Important Climate Variables

In point of fact, when considering the weathering performance of plastic materials, there exists even more interplay between weathering factors than the factors noted above, such as the ambient temperature, temperature of the actual specimens under exposure and the humidity during exposure of the materials. If the 

It should be noted that in spite of the lack of fundamental understanding of the complexities of degradation during weathering exposure, the judgement of worst 

Although the subject of a standard weathering protocol is not within the scope of this present chapter, we wish to briefly comment that one must never look upon a year s exposure in any of these locations as reflecting a standard in exposure in an absolute sense. It should be intuitively obvious that there is not a Florida year , for example, as conditions do vary from year to year. For this reason, one always needs to expose the particular sample material of interest along with some standard material(s) for which the long-term exposure effects are well known, so that one may have a good basis for comparison. 

---

Tieszen 1991). Water stress, for instance, lowers photo synthetic discrimination against C, resulting in isotopic enrichment. C4 plants are not affected isotopically by environmental parameters although their distributions are (Ehleringer et al. 1997). Under conditions of increasing aridity, the climate variable of most likely importance in African sites, C3 plants should become slightly more enriched on average. Therefore one should be cautious about use... 

The ET cover cannot be tested at every landfill site so it is necessary to extrapolate the results from sites of known performance to specific landfill sites. The factors that affect the hydrologic design of ET covers encompass several scientific disciplines and there are numerous interactions between factors. As a consequence, a comprehensive computer model is needed to evaluate the ET cover for a site.48 The model should effectively incorporate soil, plant, and climate variables, and include their interactions and the resultant effect on hydrology and water balance. An important function of the model is to simulate the variability of performance in response to climate variability and to evaluate cover response to extreme events. Because the expected life of the cover is decades, possibly centuries, the model should be capable of estimating long-term performance. In addition to a complete water balance, the model should be capable of estimating long-term plant biomass production, need for fertilizer, wind and water erosion, and possible loss of primary plant nutrients from the ecosystem. 

Arid areas (0.05 < P/PET < 0.20) mean annual precipitation values up to about 200 mm in winter rainfall areas and 300 mm in summer rainfall areas but more importantly inter-annual variability in the 50-100% range. Pastoralism is possible but without mobility or the use of groundwater resources is highly susceptible to climatic variability. 

Despite its importance in ecosystem C fluxes, soil respiration has limitations as a constraint on SOM turnover, for two main reasons. First, it is difficult to partition soil respiration into its two sources (1) decomposition of SOM by microbes (heterotrophic respiration) and (2) respiration from live plant roots (autotrophic respiration) (Kuzyakov, 2006). As a result, an increase in soil respiration may indicate not only an increase in SOM decomposition but also an increase in root respiration. Second, it is likely that in most soils only a small fraction of total SOM contributes to heterotrophic respiration. As a result, respiration measurements provide information about the dynamic fraction of SOM (particularly when combined with 14C measurements of respiration) but do not provide information about the large, stable pools unless they are destabilized and contribute to respiration (detectable with 14C02 respiration measurements). Attributing the sources of respiration from different SOM reservoirs, which may respond differently to climatic variables, is not... 

Next to the temperature gradient inside the snowpack, an important driving force for snow metamorphism is wind, that lifts, transports and redeposits snow crystals, changing snowpack mass and density " and deposits aerosols inside the snowpack.Wind and temperature are climatic variables that determine metamorphism and snowpack physical properties such as albedo and heat conductivity. These properties affect the energy balance of the snow-atmosphere and of the soil-snow interfaces, which in turn affect climate. 

Manufacturers need to have confidence that a continual uninterrupted supply of raw material can be sustained throughout the life cycle of a product. It is of equal importance that the feedstock should not be restricted by geographical and climatic conditions or that yield does not dramatically vary when harvested in different locations and at a particular time of the year. The key to an increased usage of natural products by industry is in the control of the above variables so that the end performance of the product remains consistent. 

---