The World in 2050: Four Forces Shaping Civilization's Northern Future

during medieval times.²⁴⁶ These Perfect Droughts were as bad as or worse than the Dust Bowl but lasted much longer, persisting as long as five to seven decades (the Dust Bowl lasted barely one). These prehistoric data tell us that this heavily populated region is capable of experiencing droughts far worse than anything experienced since the first European explorers arrived.

One reason for these massive prehistoric droughts was that between seven hundred and nine hundred years ago temperatures rose. The increase was similar to what we are beginning to see now but not so high as what climate models are projecting by 2050. The reason for the medieval temperature rise (fewer volcanic eruptions plus higher solar brightness) was different from what’s happening today, but it nonetheless provides us with a glimpse of how our planet might respond to greenhouse warming.²⁴⁷

Not only did the medieval climate warming increase the drying of soils directly, it may also have altered an important circulation pattern in the Pacific Ocean, by shifting relatively cool water masses off the western coast of North America for many decades at a time (this would be a prolonged negative phase of the so-called “Pacific Decadal Oscillation,” an El Nino- like oscillation in the northern Pacific that currently vacillates over a 20-30-year time scale). This likely created pressure systems driving rain-bearing storm tracks north, rather than south, across the western United States, triggering drought conditions in the American Southwest. Should the projected rise in air temperatures cause the Pacific circulation to behave like this again, the prolonged medieval megadroughts could return. Similar connections between shifting sea-surface temperatures and geographic rainfall patterns over land exist for the Atlantic and Indian oceans as well.

MacDonald points out that by the time Schwarzenegger declared a state of emergency in 2009, most of the southwestern United States was actually in its eighth year of drought, not third. “Arguably, we are now into the great Twenty-first Century Drought in western North America,” he mused to me. “Could we be in transition to a new climate state? Absolutely. Should we be worried? Absolutely.” His concerns are echoed by Richard Seager at Columbia University’s Lamont-Doherty Earth Observatory. In a widely read Science article,²⁴⁸ Seager and his colleagues showed consensus among sixteen climate models that projected greenhouse warming will drive the American Southwest toward a serious and sustained baking. Their result, of course, is dependent on the group of models analyzed, and the simulation is imperfect because today’s coarse-scale climate models don’t represent mountainous areas very well (e.g., the Rockies, which produce most of the region’s snowpack water). But if these model projections prove correct, then the drought conditions associated with the brief American Dust Bowl could conceivably become the region’s new climate within years to decades.

Risky Business

“Stationarity Is Dead,” announced another Science article in 2008, sending a cold shiver through the hearts of actuaries around the world.²⁴⁹ A hydrology dream team of Chris Milly, Bob Hirsch, Dennis Lettenmaier, Julio Betancourt, and others had just told them that the most fundamental assumption of their job description—reliable statistics—was starting to come apart.

Stationarity—the notion that natural phenomena fluctuate within a fixed envelope of uncertainty—is a bedrock principle of risk assessment. Stationarity makes the insurance industry work. It informs the engineering of our bridges, skyscrapers, and other critical infrastructure. It guides the planning and building codes in places prone to fires, flooding, hurricanes, and earthquakes.

Take river floods, for example. By continuously measuring water levels in a river for, say, twenty years, we can then use the stationarity assumption to calculate the statistical probability of rarer events, e.g., the “fifty-year flood,” “hundred-year flood,” “five-hundred-year flood,” and so on. This practice, while creating enormous misunderstanding with the public,²⁵⁰ has also made us safer. Hard statistics, rather than the whims of developers or mayors, are used to design bridges and for zoning. But flood prediction, and most other forms of natural-hazard risk assessment, rest on the core assumption that the statistics of past behavior will also apply in the future. That’s stationarity. Without it, all those risk calculations go straight out the window.

A growing body of research is showing that our old statistics are starting to break down. Climate change is not the sole culprit. Urbanization, changing agricultural practices, and quasi-regular climate oscillations like El Nino all influence the statistical probabilities of flooding. However, the dream team’s paper and others like it²⁵¹ tell us that climate change is fundamentally altering the statistics of extreme floods and droughts, two things of enormous importance to humans. “In view of the magnitude and ubiquity of the hydroclimatic change apparently now under way,” they wrote, “we assert that stationarity is dead and should no longer serve as a central, default assumption in water-resource risk assessment and planning. Finding a suitable successor is crucial for human adaptation to changing climate.”²⁵²

Unfortunately, we have no good replacement for stationary statistics yet, certainly nothing that works as well as they once did. Moreover, there has been hardly any basic research done in this area since the 1970s. We can’t just invent a completely new branch of mathematics and train a new generation of water experts in it overnight. “Water resources research has been allowed to slide into oblivion over the past thirty years,” Lettenmaier growled later in a separate editorial. “Certainly the profession has been slow to acknowledge these changes and acknowledge that fundamentally new approaches will be required to address them.”²⁵³ So even as we’re beginning to grasp the enormity of this problem, we presently have no clear replacement for our old way of doing things. Until we find one, risks will be harder to predict and to price. We can expect insurance companies to react accordingly. In 2010, after failing to win a nearly 50% rate increase from state regulators, Florida’s largest insurance company abruptly canceled 125,000 homeowner policies in the state’s hurricane-prone coastal regions, saying the recent series of devastating hurricanes had rendered its business model unworkable. ²⁵⁴ Get ready for higher premiums, uninsurable properties, and failed or overbuilt bridges.

Nonreturnable Containers

Changing drought and flood statistics are not the only way that rising greenhouse gases harm our water supply. All of our reservoirs, holding tanks, ponds, and other storage containers are trifling compared to the capacity of snowpacks and glaciers. These are free-of-charge water storehouses, and humanity depends upon them mightily.

Snow and ice hoard huge amounts of freshwater on land, then release it in perfect time for the growing season. They do this by bulking up in winter, then melting back in spring and summer. They are the world’s hugest water-management system and, unlike a dam reservoir, displace no one and cost nothing. Glaciers (and permanent, year-round snowpacks) are especially valuable because they outlast the summer. This means they can hoard extra water in cool, wet summers, but give it back in hot, dry summers, by melting deeply into previous years’ accumulations. Put simply, glaciers sock away water in good years when farmers need it least, and release water in bad years when farmers need it most. Glaciologists call these “positive mass-balance” and “negative mass-balance” years, respectively, and they are a gift to humanity. Glaciers keep the rivers full when all else is dry. They are the ultimate sunny-day fund.

If you read the news, then you already know that many of the world’s glaciers are beating a hasty retreat, whether through warmer temperatures, less precipitation, or both. Ohio State University’s glaciologist power-couple Lonnie Thompson and Ellen Mosley-Thompson have been photographing the deaths of their various study glaciers since the 1970s. Some of these are even wasting away at their summits, which is a death knell for a glacier. There are ski resorts in the Alps trying to save theirs by covering them with reflective blankets. Most glaciologists expect that by 2030, Montana’s Glacier National Park will have no glaciers left at all.

Seasonal snowpack, which does not survive the summer, cannot carry forward water storage from year to year like glaciers do, but it is also a critically important storage container. It creates a badly needed time-delay, releasing water when farmers need it the most. By holding back winter precipitation in the form of snow, the retained water flows downstream to farmers later, in the heat of the growing season. Without this huge, free storage container, this water would run off uselessly to the ocean in winter, long before growing season. Rising air