Archive for the ‘Consensus’ Category

The role of scientific consensus in moving the public debate forward

February 7, 2014

Mike Hulme had an interesting essay at The Conversation, the main message of which was

In the end, the only question that matters [for the public debate about climate change] is, what are we going to do about it?

Hulme correctly argues that the basic science is clear enough so that for society the important issues to discuss are not science related, but policy related. I argued much the same here. He writes:

What matters is not whether the climate is changing (it is); nor whether human actions are to blame (they are, at the very least partly and, quite likely, largely); nor whether future climate change brings additional risks to human or non-human interests (it does).

Let’s leave the minor quibble aside that AR5 puts the anthropogenic contribution at ‘extremely likely’ having caused more than half of the recent global warming.

The part where I disagree with Hulme is where he argues that showing the existence of a scientific consensus on the above (it is warming; it’s due to us; it’s bad news) somehow stands in the way of  getting society to discuss that most important question. I think the opposite is true. It is the continuous doubt about the science, sowed by those who oppose a serious discussion about what to do, that is a stumbleblock. Showing that a consensus amongst experts exists would enable society to more swiftly move on to the important conversation on what to do about it. I agree with Hulme that on this deeply ethical question there is, and ought to be, a multitude of opinions.

As Stephan Lewandowsky and John Cook write in a response to Mike Hulme:

The public’s perception of that scientific consensus is necessary to stimulate political debate about solutions.

Another element that’s missing from this discussion is that scientific and ideological arguments  should be clearly distinguished from each other (“is” vs “ought”).

Unfortunately, ideological arguments are often dressed in a sciency-looking cloak. From that perspective, I appreciate the honesty in Lindzen stating blunty “we’ll all be dead by then”, the obvious implication being: so why care. That’s indeed what a lot comes down to: How do you value the future compared the present?

Scott Denning’s smashing presentation at Heartland climate conference ICCC6

August 13, 2011

Listen to Scott Denning’s sharp and to-the-point presentation, which he gave at Heartland’s climate conference, here. It’s worth the full 16 minutes of it. He rocks. Alternatively, read this little recap:

Denning attended the Heartland conference for the second year in a row and it seems like he’s outdone himself by giving an even better and sharper presentation than last years (which was excellent as well).

He emphasized some very important things:

- The big picture is what matters; details do not (at least in terms of policy relevance; for science nerds of course it’s different)

- Part of that big picture is that, whatever the sensitivity, a 400% increase in CO2 is going to make a big difference to the climate, because of the simple fact that adding heat warms things up.

- He offered a big challenge to the (strongly contrarian and libertarian) audience: Propose and advocate for effective solutions, otherwise others will. Policy will be enacted anyway. His challenge got particularly strong when he said “do you want Greenpeace to dictate the policy? (…) Are you cowards?”

(more…)

Eric Wolff on areas of agreement and on the public debate about climate science

May 25, 2011

Dr. Eric Wolff is spot on (see also further below): 

as an outsider to the blogosphere, it surprises me that so many people, presumably mostly with even less knowledge and training than me, seem absolutely convinced they have mastered every area of climate science.

A peculiar line-up of speakers assembled recently at the Conference on the Science and Economics of Climate Change in Cambridge: Phil Jones, Andrew Watson, John Mitchell, Michael Lockwood, Henrik Svensmark, Nils-Axel Morner, Ian Plimer, Vaclav Klaus and Nigel Lawson. Bishop Hill reports that

Dr Eric Wolff of the British Antarctic Survey tried valiantly to find a measure of agreement between the two sides.

This proved an interesting exercise and resulted in a useful list (also reproduced by Judith Curry) on what we can all agree on (perhaps excluding those too far out on the fringes; links added by me):

