I wished that I had a dime for every time I heard people complain about how big the AGU meeting has grown! It is an enormous meeting: the number of participants this year was rumored to be around 22,000 people. Moscone South, the venue for the poster sessions, stretches one entire city block so that if you forget something at one end and remember it only at the other end, you are in for a hike back to retrieve your stuff! And shuttling back and forth between Moscone South and Moscone West, where the sessions are held, became a bit like a salmon run with hundreds of researchers streaming from one venue to the other. It was hard to advance if you are going against the flow.
But it is the very size of the AGU that makes it such a useful meeting. While not all the world's earth science researchers attend, a significant fraction do, including very strong representations from East Asia. And the AGU meeting management provides very good tools for navigating the 12,000 posters and 6,000 invited presentations.
I found so much relevant material at the AGU meeting that I have decided to break this blog entry into two parts. This first part will explain the informational resources that I have brought back from the meeting and highlight some of the talks that caught my attention. The second will explore some of themes that I saw emerging from the conference as relevant to MRI.
Informational Resources
The AGU Scientific Program webpage appears to be public so that you can search the program and create an itinerary (complete with abstracts) as I did (see below) even if you were not registered to attend.
In addition, poster presenters were encouraged to submit their posters to an "ePosters" site. Thus if you know the session code for the poster (and if the presenters uploaded their poster to the site, which alas many did not), one can download the poster! For instance the very first poster in my itinerary, C11B-0674. Glacier Surge-like signals detected by SAR-based technique in West Kunlun Shan, NW Tibet T. Yasuda; M. Furuya, has been uploaded to the site. By inserting the code "C11B-0674", I can download the poster itself.
Finally, the AGU has finally begun to record some of the presentations and has made them available via a Sessions on Demand button. The AGU recorded numerous Union sessions and plenary lectures over the five days of the meeting. I suggest that you look at all five days to see what might be of interest to you. I particularly suggest the sessions GC43G Stephen Schneider session and the GC43H session on the history of global warming, both on 8 December 2011.
What exactly did I do? I searched the program using keywords such as "mountain", "Sierra", "Himalaya", "Tibet", and so on. After several iterations, I arrived at a nearly feasible itinerary focused on mountain-related topics, which runs to 254 pages and 18.3 MB. This itinerary kept me shuttling back and forth between sessions and posters for the whole time that I was there. I was extremely pleased with this modus operandi as I felt like I was able to focus right in on the most relevant work presented at the meeting. While I was not present on Friday, I included Friday in my itinerary document so that the full five days were searched.
How can you use this mountain-focused itinerary of posters and papers? If you browse the first pages of the itinerary you will find the titles of papers and posters by session. Yes, there are 27 pages to this section of the document but as the papers and posters are organized by session title, you should be able to see quickly those that are of interest to you.
To see the abstract of any of the posters or papers listed there, simply search the rest of the document for the name of the first author and you will eventually find the abstract.
Papers and posters that made an impression on me
B12B-01. Mechanisms of Alpine Treeline Stability (Invited) W.K. Smith; G. Wieser; F. Holtmeier
I am always taken by papers that explain something at one level by mechanisms at another. Bill Smith assessed treeline dynamics by looking first at seeding survival, then at growth of seedling to tree stature and finally the facilitation of survival and growth by the presence of existing vegetation. Seedling survival was a question not just of carbon acquisition under low temperatures, high radiation loads and water stress but also of the processing of that carbon into plant structures. Snow played an important role is protecting seedlings and young trees but also presented physical challenges, especially abrasion, to growth above the snow layer into tree form. Finally, the presence of other plants greatly influenced the success of plants moving from one life stage to the next, a point also made by Lara Kueppers in one of her several papers or posters on the Alpine Treeline Warming Experiment on Niwot Ridge (though I can't seem to find mention of it in the abstracts). Smith emphasized that from an ecophysiological point of view, high elevations differ considerably from low-elevation polar environments in at least two ways - very high incoming radiation which often leads to photoinhibition of carbon processing, and very low partial pressures of CO2 with large impacts of fluxes. These two points seem directly relevant to the "why are mountains different" theme that was proposed by Mark Williams and Dave Schimel in Perth last year.
