Lateral Transport Processes and Climate Change in Australia - Case Study Example

Introduction In this paper the influence of lateral transport processes in Australia and globally has been discussed. The processes that dominating current climatic conditions have been discussed first where air mass movement features most. In 20ka the dominant process has been found to be glaciations. Current climate The current climatic conditions are predominantly determined by air mass movement. The determinant of the earth climate is complex biological, physical and chemical processes that are experienced on land, in the atmosphere and ocean. The radioactive properties of the atmosphere is important factor in determination of Earth’s climate and are greatly affected by the Earth’s surface biophysical state as well as the presence of a variety of trace compounds. The constituents include long lived greenhouse gases (LLGHGs) including gases such as methane (CH4), nitrous oxide (N2O), and Carbon dioxide (CO2), in addition to ozone and aerosols which are radioactive constituents (Broecker, W.S., 1991). The atmospheric composition are affected by various processes including natural and anthropogenic emissions of aerosols and gases, transport activities, chemical and microphysical transformations, surface uptake and wet scavenging and oceans and their ecosystem. Before 1750, the level of CO2 in the atmosphere was stable with values between 260 and 280 ppm being maintained for 10 kyr. This was because in this period the disturbance of carbon cycle as a result of human activities was not significant when compared to variability that occurred naturally. There has been increasing concentration level of CO2 in the atmosphere since then (1750) from 280 to about 380 ppm in 2005 (Brasseur, G.P., et al., 1998). This increase in the level of CO2 is caused by human activities majorly through burning of fuels and deforestation, in addition to production process of cement and changes in land management. Even though there are many human activities that contribute to climate change directly or indirectly, the emission of CO2 is considered to be to be the single largest anthropogenic factor that contributes to climate change being experienced in Australia and globally. There has also been an increase in CH4 concentrations from 700 ppb in 1750 to a level of about 1,775 ppb in 2005 with the contributing sources being landfills and waste treatments, fossil fuels, wetlands, rice paddies and ruminant animals. The increase in radiative forcing associated with CH4 about a third of what comes from CO2 and this puts it in second position in terms of effects as a greenhouse gas. Both gases are important in the natural cycle of carbon, which involve continuous flow in the oceans, land biosphere and atmosphere. 20ka processes Sand movement has been one of the geological activities that have been witnessed in 20ka where there has been downwind migration of sand leading to formation of linear dunes. Sand entrainment and deposition is affected by vegetative surface stabilization, the direction and speed of wind that are dependant on regional climate and local factors such as ground water levels. Geological evidence has shown that in Tasmaina region of Australia there has been at least five glaciations events including the early Last Glacial (70ka) and the LGM (23-17ka) (Colhoun et al. 1996) with chances of there being other undetected glaciations events. The biggest ice event is believed to have taken place in the Early Pleistocene where about 7000km2 of Tasmania was under ice as compared to 1100km2 in LGM. There was light glaciation of Kosciuszko region of New South Wales in LGM (Barrows et al. 2001). The vegetation cover in Late Pliocene and early Quaternary are believed to have been as compared to those of other periods. Diverse rainforests covered parts of central Victoria until 1.4Ma and currently the region only supports dry climate type of vegetation. There is evidence of significant plant extinction occurring in the Early Pleistocene as about 45% of species in one of plant macrofossil which is diverse and well documented in the period are no longer in existence (Jordan 1997). There is indication process the extinction process taking place in steps, beginning in Late Pliocene (Macphail et al., 1995). There has also indication of extinction occurring in Late Pleistocene (120-12ka) even though fossil assemblages derived from Middle to Late Plaistocene are seen to be essentially floristics. This has the implication that there was a significant change in vegetation in the early Quaternary which refers to the period before 788ka. The driving force behind these changes is likely to have been the climatic events that resulted to most extensive glaciations in regions like Tasmania. Reconstruction using pollen on Australian climate has indicated variation in the level of aridity was the major climatic feature in second half Quaternary period (Kershaw & Nanson 1993). The vegetation is believed to fallow Milankovitch cycles in changing between those similar to those that exist today and those that are adapted to drier conditions. Typically there was replacement of rainforest with dry forests with some wet forests being included as isolated patches, and there was replacement of dry forests by low open shrubland and open woodlands. In Tasmania region both