HR: 09:00h
AN: H51I-04    [Abstracts]
TI: Can We Detect a Signal of Anthropogenic Climate Change in California During the 20th Dentury?
AU: * Bonfils, c
H51I-04 AF: University of California, Merced, PO Box 2039, Merced, ca 95344 United States
AU: Duffy, p
H51I-04 AF: University of California, Merced, PO Box 2039, Merced, ca 95344 United States
AU: Duffy, p
H51I-04 AF: Lawrence Livermore National Laboratory, L-103, PO Box 808, Livermore, ca 94550 United States
AU: Santer, B
H51I-04 AF: Lawrence Livermore National Laboratory, L-103, PO Box 808, Livermore, ca 94550 United States
AU: Wigley, T
H51I-04 AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305 United States
AB: Detection of climate change involves finding an unusual trend in climate observations. To attribute an observed changes to human causes, one must demonstrate that it is unlikely to be explained by the natural internal climate variability alone, or by natural forcings (e.g. solar variability and volcanic aerosols). Most studies of the possible causes of the 20th century climate change are based on statistical comparisons of observed and simulated quantities, such as surface temperature, height of the tropopause or ocean heat content on the global scale. Detection and attribution of climate change to human causes at continental or regional scale is more challenging, because natural climate variability becomes larger, the forcings are more heterogeneous and the models are less skillful. The objective of this study is to investigate signatures of 20th-century climate change related to human activities, with an emphasis on the state of California. To look for human-induced climate change in California, we use several observational climate records of surface temperature, precipitation and diurnal temperature range along with the latest pre-industrial and historical GCM simulations available in the context of the IPCC Fourth Assessment (AR4). In the detection component, we investigate whether or not an estimate of natural internal variability of the climate system deduced from the IPCC pre-industrial runs can explain observed historical climate changes in California. Next, we assess if we can attribute the observed trends to our "best estimate" of effects of historical forcings described by the IPCC AR4 20th century ensemble simulations. This should also indicate if the inclusion of new anthropogenic forcings (such as the black carbon emission, or land use) to the ones usually applied (greenhouse gases, direct effect of sulfate aerosols) affects the regional detection of climate change.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1626 Global climate models (3337, 4928)
DE: 1632 Land cover change
DE: 1637 Regional climate change
DE: 1834 Human impacts
SC: Hydrology [H]
MN: Fall Meeting 2005