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).