  1. CO2 does absorb infrared radiation
  2. The greenhouse effect (however badly named) does occur in practice: our planet and the others with an atmosphere are warmer than they would be because of the presence of water vapour and CO2.
  3. The greenhouse effect does not saturate with increasing CO2
  4. The CO2 concentration in the atmosphere has risen significantly over the last 200 years
  5. This is because of anthropogenic emissions (fossil fuels, cement production, forest clearance). [Ian Plimer disagreed, but as Curry stated: "the anthropogenic contribution is (should be) undisputed"]
  6. If we agree all these statements above, we must expect at least some warming. [Bishop Hill noted “broad agreement” with this point]
  7. The climate has warmed over the last 50 years, [as is evident from] land atmospheric temperature, marine atmospheric temperature, sea surface temperature, and (from Prof Svensmark) ocean heat content, all with a rising trend.
  8. We probably don’t agree on what has caused the warming up to now, but it seemed that Prof Lockwood and Svensmark actually agreed it was not due to solar changes, because although they disagreed on how much of the variability in the climate records is solar, they both showed solar records without a rising trend in the late 20th century. [Excellent point and ironically hitting Svensmark with a stick of his own making. Note the distinction between variability and trend.]
  9. On sea level, I said that I had a problem in the context of the day, because this was the first time I had ever been in a room where someone had claimed (as Prof Morner did) that sea level has not been rising in recent decades at all.  I therefore can’t claim we agreed, only that this was a very unusual room.  However, I suggested that we can agree that, IF it warms, sea level will rise, since ice definitely melts on warming, and the density of seawater definitely drops as you warm it.
  10. Finally we come to where the real uncertainties between scientists lie, about the strength of the feedbacks on warming induced by CO2 [i.e. climate sensitivity]

Eric Wolff also chimed in with a substantial comment over at Bishop Hill’s, rebutting some commonly heard arguments and making some very spot-on remarks:

(…)

I should first state the rationale for the summary I made at the Downing event. The meeting was about the science and economics of climate change, and I was asked to lead a discussion that came between the science talks and the two economics talks. I therefore felt the most useful thing I could do was to try to summarise what we had heard, as a basis for the discussion of whether society should do anything in response to that, and if so what. In particular I did hear a surprising number of things on which almost everyone in the room could agree, and it seemed worth emphasising that, rather than rehearsing old arguments.

I notice in the thread here several comments about who sets the “terms of the debate”, and about the “context of the debate”. While such phrasings may make sense in discussing energy policy, it is a strange way to discuss the science. Our context is the laws of physics and our observations of the Earth in action; our aim as scientists is to find out how the Earth works: this is not a matter of debate but of evidence. I think some of the comments on this blog come dangerously close to suggesting that we should first decide our energy policy, and then tell the Earth how to behave in response to it.

Regarding Plimer’s proposal that volcanic emissions were more important than we thought, (…) if volcanoes were “causing” the recent increase, then around 1800 their emissions would have had to rise above their stable long-term rate, and then stayed high. This is however a rather hypothetical discussion because the change in the isotopic composition of CO2 in the atmosphere over the industrial period is not consistent with an increased volcanic source anyway.

Regarding the idea that the “temperature increase stopped in 2000”: my point is that we know there are natural variations (due eg to El Nino) that cause runs of a few years of temperature colder than the average or a few years warmer. Look on the record at the decade around 1910 for example when there was a long run of cold years on a flat background.

Such a period superimposed on a trend would look like the last decade (but more so). The point of my analogy is that you can’t determine the trend over several months by measuring the gradient in a run of a few days. Similarly, you simply can’t determine a multidecadal trend by measuring the gradient over a few years because all you get is the “noise” of natural variability.

Professor Morner claims that globally sea level has not risen at all; he dismisses the evidence, from both satellites and the global tide gauge network, that it has. (…) There are numerous reasons why a single site can show a sea level signal, either real or apparent, that departs from the global mean.

I am not the best person to discuss models and feedbacks in detail (see comment on expertise below). However, I could not let two issues pass. Firstly, when models are run out for a century into the future, they do indeed show runs of years with flat temperatures amidst a trend (…) (because of El Nino and other natural factors). I am therefore not clear why this is evidence that something is missing. Regarding positive feedbacks: a positive feedback implies amplification, but not a system out of control; this is only the case if the sum of the gain factors is greater than 1.

Finally, a few specific issues that interested or worried me.

(…) CO2 emits infrared as well as absorbing it. (…) indeed, this property is precisely why its effects do not saturate (but fall logarithmically), because it allows the height from which the emitted radiation finally escapes to rise into regions with less and less air.

