Climatic shifts

Climatic change may occur as fluctuations in means and/or extremes of climatic variables. Most studies of climatic change, however, focus almost exclusively on trends in mean values of climatic variables (usually temperature). In fact, a climatic shift also may be manifest as an increase or decrease in the frequency of occurrence of extremes. That is, episodes of drought or excessive rainfall or record high or low temperatures may become more or less frequent. Changes in frequency of extremes may occur with little or no concurrent change in means. 

Research is needed to evaluate the interactions of all cultivation variables that influence plant product composition. Climate induces a large variation in levels of phytochemicals and so data from more than one year are needed. This is reinforced by the global climatic changes we are currently facing and also based on future predictions of climate shifts. 

At sea level, Pj is approximately 1 atm, but exhibits some temporal and spatial variability. For example, the annual mean pressure in the northern hemisphere is 0.969 atm and in the southern hemisphere is 0.974 atm, with monthly averages varying by as much as 0.0001 atm, i.e., about 1 mbar (1 atm = 1013.25 mbar). These fluctuations are caused by spatial and temporal variations in atmospheric temperature and water vapor content associated with weather, and seasonal and longer-term climate shifts. Pj is also affected by diurnal atmospheric tides, and it decreases with increasing altitude above sea level. Some gases, such CO2 and O2, exhibit seasonal variability that is caused in part by seasonal variability in plant and animal activity (see Figures 25.4 and 6.7). 

The global distribution of continental shelves, including their widths, has fluctuated over geologic time in response to (1) tectonism that changes the shape and elevation of the crustal plates, (2) isostatic readjustments in the elevation of land masses, and (3) climate shifts that alter the volume of the ocean. Changes in the extent and width of the shelves have affected the magnitude of various sedimentary sinks over time, with significant impacts on ocean chemistry. This topic is discussed further in Chapter 21. 

Dayton, P. K., Interdecadal variation in an antarctic sponge and its predators from oceanographic climate shifts, Science, 245, 1484, 1989. 

Rosenthal et al., 2003). A paleosalinity proxy has always been a difficult prospect, but it appears now that comparison of extracted O-water will make it possible to reconstruct patterns of salinity change in the past (Lea, 2002). Such reconstructions will be invaluable in understanding paleo-climate shifts in the tropics. 

At middle and southern European latitudes, farther from the immediate impact of glacier advances and retreats, well-dated isotope records from speleothems from widely spaced caves allow comparison of regional climate shifts. McDermott et al. (1999) found, for example that early Holocene warm conditions prevailed on the Atlantic seaboard (southern Ireland) while relatively cool conditions occurred in the Mediterranean region of southern France. At 3500 years these conditions were shown to reverse. In the eastern Mediterranean, oxygen and carbon isotope ratios have been used to determine wet and dry periods (Frumkin et al., 1994 Frumkin et al., 1999a, b Bar-Matthews et al., 1996). The wetter climate of the Holocene is recorded in the speleothems. 

The great value of speleothem records is that they are continental records with high time resolution and the possibility of accurate dating. Enough data have been collected to show that the speleothem records very often agree well with other indicators of paleoclimate. A likely application for speleothem records will be to fill in much detail on the timing of climate shifts across continental masses where local climate can vary substantially over relatively short distances. 

At the end of the last major ice age, about twelve thousand years ago, melting glaciers etched exposed lands with rivers. As climates shifted, new ecosystems appeared and continued to be transformed. Through millennia, either from natural or from man-made causes, jungles evolved into savannas and in many cases became deserts. Coincident with the retreat of the glaciers, the human species became less nomadic and more dependent upon planted crops. Many believe this marked the beginning of the path leading to civilization as we know it today. 

The common element of oxygen has eight protons and eight neutrons. A stable isotope with two additional neutrons is also relatively common. Because water-containing lsO evaporates more slowly and condenses more rapidly, the ratio of 180/160 in Antarctic ice cores indicates major climate shifts since early in geologic time. Increased lsO indicates a sudden warming, and increased lsO indicates a sudden cooling. 

In particular, it has been suggested that chlorophyll concentrations in the euphotic zone at stations Climax and ALOHA document the impact of PDO, and specifically the climate shift of 1976-77 on oligotrophic gyre productivity (Karl, 1999 Karl etal., 2001b). The current hypothesis suggests a shift from a eukaryotic phytoplankton community to one dominated by nitrogen-fixing prokaryotes. The shift to prokaryotic dominance is caused by physical conditions... 

The threshold at which the weather starts to change into something far less hospitable to the plants and animals we depend on is thought to be 350 parts per million. That threshold has not been crossed significantly in the past 400,000 years—until now. We are living in the red zone. Life can evolve and adapt to gradual changes in climate. But the last time climate shifted as rapidly as man is now... 

The important consideration is the equilibration of the artifact to its surroundings. The damage caused by dramatic climate shifts may not be readily visible at first, and so equilibration is essential. Johnson and Cairns... 

Eilperin, J. (2006). Debate on Climate Shifts to Issue of Irreparable Change. The Washington Post, 29 January. 

Skill 15.1 Analyze and explain large-scale dynamic forces, events, and processes that affect Earth s land, water, and atmospheric systems, including conceptual questions about plate tectonics, El Nino, drought, and climatic shifts. 

Burke, W. Warner and William Trahant. 2000. Business climate shifts. Woburn, MA Butterworth-Heinemann. 

The resolution of these records can be finer than a year up to 100 thousand years back in time, which allows die stu of annual cycles as well as singular events in the Earth s history, like volcanic eruptions and sharp climatic shifts. 

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