Hurricane Epsilon petered out on Dec. 9, after putting an exclamation mark on the strongest and longest Atlantic storm season in modern history. The year 2005 saw a record 26 named storms in the Atlantic, and 14 hurricanes—including the most powerful hurricane ever charted.

And there’s more to come. On Dec. 6, hurricane forecasters Phil Klotzbach and Bill Gray of Colorado State University predicted that the 2006 season will be another doozy, with a “net tropical cyclone activity”—an index of predicted storm energy—of 195 (100 is normal).

Is all this another sign of global warming? Perhaps. Over the past year, two studies have confirmed a relationship between ocean warming and hurricanes. In July, Kerry Emanuel of the Massachusetts Institute of Technology showed that hurricanes worldwide have increased in duration and intensity by about 50 percent since 1970. In September, when Peter Webster of the Georgia Institute of Technology published a paper in Science Magazine, he ascribed a sharp increase in hurricane intensity to rising sea surface temperatures due to global warming. The report made headlines because it followed just two weeks after Hurricane Katrina, and it remained newsworthy because Rita arrived just a week later. When Wilma proved to be the most powerful hurricane of the modern era, it simply seemed to confirm the findings of the two papers.


Hurricanes and Skiing
What has this got to do with skiing? It has everything to do with global warming, and thus with the elevation of the snowline. We all know that hurricanes form when warm seawater heats humid air. When the ocean warms, hurricanes grow more intense—and continents downwind of the warm water also heat up, leading to shorter and possibly rainier winters. More hurricanes, signalling a rise in temperature, may mean that Tahoe gets rain until Christmas (hmm, isn’t that what happened this year?), and lower-elevation resorts in Europe may not be able to make snow at all. A longer Atlantic hurricane season may mean that New England starts its winter with powerful wet storms (hmm, that happened this year, too).

The question for ski area managers and owners: How warm does it have to get before the business is no longer sustainable?

Probably a lot warmer than it will be in the foreseeable future. So don’t sell out quite yet. It’s beginning to look as if global warming, at least in the northern temperate zone where we do most of our skiing, proceeds as a series of upward steps, followed by cooling periods. The current sharp upswing, which began in 1975 (see the NOAA chart next page), will probably peak around 2020. Then North America and Europe are in for a modest cooling-off period, in which temperature (and snow) levels may return to 1985 levels—for awhile. Average global temperature may sink back to the 1950 peak by around 2050, then climb again to about 1.5 degrees F above the 20th Century mean by about 2090.

The good news is that no one is currently forecasting a disastrous 3.5 to 8 degrees F rise by 2100, as some experts have predicted in the recent past. If you were to project the steep rise from 1975 to now forward by a century, that alarming temperature rise would indeed seem likely—but that’s not what’s really going to happen. The current temperature rise will soften, slacken, and then resume in the latter half of this century.

And what is causing this stepping-up pattern? No one except minions of the oil industry still believes that global warming is primarily due to anything other than the greenhouse effect, exacerbated by the carbon emissions due to human burning of fossil fuels. While the degree of human influence is still up for debate, scientists generally believe that human impacts are the greatest driver.


Old Data, New Analysis
This analysis is based not on new data, but on new statistical methods of analyzing data. In 1994, Michael Schlesinger, professor of atmospheric sciences at the University of Illinois, with graduate student Navin Ramankutty, applied some new mathematical tools to sea-temperature records, which for the Atlantic are reliable from 1850 onward. Their analysis showed that the average sea temperature rose to a peak in 1880, then cooled until 1910. It rose again, peaking in 1950, then cooled until 1975. This led them to describe a 70-year cycle, implying that temperature will peak again around 2020, cool a bit, and peak again around 2090.

This cycle, now widely accepted by meteorologists and climatologists, is called the Atlantic Multidecadal Oscillation, or AMO. Schlesinger doesn’t much like the name, because the phenomenon also exists in the North Pacific Ocean and across both North America and Eurasia. “Michael Mann (at the University of Pennsylvania) has traced the global oscillation a thousand years back,” Schlesinger points out.

