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INTERMOUNTAIN WEST CLIMATE SUMMARY, JANUARY 2008 Research Notes Compiled and written by Koren Nydick, Mountain Studies Institute (www.mountainstudies.org) The Research Notes is a new page with summaries of recent journal articles relevant to climate and water resources in the west. We will feature this page approxin1ately four times a year in the IMW Climate Sum/nary. If you have any articles that you would like to see in afuture Research Notes page, please e/nail us at wwasu/nmary@wwa.colorado.edu. Raupach, M.R., et al. 2007. Global and regional drivers of accelerating C02 emissions. Proceedings of the National Academy of Sciences 104: 10288 - 10293. & Canadell, J.G et al. 2007. Contributions to accelerating atmospheric C02 growth from eco- nomic activity, carbon intensity, and efficiency of natural sinks. Proceedings of that National Academy of Sciences 104: 18866-18870. Growth in atmospheric C02 is accelerating and could lead to stronger-than-expected-and sooner-than-expected climate changes. Three reasons are given for this acceleration: 1) increased economic activity, 2) increasing carbon intensity of the global economy, and 3) reduced efficiency of land and water in taking up carbon emissions. Global C02 emissions from fossil-fuel burning and industry grew by >3% per year in 2000-2004 compared to 1.1 % per year in the 1990s. In the 1990's the amount of C02 emissions produced per unit of economic activity began to decrease (due to increased energy efficiency), but since 2000 this trend has flattened or reversed. Growth rate in C02 emissions is strongest in developing countries like China, but developed countries currently still emit the majority of emissions. Meko, D.M. et al. 2007. Medieval drought in the upper Colorado River basin, Geophysical Research Letters, 34, LI0705, doi: 10.1029/2007GL029988. New tree-ring records extend the historical reconstruction of Colorado River streamflow at Lee's Ferry back to A.D. 762. The long-term record illustrates patterns of multidecadal variability in stream flow, including large swings from very wet to very dry conditions. A major period of low flow is shown in the mid-ll00s that exceeds even the late-1500s North American megadrought. The 1100s Medieval drought includes periods of very low flow embedded in a generally dry 62 year period that lacked any high flows. Several other tree-ring reconstructions from the western United States suggest that this drought occurred over a large region but varied in intensity in different locations. Seager, R. et al. 2007. Model Projections of an Imminent Transition to a More Arid Climate in Southwestern North America. Science, 316: 1181-1184. Eighteen of 19 climate models show a drying trend in the 21st century for SW North America. A decrease in precipitation of 0.1 mm/day occurs in many of the projections by mid-century, but some models sho\v that it could happen sooner. For comparison, precipitation during the Dust Bo\vl and 1950s SW droughts \vas 0.09 and 0.13 mm/day lower than average, respectively. The projected drying appears to be caused by changes in atmospheric circulation cells rather than shifts in tropical sea surface tem- peratures, which were responsible for major 20th century droughts. Instead, events such as La Nina will be superimposed upon drier average conditions, possibly causing droughts worse than any since the Medieval period. McCabe G. J., D. M. Wolock. 2007. Warming may create substantial water supply shortages in the Colorado River basin, Geo- physical Research Letters, 34, L22708, doi:l0.l029/2007GL031764. Potential effects of t\VO levels of warming (+0.860C, +20C) on streamflow in the Colorado River basin were evaluated with a water balance model. The warming scenarios were applied to 20th cen- tury climate data and to the driest century from a tree-ring reconstruction of streamflo\v for 1490-1998. Warming by +20C applied to the 20th century climate or +0.86 or +20C applied to the driest century resulted in lower streamflow and water shortages more severe than those inferred from the tree-ring reconstructions. A flow/surplus water-supply model indicated that expanding storage capacity would not alleviate shortages in most cases. Painter, T. H. et al. 2007. Impact of disturbed desert soils on duration of mountain snow cover, Geophysical Research Letters, 34. L12502, doi:l0.l029/2007GL030284. Field measurements and snowmelt modeling show that deposition of desert dust reduced the duration of snow cover in a San Juan Mountain (SW Colorado) watershed by 18-35 days. The dust increased energy absorption, resulting in faster melting. Three to 4 dust events per year were observed from 2003-05. Eight events occurred in 2006, which was a year of intense drought in the CO Plateau. More frequent and heavy dust events, less post-event sno\vfall, and clearer skies resulted in more energy absorption and faster melting in 2006 than 2005. Other measurements suggest that the dust originates SW of the study site in AZ and NM. More intense and frequent droughts in the desert SW may increase dust emissions, which could further reduce snow cover duration. RESEARCH NOTES I 20i~