C23F-03. Mountain front precipitation accumulation over a 3300m elevation gradient from scanning LiDAR snow depth and in-situ instrumental measurements, southern Sierra Nevada, California P.B. Kirchner; R.C. Bales; J. Flanagan; K.N. Musselman; N.P. Molotch
I am always on the lookout for papers that examine the relationship between elevation and precipitation. Pete Kirchner created a very high resolution dataset on spring snow depths from the difference between snow-on and snow-off LIDAR measures, and found three distinction relationships between snow depth and elevation: a steep relationship below 2100m where precipitation was frequently mixed rain and snow, a shallower but highly significant relationship above 2100m (in non-forested areas), and then a flat relationship but with great variance at high elevation where snow redistribution was dominant.
Related talks included Danny Marks who reported on trends and projections of the rain-snow transition line and its impacts on runoff, a poster by Anders looking at elevation- precipitation relationships from different mountain regions around the world, and another poster by Minders looking at the mechanisms for ascent-forced convective precipitation over a mountainous island in the Caribbean. Minder also gave a good paper on the mechanisms for a lowering of snow line as the rain-snow transition zone approached mountain fronts.
A23E-06. Representation of the Sierra Barrier Jet in 11 years of a high-resolution dynamical reanalysis downscaling M.R. Hughes; P.J. Neiman; E. Sukovich; F.M. Ralph
Just prior to Minder's paper on declining snow line, I listened to a fascinating talk about a low level jet that runs parallel to the Sierra Nevada in California. For years I lived in the foothills of the Sierra, and never did I suspect that a thousand feet above me was a river of air moving parallel to the crest that forced upward incoming Pacific moisture and thus initiated precipitation well before the mountains. Several other talks in this session examined the nature and the impacts of the jet. I wondered if such jets were features in other mountain ranges as well, such as the Himalaya, that block prevailing winds.
H24D-05. Widespread hillslope gullying on the southeastern Tibetan Plateau: Human or climate-change induced? (Invited) J.D. Pelletier; J. Quade; R. Goble; M. Aldenderfer
Having seen these gullies myself, I had to go to this talk, which concluded quite simply that the advent of pastoralism with a reduction in vegetation cover was insufficient in itself to initiate gullying, as gullying had not begun in earlier, drier periods when the vegetation cover had been previously reduced. The gullying required as well on-going and increasing precipitation of the late Holocene to push the landscape over a threshold. I like this line of inquiry as I think climate change impacts on geomorphology in mountains is not well researched.
GC32B-03. The Modification of Orographic Snow Growth Processes by Cloud Nucleating Aerosols (Invited) W.R. Cotton; S. Saleeby
I listened to Bill Cotton four years ago at a meeting that MRI recorded in Boulder CO . I found his talk quite interesting then and so I expected a good talk this time. I was not disappointed. Here he talked about how aerosols, which can come from pollution, changed the rate at which snow flakes form and fall, so much so that horizontal winds push the precipitation further downwind often for 10's of kilometers. In the area of the study (on the Continental Divide in Colorado) this horizontal shift in precipitation moved significant amounts of precipitation from the Colorado River Basin on the Pacific side of the Divide to the North Platte River on the Atlantic side. Thus aerosol pollution can change not only the amount but also the location of precipitation.
GC32B-04. Hydrometeorological Scales Interactions in the Andes and their Impact on the Amazon Climate (Invited) R. Avissar; D. Medvigy; R.L. Walko
This talk showed the importance of mountains to the climate of surrounding areas. These researchers use the Ocean-Land-Atmosphere Model, which, besides featuring these coupled elements, models the entire planet using a variable sized grid. It thus produces regional climate predictions from a single model with a very fine grid spacing in regions of interest and larger grid spacing over the rest of the globe. Here they demonstrated that if one did not model the topography of the Andes at a sufficiently fine scale, then predictions of the inter-annual variability of precipitation over the Amazon were incorrect. I would have liked to have heard exactly what about the topography was important in getting better predictions of precipitation over the Amazon, but a little more digging in ISI will probably lead me to the answer.
