A commentary on the PBS NewsHour’s report: Stalagmites Provide Clues in Changing Rainfall Patterns
It’s not often that a TV program leaves me with a visceral feeling, but that was the case during the concluding segment of the Jim Lehrer NewsHour on PBS the evening of June 2, 2009. It was a short news story on one of the most popular themes of the day, global change.
The segment, produced by Tom Clarke of Independent Television News (ITN), opened with a cave explorer crawling, squeezing through a very tight, horizontal crevice, a mere crack, at the base of a rock face deep in a cavern. I confess that I could not help having a nervous twitch of claustrophobia as I watched.
The segment had to do with a British scientific team analyzing the growth of stalagmites – those iridescent, conical rock deposits rising from the floors of caverns (stalactites grow from the cave’s roof). According to the report, as these deposits grow layer-by-layer like tree-rings over hundreds to thousands of years, they apparently record past patterns of climate in the minerals left behind by evaporating water.
Opening the story, Tom Clarke pointed out that climate scientists reconstructing weather patterns for the past have at most only a few hundred years of actual recorded data from weather stations as we know them. To compensate for our dearth of observations, two British scientists – Lisa and James Baldini of Durham University – have developed techniques where they are able to look back at climate patterns over many thousands of years. They are analyzing the composition of stalagmites from a deep cavern on mainland Europe – in Poland – to reconstruct the precipitation history of the region, and from that the behavior of the North Atlantic Oscillation, not simply for the last 100 or 200 years, but for the past 20,000 years!
The backstory went on to briefly interject comments from Adam Scaife of the British Meteorological Office – a world-class scientific agency – who explained that the North Atlantic Oscillation is a significant natural phenomenon analogous to the much better known phenomenon (among the US public in particular): El Niño in the Eastern Pacific. Dr. Scaife argued, as do many British meteorologists, that if we understood the past behavior of the North Atlantic Oscillation, we would be in an excellent position to understand past patterns of weather, which would of course provide great insight into past climate change and predict what to expect in the future.
The segment cut back and forth between images of personnel and operations in the cave, and scientists in the laboratory commenting on various aspects of the study. Samples of the rock material from the cavern are taken back to the laboratory where their chemical residue is used to deduce patterns in the North Atlantic Oscillation, hence the behavior of weather in Northern Europe over the last 20,000 years. Clearly everyone interviewed was very excited about the promising results of the investigation; a young spokesman even claiming that the signature of individual past hurricanes could be detected in the material being studied.
That last point grabbed my interest. Wow! Picking out individual hurricanes in the same breath as discussing a 20,000 year long record! Now, this is the kind of fodder I might use in my hydrology class on water and climate this fall; a general elective for the more outward looking liberal arts undergraduates of all stripes at Brown University.
Not surprisingly, then, the morning following the show, as I jogged through the woods with my twin puppies, I churned over in my mind the implications of the clip. I could not help coming back to and dwelling on the style of the message. Indeed, it is the style of such reports that is precisely why the vast majority of our society accept scientific prognostications so totally and unquestionably, and perhaps explains why we allow the Executive Branch and Congress go off on programs half-cocked. We do not have a tradition in the media for discussing the uncertainties of science; the media seems preoccupied with only what they perceive to be the fun parts, or the adventure parts, of science. Science is seen as facts; seldom do we think of science as uncertainties.
My point here is that the media, whether TV, radio or print, tends to skim only the most superficial “jazzy” elements from a scientific report. As a consequence, the viewer, listener or reader has absolutely no reference points to compare the validity of the storyline, or to assess the significance of the results except as they are led there by the commentator or the writer of the story. We were provided precious little insight into how we would get to the endgame: the deeper understanding of weather patterns over thousands of years. As the little old lady on the TV commercial used to say … where’s the beef?
But the key elements, the very foundations, of the story were untouched. It is ironic that we, as a society profess to venerate critical thinking, yet we do not insist that its canons be exercised by the media, and we require even less from our policy-makers. Certainly one does not have to be a paleo-climatologist to be impressed by the claim of one of the young scientists in the NewsHour clip that this team could extract the signature of an individual hurricane from a time series of data that purportedly went back 20,000 years. As another once said, “How does he do that?” Well, … did the NewsHour answer that? Not even close. Let alone the essential followup question, “How well did he, or in this case, they, do it?”
The “beef” of the story, of course, is what I’d call “connecting the dots”. By this I mean that any scientific study, regardless of the field, has certain benchmarks, like bases in a ballgame, to be honored, which is to say certain “dots” that need to be connected to legitimize the basis and the ultimate results of the investigation. In lofty jargon, this is referred to as the “scientific method”, but it’s also the same thought process a family goes through in in planning the household budget. Cause and effect – if this happens, that will follow. Without connecting the dots, how can you understand why the study was undertaken, the principles behind the methods used, whether in fact the method has the resolution to address the question at hand, and, if it all comes together most perfectly in the best of possible worlds, how confident might we be in the conclusions?
