The tremendous success of the human race over the past century or so – our rapid population growth, increased resource use per capita, and great scientific and technological advance and social change – makes this a virtual certainty. Why? Several factors combine to make this so.
First, relatively speaking, we’ve only just started keeping records on hazards. As a result these records are typically short. They don’t go back very many years! Here’s an example. Suppose you are interested in the history of floods on the Mississippi River. You got lucky! You live in the internet age, other people have also been interested in that question, and the Mississippi actually has pretty good documentation. So, if you Google “Mississippi River floods,” many references pop up, including a nifty National Weather Service table. At first glance you think, great! This record goes back all the way to 1543. But hydrologists and engineers need actual, quantitative flood crests, in order to assess flood risk and develop design criteria for levees and other protection measures. And the table shows that information only back to around 1900.
Why are the records short? Some places haven’t seen human settlement until recent years. In a lot of cases, we lacked the needed instruments. They hadn’t been invented (think stream gauges, anemometers for measuring high winds, seismometers for quantifying earthquake intensity, and so on).
In other cases, we didn’t have the science. Geologists and paleoclimatologists have been poking around only for a century or so, and are just now learning what to look for. Increasingly, they’re been learning that the world is a scary place.
What they’ve found is that on Earth, the major extremes are quite rare. They might occur only once every century or so. Or on geologic time scales, which might amount to thousands, or hundreds of thousands of years or even longer. They look at floodplains, and come to realize that while we’ve had some bad floods since we started keeping records, the landforms in floodplains around the world and other inferential evidence show that at times, every river has seen floods much more extensive than anything we’ve recorded. Remember hearing about the dustbowl of the 1930’s? Bad as it was, the duration and severity of that drought pales in comparison to the droughts that brought about the collapse of early southwestern civilizations of indigenous populations half a millennium earlier. The eruption of Mount St. Helens in 1980? The merest puff of ash compared with the eruptions that occur every several hundred thousand years over the Yellowstone hotspot. These eruptions put out some 2000 times more material.
So this reality is the second cause for concern; the short period for which we have good records is not nearly long enough to give us a good handle on what to expect in the future. For that, scientists must rely on extended extrapolations. Even as they extrapolate, scientists remain hesitant and skeptical. At best they face a high uncertainty. At worst the estimates may be grossly misleading.
Third, we see rapid increases in vulnerability everywhere we look, due to human settlement and our growing dependence on critical infrastructure. Let’s start with Mount Rainier. This volcano erupts every 10-20 thousand years or so. But that’s not the immediate risk. Geothermally active, Rainier is host to acidic steam and water, which is constantly, inexorably leaching metals out of the rock that forms its slopes. Every so often, once every couple of centuries, area seismicity triggers landslides in this weak rock. Some of these mudslides, approaching speeds of 100 miles per hour, have reached Puget Sound. Today 100,000 homes are built atop the sites of these former mudslides, and 250,000 people commute every day across these mudslide sites. Move down the coast to the San Francisco Bay area. The cities of Oakland and Berkeley are built on the Hayward fault, which last ruptured in 1868. A repeat of that earthquake today would produce an estimated $200 billion dollars of property destruction. Seismologists put the risk at something like 30% within the next 30 years. Move east to the site of the New Madrid earthquakes, centered in today’s Missouri. The three strongest earthquakes to hit the country (all above 8.0 on today’s Richter scale) occurred there in a three-month span in 1812. No seismometers recorded the events, but reflect on this. The shaking of the Earth was so extensive that the quakes rang church bells in Boston. Today, many of the natural-gas pipelines serving the northeastern United States run through the New Madrid area. And the USGS predicts a probability of recurrence of 10% within the next 50 years.
All across the country, we have built hundreds over levees over the past century. And hundreds of thousands of Americans have since built and live in homes behind those levees. Experts believe that worst-case hurricane scenarios for New York City would include storm surge able to flood the city’s subway system. And that meteor threat? Don’t be instinctively dismissive. In the 20th century, we had two hits, in Siberia, and one or two near misses. Put any one of those in one of the world’s oceans, and we might be talking a different story.
Get the idea? This kind of pattern is common to hazards of all sorts – hurricanes, snowfalls, drought, earthquakes – you name it – at locations worldwide. The risk of any one of these particular events is small – but so many scenarios are possible that one or more are likely in any given year. So that’s why we see the tsunami of 2004. Hurricane Katrina in 2005. The Chinese earthquake of 2008. The Haitian earthquake and Pakistan flooding of 2010. Soon coming to a theater near you.
In the next post, we’ll turn to the unintended consequences of our success, and the third forecast for our future.
 In most cases in the United States, records go back only a hundred years or so. Many rivers in Europe have somewhat longer data records. Move over to the cradle of civilization, and you might find longer records still. But the further back you try to go, the more qualitative the record, and the more uncertain and unreliable the data. People frequently mention the annual Nile flood. So we’ll do the same! Note that (and we’ll see this over and over again) this flood annual flood was both a blessing and a curse. Take away the annual Nile floods, and Egyptian civilization would never have flowered. However, the Nile floods varied quite a bit from year to year, and with that variation Egyptian fortunes also ebbed and flowed. Too much or too little water, and the flood became a threat. But that is a story for another day.
 For a good read, get The Worst Hard Time: The Untold Story of Those Who Survived the great American Dust Bowl, by Timothy Egan.