C33F-08. Past peak water in Peru’s Cordillera Blanca: diagnosing the demise of glacier influence on stream discharge M. Baraer; B.G. Mark; J.M. McKenzie
Michel Baraer participated as well in the MRI KCW on 4 Dec in Berkeley. His talk here reviewed the expected time course for stream discharge from basins in which glaciers are receding, that is, an initial increase in discharge due to the melting ice volume and then when the glaciers are considerably small a reduction in discharge. He then reviewed discharge data to show that "peak water" had already occurred in the Cordillera Blanca of Peru, and that stream discharge was now on the descending limb of the expected curve. Thus the Cordillera Blanca is now where other major "glacierized" basins, such as those in the Alps, Central Asia and the Himalayas, may be in the future.
GC34A-08. Non-linear feedbacks between climate change, hydrologic partitioning, plant available water, and carbon cycling in montane forests (Invited) P.D. Brooks; M.E. Litvak; A.A. Harpold; N.P. Molotch; J.C. McIntosh; P.A. Troch; X. Zapata
Paul Brook's talk was one of eight talks in the CIRMOUNT-organized session: GC34A. Climate Change and Drought: Climatic Water Deficit and Water Balance in Mountain Systems: Biophysics, Ecohydrology, and Impacts. All the talks here revolved around the ecological importance of potential evapotranspiration, actual evapotranspiration, and the difference between the two, climatic water deficit. All of these measures integrate precipitation and energy over the annual cycle and so are more pertinent than total annual precip or mean annual temperature at explaining the distribution and abundance of organism. I recommend that you look at all the abstracts in this session.
Brook's talk focused on some of the mechanisms related to snow accumulation and melt that strongly influenced water availability to vegetation. These include sublimation of snow, which is strongly influenced by tree canopy cover, and the depth of early snow pack as it influences the depth of frost in the soil and the soil's subsequent porosity at the time of spring snow melt. Once again, factors that one might not suspect at first (e.g. the degree of tree canopy or the timing and depth of first snowfall) turn out to be very important in the ecohydrology of mountains. Only when we know these will we be able to project better the impact of future climate and land cover change.
C44A-04. Past and future glacier changes the western Nyainqentanglha Range on the Tibetan Plateau (Invited) T. Bolch; F. Chen; W. Yang; M. Buchroithner; E. Huintjes; S. Kang; A. Linsbauer; F. Maussion; F. Paul; C. Schneider; D. Scherer; T. Yao
Tobias Bolch of the University of Zürich gave several talks at the AGU, all of them excellent. One (C43A-02) focused on a summary of glacier trends over the entire Himalaya, a definitive statement of which is essential in the face of the erroneous statements in the IPCC AR4. This talk (C44A-04) highlighted a method to assess glacial area and volume over time that is applicable at the scale of an entire mountain range. The relevance and clarity of the question was matched by the scope and completeness of the answer, representing to me the best of what research can do.
GC13C-06. Hurricanes in a Warming Climate (Invited) K. Emanuel
One of the reasons to go to the AGU is to hear talks from people who have made important contributions to the climate change debate (or to other scientific questions, such as the origin of life), even if their contribution has nothing to do with mountains. Kerry Emanuel updated his findings on the growing intensity of Atlantic hurricanes. He presented an amazing map of historic tropical cyclone paths, which clearly showed that the Pacific Ocean has many more tropical cyclones than the Atlantic ( a similar image is here) and leads one to wonder why the media focuses so strongly on Atlantic hurricanes. He noted that there is no climate change signal apparent in the intensity of Pacific cyclones, which seems to vary with ENSO. However the intensity of Atlantic hurricanes does show a climate change signal, a combination of warming sea surface temperatures coupled with a cooling tropical tropopause. He emphasized that the damage from cyclones is overwhelming associated with a few high-intensity storms so even a minor increase in intensity would have major impacts on damage.