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 per spective, 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 condi tions. Paleoclimatologists are geologists who study past climates to answer ques tions 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 scientific research. Still, the most danger ous aspect of our changing climate is the uncertainty in the exact nature and rate of projected climate change.

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).

To reduce the uncertainties, USGS paleoclimatologists are studying a pos sible 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 tem peratures 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 inter val 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 con ditions 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 numeri cal models of climate designed to assess the models’ ability to “hindcast” past climates. In theory, accurately reproduc ing 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 proxies and provide the impetus for new discoveries.

Figure 3. Map of August sea-surface temperature (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.

For example, PRISM data indicate extreme warming of the mid-Piacenzian North Atlantic Ocean and nearby Arctic Ocean (fig. 3). This is where North Atlan tic 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 thermoha line circulation slows when sea surface temperatures are warmer. However, inde pendent 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 Geological Survey

For more information, please contact:

Marci Robinson or Harry Dowsett U.S.

In summary, USGS paleoclimatologists are pursu-

ing paleoclimate studies to further our understanding of the past and future warm climates and their impacts.

are inadequate in this region and are dramatically underestimating climatic consequences for the Eastern United what our climate will be in the future, or climate models 20192

Telephone: 703–648–5291/5282 Fax: 703–648–6953 926A National Center Reston, VA

model simulations of future climate. The paleoclimate data collected provide important ground truth for the models and can lead to improved

increase confidence in future climate projections. States and Western Europe. Continued comparisons of paleoclimate data and model simulations are necessary to or hdowsett@usgs.gov

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