Paleoclimate Research: Earth's Climate in Deep Time

Geological and geochemical data indicate that Earth experienced climates that were significantly warmer and colder compared to the present. Simulating Earth's climate for different geologic times allows one to study both forcings and feedbacks that establish and maintain these climate regimes. Studying climates for different time periods also allows one to look at the sensitivity of the system on a wide range of time scales. Finally, our ability to accurately simulate deep time climates under extreme forcing conditions increases our confidence in applying climate models to simulating future climate.

Deep Time Modeling Activities

NCAR's Deep Time Paleoclimate research activities are a part of the Community Climate System Modeling (CCSM) activity. A paleoclimate version of the CCSM is maintained within the Climate Change Research Section of CGD that can be applied to a wide range of deep time climate problems. Application of the CCSM to deep time climates is an important component of the overall CCSM activity. If the CCSM can accurately simulate past climate for a wide range of forcings, then one has additional confidence that the model can be used to look at future climate states. Jeffrey Kiehl and Christine Shields lead the deep time modeling activities. Christine Shields is the deep time liaison to the larger community. Simulating deep time climates extends beyond modeling the physical climate system. Kiehl and Shields have collaborated with Jean-Francois Lamarque (ACD) to model the three dimensional atmospheric chemical state of the Latest Permian (251 Ma) and the Paleocene Eocene Thermal Maximum (55 Ma) time periods. Collaborations have also been established with Natalie Mahowald (formerly of CGD, now at Cornell) to model atmospheric dust transport during the mid to late Permian. Kiehl is collaborating with Arne Winguth (U. Texas/Arlington & CGD summer visitor) on the development of an off-line ocean biogeochemical transport model, which can be driven by output from the CCSM and run for million year time scales. The goal of all of these intra-divisional and inter-divisional activities is to develop a hierarchy of modeling tools for deep time research that can be disseminated to the greater scientific community.

Important scientific findings from the current deep time CCSM3 climate simulations include:

  • Latest Permian simulations that support the hypothesis that enhanced CO2 greenhouse warming led to global ocean anoxia
  • Latest Permian atmospheric chemistry simulations indicating that release of H2S leading to an increased methane lifetime, which would cause a global collapse of the ozone layer
  • High Resolution (75 km) Latest Permian simulation that indicates the potentially important role of super hurricanes in poleward heat transport
  • Latest Permian transient simulation indicating the existence of a tipping point in high latitude ocean mixing that occurs around 2 to 3 X PAL CO2
  • Paleocene Eocene Thermal Maximum and Latest Permian cloud microphysics simulations indicating the potential role of reduced cloud condensation nuclei in increased polar warming