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U.S. Geological Survey
IntroductionOver the course of geologic history, global temperatures have increased and decreased in response to a multitude of climate forcings. Instrumental records indicate that mean annual global temperatures are presently on the rise, and this trend is supported by longer-term evidence from tree rings, carbon dioxide trapped in ice cores and stable isotope ratios. Estimates of global warming during the mid-Piacenzian Age of the Pliocene Epoch (3.264 - 3.025 Ma) (see figure) suggest temperatures were 2°C greater than today. This level of warming is within the range of the Intergovernmental Panel on Climate Change (IPCC) estimates of global temperature increases for the 21st century, and no other time period in the past three million years approaches this level of warming. Scientists have identified many primary forcing mechanisms that contribute to the current global warming, but there is uncertainty about the relative impact of each forcing and associated feedbacks. The mid- Piacenzian presents the reverse situation: global data sets reveal the mature state of a warmer world, but the forcings that led to Pliocene warming are only partially identified. The data so far compiled by the Pliocene Research, Interpretation and Synoptic Mapping group (PRISM) suggest a combination of increased greenhouse gases and increased ocean heat transport acted concurrently through undetermined feedback relationships.
PRISM work is directly relevant to the USGS mission, specifically Goal 4 of the Strategic Direction, Climate Variability and Change: Clarifying the Record and Assessing Consequences, highlighted in the FY 2010 USGS Annual Science Plan for Geology. Goal 4, Anticipate the Environmental Impacts of Climate Variability, has as a primary objective: to develop high quality records of past climates and environments and provide synoptic and dynamic reconstructions of past environmental conditions. Also, research in this field will contribute to all major goals of the US Climate Change Science Program (CCSP) as well as Goal 1 of the USGS Global Change Science Strategy, Improve Understanding of Past Global Changes in Support of Policy and Management Decisions. The continued need for fundamental research into climate change is echoed by the National Research Council of the National Academy of Sciences in America’s Climate Choices and Understanding Earth’s Deep Past where the mid-Pliocene is noted specifically due to its climatic significance.
PRISM results are featured in the Paleoclimate chapter of IPCC AR4 (Chapter 6.3.2 What Does the Record of the mid-Pliocene show?) and are slated to appear in the IPCC AR5 chapters on Impacts, Adaptation and Vulnerability and Information from Paleoclimate Archives. In addition, PRISM products and byproducts feature prominently in the International Ocean Discovery Program Science Plan for 2013-2023.
The Evolution of the ProjectWhile once only a general portrayal of a warmer world, the PRISM reconstruction has evolved into a high-resolution, multi-faceted description of the most recent warm period similar to what is expected in the coming century. As such, it is used ubiquitously to ground-truth model simulations of the Pliocene and to form the basis of future model projections. At present, PRISM3 includes dramatic advances over previous versions of the reconstruction with a new deep ocean temperature reconstruction as well as an expanded and refined sea surface temperature field. PRISM3 also includes revised and updated vegetation, topography, land ice and sea ice data sets. The PRISM3 reconstruction and PRISM4 pilot studies have been used to:
PRISM and Global Climate ModelsPRISM is a collaborative data analysis and climate modeling effort that continues to evolve into a research product ever more directly relevant to USGS and DOI goals and to the US taxpayer’s daily lives. Improved PRISM datasets, comprising the most comprehensive global reconstruction for any warm period prior to the recent past, are in constant demand by national and international global climate modelers. The PRISM reconstruction challenges our understanding of the sensitivity of key components of the climate system and how we simulate that system (i.e., polar vs. tropical sensitivity, the role of ocean circulation in a warming climate, the hydrological impact of altered storm tracks, and the regional climate impacts of modified atmospheric and oceanic energy transport systems) and is used exclusively by PlioMIP in model intercomparisons designed to identify model-specific biases as well as in testing the sensitivity of future climate models.
PRISM4D Collaborating Institutions