Columbia University
Center For Climate Systems Research



   Coupled GCM

Estimates of middle Pliocene global warming suggest that temperatures were around 2oC greater than today. This level of warming is within the range of IPCC estimates of global temperature increases for the 21st century and no other time period in the past 3 million years approaches this level of warming. Scientists have identified many primary forcings contributing to the current global warming, but there is uncertainty about the impact of those forcings and associated feedbacks. The middle Pliocene presents us with the reverse situation: global data sets reveal the mature state of a warmer world, however, the forcings that led to Pliocene warming are only partially identified. The middle Pliocene climate displays numerous characteristics akin to our expectations of the coming century: Microfaunal evidence indicates a reduced equator-to-pole temperature gradient with the greatest warming at high latitudes. Pliocene CO2 levels were elevated above pre-industrial concentrations to amounts approximately equivalent to those that the Earth's atmosphere will attain by the end of this decade. Some studies suggest that higher levels of CO2 or methane may have triggered the warming in conjunction with altered ocean circulation. However, no study has yet determined a specific set of forcings and feedbacks that led to the change in ocean circulation. The data so far compiled suggest a combination of increased greenhouse gases, altered ocean heat transports, and additional factors, acted concurrently through undetermined feedback relationships. In this study we propose a collaborative data analysis and climate modeling effort to create 3D global data sets of mid-Pliocene ocean temperature and salinity, which will form the most comprehensive global reconstruction for any warm period prior to the recent past. The data sets will be then used to drive numerical simulations designed to explore the impact of climate forcings and feedbacks during the middle Pliocene.

Annual average surface air temperature as simulated by the GISS GCM based on mid-Pliocene boundary conditions supplied by the USGS PRISM Project (version 2). The global average temperature is 2.2oC above the modern climate control run. Cooling over eastern Africa is largely related to the increased elevation of the East African rift zone during the Pliocene.