PP53A-1380 1340h
Verification of multi-proxy paleoclimatic studies: a case study
Multi-proxy studies have been the primary means of transmitting paleoclimatic findings to public policy. For policy use, such studies should be replicable in the sense of King (1995). The best-known and most widely applied multi-proxy study is Mann, Bradley and Hughes (1998) ("MBH98") and its 1999 extension, which claimed to have exceptional "robustness" and "skill". We attempted to replicate MBH98 results and found, among other problems, that MBH98 methodology included two important unreported steps: (1) Subtraction of the 1902-1980 mean prior to principal components (PC) calculations (rather than, say, the 1400-1980 mean in the AD1400 step); (2) Extrapolation of a duplicate version of the Gasp, tree ring series. We show that high early 15th century values occur in important variations and that their results are not robust to the following: (1) Presence or absence of the extrapolation of 4 years at the beginning of the Gasp, tree ring series; (2) subtraction of the 1400-1980 mean rather than subtraction of the 1902-1980 mean, while using the same number of retained PC series in each step as MBH98; (3) the presence or absence of the North American PC4, while subtracting the 1400-1980 mean and using 5 PCs in the AD1400 step; (4) presence or absence of a small subset of high-altitude tree ring sites, mostly "strip bark" bristlecone pines, mostly collected by one researcher, Donald Graybill. The subtraction of the 1902-1980 mean dramatically inflates the role of the bristlecone pine sites, which then impart a distinctive hockey stick shape to the MBH98 PC1 and then to the NH temperature reconstruction. MBH98 claimed "skill" through apparently significant Reduction of Error (RE) statistics, reporting 0.51 in the AD1400 step, as compared to a reported 99 percent significance level of 0, which they calculated through simulations using red noise with low AR1 coefficients (0.2). We benchmarked a more realistic significance level by applying MBH98 PC methods to 10,000 sets of 70 red noise series modeled through fractional difference models to have the same red noise persistence as the critical North American AD1400 tree ring network. These calculations regularly resulted in "hockey-stick" shaped PC1s with sharp inflections at the start of the 20th century. We then modeled the resulting 10,000 PC1s against NH temperature and found that the 99 percent RE significance level was 0.59. By this benchmark, the reported RE statistic (0.51) in MBH98 for the AD1400 step lacks statistical significance. Most dendroclimatic reconstructions also provide statistics other than an RE statistic, including R2 and Coefficient of Efficiency, but MBH98 does not and the authors have refused to provide supporting data from which the statistics can be calculated. In our emulations of their calculations, we have been unable to replicate anything close to the reported RE results other than through re-tuning, a procedure not described in MBH98. With a re-tuning step, for the critical AD1400 step, we have obtained an RE of 0.46, but with an R2 of only 0.02 and a CE of minus 0.26, all of which lack statistical significance. This case study illustrates for extreme caution in basing public policy on articles, such as MBH98, whose claims cannot be verified.
http://www.climate2003.com/agu.2004.html
PP53A-1381 1340h
Response of Coupled Atmosphere-Ocean GCM to Ice Age Conditions and CO2 Changes
Reconstructions of the Last Glacial Maximum (LGM, 21ka) climate from paleoclimatic data is expected to provide an opportunity for an extreme test of the possibility of Coupled Atmosphere-Ocean GCM's to simulate climate changes and help us understand the mechanism of climate change. To simulate the LGM and compare it with global warming (cooling) experiments by CO2 increase (decrease), here we use a coupled GCM of CCSR/NIES/FRCGC renewed and frozen for the submission of IPCC/AR4 optimized to be run on a super-computer "Earth Simulator". The model has a resolution of T42 (2.8 deg. for longitude and latitude) layers 20 for the atmospheric part and 1 to 0.5 deg. with 48 levels for the ocean part, which are synchronously coupled without flux adjustment and without any acceleration techniques. To separate the role of greenhouse gases and other components (mainly the ice sheet part), numerical experiments with LGM conditions as well as Glacial CO2 level are performed for 1000 years. The preliminary results show that the total LGM forcings bring about 3.2 deg of global cooling in 250 years, while the glacial CO2 has an impact to cool the climate by 2.2 deg C, and the low latitude climate sensitivity is within the range paleo-data indicate. The sensitivity of east Pacific is larger than the West Pacific whose pattern is quite similar for global warming experiment. The impact of ice sheet upon the ocean temperature is pronounced in the North Atlantic but even in the northwest Pacific region. The NADW is first strengthened from 20 Sv level to 30 Sv level in case of full LGM condition in 250 years and to 25 Sv level in case of Glacial CO2 case, although it is gradually weakening and cross the control level after 600 years. Further investigation for atmospheric circulation and ocean response compared with other GCMs are discussed in the presentation.
