The usual suspects of drought, famine, pestilence and war come to mind when one thinks of a future population crash. The ongoing drought in America’s bread basket appears to be just a foretaste of what’s in the climate chaos pipeline.

A quick review of the effect that climate change has on the global hydrologic cycle would be useful before we talk about the last study on drought.

…Climate change will also lead to changes in global rainfall patterns, intensifying both droughts and floods across the globe. The Clausius-Clapeyron equation dictates that the saturation vapor pressure of water increases nearly exponentially with temperature. Therefore, a warmer atmosphere will allow for more evaporation of water and an intensification of the hydrologic cycle, leading to increases in rainfall in some regions and decreases in others. At the present, rainfall has increased in the mid- and high-latitudes and in the tropics, while it has decreased in the sub-tropics. If global average temperature increases by 2 °C, dry-season precipitation in northern Africa, southern Europe, and western Australia is projected to decrease by ~20%, and that in the southwestern United States, eastern South America, and southern Africa to decrease by ~10%, which will have a profound impact on crop productivity and water resources. For comparison, the American “dust bowl” in the 1930s was the result of a ~10% decrease in rainfall over a decade. A reduction in mountain snow pack and glaciers will also exacerbate stresses on water resources. Climate change is also predicted to increase the frequency and magnitude of extreme weather events such as hurricanes, heat waves, heavy precipitation events, and flooding. Additionally, if global average temperature increases by 1.5- 2.5 °C, approximately 20-30% of plant and animal species will be at risk of extinction. As in the case of rising sea level, these consequences of climate change are irreversible on a 1,000-year timescale because temperature increases caused by elevated CO2 are expected to persist for that time period even if carbon emissions are fully curtailed [Solomon et al., 2009; IPCC, 2007]…

Now for the current study(actual report is here) which says that we are only eight years away from a life-altering megadrought:

Beginning in just eight years, we could see permanent climate conditions across the North American Southwest that are comparable to the worst megadrought in 1,000 years. (1)

The latest research from the Lamont-Doherty Earth Observatory at Columbia University published in December 2012 has some truly astounding news. The megadroughts referred to in the paper published in Nature Climate Change happened around about 900 to 1300 AD and are so extreme that they have no modern counterpart for comparison (these megadroughts will be referred to in the following as the “12th century megadrought”). The research was funded by the National Oceanic and Atmospheric Administration (NOAA).

We have been warned for decades that we would be facing a megadrought if we did not do something about climate pollution. We did not, and now according to the projections of a new study, that is just what the future may hold. And remember, projected conditions similar to the worst megadrought in 1,000 years would be the baseline conditions. Dry periods, which we normally refer to as drought times today, would be superimposed on top of the megadrought extremeness…

…The results of the new research are critically deserving of an alarmist tone. That we could slip into profound continuous drought so soon is certainly a surprise to most of us, to say the least. The typical consensus opinion of unrestrained climate pollution impacts by the year 2100 only tells us that permanent drought will come to many parts of the world and, basically, that dry areas could become drier. The news that we could be experiencing permanent drought on the scale of megadrought proportions – beginning in only eight years – should be considered a global threat of the highest order…

…This “most severe, but temporary, long-term decrease in flow recorded” is the concept we need to understand. This is the megadrought reference. A 10 percent reduction beginning 2021 to 2040 is extreme enough for these researchers to compare the average conditions projected for the very near future to the 12th Century megadrought. This single message is critical and it was missed by popular reporting. Just to be sure I am clear: this quote “temporary, but long-term decreases in flow” here refers to these 75- to 200 year-long megadroughts, the last one occurring about 1,000 years ago or in the 12th Century. These droughts were temporary, like the droughts of today, but in the near future, conditions comparable to these droughts will be the average climate condition. Dry periods that we know as drought today will be on top of megadrought dryness…

From ‘Climate Normals Are History‘:

And from a recent talk by Jeff Lukas, the Senior Research Associate of Western Water Assessment at the University of Colorado:

On January 17, 2013, Jeff Lukas, the Senior Research Associate of Western Water Assessment at the University of Colorado, gave an hour-long presentation at the most recent Weather and Climate Summit. The take-away from his presentation is this: droughts will be getting worse, no question about it. Cause: climate change. Time-frame: already started. And a potential megadrought, a phenomena that hasn’t reared its ugly head for at least 150 years, poses a real and serious risk that needs to be planned for…

…Megadroughts, are generally considered to be periods of 20 years or longer where continuous, or mostly continuous extreme drought covers a very large area, typically about 1/3 of the lower 48 (US states). And they’re as bad as they sound – maybe worse.

If such a drought happens, the Colorado River’s flow will drop drastically. The Bureau of Reclamation, which estimates that 25% of the US food supply is grown using Colorado River water, has already done a study to simulate a megadrought; results: Glen Canyon Dam hydro plant would have to stop generating power for about 20 years (two separate stretches of 10 years during the simulation). Both lake Mead and Lake Powell would see water levels drop by about 100 feet…

Jeff Lukas explained in his talk that there have been times in the past 1,000+ years when drought was so bad that the Colorado River (which supplies both Lake Mead and Powell) flowed at 25% below its current flow rate. And that very low level of flow was sustained for decades. Lukas says that such a scenario is definitely possible today. In fact, he says it is such a high risk that it needs to be planned for.

…For those that don’t know, the Colorado River is already maxed out. The Southwest has seen some of the highest US population growth over recent decades, and coupled with farming demands, the river water is nearly all spoken for…

…He concludes that drought is seriously underestimated as a severe threat – even if a megadrought doesn’t develop in the near-future. Because of warming he says there will be more drought than we’ve ever seen before. And the droughts that would otherwise be moderate will now be severe – intensity will ratchet upwards with temperature. He also says that trends of the past several years are worrying when compared to the record that dates back to the year 750…

 If a megadrought does unfold, past episodes may be a guide to the future. Lukas outlines a few of the effects that have been uncovered regarding past megadroughts: sand dunes forming in western Nebraska (i.e. no plants, just sand), more frequent wildfire, and rapidly dropping lake levels. One consequence that Lukas didn’t talk about was how drought-killed plants stop pulling CO₂ out of the air.

…Right now, the dams and reservoirs along the Colorado can capture and store runoff, even from severe rainfall events, but only up to their maximum storage capacity, which is around 60 million acre feet, or about 4 years worth of water demand. Groundwater can be pumped up (i.e. wells) in many places, but that resource is already in sharp decline.