness of the problem. Note that the authors do not claim that their survey is representative; less then 10% of the 1800 scientists contacted replied. Moreover, the positions that respondents had to choose between were sometimes a little ambiguous.

In an excellent presentation, Naomi Oreskes provides an overview through history to show that this consensus is actually much older than the IPCC process; the IPCC was set-up in response to the growing consensus that emerged in the late seventies. And already before World War II global warming was recognized by individual scientists. This begs the question why it takes society so long to recognize the problem, and do something about it? The second half of her presentation (similar powerpoint presentation here), Oreskes explains one of the reasons why: A successful campaign to create doubt in people’s minds about the reality of climate change, along similar lines (and starring some of the same people) as the campaign to downplay the risks of smoking. See also here and here.


Proof versus probability

Does having a broad consensus automatically make something true? No. Is there absolute proof that the climate is changing, that it is predominantly caused by human activity, and that the consequences will be severe? No, there is not (at least not in the absolute, mathematical sense). Do we need proof? If yes, then we have to wait until the disaster strikes, and even then we cannot possibly prove the abovementioned claims. 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?

Everybody makes decisions each day based on an assessment of the probability of something happening, and the consequences (positive and negative) of when it happens. Governments make policy based on such probabilities. Many of these probabilities are much weaker constrained by scientific knowledge than climate change is.

How many types of insurance do you have? You have these not because accidents are so likely to happen, but often because the effects if they happen are severe. With unmitigated climate change, not only are the effects potentially severe, but the chance of severe consequences is rather high. Isn’t that worth insuring ourselves against? Isn’t that worth serious attempts to decrease the likelihood of those consequences materializing? If you want proof, please go and find yourself another planet to play Russian roulette with. Go and board that plane. But don’t force me and my children to join you. I better be safe than sorry.


Scientific Progress

Scientific progress is a usually a gradual process. “Skeptics” and their supporters often bring up Galileo as an example of that the scientific consensus can also be wrong, and has been wrong in the past. True enough, but for every Galileo there probably are thousands of “fossil fools”. Actually, the theory that increasing the concentration of greenhouse gases could influence the climate was perceived as wildly strange and improbable at the time of its first proposition (late nineteenth century). But rather than that one person suddenly overturned current wisdom, it is a matter of accumulating evidence by many scientists over a long time period that gradually changes and sharpens the scientific picture of what is happening. That is typically how scientific progress works these days: cumulative, piece by piece. The likelihood that a tiny minority of scientists, or some new piece of evidence, radically alters this picture is very small indeed. New evidence has to be reconciled with the existing mountain of evidence; it doesn’t simply replace it. Observing a bird in the air doesn’t disprove gravity. Small changes here and there in our understanding of specifics, that happens all the time. That’s how the mountain of evidence has been built in the first place, and that is how it continues to be shaped. That’s science at work.


What if the consensus is wrong?

The only way in which the consensus view could be “wrong” is that the effect of greenhouse gases on climate is smaller than currently thought. No warming effect from greenhouse gases at all is physically impossible (the earth would be 30 degrees colder than it currently is if there were no greenhouse effect). If warming will be less severe, it means that we have some more time to take serious action; not that we can forget about doing anything about it. It reminds me of a guy’s t-shirt I once saw with the text: “Sex is like pizza. If it’s good, it’s really good. If it’s bad, it’s still pretty good”. Well, perhaps we could say that “Climate change is like Brussels sprouts. If it’s bad, it’s really bad. If it’s good, it’s still pretty bad”.

If the contribution from greenhouse gases to climate change is smaller and the contribution from natural sources is larger than currently thought, we would have to curtail their emissions even more to stabilize the climate. If a situation is undesirable (global warming), you should change the things you can (greenhouse gas emissions), and accept the things you cannot change (the sun). Not reducing our greenhouse gas emissions is simply not an option.