Geckko accidentally made an important point. S/he did not like the statement: “We can agree that if it warms the sea level will rise”, because it was too simplistic. Well, as a scientist I always like to boil things down to a statement that my brain can grasp, but that contains the essential explanation of an observation or process. And this one does, for example being demonstrably what was observed in going from a cold ice age world, with sea level 120 metres below the present level, to the present. However, you are right: there are factors that could make this statement false, such as increased snowfall when it warms, adding more ice into ice sheets. As soon as several such competing processes have to be taken into account, our brains cannot predict the outcome, and so we have to resort to putting all the “millions of assumptions” into a numerical model and seeing which of them “win”. An argument for models?

Coldish made a good point about expertise, and this is where I am going to go into a slightly more challenging area. I freely admit that I am not an expert on all, or even most, aspects of climate. When I reach a topic that I have not previously studied, I go to those who are experts, either in person or by reading their work. I maintain scepticism about some of their conclusions, but my working assumption is that they are intelligent and that they have probably thought of most of the issues that I will come up with. Can I observe as an outsider to the blogosphere, that it surprises me that so many people, presumably mostly with even less knowledge and training than me, seem absolutely convinced they have mastered every area of climate science.

and more so, convinced that they are right and almost all of the experts are wrong. That must be the height of hubris.

However, Coldish specifically mentioned IPCC, and I think there is also an interesting point to make about that. At the Downing event, there seemed to be two IPCCs in the room. To some it was a huge plot, masterminded by some mysterious power that manipulates troublesome scientists. To me and the scientists in the room, it is (at least in WG1) simply a set of well-researched review papers, describing the present state of the peer-reviewed literature. I mention this only because I think the former view is a type of groupthink where, because people form an extreme opinion in their private space, they think it is widely held, or even true.

Alas, Wolff’s forray into the blogosphere was short, as is evident from a short comment a while later:

Just in case anyone thinks they are addressing me with their remarks:

I thought this might indeed be a chance for a civilised discussion, and some of the respondents seem happy to have that. However there are also a lot of remarks on here that are frankly rude and aggressive, and I won’t be returning. Now I remember why I hate the blogosphere.

IPCC history and mandate

October 1, 2010

The purpose of the IPCC was to assess the state of knowledge on the various aspects of climate change including science, environmental and socio-economic impacts and response strategies.

I.e. it was meant to report on and asses the scientific knowledge. This includes the question of how much evidence and (as a result) how much agreement amongst experts (consensus) there is for human induced climate change.

Some science historians point to other important aspects of IPCC’s history. The National Academy of Sciences wrote in 1979:

A plethora of studies from diverse sources indicates a consensus that climate changes will result from man’s combustion of fossil fuels and changes in land use.

Oreskes shows that the IPCC was set up in response to the emerging consensus in the 70’s/80’s that global warming due to GHG emissions would likely become a problem.

Spencer Weart writes:

The concern [about impending climate change] gave rise to the IPCC.

And also points to the Reagan administration being in favor of the clumsy IPCC approach, hoping that it would downplay the scientists’ fears.

When pointing to scientists who disagree with the IPCC consensus, it is important to note that people can agree in basically two directions. The survey by Brown, Pielke Sr and Annan for example shows this to be an approximate bell curve: Most (45-50%) of the respondents (scientists) more or less agree with the main thrust, and sizeable minorities (15-20%) think that IPCC overstated or understated its case. I discussed this survey and the broader question of why the consensus matters before. And I probably will pick this up again soon.

Scientifically, the more uncertain areas are the most interesting. However, if I look at the political decision making in terms of emission reductions and knowledge of the big picture (and the length of time that we’ve known about this big picture, albeit in gradually more certain terms), I can’t but conclude that the politics is hopelessly lagging behind the scientific knowledge in taking this problem seriously. (see e.g. my Dutch post “tijd voor de politiek om wetenschap serieuzer te nemen”.) Of course I’m aware that there’s more that informs politics than just the science, but still, there seems to be an uncomfortably big disconnect there. Stark warnings from science are ignored at our peril.

At this point in time, the uncertainties are pretty much irrelevant for policymaking, because any realistic change in the uncertain details is not going to affect the main trust of what we know, and thus the policy response that people may favour. For the long term, of course we need to finetune our knowledge, so research is still needed. (Hey, I’m a scientist, so I kind of have to say that, right?)

As Herman Daly said:

“Focusing on them [the big picture of what we know] creates a world of relative certainty, at least as to the thrust and direction of policy.” On the other hand, focusing on the more uncertain rates and valuations creates “a world of such enormous uncertainty and complexity as to paralyze policy”.