In my view the underlying weakness of most stories like this is that the dots are never connected. Let me take one of the basic components of the NewsHour report as an example. We do not know, or are not told, what the North Atlantic Oscillation actually is; we are not told that under the best conditions, from the most direct observations over the last half dozen decades for which we actually have the relevant weather data, the North Atlantic Oscillation is an extremely ratty signal to get any information from. In simple terms, as a historical database, the North Atlantic Oscillation is a large scale spatial and temporal variation of barometric pressure over the mid to northern Atlantic Ocean. The metric by which the strength of the North Atlantic Oscillation is quantified depends on two atmospheric phenomena that should be familiar to many Americans: the Bermuda High often referred to by our weathercasters in the North East US; and the Arctic Low, a prodigiously low-pressure atmospheric system emanating from the polar latitudes, often affecting the weather in the vicinity of Greenland, Iceland and Northern Europe. The North Atlantic Oscillation (NAO) is fundamentally the difference in magnitude of the barometric pressure beneath these two weather systems as measured at two standardized, reference weather stations: a particular weather station in Iceland and a particular sister weather station in the Azores. These two stations became the gold standard for the NAO.
Most people realize from their hometown news that their barometric pressure is extremely variable over a day, a week, a month or a year. It’s understandable that a number of responsible, credible scientists have attempted and are attempting to develop procedures through which we can extricate any long-term systematic behavior of these pressure differences, and in turn relate them to weather and climate patterns in a meaningful, predictable way. This proves challenging even for the actual observations of atmospheric pressure; even to those who have their hands on high quality data for a period of record for which actual observations are reasonably accurate, continuous and, most importantly, well-timed. Pity the challenge therefore to a scientific team that has to extricate this information from proxy data, such as the fossil tree-ring-like deposits of a stalagmite.
So let’s call this the first “dot” to be connected in our story: How well do we really understand the connectivity between the so-called North Atlantic Oscillation and the forcing terms of weather patterns crossing the “pond” of the North Atlantic? I’m not convinced that the bi-weekly to monthly forecast in Great Britain is much better than it is in Boston. Massachusetts.
And there were many other “dots” in the story that needed to be connected: What was being deposited by the drop of water running down the outside of the stalagmite? Remember, only selected mineral samples will have the right atoms bound up in their framework to carry the message. Many samples will not contain the “right” water-bound mineral atoms, but rather will contain atoms that were in the ground and picked up by the groundwater before a particular storm, or contain atoms that might be introduced into the ground by a rain event after the particular storm we are trying to trace, and fell from a completely different storm-system that originated from a totally different geographic area. This “old” water and “new” water mixes with the water of our signature droplet as it seeps through the ground before it reaches and evaporates from the sampled stalagmite.
So, dare we to ask in counterpoint, is it really possible to tease out the signature of an individual hurricane from all the other sources of water that might run down the walls of the stalagmite? Can we really make the connection to the North Atlantic Oscillation and global teleconnections?
By now, of course, we have exceeded the 10-minute time slot allotted for the Jim Lehrer story, but these are a few of the thoughts I turned over in my mind during my jog with my pups in the early morning following the program. But, truth-be-told, the story was quite good. As Jim Lehrer intended, it got me thinking. As a scientific venture, the study itself is promising. But the larger public needs to understand – and to be constantly reminded by a news media that understands – that scientific conclusions are based on procedures that need to be critically assessed at each step of their application; and that scientific results are only as good as the procedure, the data and the models used to reach them. The public needs to question the fundamental basis of the “facts” underpinning the scientific conclusions; and it needs to separate what is simply a speculation from what is a legitimate conclusion.
This perspective is critically important as major economic and political policies increasingly rely on the opinion of scientists. Or, on the other face of the coin, this perspective becomes even more important as industry and government increasingly tend to use scientific opinion as a foil to foster particular economic and political agendas that, in fact, have no, or at best ambiguous, scientific merit.
A geophysics professor at Brown University, John Hermance knows a lot about life's most necessary substance, water. He has taught hydrology and environmental geophysics for more than three decades and directed numerous field projects in Iceland, the Azores, the Yukon, and throughout the U.S. He is author of the Mathematical Primer on Groundwater Flow, published by Prentice Hall, and more than 70 peer-reviewed publications in scientific journals. His current research interests include regional-to-continental-scale hydrology, signal processing, and the application of geophysical field methods to modeling groundwater flow and related watershed processes.