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 any human related changes must take into account natural climate variability and the complex interactions of the different components of the Earth’s climate system. As part of the USGS  Global Change Research effort,   the 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.

   The PRISM Project had two primary goals.  The first was to identify and characterize the nature and variability of climate during this time of past global warming as an indication of how the Earth might respond to future warming.  The second goal was to develop a series of global scale, quantitative datasets for use in experiments to model climate and environmental conditions during the mid Pliocene.   The Pliocene reconstruction is being used to test the ability of climate models to simulate past warmer conditions on earth and to provide insights into the mechanisms and effects of global warming.

   The purpose of this report is to document and explain the PRISM2 mid Pliocene reconstruction.  The PRISM2 reconstruction consists of a series of 28 global scale data sets on a 2° latitude by 2° longitude grid.  As such, it is the most complete and detailed global reconstruction of climate and environmental conditions older than the last glacial.