PP53A-1382 1340h
Pliocene Sea Surface Temperature Variability
Anthropogenic greenhouse gas emissions and modification of land surfaces are expected to cause the earth's climate to warm. However the amount and details of the warming are still highly uncertain. Identifying and predicting human related changes must take into account natural climate variability and the complex interactions of the different components of the Earth's climate system. The USGS PRISM (Pliocene Research, Interpretation and Synoptic Mapping) Project has documented the characteristics of middle Pliocene climate on a global scale. The middle Pliocene was selected for detailed study because it spans the transition from relatively warm global climates when glaciers were absent or greatly reduced in the Northern Hemisphere to the generally cooler climates of the Pleistocene with expanded Northern Hemisphere ice sheets and prominent glacial-interglacial cycles. Present work focuses on establishing reasonable limits of variability around the PRISM2 SST reconstruction. Minimum and maximum possible warming, based upon the peak averaging technique, was established at each of the 72 original data localities. Minimum possible February and August contour maps were created and the derivative 10 months manufactured using standard procedures. The same methodology was utilized for the maximum possible warming. These 24 new monthly data sets establish limits about the original PRISM2 SST reconstruction and are useful for modeling experiments where the PRISM2 reconstruction and model results are not in agreement.
http://geology.er.usgs.gov/eespteam/prism/prism3main.html
PP53A-1383 1340h
The Need for More Precise, Accurate, and Complete Plant Distribution Data, and Its Importance in Reconstructing Past Climates
Paleoecological climatic reconstructions and predictions of future vegetation change usually rely on changes in plant distributions relative to those of today. Unfortunately, modern distributions of most plant species are poorly known, or they are mapped with very low accuracy, or incompletely, sometimes omitting entire regions of occurrence. This research compares climatic inferences from some plant species based on different modern distribution datasets. The most complete dataset, compiled by Elbert Little prior to the advent of geospatial technology, is generalized and contains displacement errors of up to 15 km. These data were compared to more detailed distribution maps constructed through compilation of georeferenced data from multiple sources to map the same species with greater precision. Each distribution was processed through ClimLim, a program that determines which climatic variables statistically limit the spatial range of a distribution. Results indicate large differences in the paleoclimate implications of the two distributions, emphasizing the importance of improved datasets in reconstructing past climates and future species distributions. Hence, it should be a priority to acquire or produce highly accurate plant species distribution data.
PP53A-1384 1340h
Differential Response in Plant Taxa Morphology and Physiology During Increases in Late-Quaternary Atmospheric CO$_{2}$ Concentrations Affect Plant-Climate Interactions.
The effects of changing atmospheric CO$_{2}$ on plant physiology mediate vegetation response to climate change. For example, growth chamber studies on short-lived plants show significant changes in plant morphology and physiological parameters such as changes in biomass and water-use efficiency (WUE; the amount of carbon assimilated to plant water-loss) as atmospheric CO$_{2}$ concentrations increases from $\sim$200 p.p.m. to modern concentrations and beyond. Many modern studies show WUE increases linearly with rising atmospheric CO$_{2}$ meaning that less water is expended for each unit of carbon assimilated. To test for the consistency of these findings with past, long-lived plants and in past communities growing under a similar range of atmospheric CO$_{2}$ levels, macrofossils of select species were analyzed from packrat ({\it Neotoma} sp.) midden chronologies gathered throughout western North America. Measurement of and analysis for the stable isotope content of these macrofossils shows greater morphological and eco-physiological differences between species than expected from study results using growth chambers. For example, isotopic analysis shows long-standing associates, {\it Pinus edulis} and {\it Juniperus} spp. have significantly different WUE during the transition from the Pleistocene to the Holocene. The WUE in {\it Pinus edulis} matches changes in atmospheric CO$_{2}$ whereas {\it Juniperus} spp. does not. Yet over the same period, changes observed in {\it Pinus flexilis} needles from trees growing in cooler habitats above the pinyon-juniper woodlands are more similar to {\itJuniperus} spp. changes compared against trends in the more closely related {\it Pinus edulis}. Morphology changes occurring during this period include increased biomass and reduced stomata. These results show taxonomic differences in the morphological and physiological adaptation to changing CO$_{2}$ concentrations. These responses need further assessment especially in light of their direct affect on plant-climate interactions.
PP53A-1385 1340h
Improving the usefulness of paleoenvironmental data: moving from archival to research data bases
Archival databases seek to faithfully represent published data, although sometimes with slight modifications for updated taxonomy or standard descriptions. Over the past decade NOAA, the USGS, other agencies, and groups have produced archival databases for present-day and late-Quaternary North American pollen, woody plant distributions, plant traits, packrat middens, and lake-levels. These archival databases provide valuable information on environmental change, but are of use largely to experts in these fields. With our collaborators, we seek to develop "research databases" that transform, concatenate, and/or summarize paleoenvironmental data in ways that provide meaningful access to a wider community of scientists studying and modeling paleoenvironmental and paleoclimatic change. For example, the USGS/NOAA North American Packrat Midden Dataset is an archival dataset composed of plant macrofossil data derived from packrat middens in western North America. A subsequent research dataset derived from the archival data by transforming raw relative abundance data into standardized presence absence data is of greater use to non-experts. Going a step further, the BIOME6000 project has developed methods to transform disparate arrays of paleobotanical information (stored in separate databases) into uniform descriptions of the past occurrences of plant functional types and biomes. These plant types and biomes can be compared globally and used to test model prediction. Similarly, the interpretation of paleoecological and paleohydrographic data in terms of changes in "effective moisture" by COHMAP provides a means of interpreting synoptic-scale changes in climate, and such changes can be compared with model simulations.
