Dimethylsulphide production in the subantarctic Southern Ocean under enhanced greenhouse conditions

Dimethylsulphide (DMS) is an important sulphurcontaining trace gas produced by enzymatic cleavage of its precursor compound, dimethylsulphoniopropionate (DMSP), which is released by marine phytoplankton in the upper ocean. After ventilation to the atmosphere, DMS is oxidised to form sulphate aerosols which in the unpolluted marine atmosphere are a major source of cloud condensation nuclei (CCN). Because the microphysical properties of clouds relevant to climate change are sensitive to CCN concentration in air, it has been postulated that marine sulphur emissions may play a r䬥 in climate regulation. The Subantarctic Southern Ocean (41-53ө is relatively free of anthropogenic sulphur emissions, thus sulphate aerosols will be mainly derived from the biogenic source of DMS, making it an ideal region in which to evaluate the DMSclimate regulation hypothesis. We have extended a previous modelling analysis of the DMS cycle in this region by employing a coupled general circulation model (CGCM) which has been run in transient mode to provide a more realistic climate scenario. The CGCM output provided meteorological data under the IPCC/IS92a radiative forcing scenario. A DMS production model has been forced with the CGCM climate data to simulate the trend in the seatoair DMS flux for the period 1960 to 2080, corresponding to equivalent CO2 tripling relative to preindustrial levels. The results confirm a minor but nonnegligible increase in DMS flux in this region, in the range +1% to +6% predicted over the period simulated. Uncertainty analysis of the DMS model predictions have confirmed the positive sign for the change in DMS flux, that is a negative DMS feedback on warming.Griffith Sciences, Griffith School of EnvironmentNo Full Tex

The use of uncorrected regional climate model output to force impact models: A case study for wheat simulations

Computationally-expensive regional climate models (RCM) are increasingly being used to generate local climate data for climate change impact studies. These studies usually process RCM output to remove errors in the simulated climate. However, this paper investigates the suitability of raw output from simulations of a single RCM as input to a biophysical impact model. Our study analyses errors in wheat yields simulated for New South Wales (NSW), Australia by the Agricultural Production Systems Simulator (APSIM) model forced with output from 2 RCM simulations with horizontal resolutions of approximately 50 and 10 km over NSW and with output from the global climate model (GCM) simulation that they downscale. Overall, across the NSW wheat belt, the ∼50 km simulation has a better simulation of mean yields for the 1990-2010 period than the GCM simulation, and the ∼10 km simulation has a better simulation than the ∼50 km simulation. The average mean yield from APSIM simulations forced with observations is 3.5 t ha-1. The average magnitudes of errors in mean yields for the GCM, ∼50 km and ∼10 km simulations are 1.2, 1.0 and 0.5 t ha-1 respectively. We suggest that the improvement in the simulation of mean yields with increasing climate model resolution is largely due to an improvement in the simulation of mean rainfall totals for the growing season. However, for a given value of mean growing season total rainfall, all 3 climate model simulations have a climate that is more conducive to high yields than the observed climate. This difference must be due to errors in other aspects of the simulated climates

Climate projections for southern Australian cool-season rainfall: insights from a downscaling comparison

The projected drying of the extra-tropics under a warmer climate has large implications for natural systems and water security in southern Australia. The downscaling of global climate models can provide insight into regional patterns of rainfall change in the mid-latitudes in the typically wetter cool season. The comparison of statistical and dynamical downscaling model outputs reveals regions of consistent potential added value in the climate-change signal over the 21st century that are largely related to finer resolution. These differences include a stronger and more regionalised rainfall decrease on west coasts in response to a shift in westerly circulation and a different response further from the coast where other influences are important. These patterns have a plausible relationship with topography and regional drivers that are not resolved by coarse global models. However, the comparison of statistical and dynamical downscaling reveals where the method and the configuration of each method makes a difference to the projection. This is an important source of uncertainty for regional rainfall projections. In particular, the simulated change in atmospheric circulation over the century is different in the dynamical downscaling compared to the global climate model inputs, related in part to a different response to patterns of surface warming. The dynamical downscaling places the border between regions with rainfall increase and decrease further north in winter and spring compared to the global climate models and therefore has a different rainfall projection for southeast mainland Australia in winter and for Tasmania in spring

Climate Change Impact on Water and Salt Balances: An Assessment of the Impact of Climate Change on Catchment Salt and Water Balances in the Murray-Darling Basin, Australia

Climate change has potentially significant implications for hydrology and the quantity and quality of water resources. This study investigated the impacts of climate change and revegetation on water and salt balance, and stream salt concentration for catchments within the Murray-Darling Basin, Australia. The Biophysical Capacity to Change model was used with climate change scenarios obtained using the CSIRO DARLAM 125 (125 km resolution) and Cubic Conformal (50 km resolution) regional climate models. These models predicted up to 25% reduction in mean annual rainfall and a similar magnitude of increase in potential evapotranspiration by 2070. Relatively modest changes in rainfall and temperature can lead to significant reductions in mean annual runoff and salt yield and increases in stream salt concentrations within the Basin. The modelled reductions in mean annual runoff were up to 45% in the wetter/cooler southern catchments and up to 64% in the drier/hotter western and northern catchments. The maximum reductions in salt yield were estimated to be up to 34% in the southern catchments and up to 49% in the northern and western catchments. These changes are associated with average catchment rainfall decreases of 13 to 21%. The results suggest that percentage changes in rainfall will be amplified in runoff. This study demonstrates that climate change poses significant challenges to natural resource management in Australia