By Joe Romm
This heat wave has broken thousandsÂ of temperature records. Climate Central reported Satuday, â€œIn many cases, records that had stood since the Dust Bowl era of the 1930s have been equaled or exceeded, and this event is likely to go down in history as one of Americaâ€™s worst.â€
In general, we expect the greatest number of temperature records to be set during a widespread drought. I explained why that is the the case in my Nature article last year on â€œThe next dust bowlâ€ (full text here):
Warming causes greater evaporation and, once the ground is dry, the Sunâ€™s energy goes into baking the soil, leading to a further increase in air temperature. That is why, for instance, so many temperature records were set for the United States in the 1930s Dust Bowl; and why, in 2011, drought-stricken Texas saw the hottest summer ever recorded for a U.S. state.
Withering Heat in Our Future
Why is this bad news? Because the Earth has warmed only a bit more than 1Â°F since the catastrophic Dust Bowl â€” and we are poised to warm an astounding 9-11Â°F this century if we stay anywhere near our current greenhouse gas emissions path.
Much as our current monster heat wave has been made worse by human activity (man-made global warming) so too was the Dust Bowl â€” but in that case it was bad agricultural practices. As NOAAâ€™sÂ discussion of â€œThe Dust Bowl Droughtâ€ explains:
The drought came in three waves, 1934, 1936, and 1939-40, but some regions of the High Plains experienced drought conditions for as many as eight years. The â€œdust bowlâ€ effect was caused by sustained drought conditions compounded by years of land management practices that left topsoil susceptible to the forces of the wind.
For discussion of some of those land management practices, see here.
Unfortunately, while we have improved much of our land management since then, we have chosen to ignore decades of warning by climate scientists that unrestricted emissions of greenhouse gases would cause ever-worsening droughts. A 1990 Journal of Geophysical Research study, â€œPotential evapotranspiration and the likelihood of future drought,â€ projected that severe to extreme drought in the United States, then occurring every 20 years or so, could become an every-other-year phenomenon by mid-century.
Aiguo Dai of the National Center for Atmospheric Research, in his 2010 study, â€œDrought under global warming: a review,â€ had a similar conclusion. I will blog shortly on his updated findings, but here is a rough representation of where his analysis projects the PDSI [Palmer Drought Severity Index] will be soon after mid-century, again, if we donâ€™t dramatically reverse greenhouse gas emissions trends:
The PDSI in a moderate emissions scenario soon after mid-century. In the Great Plains during the Dust Bowl, the PDSI apparently spiked very briefly to -6, but otherwise rarely exceeded -3 for the decade (see here).
Dai found that:
By the end of the century, many populated areas, including parts of the United States and much of the Mediterranean and Africa, could face readings in the range of -4 to -10. Such decadal averages would be almost unprecedented.
We Have Been Warned
Whereas in the 1930s, you could certainly make a case that people didnâ€™t know just how destructive their land management practices were. But we have been warned again and again that we face ever-worsening warming and drought conditions. Here are a few more studies:
- In 2007, Science (subs. reqâ€™d) published research that â€œpredicted a permanent drought by 2050 throughout the Southwestâ€ â€” levels of aridity comparable to the 1930s Dust Bowl would stretch from Kansas to California. And they were also only looking at a 720 ppm case.
- In December 2008, the Bush Administration quietly released a U.S. Geological Survey stunner: SW faces â€œpermanent dryingâ€ by 2050, which found:
- The serious hydrological changes and impacts known to have occurred in both historic and prehistoric times over North America reflect large-scale changes in the climate system that can develop in a matter of years and, in the case of the more severe past megadroughts, persist for decades. Such hydrological changes fit the definition of abrupt change because they occur faster than the time scales needed for human and natural systems to adapt, leading to substantial disruptions in those systems. In the Southwest, for example, the models project a permanent drying by the mid-21st century that reaches the level of aridity seen in historical droughts, and a quarter of the projections may reach this level of aridity much earlier.
- NOAA: Climate change â€œlargely irreversible for 1000 years,â€ with permanent Dust Bowls in Southwest and around the globe.Â This January 2009 PNAS paper finds:
â€¦ the climate change that is taking place because of increases in carbon dioxide concentration is largely irreversible for 1,000 years after emissions stopâ€¦.Â Â Among illustrative irreversible impacts that should be expected if atmospheric carbon dioxide concentrations increase from current levels near 385 parts per million by volume (ppmv) to a peak of 450-600 ppmv over the coming century are irreversible dry-season rainfall reductions in several regions comparable to those of the â€œdust bowlâ€ era
- Michael Wehner et al., â€œProjections of Future Drought in the Continental United States and Mexicoâ€ (2011). A good PDF of aÂ PowerPoint presentation is here.
The â€˜debateâ€™ about the future of drought in the United States under business-as-usual emissions, such as it is, is how far into the northern U.S. Great Plains and Midwest Dust Bowl conditions will extend â€” and thatâ€™s without even considering the impact of the increasingly early loss of the winter snowpack, which most of these studies donâ€™t even model.
Are we really so blinkered that we we are going to take the risk ruining the breadbasket of the world just as we are adding another 2 billion people to the planet? Î¦
Joe Romm is a Fellow at American Progress and is the editor of Climate Progress, which New York Times columnist Tom Friedman called “the indispensable blog” and Time magazine named one of the 25 “Best Blogs of 2010.” In 2009, Rolling Stone put Romm #88 on its list of 100 “people who are reinventing America.” Time named him a “Hero of the Environmentâ€³ and â€œThe Webâ€™s most influential climate-change blogger.” Romm was acting assistant secretary of energy for energy efficiency and renewable energy in 1997, where he oversaw $1 billion in R&D, demonstration, and deployment of low-carbon technology. He is a Senior Fellow at American Progress and holds a Ph.D. in physics from MIT.