PP53A-1386 1340h
Combining Paleoenvironmental Data with Model Simulations to Understand Long-term Environmental Changes in the Upper Colorado Basin
The Upper Colorado Basin (UCB) is an important source of water and power for cities, farms, and other interests from the plains of Colorado to the Pacific Ocean. The region is currently experiencing a multi-year drought that is affecting Colorado River flows and is implicated in the high mortality rate of pinyon pines in the region among other ecosystem impacts. Tree-ring studies indicate that large-scale droughts are a persistent feature of the past 700 years and severe droughts have occurred throughout the historic period. How will future climate change alter the magnitude and frequency of droughts in the UCB region? This presentation describes a research framework for integrating paleoenvironmental data with model simulations to assess both past and potential future changes in climate variability and the magnitude and frequency of drought for the UCB. Late Pleistocene and Holocene paleoenvironmental data are available from several areas within the UCB, with packrat midden studies available from the lower elevations and lacustrine and palynological records available from moist environments in the mountains. Collectively these data reveal that large-scale changes in the distribution of ecosystems have occurred through time in the UCB, suggesting variations in sources and amounts of precipitation over the course of centuries and millennia. These past variations greatly exceed those observed in the instrumental and dendrochronological data for the last several centuries. The latter data provide some context for assessing the severity of the current drought in regard to the current climate state, whereas the longer-term paleoenvironmental variations may be more similar in amplitude to potential future changes in climate in the UCB. Assessment of the potential effects of future climate change on the UCB requires: 1) devising means to integrate the instrumental, dendrochronological, and paleoecological records to provide a long-term synthesis of paleoclimatic variability, 2) developing a nested approach of global-regional-process models to simulate past conditions, 3) using the comparisons between the paleoenvironmental data and model simulations to evaluate model performance, and, 4) using the models to simulate potential future variations in environmental conditions in the UCB.
PP53A-1387 1340h
NSF-PARCS: A Case Study in Proxy Climate Syntheses for the CCSP Assessment
The research agenda of the NSF-funded Paleoenvironmental Arctic Sciences (PARCS) program has focused recently on high-resolution records that provide quantifiable estimates of past climates. Syntheses of this research are planned to meet the needs of both the research community and the US Climate Change Science Program. PARCS provides a case study into how proxy climate data generated by a group of collaborating scientists have input into a broader assessment. PARCS was founded in 1999 as an NSF initiative straddling the Arctic System Science (ARCSS) and the Earth System History (ESH) programs to foster a wide range of research on paleoenvironmental change in the Arctic. In March 2001, the PARCS scientific community met to focus its research agenda with the goal of more directly contributing to global-change assessments by providing high-resolution, quantified estimates of past climate. The result was the science plan, "Modes of Arctic Climate Variability and Warmth," an area of research interest under the ESH Program. The plan identified a suite of deliverables that mesh with products now identified by the 2003 CCSP. PARCS has organized workshops addressing this suite of deliverables on the subjects of warm Arctic scenarios (the last interglacial and the Holocene thermal maximum) and variability in Arctic summer temperatures (annual to decadal scale resolution) to review and assemble proxy climate data in preparation for peer-reviewed summaries and for broader dissemination of data syntheses. The goal is to generate data related to these specific themes, and to integrate these data with records currently being produced by other groups nationally and internationally. The data will be assembled, analyzed, and presented as part of a searchable geo-referenced database. PARCS' vehicle for presenting these syntheses beyond peer-reviewed publication is a web-enabled database. The database is being assembled by a PARCS-dedicated data manager whose duties include creation of data-visualization products. Initial PARCS data syntheses and presentations were accomplished by combining the synthesis results with methods, visualizations, and primary data accessible through static html pages on the World Wide Web. With the most recent PARCS efforts, we are expanding our approach by co-developing a single, multi-proxy database with the World Data Center for Paleoclimatology (WDCP) to house these and other non-PARCS projects. One goal of this database, termed "Open", is to meet the data needs of global-change assessments at the national and international levels. Open will maintain links between primary and synthesized data, allow expanded searches (e.g. searching in spatial, temporal, and/or structural contexts across proxies) and provide improved data viewing via maps, animations and time series. In short, Open includes both the database, and the tools to help the user explore the proxy climate data. An up-dated version of PARCS data will be available through Open by August 2005 and will contribute to the "two-year" goals of the 2003 CCSP.
http://www.ncdc.noaa.gov/paleo/parcs