Climate Change Research
A millennium of climate change
Researchers at the National Center for Atmospheric Research continued their benchmark 1,000-year Community Climate System Model (CCSM) control run and extended the Parallel Climate Model (PCM) control run to nearly 1,500 years (Figure 5). Science experiments with the PCM included historical 20th century climate simulations using various combinations of specified greenhouse gases, atmospheric sulfate concentrations, solar and volcanic forcing, and tropospheric and stratospheric ozone. This set of experiments represents the most extensive set of 20th century forcing climate simulations ever attempted.
A. Dai, A. Hu, G. A. Meehl, W. M. Washington, and W. G. Strand, “North Atlantic Ocean circulation changes in a millennial control run and projected future climates,” Journal of Climate (in press). BER, SciDAC, NSF
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Figure 5. |
Multiresolution climate modeling
Baer and colleagues have developed the Spectral Element Atmospheric Model (SEAM) to incorporate local mesh refinement within a global model. This makes it feasible to model the interaction between coarse-scale and fine-scale phenomena. The method implies improved climate and turbulence simulations by allowing increased resolution in a few dynamically significant areas, such as fronts or regions of dense topography. Similarly, regional climate simulations may be improved by allowing regional resolution to be incorporated within a global model in a two-way interactive fashion.
F. Baer and J. J. Tribbia, “Sensitivity of atmospheric prediction models to amplitude and phase,” Tellus (submitted, 2003). BER, SciDAC
Sorting out the sources of tropospheric ozone
Ozone in the troposphere is both formed in situ and transported from the stratosphere, which has much higher ozone levels. The importance of each source may vary both regionally and seasonally. Atherton et al. analyzed the results of a simulation in Phoenix from April 1 through October 31, 2001. Their results showed that there are periods of time during the “ozone season” in which higher levels of surface ozone may be due to transport of stratospheric ozone from above, rather than created by ground-level (and energy-related) processes.
C. Atherton, D. Bergmann, P. Cameron-Smith, P. Connell, D. Rotman, and J. Tannahill, “Large scale atmospheric chemistry simulations for 2001: An analysis of ozone and other species in central Arizona,” American Meteorological Society 83rd Annual Meeting, Long Beach, California, February 2003. BER
Do soot and smoke contribute to climate change?
Soot and smoke contain black carbon which absorbs solar radiation. These aerosols have been thought to enhance climate warming by absorbing radiation that might otherwise be scattered and by reducing overall cloudiness. Penner et al. evaluated forcing and changes in atmospheric temperature and clouds associated with both direct and indirect effects of soot and smoke using an atmospheric-climate model coupled to their chemical-transport model. They found that climate forcing by soot and smoke was not as large as previously claimed, because the adjustment of the atmospheric temperature and clouds to aerosols tends to decrease the forcing, particularly if the aerosols reside at higher levels within the atmosphere.
J. E. Penner, S. Y. Zhang, and C. C. Chuang, “Soot and smoke aerosol may not warm climate,” J. Geophys. Res., in press (2003). BER
Carbon-cycle feedback in climate change
Taking into account the feedback effects of climate change on absorption of carbon by the ocean and terrestrial biosphere will allow better predictions of future climate; however, these effects are ignored in present U.S. climate models. Thompson et al. have obtained the first results from a fully coupled, non-flux-corrected, multi-century climate-carbon simulation. They have performed three complete simulations: a control case with no emissions, a standard case, and a case where the uptake of CO2 by vegetation is limited. The limited case shows that substantially more CO2 stays in the atmosphere when carbon uptake by vegetation is reduced, thus giving a range of uncertainty in current carbon-climate modeling.
S. Thompson, B. Govindasamy, J. Milovich, A. A. Mirin, and M. Wickett, "A comprehensive GCM-based climate and carbon cycle model: Transient simulations to year 2100 using prescribed greenhouse gas emissions," Amer. Geophys. Union Mtg., San Francisco, CA, December 2002; Lawrence Livermore National Laboratory technical abstract UCRL-JC-149761. BER, LLNL