Perhaps that’s indeed what’s happening now, also cf. Judith’s uncertainty monster and complexity monster.

“To make the point more simply, if you jump out of an airplane you need a crude parachute more than an accurate altimeter.”

Funny how Daly and Curry both address the huge issues of uncertainty and complexity and arrive at diametrically opposed strategies of dealing with them. In terms of public communication, I’m with Daly.

From the principles governing IPCC work:

The role of the IPCC is to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation.

IPCC reports should be neutral with respect to policy, although they may need to deal objectively with scientific, technical and socio-economic factors relevant to the application of particular policies.

Funnily enough, a commenter at Judith’s, Paul in Sweden, took this as proof of a “blatantly biased agenda”. Which is a little strange in light of the history of climate science and of the IPCC as mentioned above. Its mandate is a consequence of the scientific evidence for human induced climate change having become increasingly strong and societally relevant. It doesn’t state what the conclusion ought to be –it has to follow the science-, but of course it states what it’s supposed to assess.

Judith Curry also seems to suggest that the IPCC reports are working towards a predetermined conclusion, when she claims that they are akin to a legal brief (meant to persuade). If true, that should be reflected by large differences between the scientific evidence and the IPCC reports, and between scientists’ opinions and the IPCC reports.  I have not seen evidence of either.

Tom Curtis made some very thoughtful comments on the consensus thread at Judith’s, e.g.

In other words, the IPCC was tasked with reporting the consensus view of the science, were such a consensus existed; and to explain and report the differing opinions where no such consensus existed. Whether they have done that is not best judged by whether they have explained and included the opinions of every crackpot fringe group with an axe to grind on global warming; nor even those of every climatologist, no matter how small a number might support their views. Rather, they are to be judged by the agreement between the IPCC reports and the known consensus and divergences of scientific opinion.

Fortunately, we have available several anonymous surveys of the scientists opinions, which show conclusively that the IPCC reports fairly represent the consensus of relevant scientists on those topics on which it reports. (…)

The purpose of IPCC is to provided as succinctly as possible the best possible scientific advice for policy deciders to operate on. If they were required to consider all and every idea on climate change that circulates on the blogosphere; then the resulting document would be to large, and to ill organised to be usefull as a guide to policy.

Nevermind that the politicans still wouldn’t have a clue as to what is more likely true. The science has to be assessed and weighted; that is what makes the IPCC process useful. There already is another outlet for every crackpot idea out there (NIPCC report); it doesn’t need to be done by the IPCC as well.

To quote the Dutch newspaper “Volkskrant” again:

its work has political implications, but that that doesn’t mean that it’s engaged in doing politics.

And since I discussed history as well, see also my first blog post where I described the IPCC process. I don’t think anyone has read it yet, so I’d be much obliged. And while doing self-promotion, I kind a like this oldie featuring Fred Singer.

What do we know?

October 26, 2009

- The direction of the (expected) changes is clear

      – Globe is warming

      – It’s due to us

      – It’s bad news

- Carbon is forever; Aerosols are not

- Uncertainty + Inertia = Danger

That is the short version of what scientists know about climate change.

And a normative statement: 

- Science should inform policy measures. We are used to that regarding human health; we should also get used to it regarding climate change.

update: See here for a more elaborate description of the scientific consensus on climate change.

The NIPCC report: don’t be fooled

June 13, 2009

(Nederlandse samenvatting hier)              (For a sneak preview, see the bottom line below)

The new ammunition put forward by “skeptics” seems to be the Heartland InstitutesNIPCC report 2009 (“Climate change reconsidered”). It is made to resemble, at least in format and in name, the IPCC report. According to Dutch “skeptic” (and contributor to the report) Hans Labohm it completely shatters the AGW (anthropogenic global warming) theory (e.g. here, in Dutch). That’s a very bold assertion, which should be backed up by very strong evidence for it to be taken seriously. Let’s take a look at the executive summary…

Second opinion
The preface starts as follows: “Before facing major surgery, wouldn’t you want a second opinion?”
Now that’s funny. I recently described the IPCC process using the same analogy: If you get a second opinion on your health condition, and it confirms what your specialist said in the first place, your trust in the diagnosis probably increases. Now imagine that you collect the interpretations of medical professionals all over the world, and by and large they their conclusions converge to the same broad picture. This happens to be how the IPCC comes to its conclusions.
Their opening statement is actually a strong argument for going with the consensus position on a complex topic. Yet they use it to argue in the opposite direction; very peculiar.