temperature and aridity are believed to play important roles, where the Darwin Crater core found in Western part of Tasmania exhibiting vegetation cycles ranging from wet forest to herbaceous vegetation and subalpine heaths (Colhoun & van der Geer 1998). During the cold periods, the eucalyptus which currently adapted to mid to high altitude habitats is believed to have been able to survive in local refugia through exhibition of altitudinal migrations, where as for the lowland species they were edged out to island with some being forced to extinction. The records from Victoria have indicated that xerophytic woods and scrub featured prominently in southeastern Australia more than what is observed presently (Pickett et al. 2003). Pollen and charcoal obtained fro two areas have indicated that the Victorian south-central highlands had no trees in LGM (McKenzie 1997). In Tasmania region it indicated by the altitudes of cirques that the temperatures were 6°C to 6.5 °C in comparison present temperatures for the LGM (Colhoun et al. 1996). Future climate There is a projected increase in global mean surface air temperature of 1.1 to 6.4 through the 21st Century as a result of the accumulation of greenhouse gases and this has been predicted to also be experienced in Australia (Hennessy et al, 2007). It is also expected that there will be an increase of 8% in evaporation, but there is no certainty in rainfall prediction (Meehl et al., 2007). With 1990 being the base, it is expected that various parts of Australia will be warmed by 0.1°C to 1.5 °C come the year 2020 (Hennessy et al., 2007), where there will be more days per year having temperatures of over 35°C. It is observed by IPCC that there may be a decrease in the level of rainfall in the southern and subtropical Australia with the runoff in southern and eastern Australia experiencing in a decline in runoff. Through simulation the prediction is that there will be an increase of 20% in drought over the majority of Australia come year 2030, with an increase in Palmer Drought Severity Index (PDSI) in the eastern Australia (Burke et al. 2006). It has been shown that the mean minimum and mean maximum temperature in Murray-Darling Basin (MDB) have exhibited an increasing linear trend over the years from 1952 to 2002. From 1952 a mean maximum of 1.75 ºC and a minimum temperatures increase rate of 1.74 ºC per century have been recorded. This has brought about more severe drought, for a given deficiency in rainfall, as a result of rapid soil moisture and high demand of water being experienced (Nicholls, 2004). It is predicted that there will be a decrease of 12-35% of mean flow will be experienced in MDB by the year 2050 while other models have predicted the flow of streams into Burrendong Dam will experience a decrease of 0-15% by 2030 and a decease of up to 35% by the year 2070 (Hughes, 2003). The annual rate of flow of streams in MDB is may drop 10-25% by 2050 with there being a 50% chance of the average salinity in the Lower Murray River exceeding the threshold of 800 EC by 2020 (Hennessey et al., 2007). The scenarios of drying that will be experienced could be interpreted as a pointer that systems that depend on fresh water are likely to be impacted by the changing droughts pattern, floods as well as water quality. Spatial correlation fields comparing observed (left) and reconstructed (right) September- January Australasian Palmer Drought Severity Index (PDSI), 1925-2000. The major flood and drought events experienced in Australia are linked to Inter-annual variability of ENSO. The variations are expected to persist in the climate models and in the enhanced greenhouse conditions. This is expected to result to greater hydrological extremes emanating from highly intensified rainfall in La La Niña periods and more intense drought that will be caused by high evaporation rates during El Niño (McCarthy et al., 2001). In case there will be the El Niño-like mean state of the tropical Pacific Ocean that have been suggested by some climate models, the implication will be that the frequency of draought will be increased this being in similar to the dying trend experienced in MDB model simulation (Arnell, 1999). Conclusion From this paper the transportation processes that have played dominant roles in different on Australia continent have been discussed. Current climatic conditions have been found to be affected greatly by greenhouse gases such as carbon dioxide which have been in concentration in the ecosystem due to human activities. it has also been seen that there will be drastic climatic change in Australia in this century. References Arnell, N.W., (1999). Climate change and global water resources. Global Environmental Change, 9, S31-S46. Barrows, T. T. el at ( 2001) Late Pleistocene glaciation of the Kosciuszko Massif,Snowy Mountains, Australia. Quatern. Res. 55, 179–189. Brasseur, G.P., et al., (1998). Past and future changes in global tropospheric ozone: impact on radiative forcing. Geophys. Res. Lett., 25(20), 3807–3810. Broecker, W.S., (1991). Keeping global change honest. Global Biogeochem.Cycles, 5, 191–195. Burke, E.J., Brown, S.J., Christidis, N. 2006. Modelling the recent evolution of global drought and projections for the 21st century with the Hadley Centre climate model. Journal of Hydrometeorology, 7, 1113-1125. 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