A Nagging Uncertainty

Recently, a small item surfaced in Google News that caught my attention. This article was about a group of scientists from Yale who had just completed what amounts to a census of the world’s trees. After several years of work involving researchers from around the world, the team came up with an estimate of just over three trillion, or about 420 trees for every living human.

By any measure that’s a lot of trees. It’s also a eight-fold increase over the previous best guess of around four hundred billion. The new estimate results from a refined method. Previous estimates were largely derived from aerial images, which turn out not to be not all that good for estimating actual numbers. So for this latest effort, scientists relied on a host of independent studies in which researchers actually went into the wild all over the world and counted trees by hand. This manual method, combined with an improved system for estimating aerial images, led to the higher number.

Of the total, about 1.39 trillion trees are estimated to grow in the tropics and sub-tropics, 0.61 trillion in temperate regions, and 0.74 trillion in the boreal regions, the high-latitude forests that circle the north polar region just below the tundra.

Experts in the field rush to point out that there are many uncertainties in this tally, however. The official estimate is on the low end of the probable range; the actual number could be anywhere from three to ten times higher. The study’s authors acknowledge that this latest effort is hardly the last word on the matter.

And we thank them for their refreshing candor. Because so often we encounter the opposite, in which experts or those who purport to speak for them deliver gravely and improbably precise projections with the assurance that there is little if any room for doubt as to their accuracy.

This finding is yet another example of the uncertainties inherent in understanding the natural world. The idea seems to have taken hold that we humans pretty much have things all figured out, that there is nothing new, there are no surprises, and so now it’s just down to hashing out fine details. And then something like this comes along and blows that certainty right out of the water.

What’s interesting about this result is that as large scientific problems go, this one is relatively straightforward and ought to generate minimal uncertainty. By definition your objectives are completely visible, they don’t move around and muck up your count, their numbers don’t change significantly over time, and their magnitude is not influenced by any other interlinked variables. It’s just a bunch of static objects spread out over a large area. How hard can it be just to count them?

Yet somehow it is. Think about it: The best efforts of capable, dedicated, highly trained individuals using the best methods available produced an estimate that overturns by a factor of eight the previous official best estimate, which was itself achieved by trained and capable individuals using the best and most current methods available. And this new figure may be in error by as much as a factor of ten, by the authors’ own admission.

Keep this in mind the next time some self-proclaimed expert body claims to be able to accurately predict, far into the future, the behavior of natural systems, for example our planet’s climate, that are vastly more complex and less well-understood.




© 2015 By Scott P. Snell

Right of reuse is freely granted with proper attribution.

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