Several years ago a college in Colorado issued a report that confidently predicted the precise levels of retreat of snowlines at ski areas in the Rocky Mountains during coming years as greenhouse gases accumulate in the atmosphere. By 2081, for example, the report predicted Taos will lose 89 percent of its April 1 snowpack.

No doubt, there is value in estimating snow retreat. Climatic change is already happening, and the large majority of scientists believe that the greenhouse gases resulting from the burning of fossil fuels play a substantial or even overwhelming role. Projections like the one above suggest the magnitude of change being contemplated.

But too often, the story of climate change gets oversimplified or oversold. In some cases, predictions like the one above become branded with a certainty that just does not yet exist—and may never exist.

In fact, global warming theory is rife with gaps. Scientists believe they have the big picture right. Temperatures will rise—that is clearly understood. But whether the increases will be 2º F or 10º F in the next 100 years, no one can say for sure. Precipitation levels remain uncertain. Above all, while scientists say they understand the global energy balance well, local energy balances are more uncertain.


FACT V. PREDICTION

Among the biggest gaps in the computer models is how clouds operate. They reflect light and hence heat. But they also prevent the loss of heat. What’s the difference between a winter night with clouds and one without? The energy balance isn’t clearly understood, a big question mark given that clouds—water vapor—represent 60 percent of the greenhouse effect.

Neither do scientists understand many of the physical processes, such as those involving moisture produced by plants, which may play a role in influencing the rate of climate change. Also, how will plants react to higher levels of carbon dioxide? If plants disappear, because of more drought (as is predicted for the American Southwest), scientists say temperatures are likely to become more extreme, like the Sahara—both hotter by day and colder by night.

Computers still lack the power to fully reflect the complexity of atmospheric processes and topography, including mountains. Until recently, the Rocky Mountains and Sierra Nevada were only the slightest bumps in global circulation models. Even newer, more powerful computer models continue to deliver somewhat vague images of the future in localized areas, far fuzzier than the pinpoint-sharp images suggested by many studies.

Does any of this uncertainty suggest ski areas—and our planetary civilizations—can continue business as usual? No. But knowing the uncertainties makes at least some climate scientists a bit uneasy by the brashness of seeming supporters.


THE LIMITS OF SCIENCE

Kevin Trenberth, a native of New Zealand, heads the climate analysis section of the National Center for Atmospheric Research. He admits to squirming a bit when hearing some blanket statements from Al Gore and others. “We know enough to know there is a substantial problem, and the planet will become a very different planet in 50 years, based on our current knowledge. But the science is far from being done in terms of specifying any detail about that, especially locally and regionally,” says Trenberth, who was lead author of the scientific assessments issued in 1995, 2001 and 2007 by the Intergovernmental Panel on Climate Change (IPCC).

“I don’t think people have accurately reflected those uncertainties in their statements about the future,” he says, referring especially to some environmental groups. While there are compelling reasons to change our combustion of fossil fuels, he went on to say, climate change, unlike the disappearing ozone hole, is not necessarily an unmitigated disaster. “If it occurs gradually enough, some of the changes are not necessarily bad, and I don’t think that is sometimes adequately appreciated.”

There will be, Trenberth says, both winners and losers. Houston and Miami will lose because of rising sea levels. The Rocky Mountains, being high and inland, might be OK in the shorter time frame, but lose in the longer term because of increased wildland fires, longer droughts, and far shorter and warmer winters. Ski areas, in time, could become big-time losers as they’re currently operated, unless the change is slowed.

This is not to suggest that there is unanimity about global warming theory. There is not. The dissent cannot be simplistically attributed to brainless “deniers.” Particularly those scientists trained as meteorologists have reservations. There are others, as well, including Freeman Dyson, a highly regarded theoretical physicist and mathematician, whose skepticism on aspects of global warming theory was documented in a New York Times Magazine profile published in March.

One long-standing critic is Roger Pielke Sr., a senior research associate in the Department of Atmospheric and Oceanic Sciences at the University of Colorado-Boulder. Pielke does not dispute that the climate is changing. He does argue the relative responsibility of various causes. For decades he has maintained that mainstream climate change theory attributes too much causality to emissions of carbon dioxide, the most common greenhouse gas emitted by human activity. He believes that changes in land use resulting from the activities of people and what he describes as the spatial variations in pollution particles bear at least equal responsibility.

“Tropical deforestation clearly has an effect on both regional and global climate that is at least as important as the radiative effect of adding carbon dioxide,” Pielke told one interviewer in 2007, and he made similar comments to a Congressional committee in 2008. The role of land resource processes was underreported in the body of the 2007 IPCC report, he claims, and essentially ignored in the companion IPCC Statement for Policymakers.

Aerosols—tiny particles suspended in the atmosphere resulting from wildfires, combustion of fossil fuels, and dust storms—also have an underappreciated role, he insists.

If Pielke is correct, reduction of carbon dioxide should be just one of a host of menu options. “The current focus on using reductions in C02 emissions as the primary currency for achieving benefits to society and the environment clearly represents a very flawed approach,” he told EcoWorld.com.

Trenberth—and the majority of climate change scientists—reject many of Pielke’s assertions as overstated or downright wrong. But Trenberth readily concedes the failure of computer global climate models to reflect the enormous heterogeneity of land surfaces. “You need only look out the window to see all the different human influences, the roads and villages and towns, that are altering the landscape,” he says. “Those are not adequately dealt with in climate models, there’s no doubt about that.”


THE LITTLE PICTURE: FUZZY

Yet some factors are more important than others. Trenberth believes that the aerosol production from cities, while able to influence weather and ultimately the climate on a local and even regional scale, does not have global influence. More consequential, he says, is the inability of computer models to accurately represent mountains.

