By Dr. Robert Thorson

A gnawing sense of uncertainty. Perhaps that will motivate us to move faster on climate change than all the predictions in the world.

In their recent book, “Climate Change and Biodiversity,” conservation biologists Thomas E. Lovejoy and Lee Hannah write “Much has been learned that is new, and yet our understanding is dwarfed by the vast and complex changes to come.” There are two principal sources of uncertainty. First, “species respond to climate change individually and idiosyncratically, not as coherent communities.” Second, natural systems more fundamental than ecology are simply too complex to predict at the level of detail we are comfortable with.

With respect to individual species, there are dozens of excellent case histories discussed in the volume from polar bears to avian malaria. My main concern is with the subspecies of Homo sapiens now sprawling across the sun-baked cities of the American West. What will their population look like when individual families give up this unsustainable existence and seek cooler moister climes? Consider Nevada, where the population increased an astonishing 66 percent from 1990 to 2000, based on the last U.S. census, much of it near Las Vegas. The remaining four of the top five highgrowth states — Arizona (40 percent), Colorado (31percent), Utah (30 percent) and Idaho (29 percent) — also have cities sprawling into triple digit heat waves.

From Idaho to Texas the wildfires are spreading, the water budget is shrinking and the demand for electricity — especially for air conditioning — is growing. Much of this demand is being met by burning coal, the worst carbon emitter of all, despite great opportunities for solar, wind and geothermal power. (And what about nuclear power? Well, we haven’t heard much about that since Nevada’s Harry Reid became Senate Majority Leader. Before his election, the nation was actively developing its first permanent radioactive waste disposal site at Yucca Mountain, Nev. Things are now more or less on hold.) Can anyone predict where the Homo sapiens from western cities will go when they give up for lack of water, the elixir of life?

Uncertainty about the future also stems from the complexity of natural systems. Consider weather forecasters. Despite Doppler radar, geostationary satellites and automated computer models, they still frequently get it wrong, becoming the butt of many jokes. This July 4th for example, communities such as Newport, R.I. launched their fireworks in steady, heavy rain because they had to abide by a decision based on a morning weather forecast. Smaller adjacent communities looked at the sky at night and rescheduled. TV weather forecasters are what amounts to good-looking witch doctors, especially in places like New England. Their job is to put a human face on the mysteries of the atmosphere.

Yet these meteorologists have it easy compared to hydrologists. That’s because the job of the hydrologist is to forecast soil moisture, snow pack thickness, groundwater budgets and river discharge based on the predictions of the meteorologist. And the hydrologists have it easy compared to the ecologists, whose job it is to forecast species migrations and food webs based on the predictions of the hydrologists.

To illustrate the complexity in the middle of this chain of logic, consider the headline from an article published by Richard Kerr in last month’s Science: “River-level forecasting shows no detectable progress in 2 decades.” The physics of river forecasting is straightforward, and hydrologists are doing a fairly decent job. But despite two decades of hard effort, they are not doing any better now than before, at least not for the 11 large Missouri River flow stations examined. There are just too many variables involved — slope, soil, direction, temperature, irrigation, snow, moisture, wind, permeability, etc.

Thinking about complexity gave me an idea. What if concerned scientists like me gave up trying to predict the future and parroted what the climate change naysayers have been saying all along: “We just don’t know.” Would this confession translate to the body politic as yet another reason to marvel at the mysteries of nature? Or would it translate as gnawing apprehension for the future? In either case, would that be enough to make us stop burning coal to cool our bodies in places where it’s naturally hot?

I just don’t know.