Fossil fuels are finite, and it is only a matter of time that the oil production will start to decline. We will have to develop alternative energy sources. There is still plenty of coal, but the air pollution that it causes is reason enough to curtail its use. Already now hundreds of thousands of people die prematurely from air pollution. The CO2 that is emitted form fossil fuel burning causes the oceans to become more acidic, with potentially severe consequences for ocean life and fisheries. There are also geo-political reasons to want to become less reliant on fossil fuels, and oil in particular. Reducing our greenhouse gas emissions by changing our energy system and agricultural practices does not only cost money; it also creates (economic) opportunities. There will be winners and losers. The ones foreseeing that they’re losing are often the ones claiming the loudest that climate change is not occurring, or is natural, or even beneficial. All in all, developing alternative energy sources makes a lot of sense for many other reasons than climate change.


What if the consensus is right?

That one’s easy. We better be happy that we started reducing our greenhouse emissions soon and strongly. Act and vote accordingly. And don’t move to the Netherlands, as I did.


Final remarks

Which situation would you be rather in: 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 even more severe than expected?


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4 Responses to “How do we know there’s a consensus, and why does it matter?”

  1. Paulidan Says:

    The only way the consensus could be wrong is if the temperature predictions in their models do not match observed reality. They do not match and therefor the consensus is wrong.

    Where they do not match

    1) 2000-2010 will see about .3 degrees of warming.

    2) The tropical troposphere will warm the fastest.

    3) The poles will BOTH warm faster than the rest of the earth surface.

    The reality is

    1) This decade is seeing pronounced cooling

    2) The tropical troposphere is cooling.

    3) Antarctica is cooling and the arctic is warming, this decoupling completely contradicts the ex cathedra Word of the consensus.

  2. Bart Says:

    1) The trends in predictions and observations since 1975 are both around 0.2 degrees of warming per decade (not 0.3) and agree very well. I learned in high school that climate is the average of the weather over 30 years. 8 years is too short of a period to clearly observe a change in the climate amidst the variability of the weather. Or would you claim that global warming stopped in 1980 and 1990 as well? (See e.g.

    2) There is no clear model-data discrepancy in tropical tropospheric trends once you take the systematic uncertainties in data and models seriously.

    3) It has been both predicted and observed that the Antarctic continent will hardly warm. (As an aside: all other continents have warmed significantly, and most people live on one the others.) This is primarily due to the large heat capacity of the Southern Ocean surrounding the Antarctic. (See e.g.

    You are clutching at straws.

  3. Peter Simmons Says:

    First poster is a denier, how apt. They appear like flies around a dog turd. Full of the usual garbage that passes for knowledge among the ignorant and ill-educated. Such as ‘This decade is seeing pronounced cooling’ when everyone knows just by living in the world that it’s been getting hotter; this year alone Norfolk UK has been hotter than Delhi [India] on at least one day. Everywhere people, forecasters and scientists have been talking about it getting hotter, and this mug claims its cooler. Having to have to admit to the arctic warming, after all, a shipping route for the first time in how long can’t be ignored even by idiots. There are also signs that antarctica isn’t warming at the same rate, but no one has ever claimed there would be uniform effects, many mechanisms are involved with climate, obviously far too complex for deniers to grasp.
    It was a bad move, to the Netherlands, but then I moved to the North Sea coast of Norfolk, as flat as the Netherlands since we used to be connected before the seas rose last time. Since sea level rise is presently measured at 3.6mm a year, I think I’m ok with the time I have left on the planet, but half look forward to the excitement of major flooding events, and I have an inflateable ready and waiting! I can see three offshore windfarms along the coast, a sign of hope to someone with grandchildren and concerned they will have no future along with my existing concerns with the other species we are consigning to extinction along the way. Deniers aren’t concerned with any other species, or even other humans, just themselves. But their world is about to come crashing down, evidence points to a speeding up, with many feedback mechanisms to account for it.
    I would love it to have all been a mistake, for all the denier claims to be correct, it would mean hope for my grandchildren. But since science isn’t on their side, and science always gets at the truth, I can’t see that happening.

  4. Rachel Says:

    I completely agree with you about brussels sprouts! Yuk!

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