"And the wind blows, the dust clouds darken the desert blue, pale sand and red dust drift across the asphalt trails and tumbleweeds fill the arroyos. Good-bye, come again."

The global dust cycle is the most important thing that most people have never heard of. Drylands emit sediment that can be transported long distances. In many cases this is an entirely natural phenomenon, e.g. ancient lake basins tend to be poorly vegetated due to salinity and tend to be full of transportable sediment. When they were lakes they trapped dust, now they expel it. These are often the dust hotspots of the world (e.g., Koren et al. 2006). Land use including tillage and grazing are also major contributors in other cases; desertification and dust emissions are tightly linked (Breshears et al. 2003). These disturbances can turn large areas into dust emitters. Drought, which we expect to be strongly affected by climate change, can also greatly enhance dust emissions across the board (Belnap et al. 2009). Thus, dust can be considered a secondary global change factor.

The obvious impact of dust emissions in rangelands is that fertility is leaving the site (Neff et al. 2005). The less obvious impacts occur sometimes halfway around the world. Some cities regularly experience crippling dust storms which impact human respiratory health and create blinding conditions on roadways. Beijing is an excellent example, where desertification-linked dust storms have gone from a decadal phenomenon to an annual one, even closing airports for days. In the southwest USA, an endemic fungus responsible for valley fever (a disease causing pheumonia-like symptoms) is transported in dust. Some of the more amazing impacts of dusts may be positive on a global scale, in terms of our prospects for sinking carbon. The two great photosynthetic engines of the Earth, the Amazon rainforest and the oceanic phytoplankton, are both subsidized by dust-borne nutrients from drylands (Fung et al. 2000, Koren et al. 2006, Mahowold 2010).

• Beijing dust storm (Photo: Prof. Zev Levin, Dept. of Geophysics and Planetary Sciences, The Porter School of Environmental Studies, Tel Aviv, Israel)

Recently two excellent papers have appeared in Proceedings of the National Academy of Sciences about dust emissions and their impacts, and to a lesser degree the role of biocrusts as soil stabilizers.

Painter, T.S., Deems, J.S., Belnap, J., Hamlet, A.F., Landry, C.C., Udall, B. 2010. Response of Colorado River runoff to dust radiative forcing in snow. Proceedings of the National Academy of Sciences 108: 3854 - 3959. 
Back in 2006, I was shocked to hear Jayne Belnap on National Public Radio. NPR was doing a two-part series on dust research focused around the work on Tom Painter. The radio journalist even dropped the word "crusties" a time or two.










Four years later, they published this paper which documents the impacts of dust originating form the Colorado Plateau and southwest US drylands and accumulating on Rocky Mountain snowpack. Because the dust is much darker than the soil, it increases albedo and hastens melting. The authors estimate that this has resulted in initiation of melting 3 weeks earlier than ambient conditions. More importantly, the radiative forcing enhances sublimation -- the transition of solid snow to vapor -- which the authors estimate has decreased water supply to the Colorado River Basin by 5 %. This is of tremendous importance as most of the fastest growing urban areas in the USA are in the southwest and at least partially dependent on Colorado River water. As an example, Las Vegas, the city I was born in increased from about 200,000 residents to about 2,000,000 in 3 decades. All of this growth has been founded on the fantasy that there will be enough water, despite that the Colorado River has been 100% allocated for many years. Increasing dust emissions seem to argue otherwise.

Munson, S.M., Belnap, J., Okin, G.S. 2011. Responses of wind erosion to climate-induced vegetation changes on the Colorado Plateau. Proceedings of the National Academy of Sciences  doi: 10.1073/pnas.1014947108. 

The authors use a trifecta of long-term monitoring data, a wind erosion model, and an experimental validation of results using a portable wind tunnel. Primarily in perrennial grasslands the previous year temperatures dictate grass biomass in the following years. Plugging these data into Okin's wind erosion (WEMO) model suggests greater risk for enhanced dust fluxes due to probable climate warming. The fluxes are small, however, unless the biocrust is disturbed. When heavy crust disturbance is coupled with drought-stricken grasses, the fluxes have the potential to be off the hook.

 This paper is getting considerable press, e.g. the Salt Lake Tribune. For those in other countries just check out the comments on that paper to see how effective the smear campaign on climate science has been in the USA. We have an uphill battle.

Post title: Edward Abbey, The Monkeywrench Gang 

References:
Belnap, J., R. L. Reynolds, M. C. Reheis, S. L. Phillips, F. E. Urban, and H. L. Goldstein. 2009. Sediment losses and gains across a gradient of livestock grazing and plant invasion in a cool, semi-arid grassland, Colorado Plateau, USA. Aeolian Research 1:27–43.

Breshears, D. D., J. J. Whicker, C. B. Zou, J. P. Field, and C. D. Allen.  2009. A conceptual framework for dryland aeolian sediment transport along the grassland-forest continuum: Effects of woody plant canopy cover and disturbance. Geomorphology 105: 28-38.

Fung, I.Y., Meyn, S.K., Tegen, I., Doney, S.C., John, J.G., Bishop, J.K.B., 2000. Iron supply and demand in the upper ocean. Global Biogeochemical Cycles 14, 281–295.

Koren, I., Kaufman, Y.J., Washington, R., Todd, M.C., Rudich, Y., Martins, J.V., Rosenfeld, D., 2006. The Bodélé depression: a single spot in the Sahara that provides most of the mineral dust to the Amazon forest. Environmental Research Letters 1, 0140055.

Mahowald, N.M., Kloster, S., Engelstaedter, S., Moore, J.K., Mukhopadhyay, S., McConnell, J.R., Albani, S., Doney, S.C., Bhattacharya, A., Curran, M.A.J., Flanner, M.G., Hoffman, F.M., Lawrence, D.M., Lindsay, K., Mayewski, K.A., Neff, J., Rothenberg, D., Thomas, E., Thornton, P.E., Zender, C.S., 2010. Observed 20th century desert dust variability: impact on climate and biogeochemistry. Atmospheric Chemistry and Physics 10, 10875–10893.

Neff, J. C., R. L. Reynolds, J. Belnap, and P. Lamothe. 2005. Multi-decadal impacts of grazing on soil physical and biogeochemical properties in southeast Utah. Ecological Applications 15:87–95.