Risk
It continues: “When a nation faces an important decision that risks its economic future, or perhaps the fate of the ecology, it should do the same.” (i.e. getting a second opinion)
Huh? Risking our economic future? If they’re talking about the costs of emission reduction, they are seriously exaggerating. Who is being alarmist here? There will be winners and losers, yes, but that’s something entirely different. Everybody has a choice to join the winners or the losers. Different from the horse races, it’s easy this time to predict who (in the long run) will be the winners and who will be the losers. Take your pick.

The usual stuff
The previous NIPCC report has already been commented on by RealClimate, and it doesn’t seem like there’s much news under the sun this time. The same old and tired arguments feature in the current report. The RealClimate article has many links that debunk the various talking points, and I’m not going to repeat all of them here. A presentation from the lead author, Fred Singer, has been briefly discussed at RealClimate as well. It’s a good example of yet another groundhog day. For those who have followed the staged ‘climate debate’, the list of authors is revealing: Many of the usual suspects, with a history so to speak.

There are the usual, to be expected arguments, like that it’s all the sun’s fault. And logical fallacies, like ‘the climate changed before without human activity being involved, so therefore it must be natural now as well’. Try that line of argument in a court of law against a pyromaniac, by saying that forest fires have always happened naturally. It won’t fly, and it reveals that this report is not about science. The good thing is, with such erroneous lines of reasoning, no specialized knowledge is needed to see that.

Degrees of uncertainty
What I didn’t expect, however, was to see otherwise interesting research be put in a context as if it somehow “falsifies the AGW theory”. In many cases, it hardly has any relevance to the attribution of current climate change, or to future projections.

Ironically, their main argument against climate modeling is its associated uncertainty (mistaking it for knowing nothing, and ignoring that uncertainty goes both ways). That doesn’t stop them from putting forward hypothetical feedbacks that have no evidence whatsoever of operating on a globally significant scale. By the way, climate modeling is mocked in the report as merely being “the opinions of scientists transformed by mathematics and obscured by complex writing”. Doesn’t sound like they know what a climate model really is.

Feedbacks
The report goes on to describe many hypothetical feedbacks in the climate system. Of course, they are all negative: They counteract the initial warming, independent of the cause for the warming. Their combined effect, is the hope, should be evidence that the climate sensitivity is an order of magnitude (!) smaller than the commonly accepted range (between 1.5 and 4.5 degrees C for a doubling of CO2). Not just 50%, no, a factor of 10, I kid you not. My alarm bells go off. Let’s see what the implications of such low climate sensitivity would be. Any climate forcing (whether natural or human induced) would be so strongly damped as to hardly have any effect on global temperatures. But then how come the globe is warming, and has warmed and cooled in the past? A logical consequence of their theory (negligible climate sensitivity) is that it’s hardly possible for the earth’s climate to change. Indeed, there is no physics-based climate model that can satisfactorily model both the current and past climates with such low climate sensitivity.

Aerosols
Many of the proposed feedbacks involve the cooling effects of aerosols. They suggest that these cooling effects are larger than reported by the IPCC. That is contradicted by climate models providing a very decent match to the observed cooling following a major volcanic eruption (emitting sulfate aerosol in the stratosphere). Moreover, some have argued that a strong aerosol radiative forcing means that the climate sensitivity has to be large in order to still be able to explain the temperature trend of the last 100 years, so they seem to be shooting in their own foot.

They come up with all kinds of hypothetical feedback mechanisms involving more natural aerosol emissions in response to global warming: Dimethylsulfide from marine phytoplankton (although a very intriguing possibility, this has never been confirmed to be a significant feedback mechanism, and there is ample evidence to the contrary, which is omitted from the report), biological aerosols (idem), carbonyl sulfide (idem), nitrous oxide (idem), and iodocompounds (idem), about which they write the following:
“Iodocompounds—created by marine algae— function as cloud condensation nuclei, which help create new clouds that reflect more incoming solar radiation back to space and thereby cool the planet.”
Nou breekt mijn klomp (“Now my clogg breaks”), as I would say in Dutch. This route to atmospheric particle formation may be important at coastal sites with exposed seaweed, but its global importance is questionable to say the very least; at present it could best be considered an interesting thought experiment. Moreover, freshly nucleated particles have to grow by about a factor of 100,000 in mass before they start affecting climate, and a lot can happen to them before they reach the necessary size.

