Cement, Energy and Environment

20 per cent, there was no net change in either the mean onset date or duration of snow cover for the continent of North America. There appears to have been a downward trend in blizzards . • Storm surges have not increased in either frequency or magnitude as C0 2 concentrations in the atmosphere have risen. In the majority of cases investigated, they have tended to decrease. • Air temperature variability almost always decreases when mean air temperature rises, be it in cases of temperature change over tens of thousands of years or over mere decades, or even between individual cooler and warmer years when different ENSO states are considered. The claim that global warming will lead to more extremes of climate and weather, including more extremes of temperature itself, is not supported by real-world data. • Although one can readily identify specific parts of the planet that have experienced both significant increases and decreases in land area burned by wildfires over the last two to three decades of the twentieth century, for the globe as a whole there was no relationship between global warming and total area burned over this period. Chapter 7. Biological Effects of Carbon Dioxide Enhancement • A 300-ppm increase in the air's C0 2 content typically raises the productivity of most herbaceous plants by about one-third; and this positive response occurs in plants that utilize all three of the major biochemical pathways (C 3 , C4, CAM) of photosynthesis. For woody plants, the response is even greater. The productivity benefits of C0 2 enrichment are also experienced by aquatic plants, including freshwater algae and macrophytes, and marine microalgae and macroalgae. • The amount of carbon plants gain per unit of water lost - or water-use efficiency - typically rises as the C0 2 content of the air rises, greatly increasing their ability to withstand drought. In addition, the C0 2 -induced percentage increase in plant biomass production is often greater under water– stressed conditions than it is when plants are well watered. • Atmospheric C0 2 enrichment helps ameliorate the detrimental effects of several environmental stresses on plant growth and development, including high soil salinity, high air temperature, low light intensity and low levels of soil fertility. Elevated levels of C0 2 have additionally been demonstrated to reduce the severity of low temperature stress, oxidative stress, and the stress of herbivory. In fact, the percentage growth enhancement produced by an increase in the air's C0 2 concentration is often even greater under stressful and resource-limited conditions than it is when growing conditions are ideal. • As the air's C0 2 content continues to rise, plants will likely exhibit enhanced rates of photosynthesis and biomass production that will not be diminished by any global warming that might occur concurrently. In fact, if the ambient air temperature rises, the growth-promoting effects of atmospheric C0 2 enrichment will likely also rise, becoming more and more robust. • The ongoing rise in the air's C0 2 content likely will not favour the growth of weedy species over that of crops and native plants. • The growth of plants is generally not only enhanced by C0 2 -induced increases in net photosynthesis during the light period of the day, it is also enhanced by C0 2 - induced decreases in respiration during the dark period. • The ongoing rise in the air's C0 2 content, as well as any degree of warming that might possibly accompany it, will not materially alter the rate of decomposition of the world's soil organic matter and will probably enhance biological carbon sequestration. Continued increases in the air's C0 2 concentration and temperature will not result in massive losses of carbon from earth's peatlands. To the contrary, these environmental changes -if they persist- would likely work together to enhance carbon capture. • Other biological effects of C0 2 enhancement include enhanced plant nitrogen-use efficiency, longer residence time of carbon in the soil, and increased populations of earthworms and soil nematodes. 31