But further analysis, completed over the past couple of years, suggests that each swing of the cycle is warmer than the last. Schlesinger’s data actually show that the crests and troughs grow warmer with time. The 1950 temperature crest was warmer than the 1880 crest, by .2 degree Celsius, and the current 2000-era upswing is warmer than 1950, by .3 degree Celsius. The 1980 trough (the coolest point in the cycle) was warmer than the 1910 trough. The chart looks like a snake undulating its way uphill. If it continues in this pattern, the 2050 trough will be as warm as the 1950 crest, and the 2090 peak will be .3 degree Celsius warmer than today’s climate.

Another chart, not shown here, was released last September by Judith Curry and Peter Webster, the husband-and-wife team at the Georgia Institute of Technology, who co-authored a report on hurricane intensity in Science magazine. Their analysis shows the same up-stepping pattern of temperature and storm energy.

The good news is that for snowmaking purposes and snowfall potential, the 2050 trough will be cooler than the peak in 2020, which gives wintersports resorts the prospect of a three-decade respite before global warming again threatens our livelihood. The bad news is, weather patterns could get worse before they get better. A report on the NOAA website, posted ten days after Hurricane Katrina, referred to the Schlesinger data and commented, “When the AMO increases, as from 1975 to the present, global warming is exaggerated.”

The key questions for winter resorts are, how much will temperatures rise, and how fast? A growing number of climatologists figure the upward-snaking pattern will continue to repeat itself, moving steadily upward in 70-year cycles. That would make temperatures for snowmaking impossible at 8,000 feet in the Colorado Rockies sometime after the year 2200.


Near-Term Uncertainties
It’s critical to understand that these temperature trends are at play over decades. As the temperature chart clearly shows, the year-to-year pattern is so spiky as to be unpredictable. Just because last year was warm doesn’t mean this year will be warm (or warmer).

And no one is very sure what the long-term temperature pattern means for natural snowfall, either. Warmer seawater probably means more precipitation on the western slopes of mountain ranges—but whether that comes in the form of snow or rain depends, of course, on the air temperature. Some climate models predict that as coastal ranges grow wetter, continental interiors—North America’s Rockies, for example—may grow drier. This winter’s weather pattern shows no evidence of that, and these “dry interior” models may prove inaccurate.

And there’s another element missing from the models: El Niño. Michael Alexander, a meteorologist at the National Oceanic and Atmospheric Administration Climate Diagnostics Center in Boulder, notes that no one has begun working yet on how the El Niño pattern fits into the multidecadal cycle—and most meteorologists base their short-range forecasts (by short-range, we mean year-to-year) on what El Niño is doing.

All this creates a bit of tension and misunderstanding between meteorologists, who look at year-to-year data, and climatologists, who look at century-to-century data. Climatologists believe in long-term global warming; many meteorologists don’t, because they don’t see the long-term data.

Even if they did, some of it can be tricky to interpret. Consider snowfall and snowmelt patterns. Scientists have recently recorded more snowfall, and a thickening of the ice, in the middle of the Greenland ice cap. At the same time, the ice is melting and glaciers retreating at the edges of the cap. This makes sense only if you figure that warm air is carrying more moisture from a warming Arctic Ocean into the inland regions of Greenland where it falls as snow, and that the same warm air is melting the fringes of the icecap. But a global-warming skeptic might single out the increased snowfall at the center and say “There! There! Global warming is a myth!”

If you’re not confused yet, consider this: The present warming trend may reverse suddenly if melting polar icecaps interrupt the AMO cycle by diluting the North Atlantic with fresh water. In that case, the Gulf Stream could slacken, and colder weather in Europe could create a new Golden Age for skiing in the Alps—and completely disrupt the world’s agricultural economy. The last four or five Ice Ages began very suddenly after warming trends reached about 10 degrees F above the past century’s mean, and oceanographers think that a Gulf Stream interruption may be just what started them.

So there’s no immediate climatological reason to sell the hill. But if you want your grandkids to inherit a going ski resort, stop burning fossil fuels, start putting biodiesel into the grooming machines, and buy renewable-source electricity for your lifts.



Longtime SAM contributor Seth Masia is now a graduate student in environmental journalism at the University of Colorado, but still does most of his research above snowline.