Paleoclimate

Paleoclimate research has both historical and applied scientific objectives. The study of past climates helps us to more fully understand the evolution of the Earth's atmosphere, oceans, biosphere and cryosphere. Additionally, paleoclimate studies help us to quantify properties of Earth's climate, including the forces that drive climate change and the sensitivity of the Earth's climate to those forcings.

At GISS, paleoclimate research focuses mainly upon the use of global climate models (GCMs) to generate simulations of past climates. We use GCMs in combination with geophysical, geochemical and sedimentological data analyses to reconstruct various time periods and events in Earth's climate history. Paleoclimate simulations are also used to validate the ability of our computer models to accurately represent climates that differ significantly from the present. The ability to simulate know climate changes that occurred in the past strengthens our confidence in the conclusions drawn from simulations of future climate.

Commonly, GCM simulations are used to corroborate or refute hypotheses first drawn from paleoclimate data or to sort out conflicting data interpretations. However, since GCMs are capable of simulating numerous climate variables that are largely unattainable from the geologic record (e.g., cloud distribution, wind patterns, energy transports and radiative fluxes), they offer insight into a broad range of complex processes. Models also provide complete global coverage while data provide unequal, perhaps biased, coverage of Earth's surface. Finally, because paleoclimate simulations can, to a certain degree, be verified, they help us test and improve developmental GCM formulations.

Numerous time periods throughout Earth history have been simulated using the GISS GCM. The climates of the past interglacial and the onset of the most recent glaciation (c. 125,000 years ago) plus the climate of the Last Glacial Maximum and Holocene have received great attention. Vast amounts of data exist for these relatively recent periods, providing an excellent validation set for the models as well as a test of the model's sensitivity to carbon dioxide change. Climates of much older time periods have also been simulated, including the extreme glacial periods of the Neoproterozoic (750 million and 600 million years ago), which have been referred to as "Snowball Earth" periods because much of the Earth was covered by ice. Such ancient climates test the sensitivity of the GCM to large changes in geography, greenhouse gases, solar luminosity and ocean heat transports. Conversely, climate change simulations of the last 500 years test the effects of very small forcing changes in solar radiation and atmospheric constituents.

Of course, several warm time periods are also of particular interest because of the insights they reveal regarding processes and impacts related to global warming scenarios. For most of the Phanerozoic Era (the past 600 million years) the Earth has been warmer than it is at present. Thus, there are numerous warm periods and warming events that we explore. The middle Pliocene (3 Ma), the Late Paleocene (58 Ma), the Paleocene-Eocene Thermal Maximum (55 Ma), the Cretaceous (130 Ma-65 Ma), and the Early Jurassic (180 Ma) are among the warm periods that we have studied using both climate modeling and paleoclimate data analyses.

Related News and Science Briefs

January 2007:
Sea Level Rise, After the Ice Melted and Today

November 2005:
Mineral Clues to Past Climates

May 2005:
Marshes Tell Story of Medieval Drought, Little Ice Age, and European Settlers near New York City

January 2003:
Ocean Burps and Climate Change?

October 2002:
Did the Snowball Earth Have a Slushball Ocean?

December 2001:
Methane Explosion Warmed the Prehistoric Earth, Possible Again

November 2001:
Ocean Circulation Shut Down by Melting Glaciers After Last Ice Age