All very interesting research topics, but to claim that they are somehow evidence for negligible climate sensitivity is an extreme example of over-interpretation. In these active areas of research, where no firm conclusions have been reached yet on global significance, they selectively cite only those articles that they can somehow spin to support their desired conclusion. I feel that I’ve read enough of this report to know what it’s worth.

Bottom line
This report exhumes a very strong and unfounded faith in negative feedbacks from nature, which are hypothetical with sometimes sketchy, often contradictory, and sometimes no evidence of actually operating at a globally significant scale. This highlights an inconsistent view of uncertainty, and an unwillingness to weigh the evidence: “If it causes cooling, the uncertainty (or lack of evidence) doesn’t matter; if it causes warming, it’s too uncertain (and no evidence strong enough) to matter”.

How would you know?
Let’s apply some of my own recommendations for non-specialists on judging sources:
- The report clearly misses the forest for the trees.
- It gives a hidden argument for going with the consensus (“second opinion”), but somehow twists that around.
- It’s characterization of the IPCC process has the smell of a conspiracy to it and is full of strawmen arguments.
- To their credit (and my surprise), I couldn’t find any obvious confusion of timescales, such as confusing weather and climate.
- It contains some embarrassing mistakes in basic logic.
- The two way cause-effect relationship between temperature and CO2 is not properly recognized.
- Their strong claim of shaking the foundations of climate science is extremely unlikely; They don’t provide compelling evidence for such an extraordinary claim; They vastly overestimate the likelihood of cooling effects (feedbacks), and underestimate, deny or ignore warming effects.
- They grossly exaggerate the economic risks of emission reduction, and downplay the risk of unmitigated climate change.
- Some of the authors have historical credentials in a relevant discipline, more than a few have not. The list of signatories at the end is very thin on relevant expertise.
- The Heartland Institute is a conservative think-tank and not a reliable source of scientific information.

Climate solutions

June 4, 2009

The public debate about the reality of human-induced climate change is perhaps mostly interesting from a psychology point of view: How come some people embrace the wishful thinking and flakey arguments from small splinter groups and distrust the evidence-based conclusions from the vast majority of relevant scientists? I think that in many cases the answer is that they don’t like the perceived consequences. In other cases it’s a matter of thinking along familiar lines. And for some, it may be the attraction of being the underdog, which, in extreme cases, leads some to think of themselves as (supporting) the new Galileo. And yet others may have been fooled into thinking that there still is a real scientific debate about the big picture (with not a little help from the popular media). After all, without reading the primary literature or attending relevant conferences, how would you know who is right? 

The more relevant discussion for society is about how to deal with climate change. How do we act in the face of uncertainty, but with real risks of problematic consequences? “Skeptics” could make a very useful contribution to such a discussion, if they started thinking about how to deal with climate change while at the same time minimizing the perceived consequences they dislike so much (e.g. taxes and regulations).

Waiting until disaster strikes (as desired ‘proof’) before starting to deal with the problem, is not a rational option. If a doctor is 90% certain that you have a dangerous illness, you probably want to start treatment as soon as possible. Or would you wait with treatment until the doctor is 99% or 100% certain? The problem is, doctors and scientists are never 100% certain.

 

So what do we do?

 

I’ll be writing more about this question in the near future. Specific topics that I intend to discuss are geo-engineering (intentional engineering of the Earth’s climate), biomass, transport options (biomass/hydrogen/electric powered vehicles), and others. These are not all clear-cut ‘solutions’, and their suitability in dealing with the problem is vigorously debated, including in the scientific arena. Finally some real debate, rather than the fake stuff.

Who to believe?

February 8, 2009

 

Amidst all the different information about climate change, how is a layperson going to know who is right? There are a few clues one could follow, that don’t require any specialized knowledge.

 

-          Seeing the forest for the trees. Nitpicking on small details, and then claiming or insinuating that this challenges the foundation of a whole scientific field. Over-interpreting the significance of a specific finding. This is by far the most prevalent style of argument that one has to watch out for. It usually goes something like “This particular study proves that global warming isn’t due to greenhouse gases”. People tend to forget that observing a bird in the sky doesn’t disprove gravity.

