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CCR Highlights for Executive Summary
CCR uses climate system models to study the sensitivity and stability of the Earth
system to a variety of forcings, including changes of greenhouse gases, aerosols, solar
irradiance, volcanic forcing, land characteristics, and land use change. Also, CCR
provides a focal point for NCAR and university paleoclimate research and serves as a
resource to the paleoclimatic and climate change research community in the use of the
Community Climate System Model (CCSM).
The section’s research is supported by several agencies including the Department of
Energy.
Simulating the Climate of the Late Permian
Jeffrey Kiehl (CCR) and Christine Shields (CCR) have been researching one of the
more intriguing time periods in Earth’s history, the boundary between the Late Permian
and Triassic periods at 251 Ma (1). This boundary marks the largest extinction recorded
in Earth’s history. Kiehl and Shields are carrying out the first fully coupled climate
simulation for this time period. They find the western tropical Panthalassic ocean has a
warm pool of water with SSTs reaching 33 °C, compared to the present day western
Pacific warm pool temperatures of 30 °C. The warmest regions over land occur in the
subtropical desert regions.
Climate of the last 150,000 Years
Carrie Morrill (CCR) is creating a database of high-resolution paleoclimate records for
studying abrupt climate change during the last deglacial and the Holocene. These
records have been selected from the large number of published paleoclimate records
for their robust age models and well-supported climatic interpretations. For the midHolocene, Morrill has found several periods of preferred change, centered on ~4200
and ~5600 years ago. Abrupt changes at these times occurred over decades to
centuries and were associated with the transition from the Holocene climatic optimum to
the Neoglacial, during which temperature decreased in the middle to high latitudes and
precipitation decreased in the tropics. The event at ~4200 years ago was also
associated with archaeological evidence for the collapse of several ancient civilizations,
including the Akkadian in Mesopotamia and the Indus in India and Pakistan.
Natural Climate Variability During the Period of Annually Resolved Records
Caspar Ammann (CGD-CCR) and Robert Tomas (CGD-CCR, supported by the
Weather and Climate Assessment Science Initiative of Linda Mearns, ESIG) use highresolution paleoclimate proxy records in an attempt to extend the limited (~150 years)
instrumental record. Prior centuries and millennia have exhibited significant natural
climate variations that had a tremendous impact on the environment and societies
around the world. Climate modeling using NCAR-CSM 1.4 and NCAR-CCSM 3
Land-Atmosphere Interaction and the Water Cycle
Global climate models are often employed to investigate whether and how soil moisture
anomalies affect weather and climate both in the current and in a potentially different
future climate. A recent model intercomparison by David Lawrence demonstrated that
the degree of land-atmosphere interaction varies widely between current state-of-the-art
atmospheric general circulation models (AGCMs).
Effects of Land Cover Changes as Part of the IPCC Assessment
Johannes Feddema of the Department of Geography at the University of Kansas used
the PCM to assess the sensitivity of a fully coupled climate model to changes in land
cover. By comparing three simulations representing present day land cover from
different data sources we conclude that there is significant model sensitivity to land
cover characterization, with an observed average global temperature range of 0.21K
between the simulations.
Examination of Future Abrupt Climate Change
Aixue Hu, with Gerald Meehl and Weiqing Han (at PAOS, CU) worked on the detecting
the thermohaline circulation changes from ocean properties using NCAR’s CCSM2
model since significant changes of the thermohaline circulation (THC) are likely to
cause abrupt climate change. Here we intend to find a simple measure to detect
changes in THC through examining several factors proposed to control the THC
variations using a coupled climate model. These factors are Equatorial-South Atlantic
upper ocean temperature, Southern Ocean freshening, inter-basin sea surface salinity
contrast, and meridional steric height gradient. A new result presented here is that the
inter-basin sea surface temperature contrast between North Atlantic and North Pacific is
found to be an indicator of THC changes.
Future Climate Change: The IPCC Simulations
This production effort represents a multi-institutional distributed effort by scientists and
software engineers at the National Center for Atmospheric Research (NCAR), Oak
Ridge National Laboratory (ORNL), National Energy Research Supercomputing Center
(NERSC) and the Lawrence Berkeley National Laboratory (LBNL).The IPCC scenarios
that are being run can be categorized into two groups: a set of "commitment scenarios"
and a number of "science scenarios" that explore alternative future emissions
outcomes. The IPCC SRES science scenarios that were recommended to the global
coupled climate modeling groups by the IPCC WG1 include SRES A2, SRES A1B,
SRES B1. The A2, A1B and B1 scenarios consist of five-member ensembles run from
the year 2000 to the year 2100. Then, commitment scenarios are run with the
concentrations of all atmospheric constituents in A1B and B1 held constant at year 2100
values, and the model continues to the year 2200 with five member ensembles. One of
the ensemble members from each is continued for an additional 100 years to the year
2300 with constant year 2100 concentrations. There is also a 20th century commitment
scenario that freezes concentrations at levels observed in the year 2000, and the model
is run to the year 2100.
This production effort represents a multi-institutional distributed effort by scientists and
software engineers at the National Center for Atmospheric Research (NCAR), Oak
Ridge National Laboratory (ORNL), National Energy Research Supercomputing Center
(NERSC) and the Lawrence Berkeley National Laboratory (LBNL).
The IPCC scenarios that are being run can be categorized into two groups: a set of
"commitment scenarios" and a number of "science scenarios" that explore alternative
future emissions outcomes. The IPCC SRES science scenarios that were
recommended to the global coupled climate modeling groups by the IPCC WG1 include
SRES A2, SRES A1B, SRES B1. The A2, A1B and B1 scenarios consist of fivemember ensembles run from the year 2000 to the year 2100. Then, commitment
scenarios are run with the concentrations of all atmospheric constituents in A1B and B1
held constant at year 2100 values, and the model continues to the year 2200 with five
member ensembles. One of the ensemble members from each is continued for an
additional 100 years to the year 2300 with constant year 2100 concentrations. There is
also a 20th century commitment scenario that freezes concentrations at levels observed
in the year 2000, and the model is run to the year 2100.
This figure shows CCSM3 DOE/NSF IPCC scenario runs as of 4 October 2004.
Observed forcings (solar, volcanoes, greenhouse gases, sulfate aerosols, carbon
aerosols, and ozone) are used during the historical period, from years 1870-2000. A
variety of future forcing scenarios (20th Century freeze, B1, A1B, and A2) are used from
years 2000-2200 to simulate the most likely range of future climates. Two of the
commitment scenarios (A1B and B1) will be executed out to year 2300.