Why Study Paleoclimate?
 

U.S. Geological Survey (USGS) 

researchers are at the forefront of 

paleoclimate research, the study of past 

climates. With their unique skills and perspective, only geologists have the tools 

necessary to delve into the distant past 

(long before instrumental records were 

collected) in order to better understand 

global environmental conditions that 

were very different from today’s conditions. Paleoclimatologists are geologists 

who study past climates to answer questions about what the Earth was like in the 

past and to enable projections, plans, and 

preparations for the future. 

The Intergovernmental Panel on 

Climate Change (IPCC) has projected 

a future warmer climate that has the 

potential to affect every person on Earth. 

Extreme weather events, rising sea level, 

and migrating ecosystems and resources 

could result in worldwide socio-economic 

stresses if not met with prudent and 

proactive action plans based on quality 

Figure 1. Photomicrographs of examples 

from microfossil groups used by USGS 

researchers to study past climates. Clockwise 

from upper left: ostracode Cativella navis, 

planktic foraminifer Globigerinoides obliquus, 

diatom Actinoptychus senarius, benthic 

foraminifer Ammoelphidiella antarctica, pollen 

grain of Malabaila pumila (Umbelliferae). 

scientific research. Still, the most dangerous aspect of our changing climate is the 

uncertainty in the exact nature and rate of 

projected climate change. 

To reduce the uncertainties, USGS 

paleoclimatologists are studying a possible analog to a future warmer climate. 

The middle part of the Piacenzian Stage 

of the Pliocene Epoch, about 3.3 to 3.0 

million years ago, is the most recent 

period in Earth’s history in which global 

warmth reached and remained at temperatures similar to those projected for 

the end of this century, about 2°C to 3°C 

warmer on average than today over the 

entire globe. This past warmer time interval preceded the ice ages but was recent 

enough, geologically, to be very similar 

to today in terms of ocean circulation 

and the position of the continents. Also, 

the populations of plants and animals 

were much like those of today, and so 

geologists can use their fossils (fig. 1) to 

estimate past environmental conditions 

such as temperature and sea level. 

The USGS Pliocene Research, 

Interpretation and Synoptic Mapping 

(PRISM) Group has reconstructed global 

surface and three-dimensional ocean conditions including sea surface temperature, 

vegetation, sea ice extent, land ice extent, 

topography, deep ocean temperature, and 

sea level for the mid-Piacenzian by using 

fossils and other proxy data (fig. 2, on 

back). The PRISM digital reconstructions 

provide boundary conditions for numerical models of climate designed to assess 

the models’ ability to “hindcast” past 

climates. In theory, accurately reproducing a past climate increases confidence 

in the models’ ability to forecast a future 

climate. 

While paleoclimate studies lead to 

fewer uncertainties about future climate 

projections, paleoclimate modeling can 

also lead to improved reconstructions 

based on data. That is, unexpected model 

results often expose intriguing scientific 

questions that require expanded data 

coverage or the development of new 

Figure 3. Map of August sea-surfacetemperature (SST) anomalies produced by 

subtracting modern temperatures from midPiacenzian temperatures. Although there is 

little temperature difference near the Equator, 

a large temperature difference exists in the 

North Atlantic and Arctic Oceans where 

mid-Piacenzian water was much warmer. The 

continental outline incorporates a 25-meter 

sea-level rise due to the warmer temperatures 

and lacks glacial features like the Great Lakes 

that did not exist during the Pliocene. 

proxies and provide the impetus for new 

discoveries. 

For example, PRISM data indicate 

extreme warming of the mid-Piacenzian 

North Atlantic Ocean and nearby Arctic 

Ocean (fig. 3). This is where North Atlantic Deep Water formation occurs (when 

cold salty dense surface water sinks) and 

drives the global ocean thermohaline 

circulation. Conventional wisdom states, 

and model simulations agree, that deep 

water formation decreases and thermohaline circulation slows when sea surface 

temperatures are warmer. However, independent studies based on very different 

lines of evidence show an increase in the 

formation of North Atlantic Deep Water 

at this time. Either the mid-Piacenzian 

climate system in the North Atlantic and 

Arctic Oceans was very different from 

U.S. Department of the Interior Fact Sheet 2010–3021 Printed on recycled paper U.S. Geological Survey April 2010 
Figure 2. Map of mid-Piacenzian climate during the Pliocene Warm Period (PWP); the colors show the mean annual temperature differences in degrees Celsius 

subtracted from PWP temperatures. To meet the goals of the USGS Pliocene Research, Interpretation and Synoptic Mapping (PRISM) Group, scientists rely on prNotes on the map are examples of PRISM findings based on climate proxies. what our climate will be in the future, or climate models In summary, USGS paleoclimatologists are pursu- For more information, pleare inadequate in this region and are dramatically under- ing paleoclimate studies to further our understanding Marci Robinson or Harrestimating climatic consequences for the Eastern United of the past and future warm climates and their impacts. U.S. Geological Survey States and Western Europe. Continued comparisons of The paleoclimate data collected provide important 926A National Center paleoclimate data and model simulations are necessary to ground truth for the models and can lead to improved Reston, VA 20192 increase confidence in future climate projections. model simulations of future climate. Telephone: 703–648–52

Fax: 703–648–6953 Email: mmrobinson@us

By Marci Robinson and Harry Dowsett Web: http://geology.er.us