-     Consensus matters. If you get a second opinion on your health condition, and it confirms what your specialist said in the first place, your trust in the diagnosis probably increases. Now imagine that you collect the interpretations of medical professionals all over the world, and by and large they their conclusions converge to the same broad picture. This happens to be how the IPCC comes to its conclusions. If the professionals do their work seriously, than the existence of a consensus amongst them is absolutely relevant (though of course it is not absolute proof). The only way in which you can ignore a consensus as being irrelevant, is if you can somehow show that the professionals are all lying or incompetent. (See the next clue for what that brings you into.) Oreskes has an excellent presentation on this.

-          Beware of conspiracy theories. The consensus wouldn’t matter if somehow all those scientists had bought into the same conspiracy of wanting to take away your SUV. (Don’t laugh, there are many people who seem to think this way.)

-          Timescales. Climate is defined as the average weather over 30 years. (Year-to-year variability usually averages out over 30 years). Weather and climate are very frequently confused in the popular debate.

-          Spatial scales. Combined with the previous one, an example would be: “It was a very cold winter in the US this year (so global warming is a farce)”. This is also used the other way around: “It was a very warm winter in the US this year (so global warming is getting worse)”. Both are equally silly conclusions.

-          Logic. Some of the most heard ‘skeptical’ arguments don’t stand up to basic logic, and no knowledge of climate is needed to see that. Example: “Climate has always changed, so it is not caused by humans.” It wasn’t in the past, but that’s no evidence that it isn’t now. Try that line of argument in a court of law against a pyromaniac, by saying that forest fires have always happened naturally; it won’t fly.

-          Confusion of cause and effect. A consensus emerged as a result of the strength of the accumulated evidence, not the other way around. Activists may try to persuade you to trade in your SUV for a Prius because they’re worried about climate change; not the other way around. A tricky one is temperature and CO2: They influence each other both ways. (see also here

-          Think in terms of likelihood. How likely is the previous proposition of a mass conspiracy amongst stubborn scientists? How likely is it that scientists have for decades overlooked this little finding that supposedly shakes the foundations of a relatively well established science?

-          Think in terms of risk. What if we take measures against global warming and it turns out less bad than expected? What if we don’t take measures against global warming and it turns out worse than expected? (False positive and false negative, respectively. See also this comment at RealClimate) 

-          Check for consistency. If someone sais (rightfully) that one particular event (e.g. Kathrina) is not proof of man-made climate change, but then claims that the current cold winter is proof against, you should raise your eyebrows.

-          Expertise. In gauging the credibility of a source, their expertise is important to consider. When it concerns your health, you usually trust a doctor’s opinion more than that of a software engineer. It is not unreasonable to trust a climate scientist more than a doctor when it concerns climate. Of course this is not proof, but there is a difference in likelihood of them knowing what they’re talking about.

-          Motive. The credibility of a source also depends on their motives, both on economic and ideological grounds, for telling you a certain side of the story. What vested interests, if any, are there to the different sides of the story? In a worldview where government interference is deeply hated, could it be tempting to distort evidence that could possibly lead to calls for government action? In a worldview where societal problems are preferably tackled by government, does it make any sense to make up a phony problem to call for government action? I don’t know anyone who wants government action on a phony problem just for the sake of it. Don’t underestimate the power of ideology, but always include a sanity check. See also here and here.

 

This list is not exhaustive, so if you have other pointers to add to make sense of the public debate on climate change, please share them in a comment. Similar issues of weeding through sources have been discussed in a number of thoughtful posts here, e.g. this one on cherry picking. Other good discussions here, here and here.

 

Ideally, you would critically assess the evidence for each position to form a well founded opinion on anthropogenic global warming (AGW). In the absence of time to do so, you need to take some shortcuts to assess the flood of information about the topic. None of the clues discussed here constitute proof for or against AGW, but applying multiple clues simultaneously to gauge the credibility of a source can be helpful to ‘distinguish the chaff from the grain’ (het kaf van het koren te scheiden, as we say in Dutch).

 

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

June 14, 2008

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?

Scientific consensus on climate change

June 1, 2008

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.

Follow

Get every new post delivered to your Inbox.

Join 124 other followers