Guest essay by Kip Hansen, St Thomas, USVI
The AMERICAN METEOROLOGICAL SOCIETY just published a Special Supplement to the Bulletin of the American Meteorological Society titled: EXPLAINING EXTREME EVENTS OF 2012 FROM A CLIMATE PERSPECTIVE edited by Thomas C. Peterson, Martin P. Hoerling, Peter A. Stott, and Stephanie C. Herring. [hereafter EEE2012].
Kenneth Chang at the New York Times reported on the findings in an article, “Research Cites Role of Warming in Extremes”, on 5 September 2013. In this piece, Chang includes the following paragraph, which was picked up and repeated in the Andy Revkin’s NY Times Opinion Page blog, Dot.Earth, filed under Climate Change:
“The articles’ editors likened climate change to someone habitually driving a bit over the speed limit. Even if the speeding itself is unlikely to directly cause an accident, it increases the likelihood that something else — a wet road or a distracting text message — will do so and that the accident, when it occurs, will be more calamitous.”
This is unfortunate, for two reasons:
1) The articles’ editors said no such thing.
2) Even if they had, what Chang says just happens not to be true in and of itself.
Andy Revkin , doubling down on Chang, says: “Ken Chang’s news article in The Times ….. includes an apt analogy used in the introduction to the studies: [followed by the paragraph quoted above].” This too is unfortunately not true, for the above two reasons, an analogy can’t be apt if it wasn’t made and isn’t true, , and the fact that the analogy being referred to appears not in the introduction, but in the CONCLUSIONS AND EPILOGUE section, written by Thomas C. Peterson, Peter A. Stott, Stephanie C. Herring, and Martin P. Hoerling.
What Peterson et al actually said was:
“To help understand the difficulty of determining the anthropogenic contribution to specific extreme events, consider this driving analogy (UCAR 2012). “Adding just a little bit of speed to your highway commute each month can substantially raise the odds that you’ll get hurt some day. But if an accident does occur, the primary cause may not be your speed itself: it could be a wet road or a texting driver.” Similarly, while climate models may indicate a human effect is causing increases in the chances of having extremely high precipitation in a region (much like speeding increases the chances of having an accident), natural variability can still be the primary factor in any individual extreme event. The difficulty in determining the precise sensitivity of, according to our analogy, driving speed on risks of accidents in particular conditions (wet roads, texting drivers) can explain why somewhat different analyses of the same meteorological event can reach somewhat different conclusions about the extent to which human influence has altered the likelihood and magnitude of the event.” [EEE2012, page 64]
Point 1: The editors said no such thing:
Notice that Peterson says nothing about speed limits, nothing about speeding, and nothing about any subsequent accident being “more calamitous” – nothing at all about any of these three points. Chang makes up his own, new and improved analogy. Why? We can’t know – as a journalist, he should have reported what was actually said.
Point 2: Even if they had, what Chang says just happens not to be true in and of itself.
It is a long term, well understood fact that the safest driving speed on America’s highways is “a bit over the speed limit” – actually, more specifically, a bit over the average speed of the traffic on the road, which is often, on a wide open road, at or just a little bit over the speed limit. This is known as Solomon’s Curve, or the Crash Risk Curve, a graph that shows the least accidents happen to those who drive just a bit faster than the flow of traffic. Note that this has nothing to do with absolute speed (for example, 55 mph vs. 75 mph) but speed relative to the other cars and trucks.
So, was what was said in EEE2012 true?
“Adding just a little bit of speed to your highway commute each month can substantially raise the odds that you’ll get hurt some day.”
If you generally drive slower than the flow of traffic, if you are a strict 55 mph’er on an Interstate that flows at 67 1/2 mph, you’ll be safer if you “add a little bit of speed”, because you be involved in fewer (statistically) accidents. However, if you are recklessly already driving 75 mph on the same Interstate, and add a little bit of speed, you’ll be increasing your risk of accident and increasing the kinetic energy of any resulting crash (the last true for the 55 mph’er too).
On its face, in a plain everyday English sense, I’d say the analogy is false as used, because, well, it depends. But I’ll leave it up to the traffic engineers and statisticians — way too much wiggle-room in the phrases “just a little bit of speed” and “can substantially raise”.
My advice to journalists: Use direct quotes, stick to the facts, don’t make stuff up (and for Andy Revkin – don’t trust other journalists to have done these things, check them yourself).
My advice to Climate Scientists: Use analogies that are proven and demonstrably true – not just ones that seem true or sound nice, stick to the facts and don’t make stuff up.
Solomon’s Curve at http://www.econ.ucdavis.edu/faculty/fzfeens/trans/Transport-lecture4.ppt , see slides 53 and 55