This is one of those posts where I start writing about something on a whim, realize that it’s a big enough topic to write a grad school dissertation on, do a frantic spurt of research, and settle for writing a short and insufficient introduction.
On a recent cross-country road trip, my traveling companion decided for safety reasons that there were some areas in which I wasn’t going to be allowed to take the wheel. Those were: stretches with volcanoes, stretches with cool rock formations, the stretch where we cross the Colorado River, and others to be determined. Distractable geologists like me are a something of a hazard at the wheel because every new landscape is new puzzle to solve, and the dry, bare contours of the American West are especially tempting to scrutinize.
Working in California as a naturalist, the mountains of Peru as a field assistant, and as a student at field camp in Montana were all novel climate experiences for a Tennessee girl; I’m accustomed to thick green forests and summer air like hot soup. The inescapable dryness and ingeniously adaptable vegetation took some getting used to (I’m still finding sharp ichu grass in the mesh of my backpack, 3 years on). That lack of precipitation, though, slows the erosive powers of time and allows structures to be preserved, whether thick ridges of limestone or delicate archaeological ruins.
In that context, I find it fascinating that the last two hundred years of European exploration in the American West have actually been a WET period. When the Colorado River Compact was drawn up in 1922, it assumed a yearly flow of 20.2 square kilometers based on a few years of data collection. (source Woodhouse 2005) However, more recent tree-ring studies has suggested that the average historical flow is more like 16.7 square kilometers – 18% less than expected. Are the past few years actually an atypical drought, or just a return to “normal” conditions?
Western scientists have a bit of a bias where the medieval period is concerned – we think of it as the “Little Ice Age” of unusually cold and wet conditions in Europe. This is understandable, seeing as that’s the area where we have the easiest access to data, but data from the American West paints a different picture when we take the time to look for it. On this continent, the years 900-1300 were a warm, dry period that whose drought conditions led to the fall of cultures like the Anasazi, whose picturesque ruins tourists explore today. Is the landscape returning to those conditions, and can we, emboldened by modern engineering, continue to live there if it does?
A recent article published in Science Advances paints a worrying picture of the future of climate in the Southwest within the scope of the global climate change trends. According to those scientists from NASA, Columbia University, and Cornell University, there is an 80% chance of a 35-year “megadrought” by 2100 if current trends CO2 emissions and climate shifts continue, and fall to “only” 60 to 70% if we manage to hit the middle-of-the-road sustainability targets. I would love to figure out how approach this statistic from a municipal planning standpoint – how on earth would we react if that happened? Would the Southwest and Great Plains states slowly empty out as living there became economically untenable? Would ranchers and farmers finally find the bottom of the Ogallala aquifer in a quest to maintain their land? Climate models are tangled, precisely balanced relationships of statistics even when only atmospheric principles are in the equation; the human element, as usual, is a complete wild card.