Mountains have enormous influence on local and regional climate. Every ski area operator understands that. (So do skiers themselves.) Beaver Creek and Vail can have very different storms, despite being virtually the same elevation and only 10 miles apart. Archaeologists studying the last 10,000 years in Colorado say adjacent river basins have not shifted in complete tandem. They may both get wetter, but in different increments despite being only 50 to 100 miles apart.

Computer models do not capture any of this delicacy. They remain coarse. The basic working unit of global circulation models are squares called cells. Cells in the global circulation models used to prepare the 2007 IPCC report were 300 miles across. That could put Park City, Utah, and Winter Park, Colo., in the same cell. Intuitively, that would seem satisfactory. But that same dimension could also group Aspen and Dalhart, Texas, which seems less intuitive. The cells are only rough approximations of reality.

For global temperature, this coarseness matters little, if at all. Temperatures rise, and as temperatures rise the snow will turn to rain or else melt more rapidly. That in itself says snowlines will be rising. But how much snow will there be? That’s a more difficult prediction—and computer models have not answered with much agreement. Models for the American Southwest, including the ski areas in Colorado and Utah, all agree on significant temperatures increases, but there’s no consensus on projections about precipitation.

Someone with a special interest in mountains is Mark Williams, a fellow at the University of Colorado’s Institute of Arctic and Alpine Research. Known for wearing florid Hawaiian shirts in all seasons, Williams once owned a backcountry cross-country ski area in California, not far from Mammoth. In addition to teaching geography, in recent years he has made a cottage business of helping ski areas understand what lies ahead for them, conducting studies of the effects of a warming climate on skiing at Aspen and Park City. He is now at work on projections for two other, unidentified ski areas.

One notable uncertainty he sees is the quality of snow. Will it be light or dense, champagne or syrupy? The relatively density depends upon such things as soil radiation, wind speeds, and relatively humidity, none of which are built into existing climate models. When that happens, “then we can predict how good the skiing will be,” says Williams.


THE BIG PICTURE: CLOUDY

In the last few years, more powerful computers have become available. One such computer is operated by the U.S. Department of Energy laboratories. Newer models reduce the cell sizes down to 150 miles—better, but still coarse. Now eagerly being awaited is full funding for a $3 billion computing center planned in Cheyenne, Wyo. But even with these computers, NCAR’s Trenberth warns against expecting too much. Doubling the resolution of a model requires a 16-fold increase in computing power to fully reflect the dimensions of time, verticality and the four directions of spatial relationships.

Of course, the computer models have been wrong on some counts, but not in a way that provides comfort to skeptics. Forty percent of the Arctic sea ice melted in the summer of 2007—a milestone computer models predicted would only be reached several decades into the future. “We were all pretty shocked,” says Jim White, director of the Institute of Arctic and Alpine Research and professor of geological sciences. “We were surprised at how quickly it came. All the models called for the collapse of the sea ice, but at 2050 to 2070. None of them had it in 2007.”

New England ski areas should pay close attention to this issue of Arctic ice, says White. The amount of ice in the Arctic contributes importantly to the continuation of blasts of cold air that enable the production of snow, he says. They need the blasts of cold air from the Arctic to fuel snowfall. Less sea ice during fall and spring, says White, is probably causing less snowfall in the shoulder seasons.

The pockets of cold air in the Arctic also matter to other places, as they can influence the path of the jet stream. And as the jet stream goes, so go the storm tracks. But how quickly will the ice melt? How will it influence the jet stream? Again, there are uncertainties. That also applies to the great sheets of ice covering Greenland and West Antarctica.

The oceans themselves are at the frontier of knowledge. Trenberth says the melting of glaciers and heating of the ocean, which causes water to expand, is increasing the sea level by an average of three millimeters per year. Still, there are gaps. “We can’t put it all quite together at the moment,” says Trenberth. The ocean, he says, is “still a frontier.”

Clouds also remain poorly understood. New satellites, called CloudSat and Calipso, are expected to better represent clouds in climate models, and Trenberth hopes that mining old satellite data will also yield insights. “That is a major effort in regard to clouds,” he adds.

There’s also the task of tracking carbon emissions. Despite steady land-based measurements of carbon dioxide, scientists want a better understanding of where it’s coming from and where it’s going to. A satellite put into space from Japan was part of that effort, and high hopes also resided in a $278 million satellite launched by the National Atmospheric and Science Administration in February—which crashed into the atmosphere—causing broad dismay among scientists.

And, finally, there is the role of natural variability in changes now being observed. Nobody disputes that the climate, independent of human activities, changes. The question is to what extent changes now underway can be attributed to natural variability. “So far, in the 21st century, global warming has stabilized and no one really knows why,” writes Dr. William Cotton, a professor of atmospheric science at Colorado State University. “None of the ‘known’ climate forcing mechanisms can explain the discrepancy.” We know too little about natural variability of the climate to confidently make predictions, he insists.

In fact, 2008 globally was the coldest year since 2000. But Trenberth notes that it was still in the top 10 of globally averaged annual temperatures. The slowing of warming, he insists, is only temporary, and has something to do with the “weird formation of clouds.” Why this is, he can’t say—nor can anybody else. That is exactly the point Cotton makes.

What all this means is that global warming theory still has chinks. Questions abound. A possibility remains, if only remote, that the climate scientists have it all wrong. Waiting for every last question to be answered, though, could be devastating. How to decide what to do? Denver mayor John Hickenlooper sizes up the options in terms of risks. “Even if there is only a 3 percent chance that 95 percent of the world’s scientists are right that global warming exists,” he says, “we risk the chance of being the first generation to leave a problem for which there is no solution.”